local api, if_nil = vim.api, vim.F.if_nil

local M = {}

--- @param title string
--- @return integer?
local function get_qf_id_for_title(title)
  local lastqflist = vim.fn.getqflist({ nr = '$' })
  for i = 1, lastqflist.nr do
    local qflist = vim.fn.getqflist({ nr = i, id = 0, title = 0 })
    if qflist.title == title then
      return qflist.id
    end
  end

  return nil
end

--- [diagnostic-structure]()
---
--- Diagnostics use the same indexing as the rest of the Nvim API (i.e. 0-based
--- rows and columns). |api-indexing|
--- @class vim.Diagnostic
---
--- Buffer number
--- @field bufnr? integer
---
--- The starting line of the diagnostic (0-indexed)
--- @field lnum integer
---
--- The final line of the diagnostic (0-indexed)
--- @field end_lnum? integer
---
--- The starting column of the diagnostic (0-indexed)
--- @field col integer
---
--- The final column of the diagnostic (0-indexed)
--- @field end_col? integer
---
--- The severity of the diagnostic |vim.diagnostic.severity|
--- @field severity? vim.diagnostic.Severity
---
--- The diagnostic text
--- @field message string
---
--- The source of the diagnostic
--- @field source? string
---
--- The diagnostic code
--- @field code? string|integer
---
--- @field _tags? { deprecated: boolean, unnecessary: boolean}
---
--- Arbitrary data plugins or users can add
--- @field user_data? any arbitrary data plugins can add
---
--- @field namespace? integer

--- Many of the configuration options below accept one of the following:
--- - `false`: Disable this feature
--- - `true`: Enable this feature, use default settings.
--- - `table`: Enable this feature with overrides. Use an empty table to use default values.
--- - `function`: Function with signature (namespace, bufnr) that returns any of the above.
--- @class vim.diagnostic.Opts
---
--- Use underline for diagnostics.
--- (default: `true`)
--- @field underline? boolean|vim.diagnostic.Opts.Underline|fun(namespace: integer, bufnr:integer): vim.diagnostic.Opts.Underline
---
--- Use virtual text for diagnostics. If multiple diagnostics are set for a
--- namespace, one prefix per diagnostic + the last diagnostic message are
--- shown.
--- (default: `true`)
--- @field virtual_text? boolean|vim.diagnostic.Opts.VirtualText|fun(namespace: integer, bufnr:integer): vim.diagnostic.Opts.VirtualText
---
--- Use signs for diagnostics |diagnostic-signs|.
--- (default: `true`)
--- @field signs? boolean|vim.diagnostic.Opts.Signs|fun(namespace: integer, bufnr:integer): vim.diagnostic.Opts.Signs
---
--- Options for floating windows. See |vim.diagnostic.Opts.Float|.
--- @field float? boolean|vim.diagnostic.Opts.Float|fun(namespace: integer, bufnr:integer): vim.diagnostic.Opts.Float
---
--- Update diagnostics in Insert mode
--- (if `false`, diagnostics are updated on |InsertLeave|)
--- (default: `false`)
--- @field update_in_insert? boolean
---
--- Sort diagnostics by severity. This affects the order in which signs,
--- virtual text, and highlights are displayed. When true, higher severities are
--- displayed before lower severities (e.g. ERROR is displayed before WARN).
--- Options:
---   - {reverse}? (boolean) Reverse sort order
--- (default: `false`)
--- @field severity_sort? boolean|{reverse?:boolean}
---
--- Default values for |vim.diagnostic.jump()|. See |vim.diagnostic.Opts.Jump|.
--- @field jump? vim.diagnostic.Opts.Jump

--- @class (private) vim.diagnostic.OptsResolved
--- @field float vim.diagnostic.Opts.Float
--- @field update_in_insert boolean
--- @field underline vim.diagnostic.Opts.Underline
--- @field virtual_text vim.diagnostic.Opts.VirtualText
--- @field signs vim.diagnostic.Opts.Signs
--- @field severity_sort {reverse?:boolean}

--- @class vim.diagnostic.Opts.Float
---
--- Buffer number to show diagnostics from.
--- (default: current buffer)
--- @field bufnr? integer
---
--- Limit diagnostics to the given namespace
--- @field namespace? integer
---
--- Show diagnostics from the whole buffer (`buffer"`, the current cursor line
--- (`line`), or the current cursor position (`cursor`). Shorthand versions
--- are also accepted (`c` for `cursor`, `l` for `line`, `b` for `buffer`).
--- (default: `line`)
--- @field scope? 'line'|'buffer'|'cursor'|'c'|'l'|'b'
---
--- If {scope} is "line" or "cursor", use this position rather than the cursor
--- position. If a number, interpreted as a line number; otherwise, a
--- (row, col) tuple.
--- @field pos? integer|[integer,integer]
---
--- Sort diagnostics by severity.
--- Overrides the setting from |vim.diagnostic.config()|.
--- (default: `false`)
--- @field severity_sort? boolean|{reverse?:boolean}
---
--- See |diagnostic-severity|.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field severity? vim.diagnostic.SeverityFilter
---
--- String to use as the header for the floating window. If a table, it is
--- interpreted as a `[text, hl_group]` tuple.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field header? string|[string,any]
---
--- Include the diagnostic source in the message.
--- Use "if_many" to only show sources if there is more than one source of
--- diagnostics in the buffer. Otherwise, any truthy value means to always show
--- the diagnostic source.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field source? boolean|'if_many'
---
--- A function that takes a diagnostic as input and returns a string.
--- The return value is the text used to display the diagnostic.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field format? fun(diagnostic:vim.Diagnostic): string
---
--- Prefix each diagnostic in the floating window:
--- - If a `function`, {i} is the index of the diagnostic being evaluated and
---   {total} is the total number of diagnostics displayed in the window. The
---   function should return a `string` which is prepended to each diagnostic
---   in the window as well as an (optional) highlight group which will be
---   used to highlight the prefix.
--- - If a `table`, it is interpreted as a `[text, hl_group]` tuple as
---   in |nvim_echo()|
--- - If a `string`, it is prepended to each diagnostic in the window with no
---   highlight.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field prefix? string|table|(fun(diagnostic:vim.Diagnostic,i:integer,total:integer): string, string)
---
--- Same as {prefix}, but appends the text to the diagnostic instead of
--- prepending it.
--- Overrides the setting from |vim.diagnostic.config()|.
--- @field suffix? string|table|(fun(diagnostic:vim.Diagnostic,i:integer,total:integer): string, string)
---
--- @field focus_id? string
---
--- @field border? string see |nvim_open_win()|.

--- @class vim.diagnostic.Opts.Underline
---
--- Only underline diagnostics matching the given
--- severity |diagnostic-severity|.
--- @field severity? vim.diagnostic.SeverityFilter

--- @class vim.diagnostic.Opts.VirtualText
---
--- Only show virtual text for diagnostics matching the given
--- severity |diagnostic-severity|
--- @field severity? vim.diagnostic.SeverityFilter
---
--- Include the diagnostic source in virtual text. Use `'if_many'` to only
--- show sources if there is more than one diagnostic source in the buffer.
--- Otherwise, any truthy value means to always show the diagnostic source.
--- @field source? boolean|"if_many"
---
--- Amount of empty spaces inserted at the beginning of the virtual text.
--- @field spacing? integer
---
--- Prepend diagnostic message with prefix. If a `function`, {i} is the index
--- of the diagnostic being evaluated, and {total} is the total number of
--- diagnostics for the line. This can be used to render diagnostic symbols
--- or error codes.
--- @field prefix? string|(fun(diagnostic:vim.Diagnostic,i:integer,total:integer): string)
---
--- Append diagnostic message with suffix.
--- This can be used to render an LSP diagnostic error code.
--- @field suffix? string|(fun(diagnostic:vim.Diagnostic): string)
---
--- The return value is the text used to display the diagnostic. Example:
--- ```lua
--- function(diagnostic)
---   if diagnostic.severity == vim.diagnostic.severity.ERROR then
---     return string.format("E: %s", diagnostic.message)
---   end
---   return diagnostic.message
--- end
--- ```
--- @field format? fun(diagnostic:vim.Diagnostic): string
---
--- See |nvim_buf_set_extmark()|.
--- @field hl_mode? 'replace'|'combine'|'blend'
---
--- See |nvim_buf_set_extmark()|.
--- @field virt_text? [string,any][]
---
--- See |nvim_buf_set_extmark()|.
--- @field virt_text_pos? 'eol'|'overlay'|'right_align'|'inline'
---
--- See |nvim_buf_set_extmark()|.
--- @field virt_text_win_col? integer
---
--- See |nvim_buf_set_extmark()|.
--- @field virt_text_hide? boolean

--- @class vim.diagnostic.Opts.Signs
---
--- Only show virtual text for diagnostics matching the given
--- severity |diagnostic-severity|
--- @field severity? vim.diagnostic.SeverityFilter
---
--- Base priority to use for signs. When {severity_sort} is used, the priority
--- of a sign is adjusted based on its severity.
--- Otherwise, all signs use the same priority.
--- (default: `10`)
--- @field priority? integer
---
--- A table mapping |diagnostic-severity| to the sign text to display in the
--- sign column. The default is to use `"E"`, `"W"`, `"I"`, and `"H"` for errors,
--- warnings, information, and hints, respectively. Example:
--- ```lua
--- vim.diagnostic.config({
---   signs = { text = { [vim.diagnostic.severity.ERROR] = 'E', ... } }
--- })
--- ```
--- @field text? table<vim.diagnostic.Severity,string>
---
--- A table mapping |diagnostic-severity| to the highlight group used for the
--- line number where the sign is placed.
--- @field numhl? table<vim.diagnostic.Severity,string>
---
--- A table mapping |diagnostic-severity| to the highlight group used for the
--- whole line the sign is placed in.
--- @field linehl? table<vim.diagnostic.Severity,string>

