local health = vim.health
local executable = health.executable
local iswin = vim.loop.os_uname().sysname == 'Windows_NT'

local M = {}

local function is(path, ty)
  if not path then
    return false
  end
  local stat = vim.loop.fs_stat(path)
  if not stat then
    return false
  end
  return stat.type == ty
end

-- Resolves Python executable path by invoking and checking `sys.executable`.
local function python_exepath(invocation)
  local p = vim.system({ invocation, '-c', 'import sys; sys.stdout.write(sys.executable)' }):wait()
  assert(p.code == 0, p.stderr)
  return vim.fs.normalize(vim.trim(p.stdout))
end

-- Check if pyenv is available and a valid pyenv root can be found, then return
-- their respective paths. If either of those is invalid, return two empty
-- strings, effectively ignoring pyenv.
local function check_for_pyenv()
  local pyenv_path = vim.fn.resolve(vim.fn.exepath('pyenv'))

  if pyenv_path == '' then
    return { '', '' }
  end

  health.info('pyenv: Path: ' .. pyenv_path)

  local pyenv_root = vim.fn.resolve(os.getenv('PYENV_ROOT') or '')

  if pyenv_root == '' then
    pyenv_root = vim.fn.system({ pyenv_path, 'root' })
    health.info('pyenv: $PYENV_ROOT is not set. Infer from `pyenv root`.')
  end

  if not is(pyenv_root, 'directory') then
    local message = string.format(
      'pyenv: Root does not exist: %s. Ignoring pyenv for all following checks.',
      pyenv_root
    )
    health.warn(message)
    return { '', '' }
  end

  health.info('pyenv: Root: ' .. pyenv_root)

  return { pyenv_path, pyenv_root }
end

-- Check the Python interpreter's usability.
local function check_bin(bin)
  if not is(bin, 'file') and (not iswin or not is(bin .. '.exe', 'file')) then
    health.error('"' .. bin .. '" was not found.')
    return false
  elseif not executable(bin) then
    health.error('"' .. bin .. '" is not executable.')
    return false
  end
  return true
end

-- Fetch the contents of a URL.
local function download(url)
  local has_curl = executable('curl')
  if has_curl and vim.fn.system({ 'curl', '-V' }):find('Protocols:.*https') then
    local out, rc = health.system({ 'curl', '-sL', url }, { stderr = true, ignore_error = true })
    if rc ~= 0 then
      return 'curl error with ' .. url .. ': ' .. rc
    else
      return out
    end
  elseif executable('python') then
    local script = "try:\n\
          from urllib.request import urlopen\n\
          except ImportError:\n\
          from urllib2 import urlopen\n\
          response = urlopen('" .. url .. "')\n\
          print(response.read().decode('utf8'))\n"
    local out, rc = health.system({ 'python', '-c', script })
    if out == '' and rc ~= 0 then
      return 'python urllib.request error: ' .. rc
    else
      return out
    end
  end

  local message = 'missing `curl` '

  if has_curl then
    message = message .. '(with HTTPS support) '
  end
  message = message .. 'and `python`, cannot make web request'

  return message
end

-- Get the latest Nvim Python client (pynvim) version from PyPI.
local function latest_pypi_version()
  local pypi_version = 'unable to get pypi response'
  local pypi_response = download('https://pypi.python.org/pypi/pynvim/json')
  if pypi_response ~= '' then
    local pcall_ok, output = pcall(vim.fn.json_decode, pypi_response)
    local pypi_data
    if pcall_ok then
      pypi_data = output
    else
      return 'error: ' .. pypi_response
    end

    local pypi_element = pypi_data['info'] or {}
    pypi_version = pypi_element['version'] or 'unable to parse'
  end
  return pypi_version
end

local function is_bad_response(s)
  local lower = s:lower()
  return vim.startswith(lower, 'unable')
    or vim.startswith(lower, 'error')
    or vim.startswith(lower, 'outdated')
end

