local shared = vim
local assert = require('luassert')
local busted = require('busted')
local luv = require('luv')
local Paths = require('test.cmakeconfig.paths')

assert:set_parameter('TableFormatLevel', 100)

local quote_me = '[^.%w%+%-%@%_%/]' -- complement (needn't quote)
local function shell_quote(str)
  if string.find(str, quote_me) or str == '' then
    return '"' .. str:gsub('[$%%"\\]', '\\%0') .. '"'
  else
    return str
  end
end

--- @class test.helpers
local module = {
  REMOVE_THIS = {},
}

--- @param p string
--- @return string
local function relpath(p)
  p = vim.fs.normalize(p)
  local cwd = luv.cwd()
  return p:gsub("^" .. cwd)
end

--- @param path string
--- @return boolean
function module.isdir(path)
  if not path then
    return false
  end
  local stat = luv.fs_stat(path)
  if not stat then
    return false
  end
  return stat.type == 'directory'
end

--- @param path string
--- @return boolean
function module.isfile(path)
  if not path then
    return false
  end
  local stat = luv.fs_stat(path)
  if not stat then
    return false
  end
  return stat.type == 'file'
end

--- @return string
function module.argss_to_cmd(...)
  local cmd = ''
  for i = 1, select('#', ...) do
    local arg = select(i, ...)
    if type(arg) == 'string' then
      cmd = cmd .. ' ' ..shell_quote(arg)
    else
      for _, subarg in ipairs(arg) do
        cmd = cmd .. ' ' .. shell_quote(subarg)
      end
    end
  end
  return cmd
end

function module.popen_r(...)
  return io.popen(module.argss_to_cmd(...), 'r')
end

-- sleeps the test runner (_not_ the nvim instance)
function module.sleep(ms)
  luv.sleep(ms)
end

-- Calls fn() until it succeeds, up to `max` times or until `max_ms`
-- milliseconds have passed.
function module.retry(max, max_ms, fn)
  assert(max == nil or max > 0)
  assert(max_ms == nil or max_ms > 0)
  local tries = 1
  local timeout = (max_ms and max_ms or 10000)
  local start_time = luv.now()
  while true do
    local status, result = pcall(fn)
    if status then
      return result
    end
    luv.update_time()  -- Update cached value of luv.now() (libuv: uv_now()).
    if (max and tries >= max) or (luv.now() - start_time > timeout) then
      busted.fail(string.format("retry() attempts: %d\n%s", tries, tostring(result)), 2)
    end
    tries = tries + 1
    luv.sleep(20)  -- Avoid hot loop...
  end
end

local check_logs_useless_lines = {
  ['Warning: noted but unhandled ioctl']=1,
  ['could cause spurious value errors to appear']=2,
  ['See README_MISSING_SYSCALL_OR_IOCTL for guidance']=3,
}

function module.eq(expected, actual, context)
  return assert.are.same(expected, actual, context)
end
function module.neq(expected, actual, context)
  return assert.are_not.same(expected, actual, context)
end

--- Asserts that `cond` is true, or prints a message.
---
--- @param cond (boolean) expression to assert
--- @param expected (any) description of expected result
--- @param actual (any) description of actual result
function module.ok(cond, expected, actual)
  assert((not expected and not actual) or (expected and actual), 'if "expected" is given, "actual" is also required')
  local msg = expected and ('expected %s, got: %s'):format(expected, tostring(actual)) or nil
  return assert(cond, msg)
end

local function epicfail(state, arguments, _)
  state.failure_message = arguments[1]
  return false
end
assert:register("assertion", "epicfail", epicfail)
function module.fail(msg)
  return assert.epicfail(msg)
end

function module.matches(pat, actual)
  if nil ~= string.match(actual, pat) then
    return true
  end
  error(string.format('Pattern does not match.\nPattern:\n%s\nActual:\n%s', pat, actual))
end