--- @class vim.diagnostic.Opts.Jump
---
--- Default value of the {float} parameter of |vim.diagnostic.jump()|.
--- (default: false)
--- @field float? boolean|vim.diagnostic.Opts.Float
---
--- Default value of the {wrap} parameter of |vim.diagnostic.jump()|.
--- (default: true)
--- @field wrap? boolean
---
--- Default value of the {severity} parameter of |vim.diagnostic.jump()|.
--- @field severity? vim.diagnostic.SeverityFilter
---
--- Default value of the {_highest} parameter of |vim.diagnostic.jump()|.
--- @field package _highest? boolean

-- TODO: inherit from `vim.diagnostic.Opts`, implement its fields.
--- Optional filters |kwargs|, or `nil` for all.
--- @class vim.diagnostic.Filter
--- @inlinedoc
---
--- Diagnostic namespace, or `nil` for all.
--- @field ns_id? integer
---
--- Buffer number, or 0 for current buffer, or `nil` for all buffers.
--- @field bufnr? integer

--- @nodoc
--- @enum vim.diagnostic.Severity
M.severity = {
  ERROR = 1,
  WARN = 2,
  INFO = 3,
  HINT = 4,
  [1] = 'ERROR',
  [2] = 'WARN',
  [3] = 'INFO',
  [4] = 'HINT',
  --- Mappings from qflist/loclist error types to severities
  E = 1,
  W = 2,
  I = 3,
  N = 4,
}

--- @alias vim.diagnostic.SeverityInt 1|2|3|4

--- See |diagnostic-severity| and |vim.diagnostic.get()|
--- @alias vim.diagnostic.SeverityFilter vim.diagnostic.Severity|vim.diagnostic.Severity[]|{min:vim.diagnostic.Severity,max:vim.diagnostic.Severity}

--- @type vim.diagnostic.Opts
local global_diagnostic_options = {
  signs = true,
  underline = true,
  virtual_text = true,
  float = true,
  update_in_insert = false,
  severity_sort = false,
  jump = {
    -- Do not show floating window
    float = false,

    -- Wrap around buffer
    wrap = true,
  },
}

--- @class (private) vim.diagnostic.Handler
--- @field show? fun(namespace: integer, bufnr: integer, diagnostics: vim.Diagnostic[], opts?: vim.diagnostic.OptsResolved)
--- @field hide? fun(namespace:integer, bufnr:integer)

--- @nodoc
--- @type table<string,vim.diagnostic.Handler>
M.handlers = setmetatable({}, {
  __newindex = function(t, name, handler)
    vim.validate('handler', handler, 'table')
    rawset(t, name, handler)
    if global_diagnostic_options[name] == nil then
      global_diagnostic_options[name] = true
    end
  end,
})

-- Metatable that automatically creates an empty table when assigning to a missing key
local bufnr_and_namespace_cacher_mt = {
  --- @param t table<integer,table>
  --- @param bufnr integer
  --- @return table
  __index = function(t, bufnr)
    assert(bufnr > 0, 'Invalid buffer number')
    t[bufnr] = {}
    return t[bufnr]
  end,
}

-- bufnr -> ns -> Diagnostic[]
local diagnostic_cache = {} --- @type table<integer,table<integer,vim.Diagnostic[]>>
do
  local group = api.nvim_create_augroup('DiagnosticBufWipeout', {})
  setmetatable(diagnostic_cache, {
    --- @param t table<integer,vim.Diagnostic[]>
    --- @param bufnr integer
    __index = function(t, bufnr)
      assert(bufnr > 0, 'Invalid buffer number')
      api.nvim_create_autocmd('BufWipeout', {
        group = group,
        buffer = bufnr,
        callback = function()
          rawset(t, bufnr, nil)
        end,
      })
      t[bufnr] = {}
      return t[bufnr]
    end,
  })
end

--- @class (private) vim.diagnostic._extmark
--- @field [1] integer id
--- @field [2] integer start
--- @field [3] integer end
--- @field [4] table details

--- @type table<integer,table<integer,vim.diagnostic._extmark[]>>
local diagnostic_cache_extmarks = setmetatable({}, bufnr_and_namespace_cacher_mt)

--- @type table<integer,true>
local diagnostic_attached_buffers = {}

--- @type table<integer,true|table<integer,true>>
local diagnostic_disabled = {}

--- @type table<integer,table<integer,table>>
local bufs_waiting_to_update = setmetatable({}, bufnr_and_namespace_cacher_mt)

--- @class vim.diagnostic.NS
--- @field name string
--- @field opts vim.diagnostic.Opts
--- @field user_data table
--- @field disabled? boolean

--- @type table<integer,vim.diagnostic.NS>
local all_namespaces = {}

---@param severity string|vim.diagnostic.Severity
---@return vim.diagnostic.Severity?
local function to_severity(severity)
  if type(severity) == 'string' then
    assert(M.severity[string.upper(severity)], string.format('Invalid severity: %s', severity))
    return M.severity[string.upper(severity)]
  end
  return severity
end

--- @param severity vim.diagnostic.SeverityFilter
--- @return fun(vim.Diagnostic):boolean
local function severity_predicate(severity)
  if type(severity) ~= 'table' then
    severity = assert(to_severity(severity))
    ---@param d vim.Diagnostic
    return function(d)
      return d.severity == severity
    end
  end
  if severity.min or severity.max then
    --- @cast severity {min:vim.diagnostic.Severity,max:vim.diagnostic.Severity}
    local min_severity = to_severity(severity.min) or M.severity.HINT
    local max_severity = to_severity(severity.max) or M.severity.ERROR

    --- @param d vim.Diagnostic
    return function(d)
      return d.severity <= min_severity and d.severity >= max_severity
    end
  end

  --- @cast severity vim.diagnostic.Severity[]
  local severities = {} --- @type table<vim.diagnostic.Severity,true>
  for _, s in ipairs(severity) do
    severities[assert(to_severity(s))] = true
  end

  --- @param d vim.Diagnostic
  return function(d)
    return severities[d.severity]
  end
end

--- @param severity vim.diagnostic.SeverityFilter
--- @param diagnostics vim.Diagnostic[]
--- @return vim.Diagnostic[]
local function filter_by_severity(severity, diagnostics)
  if not severity then
    return diagnostics
  end
  return vim.tbl_filter(severity_predicate(severity), diagnostics)
end

--- @param bufnr integer
--- @return integer
local function count_sources(bufnr)
  local seen = {} --- @type table<string,true>
  local count = 0
  for _, namespace_diagnostics in pairs(diagnostic_cache[bufnr]) do
    for _, diagnostic in ipairs(namespace_diagnostics) do
      local source = diagnostic.source
      if source and not seen[source] then
        seen[source] = true
        count = count + 1
      end
    end
  end
  return count
end

--- @param diagnostics vim.Diagnostic[]
--- @return vim.Diagnostic[]
local function prefix_source(diagnostics)
  --- @param d vim.Diagnostic
  return vim.tbl_map(function(d)
    if not d.source then
      return d
    end

    local t = vim.deepcopy(d, true)
    t.message = string.format('%s: %s', d.source, d.message)
    return t
  end, diagnostics)
end

--- @param diagnostics vim.Diagnostic[]
--- @return vim.Diagnostic[]
local function reformat_diagnostics(format, diagnostics)
  vim.validate('format', format, 'function')
  vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')

  local formatted = vim.deepcopy(diagnostics, true)
  for _, diagnostic in ipairs(formatted) do
    diagnostic.message = format(diagnostic)
  end
  return formatted
end

--- @param option string
--- @param namespace integer?
--- @return table
local function enabled_value(option, namespace)
  local ns = namespace and M.get_namespace(namespace) or {}
  if ns.opts and type(ns.opts[option]) == 'table' then
    return ns.opts[option]
  end

  local global_opt = global_diagnostic_options[option]
  if type(global_opt) == 'table' then
    return global_opt
  end

  return {}
end

--- @param option string
--- @param value any?
--- @param namespace integer?
--- @param bufnr integer
--- @return any
local function resolve_optional_value(option, value, namespace, bufnr)
  if not value then
    return false
  elseif value == true then
    return enabled_value(option, namespace)
  elseif type(value) == 'function' then
    local val = value(namespace, bufnr) --- @type any
    if val == true then
      return enabled_value(option, namespace)
    else
      return val
    end
  elseif type(value) == 'table' then
    return value
  end
  error('Unexpected option type: ' .. vim.inspect(value))
end

--- @param opts vim.diagnostic.Opts?
--- @param namespace integer?
--- @param bufnr integer
--- @return vim.diagnostic.OptsResolved
local function get_resolved_options(opts, namespace, bufnr)
  local ns = namespace and M.get_namespace(namespace) or {}
  -- Do not use tbl_deep_extend so that an empty table can be used to reset to default values
  local resolved = vim.tbl_extend('keep', opts or {}, ns.opts or {}, global_diagnostic_options) --- @type table<string,any>
  for k in pairs(global_diagnostic_options) do
    if resolved[k] ~= nil then
      resolved[k] = resolve_optional_value(k, resolved[k], namespace, bufnr)
    end
  end
  return resolved
end

-- Default diagnostic highlights
local diagnostic_severities = {
  [M.severity.ERROR] = { ctermfg = 1, guifg = 'Red' },
  [M.severity.WARN] = { ctermfg = 3, guifg = 'Orange' },
  [M.severity.INFO] = { ctermfg = 4, guifg = 'LightBlue' },
  [M.severity.HINT] = { ctermfg = 7, guifg = 'LightGrey' },
}