-- Get version information using the specified interpreter.  The interpreter is
-- used directly in case breaking changes were introduced since the last time
-- Nvim's Python client was updated.
--
-- Returns: {
--     {python executable version},
--     {current nvim version},
--     {current pypi nvim status},
--     {installed version status}
-- }
local function version_info(python)
  local pypi_version = latest_pypi_version()

  local python_version, rc = health.system({
    python,
    '-c',
    'import sys; print(".".join(str(x) for x in sys.version_info[:3]))',
  })

  if rc ~= 0 or python_version == '' then
    python_version = 'unable to parse ' .. python .. ' response'
  end

  local nvim_path
  nvim_path, rc = health.system({
    python,
    '-c',
    'import sys; sys.path = [p for p in sys.path if p != ""]; import neovim; print(neovim.__file__)',
  })
  if rc ~= 0 or nvim_path == '' then
    return { python_version, 'unable to load neovim Python module', pypi_version, nvim_path }
  end

  -- Assuming that multiple versions of a package are installed, sort them
  -- numerically in descending order.
  local function compare(metapath1, metapath2)
    local a = vim.fn.matchstr(vim.fn.fnamemodify(metapath1, ':p:h:t'), [[[0-9.]\+]])
    local b = vim.fn.matchstr(vim.fn.fnamemodify(metapath2, ':p:h:t'), [[[0-9.]\+]])
    if a == b then
      return 0
    elseif a > b then
      return 1
    else
      return -1
    end
  end

  -- Try to get neovim.VERSION (added in 0.1.11dev).
  local nvim_version
  nvim_version, rc = health.system({
    python,
    '-c',
    'from neovim import VERSION as v; print("{}.{}.{}{}".format(v.major, v.minor, v.patch, v.prerelease))',
  }, { stderr = true, ignore_error = true })
  if rc ~= 0 or nvim_version == '' then
    nvim_version = 'unable to find pynvim module version'
    local base = vim.fs.basename(nvim_path)
    local metas = vim.fn.glob(base .. '-*/METADATA', 1, 1)
    vim.list_extend(metas, vim.fn.glob(base .. '-*/PKG-INFO', 1, 1))
    vim.list_extend(metas, vim.fn.glob(base .. '.egg-info/PKG-INFO', 1, 1))
    metas = table.sort(metas, compare)

    if metas and next(metas) ~= nil then
      for line in io.lines(metas[1]) do
        local version = line:match('^Version: (%S+)')
        if version then
          nvim_version = version
          break
        end
      end
    end
  end

  local nvim_path_base = vim.fn.fnamemodify(nvim_path, [[:~:h]])
  local version_status = 'unknown; ' .. nvim_path_base
  if is_bad_response(nvim_version) and is_bad_response(pypi_version) then
    if vim.version.lt(nvim_version, pypi_version) then
      version_status = 'outdated; from ' .. nvim_path_base
    else
      version_status = 'up to date'
    end
  end

  return { python_version, nvim_version, pypi_version, version_status }
end

function M.check()
  health.start('Python 3 provider (optional)')

  local pyname = 'python3' ---@type string?
  local python_exe = ''
  local virtual_env = os.getenv('VIRTUAL_ENV')
  local venv = virtual_env and vim.fn.resolve(virtual_env) or ''
  local host_prog_var = pyname .. '_host_prog'
  local python_multiple = {}

  if health.provider_disabled(pyname) then
    return
  end

  local pyenv_table = check_for_pyenv()
  local pyenv = pyenv_table[1]
  local pyenv_root = pyenv_table[2]

  if vim.g[host_prog_var] then
    local message = string.format('Using: g:%s = "%s"', host_prog_var, vim.g[host_prog_var])
    health.info(message)
  end

  local pythonx_warnings
  pyname, pythonx_warnings = require('vim.provider.python').detect_by_module('neovim')

  if not pyname then
    health.warn(
      'No Python executable found that can `import neovim`. '
        .. 'Using the first available executable for diagnostics.'
    )
  elseif vim.g[host_prog_var] then
    python_exe = pyname
  end

