local agenda = require 'agenda'
local getopts = require 'agenda.util'.getopts

-- If neovim was started by `agenda` the `AGENDA_FILE` env var will be set
-- with the file name.
if vim.env.AGENDA_FILE == vim.api.nvim_buf_get_name(0) then
  agenda.on_attach(0)
end

-- Callbacks in the middle of a function signature are PAIN.
local function create_user_command(name, opts)
  local command = opts.command
  opts.command = nil
  vim.api.nvim_create_user_command(name, command, opts)
end

-- TODO: Handle subcommands (kinda like git-fugitive)? Could be useful if I'll
--       add a remove subcommand.
-- TODO: Handle -E option (why not?).
create_user_command('Agenda', {
  desc = 'Open a note file/buffer for the given day or the current day',
  nargs = '*',
  bang = true,
  bar = true,
  command = function (command)
    local opts = {
      create = command.bang,
    }

    local i = 1
    for optind, opt, optval in getopts(command.fargs, 'bce:t:') do
      if opt == 'b' then
        opts.backlog = true
      elseif opt == 'c' then
        opts.create = true
      elseif opt == 'e' then
        opts.extension = optval
      elseif opt == 't' then
        opts.name = optval
      else
        local err = string.format("agenda: invalid option: '%s'", opt)
        vim.notify(err, vim.log.levels.WARN)
        return
      end

      i = optind
    end

    local args = {}
    while command.fargs[i] do
      args[#args + 1] = command.fargs[i]
      i = i + 1
    end

    local date
    if #args > 0 then
      date = table.concat(args, ' ')
    else
      date = opts.backlog and 'backlog' or 'today'
    end

    agenda.open(date, opts)
  end,
  -- TODO: Handle supported agenda edit options.
  complete = function (arg_lead, cmd_line, cursor_pos)
    local modifiers = {
      next = true,
      last = true,
    }

    local completions = {}

    local final = {}

    if cmd_line:match '^Agenda!? [%w-]*$' then
      completions = {
        'next ',
        'last ',
        'yesterday',
        'tomorrow',
        'today',
        'day',
        'week',
        'month',
        'year',
        'monday',
        'tuesday',
        'wednesday',
        'thursday',
        'friday',
        'saturday',
        'sunday',
      }
    else
      local first = cmd_line:match '^Agenda (%w+)%s+%w*$'
      if modifiers[first] then
        completions = {
          'day',
          'week',
          'month',
          'year',
          'monday',
          'tuesday',
          'wednesday',
          'thursday',
          'friday',
          'saturday',
          'sunday',
        }
      end
    end

    for _, can in pairs(completions) do
      if vim.startswith(can, arg_lead) then
        final[#final + 1] = can
      end
    end

    return final
  end,
})