--- Make a map from vim.diagnostic.Severity -> Highlight Name
--- @param base_name string
--- @return table<vim.diagnostic.SeverityInt,string>
local function make_highlight_map(base_name)
  local result = {} --- @type table<vim.diagnostic.SeverityInt,string>
  for k in pairs(diagnostic_severities) do
    local name = M.severity[k]
    name = name:sub(1, 1) .. name:sub(2):lower()
    result[k] = 'Diagnostic' .. base_name .. name
  end

  return result
end

-- TODO(lewis6991): these highlight maps can only be indexed with an integer, however there usage
-- implies they can be indexed with any vim.diagnostic.Severity
local virtual_text_highlight_map = make_highlight_map('VirtualText')
local underline_highlight_map = make_highlight_map('Underline')
local floating_highlight_map = make_highlight_map('Floating')
local sign_highlight_map = make_highlight_map('Sign')

--- @param diagnostics vim.Diagnostic[]
--- @return table<integer,vim.Diagnostic[]>
local function diagnostic_lines(diagnostics)
  if not diagnostics then
    return {}
  end

  local diagnostics_by_line = {} --- @type table<integer,vim.Diagnostic[]>
  for _, diagnostic in ipairs(diagnostics) do
    local line_diagnostics = diagnostics_by_line[diagnostic.lnum]
    if not line_diagnostics then
      line_diagnostics = {}
      diagnostics_by_line[diagnostic.lnum] = line_diagnostics
    end
    table.insert(line_diagnostics, diagnostic)
  end
  return diagnostics_by_line
end

--- @param namespace integer
--- @param bufnr integer
--- @param diagnostics vim.Diagnostic[]
local function set_diagnostic_cache(namespace, bufnr, diagnostics)
  for _, diagnostic in ipairs(diagnostics) do
    assert(diagnostic.lnum, 'Diagnostic line number is required')
    assert(diagnostic.col, 'Diagnostic column is required')
    diagnostic.severity = diagnostic.severity and to_severity(diagnostic.severity)
      or M.severity.ERROR
    diagnostic.end_lnum = diagnostic.end_lnum or diagnostic.lnum
    diagnostic.end_col = diagnostic.end_col or diagnostic.col
    diagnostic.namespace = namespace
    diagnostic.bufnr = bufnr
  end
  diagnostic_cache[bufnr][namespace] = diagnostics
end

--- @param bufnr integer
--- @param last integer
local function restore_extmarks(bufnr, last)
  for ns, extmarks in pairs(diagnostic_cache_extmarks[bufnr]) do
    local extmarks_current = api.nvim_buf_get_extmarks(bufnr, ns, 0, -1, { details = true })
    local found = {} --- @type table<integer,true>
    for _, extmark in ipairs(extmarks_current) do
      -- nvim_buf_set_lines will move any extmark to the line after the last
      -- nvim_buf_set_text will move any extmark to the last line
      if extmark[2] ~= last + 1 then
        found[extmark[1]] = true
      end
    end
    for _, extmark in ipairs(extmarks) do
      if not found[extmark[1]] then
        local opts = extmark[4]
        opts.id = extmark[1]
        pcall(api.nvim_buf_set_extmark, bufnr, ns, extmark[2], extmark[3], opts)
      end
    end
  end
end

--- @param namespace integer
--- @param bufnr? integer
local function save_extmarks(namespace, bufnr)
  bufnr = vim._resolve_bufnr(bufnr)
  if not diagnostic_attached_buffers[bufnr] then
    api.nvim_buf_attach(bufnr, false, {
      on_lines = function(_, _, _, _, _, last)
        restore_extmarks(bufnr, last - 1)
      end,
      on_detach = function()
        diagnostic_cache_extmarks[bufnr] = nil
      end,
    })
    diagnostic_attached_buffers[bufnr] = true
  end
  diagnostic_cache_extmarks[bufnr][namespace] =
    api.nvim_buf_get_extmarks(bufnr, namespace, 0, -1, { details = true })
end

--- Create a function that converts a diagnostic severity to an extmark priority.
--- @param priority integer Base priority
--- @param opts vim.diagnostic.OptsResolved
--- @return fun(severity: vim.diagnostic.Severity): integer
local function severity_to_extmark_priority(priority, opts)
  if opts.severity_sort then
    if type(opts.severity_sort) == 'table' and opts.severity_sort.reverse then
      return function(severity)
        return priority + (severity - vim.diagnostic.severity.ERROR)
      end
    end

    return function(severity)
      return priority + (vim.diagnostic.severity.HINT - severity)
    end
  end

  return function()
    return priority
  end
end

--- @type table<string,true>
local registered_autocmds = {}

local function make_augroup_key(namespace, bufnr)
  local ns = M.get_namespace(namespace)
  return string.format('DiagnosticInsertLeave:%s:%s', bufnr, ns.name)
end

--- @param namespace integer
--- @param bufnr integer
local function execute_scheduled_display(namespace, bufnr)
  local args = bufs_waiting_to_update[bufnr][namespace]
  if not args then
    return
  end

  -- Clear the args so we don't display unnecessarily.
  bufs_waiting_to_update[bufnr][namespace] = nil

  M.show(namespace, bufnr, nil, args)
end

--- Table of autocmd events to fire the update for displaying new diagnostic information
local insert_leave_auto_cmds = { 'InsertLeave', 'CursorHoldI' }

--- @param namespace integer
--- @param bufnr integer
--- @param args any[]
local function schedule_display(namespace, bufnr, args)
  bufs_waiting_to_update[bufnr][namespace] = args

  local key = make_augroup_key(namespace, bufnr)
  if not registered_autocmds[key] then
    local group = api.nvim_create_augroup(key, { clear = true })
    api.nvim_create_autocmd(insert_leave_auto_cmds, {
      group = group,
      buffer = bufnr,
      callback = function()
        execute_scheduled_display(namespace, bufnr)
      end,
      desc = 'vim.diagnostic: display diagnostics',
    })
    registered_autocmds[key] = true
  end
end

--- @param namespace integer
--- @param bufnr integer
local function clear_scheduled_display(namespace, bufnr)
  local key = make_augroup_key(namespace, bufnr)

  if registered_autocmds[key] then
    api.nvim_del_augroup_by_name(key)
    registered_autocmds[key] = nil
  end
end

--- @param bufnr integer?
--- @param opts vim.diagnostic.GetOpts?
--- @param clamp boolean
--- @return vim.Diagnostic[]
local function get_diagnostics(bufnr, opts, clamp)
  opts = opts or {}

  local namespace = opts.namespace

  if type(namespace) == 'number' then
    namespace = { namespace }
  end

  ---@cast namespace integer[]

  local diagnostics = {}

  -- Memoized results of buf_line_count per bufnr
  --- @type table<integer,integer>
  local buf_line_count = setmetatable({}, {
    --- @param t table<integer,integer>
    --- @param k integer
    --- @return integer
    __index = function(t, k)
      t[k] = api.nvim_buf_line_count(k)
      return rawget(t, k)
    end,
  })

  local match_severity = opts.severity and severity_predicate(opts.severity)
    or function(_)
      return true
    end

  ---@param b integer
  ---@param d vim.Diagnostic
  local function add(b, d)
    if
      match_severity(d)
      and (not opts.lnum or (opts.lnum >= d.lnum and opts.lnum <= (d.end_lnum or d.lnum)))
    then
      if clamp and api.nvim_buf_is_loaded(b) then
        local line_count = buf_line_count[b] - 1
        if
          d.lnum > line_count
          or d.end_lnum > line_count
          or d.lnum < 0
          or d.end_lnum < 0
          or d.col < 0
          or d.end_col < 0
        then
          d = vim.deepcopy(d, true)
          d.lnum = math.max(math.min(d.lnum, line_count), 0)
          d.end_lnum = math.max(math.min(assert(d.end_lnum), line_count), 0)
          d.col = math.max(d.col, 0)
          d.end_col = math.max(d.end_col, 0)
        end
      end
      table.insert(diagnostics, d)
    end
  end

  --- @param buf integer
  --- @param diags vim.Diagnostic[]
  local function add_all_diags(buf, diags)
    for _, diagnostic in pairs(diags) do
      add(buf, diagnostic)
    end
  end

  if namespace == nil and bufnr == nil then
    for b, t in pairs(diagnostic_cache) do
      for _, v in pairs(t) do
        add_all_diags(b, v)
      end
    end
  elseif namespace == nil then
    bufnr = vim._resolve_bufnr(bufnr)
    for iter_namespace in pairs(diagnostic_cache[bufnr]) do
      add_all_diags(bufnr, diagnostic_cache[bufnr][iter_namespace])
    end
  elseif bufnr == nil then
    for b, t in pairs(diagnostic_cache) do
      for _, iter_namespace in ipairs(namespace) do
        add_all_diags(b, t[iter_namespace] or {})
      end
    end
  else
    bufnr = vim._resolve_bufnr(bufnr)
    for _, iter_namespace in ipairs(namespace) do
      add_all_diags(bufnr, diagnostic_cache[bufnr][iter_namespace] or {})
    end
  end

  return diagnostics
end

--- @param loclist boolean
--- @param opts vim.diagnostic.setqflist.Opts|vim.diagnostic.setloclist.Opts?
local function set_list(loclist, opts)
  opts = opts or {}
  local open = if_nil(opts.open, true)
  local title = opts.title or 'Diagnostics'
  local winnr = opts.winnr or 0
  local bufnr --- @type integer?
  if loclist then
    bufnr = api.nvim_win_get_buf(winnr)
  end
  -- Don't clamp line numbers since the quickfix list can already handle line
  -- numbers beyond the end of the buffer
  local diagnostics = get_diagnostics(bufnr, opts --[[@as vim.diagnostic.GetOpts]], false)
  local items = M.toqflist(diagnostics)
  local qf_id = nil
  if loclist then
    vim.fn.setloclist(winnr, {}, 'u', { title = title, items = items })
  else
    qf_id = get_qf_id_for_title(title)

