local config = require('pending.config')

---@class pending.complete
local M = {}

---@return string
local function date_key()
  return config.get().date_syntax or 'due'
end

---@return string
local function recur_key()
  return config.get().recur_syntax or 'rec'
end

---@return string[]
local function get_categories()
  local s = require('pending.buffer').store()
  if not s then
    return {}
  end
  local seen = {}
  local result = {}
  for _, task in ipairs(s:active_tasks()) do
    local cat = task.category
    if cat and not seen[cat] then
      seen[cat] = true
      table.insert(result, cat)
    end
  end
  table.sort(result)
  return result
end

---@return { word: string, info: string }[]
local function date_completions()
  return {
    { word = 'today', info = "Today's date" },
    { word = 'tomorrow', info = "Tomorrow's date" },
    { word = 'yesterday', info = "Yesterday's date" },
    { word = '+1d', info = '1 day from today' },
    { word = '+2d', info = '2 days from today' },
    { word = '+3d', info = '3 days from today' },
    { word = '+1w', info = '1 week from today' },
    { word = '+2w', info = '2 weeks from today' },
    { word = '+1m', info = '1 month from today' },
    { word = 'mon', info = 'Next Monday' },
    { word = 'tue', info = 'Next Tuesday' },
    { word = 'wed', info = 'Next Wednesday' },
    { word = 'thu', info = 'Next Thursday' },
    { word = 'fri', info = 'Next Friday' },
    { word = 'sat', info = 'Next Saturday' },
    { word = 'sun', info = 'Next Sunday' },
    { word = 'eod', info = 'End of day (today)' },
    { word = 'eow', info = 'End of week (Sunday)' },
    { word = 'eom', info = 'End of month' },
    { word = 'eoq', info = 'End of quarter' },
    { word = 'eoy', info = 'End of year (Dec 31)' },
    { word = 'sow', info = 'Start of week (Monday)' },
    { word = 'som', info = 'Start of month' },
    { word = 'soq', info = 'Start of quarter' },
    { word = 'soy', info = 'Start of year (Jan 1)' },
    { word = 'later', info = 'Someday (sentinel date)' },
    { word = 'today@08:00', info = 'Today at 08:00' },
    { word = 'today@09:00', info = 'Today at 09:00' },
    { word = 'today@10:00', info = 'Today at 10:00' },
    { word = 'today@12:00', info = 'Today at 12:00' },
    { word = 'today@14:00', info = 'Today at 14:00' },
    { word = 'today@17:00', info = 'Today at 17:00' },
  }
end

---@type table<string, string>
local recur_descriptions = {
  daily = 'Every day',
  weekdays = 'Monday through Friday',
  weekly = 'Every week',
  biweekly = 'Every 2 weeks',
  monthly = 'Every month',
  quarterly = 'Every 3 months',
  yearly = 'Every year',
  ['2d'] = 'Every 2 days',
  ['3d'] = 'Every 3 days',
  ['2w'] = 'Every 2 weeks',
  ['3w'] = 'Every 3 weeks',
  ['2m'] = 'Every 2 months',
  ['3m'] = 'Every 3 months',
  ['6m'] = 'Every 6 months',
  ['2y'] = 'Every 2 years',
}

---@return { word: string, info: string }[]
local function recur_completions()
  local recur = require('pending.recur')
  local list = recur.shorthand_list()
  local result = {}
  for _, s in ipairs(list) do
    local desc = recur_descriptions[s] or s
    table.insert(result, { word = s, info = desc })
  end
  for _, s in ipairs(list) do
    local desc = recur_descriptions[s] or s
    table.insert(result, { word = '!' .. s, info = desc .. ' (from completion date)' })
  end
  return result
end

---@type string?
local _complete_source = nil

---@param findstart integer
---@param base string
---@return integer|table[]
function M.omnifunc(findstart, base)
  if findstart == 1 then
    local line = vim.api.nvim_get_current_line()
    local col = vim.api.nvim_win_get_cursor(0)[2]
    local before = line:sub(1, col)

    local dk = date_key()
    local rk = recur_key()

    local checks = {
      { vim.pesc(dk) .. ':([%S]*)$', dk },
      { 'cat:([%S]*)$', 'cat' },
      { vim.pesc(rk) .. ':([%S]*)$', rk },
      { 'file:([%S]*)$', 'file' },
    }

    for _, check in ipairs(checks) do
      local start = before:find(check[1])
      if start then
        local colon_pos = before:find(':', start, true)
        if colon_pos then
          _complete_source = check[2]
          return colon_pos
        end
      end
    end

    _complete_source = nil
    return -1
  end

  local matches = {}
  local source = _complete_source or ''

  local dk = date_key()
  local rk = recur_key()

  if source == dk then
    for _, c in ipairs(date_completions()) do
      if base == '' or c.word:sub(1, #base) == base then
        table.insert(matches, { word = c.word, menu = '[' .. source .. ']', info = c.info })
      end
    end
  elseif source == 'cat' then
    for _, c in ipairs(get_categories()) do
      if base == '' or c:sub(1, #base) == base then
        table.insert(matches, { word = c, menu = '[cat]' })
      end
    end
  elseif source == rk then
    for _, c in ipairs(recur_completions()) do
      if base == '' or c.word:sub(1, #base) == base then
        table.insert(matches, { word = c.word, menu = '[' .. source .. ']', info = c.info })
      end
    end
  end

  return matches
end

return M