--- Asserts that `pat` matches (or *not* if inverse=true) any line in the tail of `logfile`.
---
--- Retries for 1 second in case of filesystem delay.
---
---@param pat (string) Lua pattern to match lines in the log file
---@param logfile (string) Full path to log file (default=$NVIM_LOG_FILE)
---@param nrlines (number) Search up to this many log lines
---@param inverse (boolean) Assert that the pattern does NOT match.
function module.assert_log(pat, logfile, nrlines, inverse)
  logfile = logfile or os.getenv('NVIM_LOG_FILE') or '.nvimlog'
  assert(logfile ~= nil, 'no logfile')
  nrlines = nrlines or 10
  inverse = inverse or false

  module.retry(nil, 1000, function()
    local lines = module.read_file_list(logfile, -nrlines) or {}
    local msg = string.format('Pattern %q %sfound in log (last %d lines): %s:\n%s',
      pat, (inverse and '' or 'not '), nrlines, logfile, '    '..table.concat(lines, '\n    '))
    for _,line in ipairs(lines) do
      if line:match(pat) then
        if inverse then error(msg) else return end
      end
    end
    if not inverse then error(msg) end
  end)
end

--- Asserts that `pat` does NOT match any line in the tail of `logfile`.
---
--- @see assert_log
function module.assert_nolog(pat, logfile, nrlines)
  return module.assert_log(pat, logfile, nrlines, true)
end

function module.pcall(fn, ...)
  assert(type(fn) == 'function')
  local status, rv = pcall(fn, ...)
  if status then
    return status, rv
  end

  -- From:
  --    C:/long/path/foo.lua:186: Expected string, got number
  -- to:
  --    .../foo.lua:0: Expected string, got number
  local errmsg = tostring(rv):gsub('([%s<])vim[/\\]([^%s:/\\]+):%d+', '%1\xffvim\xff%2:0')
                             :gsub('[^%s<]-[/\\]([^%s:/\\]+):%d+', '.../%1:0')
                             :gsub('\xffvim\xff', 'vim/')

  -- Scrub numbers in paths/stacktraces:
  --    shared.lua:0: in function 'gsplit'
  --    shared.lua:0: in function <shared.lua:0>'
  errmsg = errmsg:gsub('([^%s].lua):%d+', '%1:0')
  --    [string "<nvim>"]:0:
  --    [string ":lua"]:0:
  --    [string ":luado"]:0:
  errmsg = errmsg:gsub('(%[string "[^"]+"%]):%d+', '%1:0')

  -- Scrub tab chars:
  errmsg = errmsg:gsub('\t', '    ')
  -- In Lua 5.1, we sometimes get a "(tail call): ?" on the last line.
  --    We remove this so that the tests are not lua dependent.
  errmsg = errmsg:gsub('%s*%(tail call%): %?', '')

  return status, errmsg
end

-- Invokes `fn` and returns the error string (with truncated paths), or raises
-- an error if `fn` succeeds.
--
-- Replaces line/column numbers with zero:
--     shared.lua:0: in function 'gsplit'
--     shared.lua:0: in function <shared.lua:0>'
--
-- Usage:
--    -- Match exact string.
--    eq('e', pcall_err(function(a, b) error('e') end, 'arg1', 'arg2'))
--    -- Match Lua pattern.
--    matches('e[or]+$', pcall_err(function(a, b) error('some error') end, 'arg1', 'arg2'))
--
function module.pcall_err_withfile(fn, ...)
  assert(type(fn) == 'function')
  local status, rv = module.pcall(fn, ...)
  if status == true then
    error('expected failure, but got success')
  end
  return rv
end

function module.pcall_err_withtrace(fn, ...)
  local errmsg = module.pcall_err_withfile(fn, ...)

  return errmsg:gsub('^%.%.%./helpers%.lua:0: ', '')
               :gsub('^Error executing lua:- ' ,'')
               :gsub('^%[string "<nvim>"%]:0: ' ,'')
end

function module.pcall_err(...)
  return module.remove_trace(module.pcall_err_withtrace(...))
end

function module.remove_trace(s)
  return (s:gsub("\n%s*stack traceback:.*", ""))
end