    -- If we already have a diagnostics quickfix, update it rather than creating a new one.
    -- This avoids polluting the finite set of quickfix lists, and preserves the currently selected
    -- entry.
    vim.fn.setqflist({}, qf_id and 'u' or ' ', {
      title = title,
      items = items,
      id = qf_id,
    })
  end

  if open then
    if not loclist then
      -- First navigate to the diagnostics quickfix list.
      local nr = vim.fn.getqflist({ id = qf_id, nr = 0 }).nr
      api.nvim_command(nr .. 'chistory')

      -- Now open the quickfix list.
      api.nvim_command('botright cwindow')
    else
      api.nvim_command('lwindow')
    end
  end
end

--- Jump to the diagnostic with the highest severity. First sort the
--- diagnostics by severity. The first diagnostic then contains the highest severity, and we can
--- discard all diagnostics with a lower severity.
--- @param diagnostics vim.Diagnostic[]
local function filter_highest(diagnostics)
  table.sort(diagnostics, function(a, b)
    return a.severity < b.severity
  end)

  -- Find the first diagnostic where the severity does not match the highest severity, and remove
  -- that element and all subsequent elements from the array
  local worst = (diagnostics[1] or {}).severity
  local len = #diagnostics
  for i = 2, len do
    if diagnostics[i].severity ~= worst then
      for j = i, len do
        diagnostics[j] = nil
      end
      break
    end
  end
end

--- @param search_forward boolean
--- @param opts vim.diagnostic.JumpOpts?
--- @return vim.Diagnostic?
local function next_diagnostic(search_forward, opts)
  opts = opts or {}

  -- Support deprecated win_id alias
  if opts.win_id then
    vim.deprecate('opts.win_id', 'opts.winid', '0.13')
    opts.winid = opts.win_id
    opts.win_id = nil --- @diagnostic disable-line
  end

  -- Support deprecated cursor_position alias
  if opts.cursor_position then
    vim.deprecate('opts.cursor_position', 'opts.pos', '0.13')
    opts.pos = opts.cursor_position
    opts.cursor_position = nil --- @diagnostic disable-line
  end

  local winid = opts.winid or api.nvim_get_current_win()
  local bufnr = api.nvim_win_get_buf(winid)
  local position = opts.pos or api.nvim_win_get_cursor(winid)

  -- Adjust row to be 0-indexed
  position[1] = position[1] - 1

  local wrap = if_nil(opts.wrap, true)

  local diagnostics = get_diagnostics(bufnr, opts, true)

  if opts._highest then
    filter_highest(diagnostics)
  end

  local line_diagnostics = diagnostic_lines(diagnostics)

  local line_count = api.nvim_buf_line_count(bufnr)
  for i = 0, line_count do
    local offset = i * (search_forward and 1 or -1)
    local lnum = position[1] + offset
    if lnum < 0 or lnum >= line_count then
      if not wrap then
        return
      end
      lnum = (lnum + line_count) % line_count
    end
    if line_diagnostics[lnum] and not vim.tbl_isempty(line_diagnostics[lnum]) then
      local line_length = #api.nvim_buf_get_lines(bufnr, lnum, lnum + 1, true)[1]
      --- @type function, function
      local sort_diagnostics, is_next
      if search_forward then
        sort_diagnostics = function(a, b)
          return a.col < b.col
        end
        is_next = function(d)
          return math.min(d.col, math.max(line_length - 1, 0)) > position[2]
        end
      else
        sort_diagnostics = function(a, b)
          return a.col > b.col
        end
        is_next = function(d)
          return math.min(d.col, math.max(line_length - 1, 0)) < position[2]
        end
      end
      table.sort(line_diagnostics[lnum], sort_diagnostics)
      if i == 0 then
        for _, v in
          pairs(line_diagnostics[lnum] --[[@as table<string,any>]])
        do
          if is_next(v) then
            return v
          end
        end
      else
        return line_diagnostics[lnum][1]
      end
    end
  end
end

--- Move the cursor to the given diagnostic.
---
--- @param diagnostic vim.Diagnostic?
--- @param opts vim.diagnostic.JumpOpts?
local function goto_diagnostic(diagnostic, opts)
  if not diagnostic then
    api.nvim_echo({ { 'No more valid diagnostics to move to', 'WarningMsg' } }, true, {})
    return
  end

  opts = opts or {}

  -- Support deprecated win_id alias
  if opts.win_id then
    vim.deprecate('opts.win_id', 'opts.winid', '0.13')
    opts.winid = opts.win_id
    opts.win_id = nil --- @diagnostic disable-line
  end

  local winid = opts.winid or api.nvim_get_current_win()

  vim._with({ win = winid }, function()
    -- Save position in the window's jumplist
    vim.cmd("normal! m'")
    api.nvim_win_set_cursor(winid, { diagnostic.lnum + 1, diagnostic.col })
    -- Open folds under the cursor
    vim.cmd('normal! zv')
  end)

  local float_opts = opts.float
  if float_opts then
    float_opts = type(float_opts) == 'table' and float_opts or {}
    vim.schedule(function()
      M.open_float(vim.tbl_extend('keep', float_opts, {
        bufnr = api.nvim_win_get_buf(winid),
        scope = 'cursor',
        focus = false,
      }))
    end)
  end
end

--- Configure diagnostic options globally or for a specific diagnostic
--- namespace.
---
--- Configuration can be specified globally, per-namespace, or ephemerally
--- (i.e. only for a single call to |vim.diagnostic.set()| or
--- |vim.diagnostic.show()|). Ephemeral configuration has highest priority,
--- followed by namespace configuration, and finally global configuration.
---
--- For example, if a user enables virtual text globally with
---
--- ```lua
--- vim.diagnostic.config({ virtual_text = true })
--- ```
---
--- and a diagnostic producer sets diagnostics with
---
--- ```lua
--- vim.diagnostic.set(ns, 0, diagnostics, { virtual_text = false })
--- ```
---
--- then virtual text will not be enabled for those diagnostics.
---
---@param opts vim.diagnostic.Opts? When omitted or `nil`, retrieve the current
---       configuration. Otherwise, a configuration table (see |vim.diagnostic.Opts|).
---@param namespace integer? Update the options for the given namespace.
---                          When omitted, update the global diagnostic options.
---@return vim.diagnostic.Opts? : Current diagnostic config if {opts} is omitted.
function M.config(opts, namespace)
  vim.validate('opts', opts, 'table', true)
  vim.validate('namespace', namespace, 'number', true)

  local t --- @type vim.diagnostic.Opts
  if namespace then
    local ns = M.get_namespace(namespace)
    t = ns.opts
  else
    t = global_diagnostic_options
  end

  if not opts then
    -- Return current config
    return vim.deepcopy(t, true)
  end

  for k, v in
    pairs(opts --[[@as table<any,any>]])
  do
    t[k] = v
  end

  if namespace then
    for bufnr, v in pairs(diagnostic_cache) do
      if v[namespace] then
        M.show(namespace, bufnr)
      end
    end
  else
    for bufnr, v in pairs(diagnostic_cache) do
      for ns in pairs(v) do
        M.show(ns, bufnr)
      end
    end
  end
end

--- Set diagnostics for the given namespace and buffer.
---
---@param namespace integer The diagnostic namespace
---@param bufnr integer Buffer number
---@param diagnostics vim.Diagnostic[]
---@param opts? vim.diagnostic.Opts Display options to pass to |vim.diagnostic.show()|
function M.set(namespace, bufnr, diagnostics, opts)
  vim.validate('namespace', namespace, 'number')
  vim.validate('bufnr', bufnr, 'number')
  vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')
  vim.validate('opts', opts, 'table', true)

  bufnr = vim._resolve_bufnr(bufnr)

  if vim.tbl_isempty(diagnostics) then
    diagnostic_cache[bufnr][namespace] = nil
  else
    set_diagnostic_cache(namespace, bufnr, diagnostics)
  end

  M.show(namespace, bufnr, nil, opts)

  api.nvim_exec_autocmds('DiagnosticChanged', {
    modeline = false,
    buffer = bufnr,
    -- TODO(lewis6991): should this be deepcopy()'d like they are in vim.diagnostic.get()
    data = { diagnostics = diagnostics },
  })
end

--- Get namespace metadata.
---
---@param namespace integer Diagnostic namespace
---@return vim.diagnostic.NS : Namespace metadata
function M.get_namespace(namespace)
  vim.validate('namespace', namespace, 'number')
  if not all_namespaces[namespace] then
    local name --- @type string?
    for k, v in pairs(api.nvim_get_namespaces()) do
      if namespace == v then
        name = k
        break
      end
    end

    assert(name, 'namespace does not exist or is anonymous')

    all_namespaces[namespace] = {
      name = name,
      opts = {},
      user_data = {},
    }
  end
  return all_namespaces[namespace]
end

--- Get current diagnostic namespaces.
---
---@return table<integer,vim.diagnostic.NS> : List of active diagnostic namespaces |vim.diagnostic|.
function M.get_namespaces()
  return vim.deepcopy(all_namespaces, true)
end

--- Get current diagnostics.
---
--- Modifying diagnostics in the returned table has no effect.
--- To set diagnostics in a buffer, use |vim.diagnostic.set()|.
---
---@param bufnr integer? Buffer number to get diagnostics from. Use 0 for
---                      current buffer or nil for all buffers.
---@param opts? vim.diagnostic.GetOpts
---@return vim.Diagnostic[] : Fields `bufnr`, `end_lnum`, `end_col`, and `severity`
---                           are guaranteed to be present.
function M.get(bufnr, opts)
  vim.validate('bufnr', bufnr, 'number', true)
  vim.validate('opts', opts, 'table', true)

  return vim.deepcopy(get_diagnostics(bufnr, opts, false), true)
end

--- Get current diagnostics count.
---
---@param bufnr? integer Buffer number to get diagnostics from. Use 0 for
---                      current buffer or nil for all buffers.
---@param opts? vim.diagnostic.GetOpts
---@return table : Table with actually present severity values as keys
---                (see |diagnostic-severity|) and integer counts as values.
function M.count(bufnr, opts)
  vim.validate('bufnr', bufnr, 'number', true)
  vim.validate('opts', opts, 'table', true)

  local diagnostics = get_diagnostics(bufnr, opts, false)
  local count = {} --- @type table<integer,integer>
  for i = 1, #diagnostics do
    local severity = diagnostics[i].severity --[[@as integer]]
    count[severity] = (count[severity] or 0) + 1
  end
  return count
end

