local api = vim.api
local fn = vim.fn

---Wrapper for using my `agenda` script from within neovim.
local M = {}

function M.on_attach(buf)
  vim.bo[buf].bufhidden = 'delete'
end

---@return string
function M.dir()
  if vim.env.AGENDA_DIR then
    return vim.env.AGENDA_DIR
  end

  if vim.env.XDG_DATA_HOME then
    return string.format('%/agenda', vim.env.XDG_DATA_HOME)
  end

  return string.format('%/.local/share/agenda', vim.env.HOME)
end

---Gets the first window with an agenda note buffer in a tabpage.
---@param tabpage integer Tabpage handle, or 0 for the current tabpage.
---@param opts {dir: string?}?
---@return integer? win Window handle
function M.tabpage_get_win(tabpage, opts)
  local agenda_dir = opts and opts.dir or M.dir()

  for _, win in ipairs(api.nvim_tabpage_list_wins(tabpage)) do
    local buf = api.nvim_win_get_buf(win)
    -- Better to look at the name (file path), since that state is always there
    -- (e.g. after restoring a session).
    local name = api.nvim_buf_get_name(buf)
    if vim.startswith(name, agenda_dir) then
      return win
    end
  end
end

---@class agenda.Opts
---@field backlog string? Set the -b flag.
---@field create boolean? Set the -c flag.
---@field dir string? Set this as AGENDA_DIR value.
---@field extension string? Set this as -e option value.
---@field name string? Set this as -t option value.

---Open an agenda note.
---@param date string Either the date or backlog name.
---@param opts agenda.Opts?
function M.open(date, opts)
  local filepath, err = M.agenda(date, opts)

  if not filepath or fn.filereadable(filepath) < 1 then
    if not err then
      err = string.format("agenda: file '%s' is not readable", filepath)
    end
    vim.notify(err, vim.log.levels.WARN)
    return
  end

  local win = M.tabpage_get_win(0)
  if win then
    vim.api.nvim_set_current_win(win)
    vim.cmd.edit(filepath)
  else
    vim.cmd.split(filepath)
  end

  M.on_attach(0)
end

---Query an agenda note's file path.
---@param date string Either the date or backlog name.
---@param opts agenda.Opts?
---@return string? filepath
---@return string? err
function M.agenda(date, opts)
  local env = {
    -- An empty environment table is invalid.
    AGENDA_DIR = vim.env.AGENDA_DIR
  }
  local cmd = { 'agenda', '-E' }

  if opts then
    if opts.dir then
      env.AGENDA_DIR = opts.dir
    end

    if opts.backlog then
      cmd[#cmd + 1] = '-b'
    end

    if opts.create then
      cmd[#cmd + 1] = '-c'
    end

    if opts.extension then
      cmd[#cmd + 1] = '-e'
      cmd[#cmd + 1] = opts.extension
    end

    if opts.name then
      cmd[#cmd + 1] = '-t'
      cmd[#cmd + 1] = opts.name
    end
  end

  cmd[#cmd + 1] = date

  local filepath = ''
  local err = ''
  local pid = fn.jobstart(cmd, {
    env = env,
    on_stdout = function(_, data)
      filepath = filepath .. data[1]
    end,
    on_stderr = function(_, data)
      err = err .. data[1]
    end,
  })

  local code = unpack(fn.jobwait { pid })
  if code > 0 then
    return nil, err
  end

  return filepath
end

return M