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 store = require('pending.store')
  local seen = {}
  local result = {}
  for _, task in ipairs(store.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 string[]
local function date_completions()
  return {
    'today',
    'tomorrow',
    'yesterday',
    '+1d',
    '+2d',
    '+3d',
    '+1w',
    '+2w',
    '+1m',
    'mon',
    'tue',
    'wed',
    'thu',
    'fri',
    'sat',
    'sun',
    'eod',
    'eow',
    'eom',
    'eoq',
    'eoy',
    'sow',
    'som',
    'soq',
    'soy',
    'later',
  }
end

---@return string[]
local function recur_completions()
  local recur = require('pending.recur')
  local list = recur.shorthand_list()
  local result = {}
  for _, s in ipairs(list) do
    table.insert(result, s)
  end
  for _, s in ipairs(list) do
    table.insert(result, '!' .. s)
  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 },
    }

    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 candidates = {}
  local source = _complete_source or ''

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

  if source == dk then
    candidates = date_completions()
  elseif source == 'cat' then
    candidates = get_categories()
  elseif source == rk then
    candidates = recur_completions()
  end

  local matches = {}
  for _, c in ipairs(candidates) do
    if base == '' or c:sub(1, #base) == base then
      table.insert(matches, { word = c, menu = '[' .. source .. ']' })
    end
  end

  return matches
end

return M