--- Get the previous diagnostic closest to the cursor position.
---
---@param opts? vim.diagnostic.JumpOpts
---@return vim.Diagnostic? : Previous diagnostic
function M.get_prev(opts)
  return next_diagnostic(false, opts)
end

--- Return the position of the previous diagnostic in the current buffer.
---
---@param opts? vim.diagnostic.JumpOpts
---@return table|false: Previous diagnostic position as a `(row, col)` tuple
---                     or `false` if there is no prior diagnostic.
---@deprecated
function M.get_prev_pos(opts)
  vim.deprecate(
    'vim.diagnostic.get_prev_pos()',
    'access the lnum and col fields from get_prev() instead',
    '0.13'
  )
  local prev = M.get_prev(opts)
  if not prev then
    return false
  end

  return { prev.lnum, prev.col }
end

--- Move to the previous diagnostic in the current buffer.
---@param opts? vim.diagnostic.JumpOpts
---@deprecated
function M.goto_prev(opts)
  vim.deprecate('vim.diagnostic.goto_prev()', 'vim.diagnostic.jump()', '0.13')
  opts = opts or {}
  opts.float = if_nil(opts.float, true)
  goto_diagnostic(M.get_prev(opts), opts)
end

--- Get the next diagnostic closest to the cursor position.
---
---@param opts? vim.diagnostic.JumpOpts
---@return vim.Diagnostic? : Next diagnostic
function M.get_next(opts)
  return next_diagnostic(true, opts)
end

--- Return the position of the next diagnostic in the current buffer.
---
---@param opts? vim.diagnostic.JumpOpts
---@return table|false : Next diagnostic position as a `(row, col)` tuple or false if no next
---                      diagnostic.
---@deprecated
function M.get_next_pos(opts)
  vim.deprecate(
    'vim.diagnostic.get_next_pos()',
    'access the lnum and col fields from get_next() instead',
    '0.13'
  )
  local next = M.get_next(opts)
  if not next then
    return false
  end

  return { next.lnum, next.col }
end

--- A table with the following keys:
--- @class vim.diagnostic.GetOpts
---
--- Limit diagnostics to one or more namespaces.
--- @field namespace? integer[]|integer
---
--- Limit diagnostics to those spanning the specified line number.
--- @field lnum? integer
---
--- See |diagnostic-severity|.
--- @field severity? vim.diagnostic.SeverityFilter

--- Configuration table with the keys listed below. Some parameters can have their default values
--- changed with |vim.diagnostic.config()|.
--- @class vim.diagnostic.JumpOpts : vim.diagnostic.GetOpts
---
--- The diagnostic to jump to. Mutually exclusive with {count}, {namespace},
--- and {severity}.
--- @field diagnostic? vim.Diagnostic
---
--- The number of diagnostics to move by, starting from {pos}. A positive
--- integer moves forward by {count} diagnostics, while a negative integer moves
--- backward by {count} diagnostics. Mutually exclusive with {diagnostic}.
--- @field count? integer
---
--- Cursor position as a `(row, col)` tuple. See |nvim_win_get_cursor()|. Used
--- to find the nearest diagnostic when {count} is used. Only used when {count}
--- is non-nil. Default is the current cursor position.
--- @field pos? [integer,integer]
---
--- Whether to loop around file or not. Similar to 'wrapscan'.
--- (default: `true`)
--- @field wrap? boolean
---
--- See |diagnostic-severity|.
--- @field severity? vim.diagnostic.SeverityFilter
---
--- Go to the diagnostic with the highest severity.
--- (default: `false`)
--- @field package _highest? boolean
---
--- If `true`, call |vim.diagnostic.open_float()| after moving.
--- If a table, pass the table as the {opts} parameter to |vim.diagnostic.open_float()|.
--- Unless overridden, the float will show diagnostics at the new cursor
--- position (as if "cursor" were passed to the "scope" option).
--- (default: `false`)
--- @field float? boolean|vim.diagnostic.Opts.Float
---
--- Window ID
--- (default: `0`)
--- @field winid? integer

--- Move to a diagnostic.
---
--- @param opts vim.diagnostic.JumpOpts
--- @return vim.Diagnostic? # The diagnostic that was moved to.
function M.jump(opts)
  vim.validate('opts', opts, 'table')

  -- One of "diagnostic" or "count" must be provided
  assert(
    opts.diagnostic or opts.count,
    'One of "diagnostic" or "count" must be specified in the options to vim.diagnostic.jump()'
  )

  -- Apply configuration options from vim.diagnostic.config()
  opts = vim.tbl_deep_extend('keep', opts, global_diagnostic_options.jump)

  if opts.diagnostic then
    goto_diagnostic(opts.diagnostic, opts)
    return opts.diagnostic
  end

  local count = opts.count
  if count == 0 then
    return nil
  end

  -- Support deprecated cursor_position alias
  if opts.cursor_position then
    vim.deprecate('opts.cursor_position', 'opts.pos', '0.13')
    opts.pos = opts.cursor_position
    opts.cursor_position = nil --- @diagnostic disable-line
  end

  local diag = nil
  while count ~= 0 do
    local next = next_diagnostic(count > 0, opts)
    if not next then
      break
    end

    -- Update cursor position
    opts.pos = { next.lnum + 1, next.col }

    if count > 0 then
      count = count - 1
    else
      count = count + 1
    end
    diag = next
  end

  goto_diagnostic(diag, opts)

  return diag
end

--- Move to the next diagnostic.
---
---@param opts? vim.diagnostic.JumpOpts
---@deprecated
function M.goto_next(opts)
  vim.deprecate('vim.diagnostic.goto_next()', 'vim.diagnostic.jump()', '0.13')
  opts = opts or {}
  opts.float = if_nil(opts.float, true)
  goto_diagnostic(M.get_next(opts), opts)
end

M.handlers.signs = {
  show = function(namespace, bufnr, diagnostics, opts)
    vim.validate('namespace', namespace, 'number')
    vim.validate('bufnr', bufnr, 'number')
    vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')
    vim.validate('opts', opts, 'table', true)

    bufnr = vim._resolve_bufnr(bufnr)
    opts = opts or {}

    if not api.nvim_buf_is_loaded(bufnr) then
      return
    end

    if opts.signs and opts.signs.severity then
      diagnostics = filter_by_severity(opts.signs.severity, diagnostics)
    end

    -- 10 is the default sign priority when none is explicitly specified
    local priority = opts.signs and opts.signs.priority or 10
    local get_priority = severity_to_extmark_priority(priority, opts)

    local ns = M.get_namespace(namespace)
    if not ns.user_data.sign_ns then
      ns.user_data.sign_ns =
        api.nvim_create_namespace(string.format('%s/diagnostic/signs', ns.name))
    end

    -- Handle legacy diagnostic sign definitions
    -- These were deprecated in 0.10 and will be removed in 0.12
    if opts.signs and not opts.signs.text and not opts.signs.numhl then
      for _, v in ipairs({ 'Error', 'Warn', 'Info', 'Hint' }) do
        local name = string.format('DiagnosticSign%s', v)
        local sign = vim.fn.sign_getdefined(name)[1]
        if sign then
          local severity = M.severity[v:upper()]
          vim.deprecate(
            'Defining diagnostic signs with :sign-define or sign_define()',
            'vim.diagnostic.config()',
            '0.12'
          )

          if not opts.signs.text then
            opts.signs.text = {}
          end

          if not opts.signs.numhl then
            opts.signs.numhl = {}
          end

          if not opts.signs.linehl then
            opts.signs.linehl = {}
          end

          if opts.signs.text[severity] == nil then
            opts.signs.text[severity] = sign.text or ''
          end

          if opts.signs.numhl[severity] == nil then
            opts.signs.numhl[severity] = sign.numhl
          end

          if opts.signs.linehl[severity] == nil then
            opts.signs.linehl[severity] = sign.linehl
          end
        end
      end
    end

    local text = {} ---@type table<vim.diagnostic.Severity|string, string>
    for k in pairs(M.severity) do
      if opts.signs.text and opts.signs.text[k] then
        text[k] = opts.signs.text[k]
      elseif type(k) == 'string' and not text[k] then
        text[k] = string.sub(k, 1, 1):upper()
      end
    end

    local numhl = opts.signs.numhl or {}
    local linehl = opts.signs.linehl or {}

    local line_count = api.nvim_buf_line_count(bufnr)

    for _, diagnostic in ipairs(diagnostics) do
      if diagnostic.lnum <= line_count then
        api.nvim_buf_set_extmark(bufnr, ns.user_data.sign_ns, diagnostic.lnum, 0, {
          sign_text = text[diagnostic.severity] or text[M.severity[diagnostic.severity]] or 'U',
          sign_hl_group = sign_highlight_map[diagnostic.severity],
          number_hl_group = numhl[diagnostic.severity],
          line_hl_group = linehl[diagnostic.severity],
          priority = get_priority(diagnostic.severity),
        })
      end
    end
  end,

  --- @param namespace integer
  --- @param bufnr integer
  hide = function(namespace, bufnr)
    local ns = M.get_namespace(namespace)
    if ns.user_data.sign_ns and api.nvim_buf_is_valid(bufnr) then
      api.nvim_buf_clear_namespace(bufnr, ns.user_data.sign_ns, 0, -1)
    end
  end,
}