  -- No Python executable could `import neovim`, or host_prog_var was used.
  if pythonx_warnings then
    health.warn(pythonx_warnings, {
      'See :help provider-python for more information.',
      'You may disable this provider (and warning) by adding `let g:loaded_python3_provider = 0` to your init.vim',
    })
  elseif pyname ~= '' and python_exe == '' then
    if not vim.g[host_prog_var] then
      local message = string.format(
        '`g:%s` is not set. Searching for %s in the environment.',
        host_prog_var,
        pyname
      )
      health.info(message)
    end

    if pyenv ~= '' then
      python_exe = health.system({ pyenv, 'which', pyname }, { stderr = true })
      if python_exe == '' then
        health.warn('pyenv could not find ' .. pyname .. '.')
      end
    end

    if python_exe == '' then
      python_exe = vim.fn.exepath(pyname)

      if os.getenv('PATH') then
        local path_sep = iswin and ';' or ':'
        local paths = vim.split(os.getenv('PATH') or '', path_sep)

        for _, path in ipairs(paths) do
          local path_bin = vim.fs.normalize(path .. '/' .. pyname)
          if
            path_bin ~= vim.fs.normalize(python_exe)
            and vim.tbl_contains(python_multiple, path_bin)
            and executable(path_bin)
          then
            python_multiple[#python_multiple + 1] = path_bin
          end
        end

        if vim.tbl_count(python_multiple) > 0 then
          -- This is worth noting since the user may install something
          -- that changes $PATH, like homebrew.
          local message = string.format(
            'Multiple %s executables found. Set `g:%s` to avoid surprises.',
            pyname,
            host_prog_var
          )
          health.info(message)
        end

        if python_exe:find('shims') then
          local message = string.format('`%s` appears to be a pyenv shim.', python_exe)
          local advice = string.format(
            '`pyenv` is not in $PATH, your pyenv installation is broken. Set `g:%s` to avoid surprises.',
            host_prog_var
          )
          health.warn(message, advice)
        end
      end
    end
  end

  if python_exe ~= '' and not vim.g[host_prog_var] then
    if
      venv == ''
      and pyenv ~= ''
      and pyenv_root ~= ''
      and vim.startswith(vim.fn.resolve(python_exe), pyenv_root .. '/')
    then
      local advice = string.format(
        'Create a virtualenv specifically for Nvim using pyenv, and set `g:%s`.  This will avoid the need to install the pynvim module in each version/virtualenv.',
        host_prog_var
      )
      health.warn('pyenv is not set up optimally.', advice)
    elseif venv ~= '' then
      local venv_root
      if pyenv_root ~= '' then
        venv_root = pyenv_root
      else
        venv_root = vim.fs.dirname(venv)
      end

      if vim.startswith(vim.fn.resolve(python_exe), venv_root .. '/') then
        local advice = string.format(
          'Create a virtualenv specifically for Nvim and use `g:%s`.  This will avoid the need to install the pynvim module in each virtualenv.',
          host_prog_var
        )
        health.warn('Your virtualenv is not set up optimally.', advice)
      end
    end
  end

  if python_exe == '' and pyname ~= '' then
    -- An error message should have already printed.
    health.error('`' .. pyname .. '` was not found.')
  elseif python_exe ~= '' and not check_bin(python_exe) then
    python_exe = ''
  end

  -- Diagnostic output
  health.info('Executable: ' .. (python_exe == '' and 'Not found' or python_exe))
  if vim.tbl_count(python_multiple) > 0 then
    for _, path_bin in ipairs(python_multiple) do
      health.info('Other python executable: ' .. path_bin)
    end
  end

  if python_exe == '' then
    -- No Python executable can import 'neovim'. Check if any Python executable
    -- can import 'pynvim'. If so, that Python failed to import 'neovim' as
    -- well, which is most probably due to a failed pip upgrade:
    -- https://github.com/neovim/neovim/wiki/Following-HEAD#20181118
    local pynvim_exe = require('vim.provider.python').detect_by_module('pynvim')
    if pynvim_exe then
      local message = 'Detected pip upgrade failure: Python executable can import "pynvim" but not "neovim": '
        .. pynvim_exe
      local advice = {
        'Use that Python version to reinstall "pynvim" and optionally "neovim".',
        pynvim_exe .. ' -m pip uninstall pynvim neovim',
        pynvim_exe .. ' -m pip install pynvim',
        pynvim_exe .. ' -m pip install neovim  # only if needed by third-party software',
      }
      health.error(message, advice)
    end
  else
    local version_info_table = version_info(python_exe)
    local pyversion = version_info_table[1]
    local current = version_info_table[2]
    local latest = version_info_table[3]
    local status = version_info_table[4]

