local config = require('pending.config')

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

---@param s string
---@return boolean
local function is_valid_date(s)
  local y, m, d = s:match('^(%d%d%d%d)-(%d%d)-(%d%d)$')
  if not y then
    return false
  end
  y, m, d = tonumber(y), tonumber(m), tonumber(d)
  if m < 1 or m > 12 then
    return false
  end
  if d < 1 or d > 31 then
    return false
  end
  local t = os.time({ year = y, month = m, day = d })
  local check = os.date('*t', t)
  return check.year == y and check.month == m and check.day == d
end

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

---@param text string
---@return string description
---@return { due?: string, cat?: string } metadata
function M.body(text)
  local tokens = {}
  for token in text:gmatch('%S+') do
    table.insert(tokens, token)
  end

  local metadata = {}
  local i = #tokens
  local dk = date_key()
  local date_pattern = '^' .. vim.pesc(dk) .. ':(%d%d%d%d%-%d%d%-%d%d)$'

  while i >= 1 do
    local token = tokens[i]
    local due_val = token:match(date_pattern)
    if due_val then
      if metadata.due then
        break
      end
      if not is_valid_date(due_val) then
        break
      end
      metadata.due = due_val
      i = i - 1
    else
      local cat_val = token:match('^cat:(%S+)$')
      if cat_val then
        if metadata.cat then
          break
        end
        metadata.cat = cat_val
        i = i - 1
      else
        break
      end
    end
  end

  local desc_tokens = {}
  for j = 1, i do
    table.insert(desc_tokens, tokens[j])
  end
  local description = table.concat(desc_tokens, ' ')

  return description, metadata
end

---@param text string
---@return string description
---@return { due?: string, cat?: string } metadata
function M.command_add(text)
  local cat_prefix = text:match('^(%S.-):%s')
  if cat_prefix then
    local first_char = cat_prefix:sub(1, 1)
    if first_char == first_char:upper() and first_char ~= first_char:lower() then
      local rest = text:sub(#cat_prefix + 2):match('^%s*(.+)$')
      if rest then
        local desc, meta = M.body(rest)
        meta.cat = meta.cat or cat_prefix
        return desc, meta
      end
    end
  end
  return M.body(text)
end

return M