M.handlers.underline = {
  show = function(namespace, bufnr, diagnostics, opts)
    vim.validate('namespace', namespace, 'number')
    vim.validate('bufnr', bufnr, 'number')
    vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')
    vim.validate('opts', opts, 'table', true)

    bufnr = vim._resolve_bufnr(bufnr)
    opts = opts or {}

    if not vim.api.nvim_buf_is_loaded(bufnr) then
      return
    end

    if opts.underline and opts.underline.severity then
      diagnostics = filter_by_severity(opts.underline.severity, diagnostics)
    end

    local ns = M.get_namespace(namespace)
    if not ns.user_data.underline_ns then
      ns.user_data.underline_ns =
        api.nvim_create_namespace(string.format('%s/diagnostic/underline', ns.name))
    end

    local underline_ns = ns.user_data.underline_ns
    local get_priority = severity_to_extmark_priority(vim.hl.priorities.diagnostics, opts)

    for _, diagnostic in ipairs(diagnostics) do
      -- Default to error if we don't have a highlight associated
      local higroup = underline_highlight_map[assert(diagnostic.severity)]
        or underline_highlight_map[vim.diagnostic.severity.ERROR]

      if diagnostic._tags then
        -- TODO(lewis6991): we should be able to stack these.
        if diagnostic._tags.unnecessary then
          higroup = 'DiagnosticUnnecessary'
        end
        if diagnostic._tags.deprecated then
          higroup = 'DiagnosticDeprecated'
        end
      end

      vim.hl.range(
        bufnr,
        underline_ns,
        higroup,
        { diagnostic.lnum, diagnostic.col },
        { diagnostic.end_lnum, diagnostic.end_col },
        { priority = get_priority(diagnostic.severity) }
      )
    end
    save_extmarks(underline_ns, bufnr)
  end,
  hide = function(namespace, bufnr)
    local ns = M.get_namespace(namespace)
    if ns.user_data.underline_ns then
      diagnostic_cache_extmarks[bufnr][ns.user_data.underline_ns] = {}
      if api.nvim_buf_is_valid(bufnr) then
        api.nvim_buf_clear_namespace(bufnr, ns.user_data.underline_ns, 0, -1)
      end
    end
  end,
}

M.handlers.virtual_text = {
  show = function(namespace, bufnr, diagnostics, opts)
    vim.validate('namespace', namespace, 'number')
    vim.validate('bufnr', bufnr, 'number')
    vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')
    vim.validate('opts', opts, 'table', true)

    bufnr = vim._resolve_bufnr(bufnr)
    opts = opts or {}

    if not vim.api.nvim_buf_is_loaded(bufnr) then
      return
    end

    local severity --- @type vim.diagnostic.SeverityFilter?
    if opts.virtual_text then
      if opts.virtual_text.format then
        diagnostics = reformat_diagnostics(opts.virtual_text.format, diagnostics)
      end
      if
        opts.virtual_text.source
        and (opts.virtual_text.source ~= 'if_many' or count_sources(bufnr) > 1)
      then
        diagnostics = prefix_source(diagnostics)
      end
      if opts.virtual_text.severity then
        severity = opts.virtual_text.severity
      end
    end

    local ns = M.get_namespace(namespace)
    if not ns.user_data.virt_text_ns then
      ns.user_data.virt_text_ns =
        api.nvim_create_namespace(string.format('%s/diagnostic/virtual_text', ns.name))
    end

    local virt_text_ns = ns.user_data.virt_text_ns
    local buffer_line_diagnostics = diagnostic_lines(diagnostics)
    for line, line_diagnostics in pairs(buffer_line_diagnostics) do
      if severity then
        line_diagnostics = filter_by_severity(severity, line_diagnostics)
      end
      local virt_texts = M._get_virt_text_chunks(line_diagnostics, opts.virtual_text)

      if virt_texts then
        api.nvim_buf_set_extmark(bufnr, virt_text_ns, line, 0, {
          hl_mode = opts.virtual_text.hl_mode or 'combine',
          virt_text = virt_texts,
          virt_text_pos = opts.virtual_text.virt_text_pos,
          virt_text_hide = opts.virtual_text.virt_text_hide,
          virt_text_win_col = opts.virtual_text.virt_text_win_col,
        })
      end
    end
    save_extmarks(virt_text_ns, bufnr)
  end,
  hide = function(namespace, bufnr)
    local ns = M.get_namespace(namespace)
    if ns.user_data.virt_text_ns then
      diagnostic_cache_extmarks[bufnr][ns.user_data.virt_text_ns] = {}
      if api.nvim_buf_is_valid(bufnr) then
        api.nvim_buf_clear_namespace(bufnr, ns.user_data.virt_text_ns, 0, -1)
      end
    end
  end,
}

--- Get virtual text chunks to display using |nvim_buf_set_extmark()|.
---
--- Exported for backward compatibility with
--- vim.lsp.diagnostic.get_virtual_text_chunks_for_line(). When that function is eventually removed,
--- this can be made local.
--- @private
--- @param line_diags table<integer,vim.Diagnostic>
--- @param opts vim.diagnostic.Opts.VirtualText
function M._get_virt_text_chunks(line_diags, opts)
  if #line_diags == 0 then
    return nil
  end

  opts = opts or {}
  local prefix = opts.prefix or '■'
  local suffix = opts.suffix or ''
  local spacing = opts.spacing or 4

  -- Create a little more space between virtual text and contents
  local virt_texts = { { string.rep(' ', spacing) } }

  for i = 1, #line_diags do
    local resolved_prefix = prefix
    if type(prefix) == 'function' then
      resolved_prefix = prefix(line_diags[i], i, #line_diags) or ''
    end
    table.insert(
      virt_texts,
      { resolved_prefix, virtual_text_highlight_map[line_diags[i].severity] }
    )
  end
  local last = line_diags[#line_diags]

  -- TODO(tjdevries): Allow different servers to be shown first somehow?
  -- TODO(tjdevries): Display server name associated with these?
  if last.message then
    if type(suffix) == 'function' then
      suffix = suffix(last) or ''
    end
    table.insert(virt_texts, {
      string.format(' %s%s', last.message:gsub('\r', ''):gsub('\n', '  '), suffix),
      virtual_text_highlight_map[last.severity],
    })

    return virt_texts
  end
end

--- Hide currently displayed diagnostics.
---
--- This only clears the decorations displayed in the buffer. Diagnostics can
--- be redisplayed with |vim.diagnostic.show()|. To completely remove
--- diagnostics, use |vim.diagnostic.reset()|.
---
--- To hide diagnostics and prevent them from re-displaying, use
--- |vim.diagnostic.enable()|.
---
---@param namespace integer? Diagnostic namespace. When omitted, hide
---                          diagnostics from all namespaces.
---@param bufnr integer? Buffer number, or 0 for current buffer. When
---                      omitted, hide diagnostics in all buffers.
function M.hide(namespace, bufnr)
  vim.validate('namespace', namespace, 'number', true)
  vim.validate('bufnr', bufnr, 'number', true)

  local buffers = bufnr and { vim._resolve_bufnr(bufnr) } or vim.tbl_keys(diagnostic_cache)
  for _, iter_bufnr in ipairs(buffers) do
    local namespaces = namespace and { namespace } or vim.tbl_keys(diagnostic_cache[iter_bufnr])
    for _, iter_namespace in ipairs(namespaces) do
      for _, handler in pairs(M.handlers) do
        if handler.hide then
          handler.hide(iter_namespace, iter_bufnr)
        end
      end
    end
  end
end

--- Check whether diagnostics are enabled.
---
--- @param filter vim.diagnostic.Filter?
--- @return boolean
--- @since 12
function M.is_enabled(filter)
  filter = filter or {}
  if filter.ns_id and M.get_namespace(filter.ns_id).disabled then
    return false
  elseif filter.bufnr == nil then
    -- See enable() logic.
    return vim.tbl_isempty(diagnostic_disabled) and not diagnostic_disabled[1]
  end

  local bufnr = vim._resolve_bufnr(filter.bufnr)
  if type(diagnostic_disabled[bufnr]) == 'table' then
    return not diagnostic_disabled[bufnr][filter.ns_id]
  end

  return diagnostic_disabled[bufnr] == nil
end

--- @deprecated use `vim.diagnostic.is_enabled()`
function M.is_disabled(bufnr, namespace)
  vim.deprecate('vim.diagnostic.is_disabled()', 'vim.diagnostic.is_enabled()', '0.12')
  return not M.is_enabled { bufnr = bufnr or 0, ns_id = namespace }
end

--- Display diagnostics for the given namespace and buffer.
---
---@param namespace integer? Diagnostic namespace. When omitted, show
---                          diagnostics from all namespaces.
---@param bufnr integer? Buffer number, or 0 for current buffer. When omitted, show
---                      diagnostics in all buffers.
---@param diagnostics vim.Diagnostic[]? The diagnostics to display. When omitted, use the
---                             saved diagnostics for the given namespace and
---                             buffer. This can be used to display a list of diagnostics
---                             without saving them or to display only a subset of
---                             diagnostics. May not be used when {namespace}
---                             or {bufnr} is nil.
---@param opts? vim.diagnostic.Opts Display options.
function M.show(namespace, bufnr, diagnostics, opts)
  vim.validate('namespace', namespace, 'number', true)
  vim.validate('bufnr', bufnr, 'number', true)
  vim.validate('diagnostics', diagnostics, vim.islist, true, 'a list of diagnostics')
  vim.validate('opts', opts, 'table', true)

  if not bufnr or not namespace then
    assert(not diagnostics, 'Cannot show diagnostics without a buffer and namespace')
    if not bufnr then
      for iter_bufnr in pairs(diagnostic_cache) do
        M.show(namespace, iter_bufnr, nil, opts)
      end
    else
      -- namespace is nil
      bufnr = vim._resolve_bufnr(bufnr)
      for iter_namespace in pairs(diagnostic_cache[bufnr]) do
        M.show(iter_namespace, bufnr, nil, opts)
      end
    end
    return
  end

  if not M.is_enabled { bufnr = bufnr or 0, ns_id = namespace } then
    return
  end