-- initial_path:  directory to recurse into
-- re:            include pattern (string)
-- exc_re:        exclude pattern(s) (string or table)
function module.glob(initial_path, re, exc_re)
  exc_re = type(exc_re) == 'table' and exc_re or { exc_re }
  local paths_to_check = {initial_path}
  local ret = {}
  local checked_files = {}
  local function is_excluded(path)
    for _, pat in pairs(exc_re) do
      if path:match(pat) then return true end
    end
    return false
  end

  if is_excluded(initial_path) then
    return ret
  end
  while #paths_to_check > 0 do
    local cur_path = paths_to_check[#paths_to_check]
    paths_to_check[#paths_to_check] = nil
    for e in vim.fs.dir(cur_path) do
      local full_path = cur_path .. '/' .. e
      local checked_path = full_path:sub(#initial_path + 1)
      if (not is_excluded(checked_path)) and e:sub(1, 1) ~= '.' then
        local stat = luv.fs_stat(full_path)
        if stat then
          local check_key = stat.dev .. ':' .. tostring(stat.ino)
          if not checked_files[check_key] then
            checked_files[check_key] = true
            if stat.type == 'directory' then
              paths_to_check[#paths_to_check + 1] = full_path
            elseif not re or checked_path:match(re) then
              ret[#ret + 1] = full_path
            end
          end
        end
      end
    end
  end
  return ret
end

function module.check_logs()
  local log_dir = os.getenv('LOG_DIR')
  local runtime_errors = {}
  if log_dir and module.isdir(log_dir) then
    for tail in vim.fs.dir(log_dir) do
      if tail:sub(1, 30) == 'valgrind-' or tail:find('san%.') then
        local file = log_dir .. '/' .. tail
        local fd = io.open(file)
        local start_msg = ('='):rep(20) .. ' File ' .. file .. ' ' .. ('='):rep(20)
        local lines = {}
        local warning_line = 0
        for line in fd:lines() do
          local cur_warning_line = check_logs_useless_lines[line]
          if cur_warning_line == warning_line + 1 then
            warning_line = cur_warning_line
          else
            lines[#lines + 1] = line
          end
        end
        fd:close()
        if #lines > 0 then
          local status, f
          local out = io.stdout
          if os.getenv('SYMBOLIZER') then
            status, f = pcall(module.popen_r, os.getenv('SYMBOLIZER'), '-l', file)
          end
          out:write(start_msg .. '\n')
          if status then
            for line in f:lines() do
              out:write('= '..line..'\n')
            end
            f:close()
          else
            out:write('= ' .. table.concat(lines, '\n= ') .. '\n')
          end
          out:write(select(1, start_msg:gsub('.', '=')) .. '\n')
          table.insert(runtime_errors, file)
        end
        os.remove(file)
      end
    end
  end
  assert(0 == #runtime_errors, string.format(
    'Found runtime errors in logfile(s): %s',
    table.concat(runtime_errors, ', ')))
end

function module.sysname()
  local platform = luv.os_uname()
  if platform and platform.sysname then
    return platform.sysname:lower()
  end
end

function module.is_os(s)
  if not (s == 'win'
    or s == 'mac'
    or s == 'freebsd'
    or s == 'openbsd'
    or s == 'bsd') then
    error('unknown platform: '..tostring(s))
  end
  return not not ((s == 'win' and (module.sysname():find('windows') or module.sysname():find('mingw')))
    or (s == 'mac' and module.sysname() == 'darwin')
    or (s == 'freebsd' and module.sysname() == 'freebsd')
    or (s == 'openbsd' and module.sysname() == 'openbsd')
    or (s == 'bsd' and module.sysname():find('bsd')))
end

local function tmpdir_get()
  return os.getenv('TMPDIR') and os.getenv('TMPDIR') or os.getenv('TEMP')
end

-- Is temp directory `dir` defined local to the project workspace?
local function tmpdir_is_local(dir)
  return not not (dir and string.find(dir, 'Xtest'))
end

