-- TODO(ZyX-I): Create compatibility layer.
--{{{1 package.path updater function
-- Last inserted paths. Used to clear out items from package.[c]path when they
-- are no longer in &runtimepath.
local last_nvim_paths = {}
local function _update_package_paths()
  local cur_nvim_paths = {}
  local rtps = vim.api.nvim_list_runtime_paths()
  local sep = package.config:sub(1, 1)
  for _, key in ipairs({'path', 'cpath'}) do
    local orig_str = package[key] .. ';'
    local pathtrails_ordered = {}
    local orig = {}
    -- Note: ignores trailing item without trailing `;`. Not using something
    -- simpler in order to preserve empty items (stand for default path).
    for s in orig_str:gmatch('[^;]*;') do
      s = s:sub(1, -2)  -- Strip trailing semicolon
      orig[#orig + 1] = s
    end
    if key == 'path' then
      -- /?.lua and /?/init.lua
      pathtrails_ordered = {sep .. '?.lua', sep .. '?' .. sep .. 'init.lua'}
    else
      local pathtrails = {}
      for _, s in ipairs(orig) do
        -- Find out path patterns. pathtrail should contain something like
        -- /?.so, \?.dll. This allows not to bother determining what correct
        -- suffixes are.
        local pathtrail = s:match('[/\\][^/\\]*%?.*$')
        if pathtrail and not pathtrails[pathtrail] then
          pathtrails[pathtrail] = true
          pathtrails_ordered[#pathtrails_ordered + 1] = pathtrail
        end
      end
    end
    local new = {}
    for _, rtp in ipairs(rtps) do
      if not rtp:match(';') then
        for _, pathtrail in pairs(pathtrails_ordered) do
          local new_path = rtp .. sep .. 'lua' .. pathtrail
          -- Always keep paths from &runtimepath at the start:
          -- append them here disregarding orig possibly containing one of them.
          new[#new + 1] = new_path
          cur_nvim_paths[new_path] = true
        end
      end
    end
    for _, orig_path in ipairs(orig) do
      -- Handle removing obsolete paths originating from &runtimepath: such
      -- paths either belong to cur_nvim_paths and were already added above or
      -- to last_nvim_paths and should not be added at all if corresponding
      -- entry was removed from &runtimepath list.
      if not (cur_nvim_paths[orig_path] or last_nvim_paths[orig_path]) then
        new[#new + 1] = orig_path
      end
    end
    package[key] = table.concat(new, ';')
  end
  last_nvim_paths = cur_nvim_paths
end
--{{{1 Module definition
return {
  _update_package_paths = _update_package_paths,
}