  M.hide(namespace, bufnr)

  diagnostics = diagnostics or get_diagnostics(bufnr, { namespace = namespace }, true)

  if vim.tbl_isempty(diagnostics) then
    return
  end

  local opts_res = get_resolved_options(opts, namespace, bufnr)

  if opts_res.update_in_insert then
    clear_scheduled_display(namespace, bufnr)
  else
    local mode = api.nvim_get_mode()
    if string.sub(mode.mode, 1, 1) == 'i' then
      schedule_display(namespace, bufnr, opts_res)
      return
    end
  end

  if if_nil(opts_res.severity_sort, false) then
    if type(opts_res.severity_sort) == 'table' and opts_res.severity_sort.reverse then
      table.sort(diagnostics, function(a, b)
        return a.severity < b.severity
      end)
    else
      table.sort(diagnostics, function(a, b)
        return a.severity > b.severity
      end)
    end
  end

  for handler_name, handler in pairs(M.handlers) do
    if handler.show and opts_res[handler_name] then
      handler.show(namespace, bufnr, diagnostics, opts_res)
    end
  end
end

--- Show diagnostics in a floating window.
---
---@param opts vim.diagnostic.Opts.Float?
---@return integer? float_bufnr
---@return integer? winid
function M.open_float(opts, ...)
  -- Support old (bufnr, opts) signature
  local bufnr --- @type integer?
  if opts == nil or type(opts) == 'number' then
    bufnr = opts
    opts = ... --- @type vim.diagnostic.Opts.Float
  else
    vim.validate('opts', opts, 'table', true)
  end

  opts = opts or {}
  bufnr = vim._resolve_bufnr(bufnr or opts.bufnr)

  do
    -- Resolve options with user settings from vim.diagnostic.config
    -- Unlike the other decoration functions (e.g. set_virtual_text, set_signs, etc.) `open_float`
    -- does not have a dedicated table for configuration options; instead, the options are mixed in
    -- with its `opts` table which also includes "keyword" parameters. So we create a dedicated
    -- options table that inherits missing keys from the global configuration before resolving.
    local t = global_diagnostic_options.float
    local float_opts = vim.tbl_extend('keep', opts, type(t) == 'table' and t or {})
    opts = get_resolved_options({ float = float_opts }, nil, bufnr).float
  end

  local scope = ({ l = 'line', c = 'cursor', b = 'buffer' })[opts.scope] or opts.scope or 'line'
  local lnum, col --- @type integer, integer
  local opts_pos = opts.pos
  if scope == 'line' or scope == 'cursor' then
    if not opts_pos then
      local pos = api.nvim_win_get_cursor(0)
      lnum = pos[1] - 1
      col = pos[2]
    elseif type(opts_pos) == 'number' then
      lnum = opts_pos
    elseif type(opts_pos) == 'table' then
      lnum, col = opts_pos[1], opts_pos[2]
    else
      error("Invalid value for option 'pos'")
    end
  elseif scope ~= 'buffer' then
    error("Invalid value for option 'scope'")
  end

  local diagnostics = get_diagnostics(bufnr, opts --[[@as vim.diagnostic.GetOpts]], true)

  if scope == 'line' then
    --- @param d vim.Diagnostic
    diagnostics = vim.tbl_filter(function(d)
      return lnum >= d.lnum
        and lnum <= d.end_lnum
        and (d.lnum == d.end_lnum or lnum ~= d.end_lnum or d.end_col ~= 0)
    end, diagnostics)
  elseif scope == 'cursor' then
    -- If `col` is past the end of the line, show if the cursor is on the last char in the line
    local line_length = #api.nvim_buf_get_lines(bufnr, lnum, lnum + 1, true)[1]
    --- @param d vim.Diagnostic
    diagnostics = vim.tbl_filter(function(d)
      return lnum >= d.lnum
        and lnum <= d.end_lnum
        and (lnum ~= d.lnum or col >= math.min(d.col, line_length - 1))
        and ((d.lnum == d.end_lnum and d.col == d.end_col) or lnum ~= d.end_lnum or col < d.end_col)
    end, diagnostics)
  end

  if vim.tbl_isempty(diagnostics) then
    return
  end

  local severity_sort = if_nil(opts.severity_sort, global_diagnostic_options.severity_sort)
  if severity_sort then
    if type(severity_sort) == 'table' and severity_sort.reverse then
      table.sort(diagnostics, function(a, b)
        return a.severity > b.severity
      end)
    else
      table.sort(diagnostics, function(a, b)
        return a.severity < b.severity
      end)
    end
  end

  local lines = {} --- @type string[]
  local highlights = {} --- @type table[]
  local header = if_nil(opts.header, 'Diagnostics:')
  if header then
    vim.validate('header', header, { 'string', 'table' }, "'string' or 'table'")
    if type(header) == 'table' then
      -- Don't insert any lines for an empty string
      if string.len(if_nil(header[1], '')) > 0 then
        table.insert(lines, header[1])
        table.insert(highlights, { hlname = header[2] or 'Bold' })
      end
    elseif #header > 0 then
      table.insert(lines, header)
      table.insert(highlights, { hlname = 'Bold' })
    end
  end

  if opts.format then
    diagnostics = reformat_diagnostics(opts.format, diagnostics)
  end

  if opts.source and (opts.source ~= 'if_many' or count_sources(bufnr) > 1) then
    diagnostics = prefix_source(diagnostics)
  end

  local prefix_opt =
    if_nil(opts.prefix, (scope == 'cursor' and #diagnostics <= 1) and '' or function(_, i)
      return string.format('%d. ', i)
    end)

  local prefix, prefix_hl_group --- @type string?, string?
  if prefix_opt then
    vim.validate(
      'prefix',
      prefix_opt,
      { 'string', 'table', 'function' },
      "'string' or 'table' or 'function'"
    )
    if type(prefix_opt) == 'string' then
      prefix, prefix_hl_group = prefix_opt, 'NormalFloat'
    elseif type(prefix_opt) == 'table' then
      prefix, prefix_hl_group = prefix_opt[1] or '', prefix_opt[2] or 'NormalFloat'
    end
  end

  local suffix_opt = if_nil(opts.suffix, function(diagnostic)
    return diagnostic.code and string.format(' [%s]', diagnostic.code) or ''
  end)

  local suffix, suffix_hl_group --- @type string?, string?
  if suffix_opt then
    vim.validate(
      'suffix',
      suffix_opt,
      { 'string', 'table', 'function' },
      "'string' or 'table' or 'function'"
    )
    if type(suffix_opt) == 'string' then
      suffix, suffix_hl_group = suffix_opt, 'NormalFloat'
    elseif type(suffix_opt) == 'table' then
      suffix, suffix_hl_group = suffix_opt[1] or '', suffix_opt[2] or 'NormalFloat'
    end
  end

  for i, diagnostic in ipairs(diagnostics) do
    if type(prefix_opt) == 'function' then
      --- @cast prefix_opt fun(...): string?, string?
      local prefix0, prefix_hl_group0 = prefix_opt(diagnostic, i, #diagnostics)
      prefix, prefix_hl_group = prefix0 or '', prefix_hl_group0 or 'NormalFloat'
    end
    if type(suffix_opt) == 'function' then
      --- @cast suffix_opt fun(...): string?, string?
      local suffix0, suffix_hl_group0 = suffix_opt(diagnostic, i, #diagnostics)
      suffix, suffix_hl_group = suffix0 or '', suffix_hl_group0 or 'NormalFloat'
    end
    --- @type string?
    local hiname = floating_highlight_map[assert(diagnostic.severity)]
    local message_lines = vim.split(diagnostic.message, '\n')
    for j = 1, #message_lines do
      local pre = j == 1 and prefix or string.rep(' ', #prefix)
      local suf = j == #message_lines and suffix or ''
      table.insert(lines, pre .. message_lines[j] .. suf)
      table.insert(highlights, {
        hlname = hiname,
        prefix = {
          length = j == 1 and #prefix or 0,
          hlname = prefix_hl_group,
        },
        suffix = {
          length = j == #message_lines and #suffix or 0,
          hlname = suffix_hl_group,
        },
      })
    end
  end

  -- Used by open_floating_preview to allow the float to be focused
  if not opts.focus_id then
    opts.focus_id = scope
  end
  local float_bufnr, winnr = vim.lsp.util.open_floating_preview(lines, 'plaintext', opts)
  vim.bo[float_bufnr].path = vim.bo[bufnr].path
  for i, hl in ipairs(highlights) do
    local line = lines[i]
    local prefix_len = hl.prefix and hl.prefix.length or 0
    local suffix_len = hl.suffix and hl.suffix.length or 0
    if prefix_len > 0 then
      api.nvim_buf_add_highlight(float_bufnr, -1, hl.prefix.hlname, i - 1, 0, prefix_len)
    end
    api.nvim_buf_add_highlight(float_bufnr, -1, hl.hlname, i - 1, prefix_len, #line - suffix_len)
    if suffix_len > 0 then
      api.nvim_buf_add_highlight(float_bufnr, -1, hl.suffix.hlname, i - 1, #line - suffix_len, -1)
    end
  end

  return float_bufnr, winnr
end

--- Remove all diagnostics from the given namespace.
---
--- Unlike |vim.diagnostic.hide()|, this function removes all saved
--- diagnostics. They cannot be redisplayed using |vim.diagnostic.show()|. To
--- simply remove diagnostic decorations in a way that they can be
--- re-displayed, use |vim.diagnostic.hide()|.
---
---@param namespace integer? Diagnostic namespace. When omitted, remove
---                          diagnostics from all namespaces.
---@param bufnr integer? Remove diagnostics for the given buffer. When omitted,
---                     diagnostics are removed for all buffers.
function M.reset(namespace, bufnr)
  vim.validate('namespace', namespace, 'number', true)
  vim.validate('bufnr', bufnr, 'number', true)

  local buffers = bufnr and { vim._resolve_bufnr(bufnr) } or vim.tbl_keys(diagnostic_cache)
  for _, iter_bufnr in ipairs(buffers) do
    local namespaces = namespace and { namespace } or vim.tbl_keys(diagnostic_cache[iter_bufnr])
    for _, iter_namespace in ipairs(namespaces) do
      diagnostic_cache[iter_bufnr][iter_namespace] = nil
      M.hide(iter_namespace, iter_bufnr)
    end

    if api.nvim_buf_is_valid(iter_bufnr) then
      api.nvim_exec_autocmds('DiagnosticChanged', {
        modeline = false,
        buffer = iter_bufnr,
        data = { diagnostics = {} },
      })
    else
      diagnostic_cache[iter_bufnr] = nil
    end
  end
end