--- Creates a new temporary file for use by tests.
module.tmpname = (function()
  local seq = 0
  local tmpdir = tmpdir_get()
  return (function()
    if tmpdir_is_local(tmpdir) then
      -- Cannot control os.tmpname() dir, so hack our own tmpname() impl.
      seq = seq + 1
      -- "…/Xtest_tmpdir/T42.7"
      local fname = ('%s/%s.%d'):format(tmpdir, (_G._nvim_test_id or 'nvim-test'), seq)
      io.open(fname, 'w'):close()
      return fname
    else
      local fname = os.tmpname()
      if module.is_os('win') and fname:sub(1, 2) == '\\s' then
        -- In Windows tmpname() returns a filename starting with
        -- special sequence \s, prepend $TEMP path
        return tmpdir..fname
      elseif fname:match('^/tmp') and module.is_os('mac') then
        -- In OS X /tmp links to /private/tmp
        return '/private'..fname
      else
        return fname
      end
    end
  end)
end)()

function module.hasenv(name)
  local env = os.getenv(name)
  if env and env ~= '' then
    return env
  end
  return nil
end

local function deps_prefix()
  local env = os.getenv('DEPS_PREFIX')
  return (env and env ~= '') and env or '.deps/usr'
end

local tests_skipped = 0

function module.check_cores(app, force) -- luacheck: ignore
  -- Temporary workaround: skip core check as it interferes with CI.
  if true then
    return
  end
  app = app or 'build/bin/nvim' -- luacheck: ignore
  local initial_path, re, exc_re
  local gdb_db_cmd = 'gdb -n -batch -ex "thread apply all bt full" "$_NVIM_TEST_APP" -c "$_NVIM_TEST_CORE"'
  local lldb_db_cmd = 'lldb -Q -o "bt all" -f "$_NVIM_TEST_APP" -c "$_NVIM_TEST_CORE"'
  local random_skip = false
  -- Workspace-local $TMPDIR, scrubbed and pattern-escaped.
  -- "./Xtest-tmpdir/" => "Xtest%-tmpdir"
  local local_tmpdir = (tmpdir_is_local(tmpdir_get())
    and relpath(tmpdir_get()):gsub('^[ ./]+',''):gsub('%/+$',''):gsub('([^%w])', '%%%1')
    or nil)
  local db_cmd
  if module.hasenv('NVIM_TEST_CORE_GLOB_DIRECTORY') then
    initial_path = os.getenv('NVIM_TEST_CORE_GLOB_DIRECTORY')
    re = os.getenv('NVIM_TEST_CORE_GLOB_RE')
    exc_re = { os.getenv('NVIM_TEST_CORE_EXC_RE'), local_tmpdir }
    db_cmd = os.getenv('NVIM_TEST_CORE_DB_CMD') or gdb_db_cmd
    random_skip = os.getenv('NVIM_TEST_CORE_RANDOM_SKIP')
  elseif module.is_os('mac') then
    initial_path = '/cores'
    re = nil
    exc_re = { local_tmpdir }
    db_cmd = lldb_db_cmd
  else
    initial_path = '.'
    if module.is_os('freebsd') then
      re = '/nvim.core$'
    else
      re = '/core[^/]*$'
    end
    exc_re = { '^/%.deps$', '^/%'..deps_prefix()..'$', local_tmpdir, '^/%node_modules$' }
    db_cmd = gdb_db_cmd
    random_skip = true
  end
  -- Finding cores takes too much time on linux
  if not force and random_skip and math.random() < 0.9 then
    tests_skipped = tests_skipped + 1
    return
  end
  local cores = module.glob(initial_path, re, exc_re)
  local found_cores = 0
  local out = io.stdout
  for _, core in ipairs(cores) do
    local len = 80 - #core - #('Core file ') - 2
    local esigns = ('='):rep(len / 2)
    out:write(('\n%s Core file %s %s\n'):format(esigns, core, esigns))
    out:flush()
    os.execute(db_cmd:gsub('%$_NVIM_TEST_APP', app):gsub('%$_NVIM_TEST_CORE', core) .. ' 2>&1')
    out:write('\n')
    found_cores = found_cores + 1
    os.remove(core)
  end
  if found_cores ~= 0 then
    out:write(('\nTests covered by this check: %u\n'):format(tests_skipped + 1))
  end
  tests_skipped = 0
  if found_cores > 0 then
    error("crash detected (see above)")
  end
end