    if not vim.version.range('~3'):has(pyversion) then
      health.warn('Unexpected Python version. This could lead to confusing error messages.')
    end

    health.info('Python version: ' .. pyversion)

    if is_bad_response(status) then
      health.info('pynvim version: ' .. current .. ' (' .. status .. ')')
    else
      health.info('pynvim version: ' .. current)
    end

    if is_bad_response(current) then
      health.error(
        'pynvim is not installed.\nError: ' .. current,
        'Run in shell: ' .. python_exe .. ' -m pip install pynvim'
      )
    end

    if is_bad_response(latest) then
      health.warn('Could not contact PyPI to get latest version.')
      health.error('HTTP request failed: ' .. latest)
    elseif is_bad_response(status) then
      health.warn('Latest pynvim is NOT installed: ' .. latest)
    elseif not is_bad_response(current) then
      health.ok('Latest pynvim is installed.')
    end
  end

  health.start('Python virtualenv')
  if not virtual_env then
    health.ok('no $VIRTUAL_ENV')
    return
  end
  local errors = {}
  -- Keep hints as dict keys in order to discard duplicates.
  local hints = {}
  -- The virtualenv should contain some Python executables, and those
  -- executables should be first both on Nvim's $PATH and the $PATH of
  -- subshells launched from Nvim.
  local bin_dir = iswin and 'Scripts' or 'bin'
  local venv_bins = vim.fn.glob(string.format('%s/%s/python*', virtual_env, bin_dir), true, true)
  venv_bins = vim.tbl_filter(function(v)
    -- XXX: Remove irrelevant executables found in bin/.
    return not v:match('python%-config')
  end, venv_bins)
  if vim.tbl_count(venv_bins) > 0 then
    for _, venv_bin in pairs(venv_bins) do
      venv_bin = vim.fs.normalize(venv_bin)
      local py_bin_basename = vim.fs.basename(venv_bin)
      local nvim_py_bin = python_exepath(vim.fn.exepath(py_bin_basename))
      local subshell_py_bin = python_exepath(py_bin_basename)
      if venv_bin ~= nvim_py_bin then
        errors[#errors + 1] = '$PATH yields this '
          .. py_bin_basename
          .. ' executable: '
          .. nvim_py_bin
        local hint = '$PATH ambiguities arise if the virtualenv is not '
          .. 'properly activated prior to launching Nvim. Close Nvim, activate the virtualenv, '
          .. 'check that invoking Python from the command line launches the correct one, '
          .. 'then relaunch Nvim.'
        hints[hint] = true
      end
      if venv_bin ~= subshell_py_bin then
        errors[#errors + 1] = '$PATH in subshells yields this '
          .. py_bin_basename
          .. ' executable: '
          .. subshell_py_bin
        local hint = '$PATH ambiguities in subshells typically are '
          .. 'caused by your shell config overriding the $PATH previously set by the '
          .. 'virtualenv. Either prevent them from doing so, or use this workaround: '
          .. 'https://vi.stackexchange.com/a/34996'
        hints[hint] = true
      end
    end
  else
    errors[#errors + 1] = 'no Python executables found in the virtualenv '
      .. bin_dir
      .. ' directory.'
  end

  local msg = '$VIRTUAL_ENV is set to: ' .. virtual_env
  if vim.tbl_count(errors) > 0 then
    if vim.tbl_count(venv_bins) > 0 then
      msg = string.format(
        '%s\nAnd its %s directory contains: %s',
        msg,
        bin_dir,
        table.concat(
          vim.tbl_map(function(v)
            return vim.fn.fnamemodify(v, ':t')
          end, venv_bins),
          ', '
        )
      )
    end
    local conj = '\nBut '
    for _, err in ipairs(errors) do
      msg = msg .. conj .. err
      conj = '\nAnd '
    end
    msg = msg .. '\nSo invoking Python may lead to unexpected results.'
    health.warn(msg, vim.tbl_keys(hints))
  else
    health.info(msg)
    health.info(
      'Python version: '
        .. health.system(
          'python -c "import platform, sys; sys.stdout.write(platform.python_version())"'
        )
    )
    health.ok('$VIRTUAL_ENV provides :!python.')
  end
end

return M