--- Configuration table with the following keys:
--- @class vim.diagnostic.setqflist.Opts
--- @inlinedoc
---
--- Only add diagnostics from the given namespace.
--- @field namespace? integer
---
--- Open quickfix list after setting.
--- (default: `true`)
--- @field open? boolean
---
--- Title of quickfix list. Defaults to "Diagnostics". If there's already a quickfix list with this
--- title, it's updated. If not, a new quickfix list is created.
--- @field title? string
---
--- See |diagnostic-severity|.
--- @field severity? vim.diagnostic.SeverityFilter

--- Add all diagnostics to the quickfix list.
---
---@param opts? vim.diagnostic.setqflist.Opts
function M.setqflist(opts)
  set_list(false, opts)
end

---Configuration table with the following keys:
--- @class vim.diagnostic.setloclist.Opts
--- @inlinedoc
---
--- Only add diagnostics from the given namespace.
--- @field namespace? integer
---
--- Window number to set location list for.
--- (default: `0`)
--- @field winnr? integer
---
--- Open the location list after setting.
--- (default: `true`)
--- @field open? boolean
---
--- Title of the location list. Defaults to "Diagnostics".
--- @field title? string
---
--- See |diagnostic-severity|.
--- @field severity? vim.diagnostic.SeverityFilter

--- Add buffer diagnostics to the location list.
---
---@param opts? vim.diagnostic.setloclist.Opts
function M.setloclist(opts)
  set_list(true, opts)
end

--- @deprecated use `vim.diagnostic.enable(false, …)`
function M.disable(bufnr, namespace)
  vim.deprecate('vim.diagnostic.disable()', 'vim.diagnostic.enable(false, …)', '0.12')
  M.enable(false, { bufnr = bufnr, ns_id = namespace })
end

--- Enables or disables diagnostics.
---
--- To "toggle", pass the inverse of `is_enabled()`:
---
--- ```lua
--- vim.diagnostic.enable(not vim.diagnostic.is_enabled())
--- ```
---
--- @param enable (boolean|nil) true/nil to enable, false to disable
--- @param filter vim.diagnostic.Filter?
function M.enable(enable, filter)
  -- Deprecated signature. Drop this in 0.12
  local legacy = (enable or filter)
    and vim.tbl_contains({ 'number', 'nil' }, type(enable))
    and vim.tbl_contains({ 'number', 'nil' }, type(filter))

  if legacy then
    vim.deprecate(
      'vim.diagnostic.enable(buf:number, namespace:number)',
      'vim.diagnostic.enable(enable:boolean, filter:table)',
      '0.12'
    )

    vim.validate('enable', enable, 'number', true) -- Legacy `bufnr` arg.
    vim.validate('filter', filter, 'number', true) -- Legacy `namespace` arg.

    local ns_id = type(filter) == 'number' and filter or nil
    filter = {}
    filter.ns_id = ns_id
    filter.bufnr = type(enable) == 'number' and enable or nil
    enable = true
  else
    filter = filter or {}
    vim.validate('enable', enable, 'boolean', true)
    vim.validate('filter', filter, 'table', true)
  end

  enable = enable == nil and true or enable
  local bufnr = filter.bufnr
  local ns_id = filter.ns_id

  if not bufnr then
    if not ns_id then
      diagnostic_disabled = (
        enable
          -- Enable everything by setting diagnostic_disabled to an empty table.
          and {}
        -- Disable everything (including as yet non-existing buffers and namespaces) by setting
        -- diagnostic_disabled to an empty table and set its metatable to always return true.
        or setmetatable({}, {
          __index = function()
            return true
          end,
        })
      )
    else
      local ns = M.get_namespace(ns_id)
      ns.disabled = not enable
    end
  else
    bufnr = vim._resolve_bufnr(bufnr)
    if not ns_id then
      diagnostic_disabled[bufnr] = (not enable) and true or nil
    else
      if type(diagnostic_disabled[bufnr]) ~= 'table' then
        if enable then
          return
        else
          diagnostic_disabled[bufnr] = {}
        end
      end
      diagnostic_disabled[bufnr][ns_id] = (not enable) and true or nil
    end
  end

  if enable then
    M.show(ns_id, bufnr)
  else
    M.hide(ns_id, bufnr)
  end
end

--- Parse a diagnostic from a string.
---
--- For example, consider a line of output from a linter:
---
--- ```
--- WARNING filename:27:3: Variable 'foo' does not exist
--- ```
---
--- This can be parsed into |vim.Diagnostic| structure with:
---
--- ```lua
--- local s = "WARNING filename:27:3: Variable 'foo' does not exist"
--- local pattern = "^(%w+) %w+:(%d+):(%d+): (.+)$"
--- local groups = { "severity", "lnum", "col", "message" }
--- vim.diagnostic.match(s, pattern, groups, { WARNING = vim.diagnostic.WARN })
--- ```
---
---@param str string String to parse diagnostics from.
---@param pat string Lua pattern with capture groups.
---@param groups string[] List of fields in a |vim.Diagnostic| structure to
---                    associate with captures from {pat}.
---@param severity_map table A table mapping the severity field from {groups}
---                          with an item from |vim.diagnostic.severity|.
---@param defaults table? Table of default values for any fields not listed in {groups}.
---                       When omitted, numeric values default to 0 and "severity" defaults to
---                       ERROR.
---@return vim.Diagnostic?: |vim.Diagnostic| structure or `nil` if {pat} fails to match {str}.
function M.match(str, pat, groups, severity_map, defaults)
  vim.validate('str', str, 'string')
  vim.validate('pat', pat, 'string')
  vim.validate('groups', groups, 'table')
  vim.validate('severity_map', severity_map, 'table', true)
  vim.validate('defaults', defaults, 'table', true)

  --- @type table<string,vim.diagnostic.Severity>
  severity_map = severity_map or M.severity

  local matches = { str:match(pat) } --- @type any[]
  if vim.tbl_isempty(matches) then
    return
  end

  local diagnostic = {} --- @type type<string,any>

  for i, match in ipairs(matches) do
    local field = groups[i]
    if field == 'severity' then
      match = severity_map[match]
    elseif field == 'lnum' or field == 'end_lnum' or field == 'col' or field == 'end_col' then
      match = assert(tonumber(match)) - 1
    end
    diagnostic[field] = match --- @type any
  end

  diagnostic = vim.tbl_extend('keep', diagnostic, defaults or {}) --- @type vim.Diagnostic
  diagnostic.severity = diagnostic.severity or M.severity.ERROR
  diagnostic.col = diagnostic.col or 0
  diagnostic.end_lnum = diagnostic.end_lnum or diagnostic.lnum
  diagnostic.end_col = diagnostic.end_col or diagnostic.col
  return diagnostic
end

local errlist_type_map = {
  [M.severity.ERROR] = 'E',
  [M.severity.WARN] = 'W',
  [M.severity.INFO] = 'I',
  [M.severity.HINT] = 'N',
}

--- Convert a list of diagnostics to a list of quickfix items that can be
--- passed to |setqflist()| or |setloclist()|.
---
---@param diagnostics vim.Diagnostic[]
---@return table[] : Quickfix list items |setqflist-what|
function M.toqflist(diagnostics)
  vim.validate('diagnostics', diagnostics, vim.islist, 'a list of diagnostics')

  local list = {} --- @type table[]
  for _, v in ipairs(diagnostics) do
    local item = {
      bufnr = v.bufnr,
      lnum = v.lnum + 1,
      col = v.col and (v.col + 1) or nil,
      end_lnum = v.end_lnum and (v.end_lnum + 1) or nil,
      end_col = v.end_col and (v.end_col + 1) or nil,
      text = v.message,
      type = errlist_type_map[v.severity] or 'E',
    }
    table.insert(list, item)
  end
  table.sort(list, function(a, b)
    if a.bufnr == b.bufnr then
      if a.lnum == b.lnum then
        return a.col < b.col
      else
        return a.lnum < b.lnum
      end
    else
      return a.bufnr < b.bufnr
    end
  end)
  return list
end

--- Convert a list of quickfix items to a list of diagnostics.
---
---@param list table[] List of quickfix items from |getqflist()| or |getloclist()|.
---@return vim.Diagnostic[]
function M.fromqflist(list)
  vim.validate('list', list, 'table')

  local diagnostics = {} --- @type vim.Diagnostic[]
  for _, item in ipairs(list) do
    if item.valid == 1 then
      local lnum = math.max(0, item.lnum - 1)
      local col = math.max(0, item.col - 1)
      local end_lnum = item.end_lnum > 0 and (item.end_lnum - 1) or lnum
      local end_col = item.end_col > 0 and (item.end_col - 1) or col
      local severity = item.type ~= '' and M.severity[item.type] or M.severity.ERROR
      diagnostics[#diagnostics + 1] = {
        bufnr = item.bufnr,
        lnum = lnum,
        col = col,
        end_lnum = end_lnum,
        end_col = end_col,
        severity = severity,
        message = item.text,
      }
    end
  end
  return diagnostics
end

return M