--- @return string?
function module.repeated_read_cmd(...)
  for _ = 1, 10 do
    local stream = module.popen_r(...)
    local ret = stream:read('*a')
    stream:close()
    if ret then
      return ret
    end
  end
  print('ERROR: Failed to execute ' .. module.argss_to_cmd(...) .. ': nil return after 10 attempts')
  return nil
end

function module.shallowcopy(orig)
  if type(orig) ~= 'table' then
    return orig
  end
  local copy = {}
  for orig_key, orig_value in pairs(orig) do
    copy[orig_key] = orig_value
  end
  return copy
end

function module.mergedicts_copy(d1, d2)
  local ret = module.shallowcopy(d1)
  for k, v in pairs(d2) do
    if d2[k] == module.REMOVE_THIS then
      ret[k] = nil
    elseif type(d1[k]) == 'table' and type(v) == 'table' then
      ret[k] = module.mergedicts_copy(d1[k], v)
    else
      ret[k] = v
    end
  end
  return ret
end

-- dictdiff: find a diff so that mergedicts_copy(d1, diff) is equal to d2
--
-- Note: does not do copies of d2 values used.
function module.dictdiff(d1, d2)
  local ret = {}
  local hasdiff = false
  for k, v in pairs(d1) do
    if d2[k] == nil then
      hasdiff = true
      ret[k] = module.REMOVE_THIS
    elseif type(v) == type(d2[k]) then
      if type(v) == 'table' then
        local subdiff = module.dictdiff(v, d2[k])
        if subdiff ~= nil then
          hasdiff = true
          ret[k] = subdiff
        end
      elseif v ~= d2[k] then
        ret[k] = d2[k]
        hasdiff = true
      end
    else
      ret[k] = d2[k]
      hasdiff = true
    end
  end
  local shallowcopy = module.shallowcopy
  for k, v in pairs(d2) do
    if d1[k] == nil then
      ret[k] = shallowcopy(v)
      hasdiff = true
    end
  end
  if hasdiff then
    return ret
  else
    return nil
  end
end

function module.updated(d, d2)
  for k, v in pairs(d2) do
    d[k] = v
  end
  return d
end

-- Concat list-like tables.
function module.concat_tables(...)
  local ret = {}
  for i = 1, select('#', ...) do
    local tbl = select(i, ...)
    if tbl then
      for _, v in ipairs(tbl) do
        ret[#ret + 1] = v
      end
    end
  end
  return ret
end

--- @param str string
--- @param leave_indent? integer
--- @return string
function module.dedent(str, leave_indent)
  -- find minimum common indent across lines
  local indent --- @type string?
  for line in str:gmatch('[^\n]+') do
    local line_indent = line:match('^%s+') or ''
    if indent == nil or #line_indent < #indent then
      indent = line_indent
    end
  end

  if not indent or #indent == 0 then
    -- no minimum common indent
    return str
  end

  local left_indent = (' '):rep(leave_indent or 0)
  -- create a pattern for the indent
  indent = indent:gsub('%s', '[ \t]')
  -- strip it from the first line
  str = str:gsub('^'..indent, left_indent)
  -- strip it from the remaining lines
  str = str:gsub('[\n]'..indent, '\n' .. left_indent)
  return str
end

local function format_float(v)
  -- On windows exponent appears to have three digits and not two
  local ret = ('%.6e'):format(v)
  local l, f, es, e = ret:match('^(%-?%d)%.(%d+)e([+%-])0*(%d%d+)$')
  return l .. '.' .. f .. 'e' .. es .. e
end

local SUBTBL = {
  '\\000', '\\001', '\\002', '\\003', '\\004',
  '\\005', '\\006', '\\007', '\\008', '\\t',
  '\\n',   '\\011', '\\012', '\\r',   '\\014',
  '\\015', '\\016', '\\017', '\\018', '\\019',
  '\\020', '\\021', '\\022', '\\023', '\\024',
  '\\025', '\\026', '\\027', '\\028', '\\029',
  '\\030', '\\031',
}

-- Formats Lua value `v`.
--
-- TODO(justinmk): redundant with vim.inspect() ?
--
-- "Nice table formatting similar to screen:snapshot_util()".
-- Commit: 520c0b91a528
function module.format_luav(v, indent, opts)
  opts = opts or {}
  local linesep = '\n'
  local next_indent_arg = nil
  local indent_shift = opts.indent_shift or '  '
  local next_indent
  local nl = '\n'
  if indent == nil then
    indent = ''
    linesep = ''
    next_indent = ''
    nl = ' '
  else
    next_indent_arg = indent .. indent_shift
    next_indent = indent .. indent_shift
  end
  local ret = ''
  if type(v) == 'string' then
    if opts.literal_strings then
      ret = v
    else
      local quote = opts.dquote_strings and '"' or '\''
      ret = quote .. tostring(v):gsub(
        opts.dquote_strings and '["\\]' or '[\'\\]',
        '\\%0'):gsub(
          '[%z\1-\31]', function(match)
            return SUBTBL[match:byte() + 1]
          end) .. quote
    end
  elseif type(v) == 'table' then
    if v == module.REMOVE_THIS then
      ret = 'REMOVE_THIS'
    else
      local processed_keys = {}
      ret = '{' .. linesep
      local non_empty = false
      local format_luav = module.format_luav
      for i, subv in ipairs(v) do
        ret = ('%s%s%s,%s'):format(ret, next_indent,
                                   format_luav(subv, next_indent_arg, opts), nl)
        processed_keys[i] = true
        non_empty = true
      end
      for k, subv in pairs(v) do
        if not processed_keys[k] then
          if type(k) == 'string' and k:match('^[a-zA-Z_][a-zA-Z0-9_]*$') then
            ret = ret .. next_indent .. k .. ' = '
          else
            ret = ('%s%s[%s] = '):format(ret, next_indent,
                                         format_luav(k, nil, opts))
          end
          ret = ret .. format_luav(subv, next_indent_arg, opts) .. ',' .. nl
          non_empty = true
        end
      end
      if nl == ' ' and non_empty then
        ret = ret:sub(1, -3)
      end
      ret = ret  .. indent .. '}'
    end
  elseif type(v) == 'number' then
    if v % 1 == 0 then
      ret = ('%d'):format(v)
    else
      ret = format_float(v)
    end
  elseif type(v) == 'nil' then
    ret = 'nil'
  elseif type(v) == 'boolean' then
    ret = (v and 'true' or 'false')
  else
    print(type(v))
    -- Not implemented yet
    assert(false)
  end
  return ret
end

-- Like Python repr(), "{!r}".format(s)
--
-- Commit: 520c0b91a528
function module.format_string(fmt, ...)
  local i = 0
  local args = {...}
  local function getarg()
    i = i + 1
    return args[i]
  end
  local ret = fmt:gsub('%%[0-9*]*%.?[0-9*]*[cdEefgGiouXxqsr%%]', function(match)
    local subfmt = match:gsub('%*', function()
      return tostring(getarg())
    end)
    local arg = nil
    if subfmt:sub(-1) ~= '%' then
      arg = getarg()
    end
    if subfmt:sub(-1) == 'r' or subfmt:sub(-1) == 'q' then
      -- %r is like built-in %q, but it is supposed to single-quote strings and
      -- not double-quote them, and also work not only for strings.
      -- Builtin %q is replaced here as it gives invalid and inconsistent with
      -- luajit results for e.g. "\e" on lua: luajit transforms that into `\27`,
      -- lua leaves as-is.
      arg = module.format_luav(arg, nil, {dquote_strings = (subfmt:sub(-1) == 'q')})
      subfmt = subfmt:sub(1, -2) .. 's'
    end
    if subfmt == '%e' then
      return format_float(arg)
    else
      return subfmt:format(arg)
    end
  end)
  return ret
end

function module.intchar2lua(ch)
  ch = tonumber(ch)
  return (20 <= ch and ch < 127) and ('%c'):format(ch) or ch
end

local fixtbl_metatable = {
  __newindex = function()
    assert(false)
  end,
}

function module.fixtbl(tbl)
  return setmetatable(tbl, fixtbl_metatable)
end

function module.fixtbl_rec(tbl)
  local fixtbl_rec = module.fixtbl_rec
  for _, v in pairs(tbl) do
    if type(v) == 'table' then
      fixtbl_rec(v)
    end
  end
  return module.fixtbl(tbl)
end

function module.hexdump(str)
  local len = string.len(str)
  local dump = ""
  local hex = ""
  local asc = ""

  for i = 1, len do
    if 1 == i % 8 then
      dump = dump .. hex .. asc .. "\n"
      hex = string.format("%04x: ", i - 1)
      asc = ""
    end

    local ord = string.byte(str, i)
    hex = hex .. string.format("%02x ", ord)
    if ord >= 32 and ord <= 126 then
      asc = asc .. string.char(ord)
    else
      asc = asc .. "."
    end
  end

  return dump .. hex .. string.rep("   ", 8 - len % 8) .. asc
end

-- Reads text lines from `filename` into a table.
--
-- filename: path to file
-- start: start line (1-indexed), negative means "lines before end" (tail)
function module.read_file_list(filename, start)
  local lnum = (start ~= nil and type(start) == 'number') and start or 1
  local tail = (lnum < 0)
  local maxlines = tail and math.abs(lnum) or nil
  local file = io.open(filename, 'r')
  if not file then
    return nil
  end

  -- There is no need to read more than the last 2MB of the log file, so seek
  -- to that.
  local file_size = file:seek("end")
  local offset = file_size - 2000000
  if offset < 0 then
    offset = 0
  end
  file:seek("set", offset)

  local lines = {}
  local i = 1
  local line = file:read("*l")
  while line ~= nil do
    if i >= start then
      table.insert(lines, line)
      if #lines > maxlines then
        table.remove(lines, 1)
      end
    end
    i = i + 1
    line = file:read("*l")
  end
  file:close()
  return lines
end

-- Reads the entire contents of `filename` into a string.
--
-- filename: path to file
function module.read_file(filename)
  local file = io.open(filename, 'r')
  if not file then
    return nil
  end
  local ret = file:read('*a')
  file:close()
  return ret
end

-- Dedent the given text and write it to the file name.
function module.write_file(name, text, no_dedent, append)
  local file = io.open(name, (append and 'a' or 'w'))
  if type(text) == 'table' then
    -- Byte blob
    local bytes = text
    text = ''
    for _, char in ipairs(bytes) do
      text = ('%s%c'):format(text, char)
    end
  elseif not no_dedent then
    text = module.dedent(text)
  end
  file:write(text)
  file:flush()
  file:close()
end

function module.is_ci(name)
  local any = (name == nil)
  assert(any or name == 'github' or name == 'cirrus')
  local gh = ((any or name == 'github') and nil ~= os.getenv('GITHUB_ACTIONS'))
  local cirrus = ((any or name == 'cirrus') and nil ~= os.getenv('CIRRUS_CI'))
  return gh or cirrus
end

-- Gets the (tail) contents of `logfile`.
-- Also moves the file to "${NVIM_LOG_FILE}.displayed" on CI environments.
function module.read_nvim_log(logfile, ci_rename)
  logfile = logfile or os.getenv('NVIM_LOG_FILE') or '.nvimlog'
  local is_ci = module.is_ci()
  local keep = is_ci and 100 or 10
  local lines = module.read_file_list(logfile, -keep) or {}
  local log = (('-'):rep(78)..'\n'
    ..string.format('$NVIM_LOG_FILE: %s\n', logfile)
    ..(#lines > 0 and '(last '..tostring(keep)..' lines)\n' or '(empty)\n'))
  for _,line in ipairs(lines) do
    log = log..line..'\n'
  end
  log = log..('-'):rep(78)..'\n'
  if is_ci and ci_rename then
    os.rename(logfile, logfile .. '.displayed')
  end
  return log
end

function module.mkdir(path)
  -- 493 is 0755 in decimal
  return luv.fs_mkdir(path, 493)
end

module = shared.tbl_extend('error', module, Paths, shared, require('test.deprecated'))

return module