// 任务模块前端: 自然日边界 + 保留选项可见性
// 与后端 server/task-domain/date.js 保持同一口径, 改动需同步
export const TZ = 'Asia/Shanghai'

export const RETENTION_LABEL = {
  never: '永不显示',
  today: '当天',
  '3d': '3 天',
  week: '本周',
  month: '本月',
  forever: '永久显示',
}

export const RETENTION_OPTIONS = ['never', 'today', '3d', 'week', 'month', 'forever']

export const STATUS_LABEL = { todo: '未开始', doing: '执行中', done: '完成' }
export const STATUS_OPTIONS = ['todo', 'doing', 'done']

// 任务编号 (T-TK-编号): 服务端分配 `Project.code` + 项目内自增 `Task.number`
//   - 列表 / 看板: 只显示 `#序号` (短, 不占卡片宽度)
//   - 详情页: 显示完整编号 `项目编号-序号`, 点按复制
//   - 离线新建、上行定号前的任务 number 为空 -> 两处都不出编号 (不做假编号)
/** 列表 / 看板的短编号: '#12'; 未定号返回 null */
export function taskShortId(task) {
  const n = task?.number
  return n === null || n === undefined || n === '' ? null : `#${n}`
}

/** 完整任务编号: 'IB-12'; 未定号返回 null */
export function taskFullId(task, code) {
  const n = task?.number
  if (n === null || n === undefined || n === '') return null
  return code ? `${code}-${n}` : `#${n}`
}

const FMT = new Intl.DateTimeFormat('en-CA', {
  timeZone: TZ, year: 'numeric', month: '2-digit', day: '2-digit',
})

export function toDateStr(d = new Date()) {
  return FMT.format(d instanceof Date ? d : new Date(d))
}

function toUTC(s) {
  const [y, m, d] = String(s).split('-').map(Number)
  return new Date(Date.UTC(y, (m || 1) - 1, d || 1))
}

function fromUTC(dt) {
  return dt.toISOString().slice(0, 10)
}

export function addDays(s, n) {
  const d = toUTC(s)
  d.setUTCDate(d.getUTCDate() + n)
  return fromUTC(d)
}

/** 周一为一周第一天 */
export function startOfWeek(s) {
  const dow = (toUTC(s).getUTCDay() + 6) % 7
  return addDays(s, -dow)
}

export function startOfMonth(s) {
  return String(s).slice(0, 8) + '01'
}

/** 保留选项 -> 窗口起点 ("YYYY-MM-DD") 或 特殊标记 */
export function retentionStart(option, now = new Date()) {
  const today = toDateStr(now)
  switch (option) {
    case 'never': return { mode: 'never' }
    case 'forever': return { mode: 'all' }
    case 'today': return { mode: 'since', date: today }
    case '3d': return { mode: 'since', date: addDays(today, -2) }
    case 'week': return { mode: 'since', date: startOfWeek(today) }
    case 'month': return { mode: 'since', date: startOfMonth(today) }
    default: return { mode: 'all' }
  }
}

/** 单条任务在某保留选项下是否可见 */
export function isVisibleByRetention(task, option, now = new Date()) {
  if (task.status !== 'done') return true
  const win = retentionStart(option, now)
  if (win.mode === 'never') return false
  if (win.mode === 'all') return true
  if (!task.doneAt) return false
  return toDateStr(task.doneAt) >= win.date
}

/** 按任务所属列的保留选项过滤任务 */
export function filterVisible(tasks, columns, now = new Date()) {
  const map = new Map((columns || []).map((c) => [c.id, c.retention || 'forever']))
  return (tasks || []).filter((t) => isVisibleByRetention(t, map.get(t.columnId) || 'forever', now))
}

/** 距离下一个自然日/周/月边界的毫秒数, 用于定时重算 (T-EX-18) */
export function msToNextBoundary(option, now = new Date()) {
  if (!['today', '3d', 'week', 'month'].includes(option)) return null
  const today = toDateStr(now)
  let next
  if (option === 'today' || option === '3d') next = addDays(today, 1)
  else if (option === 'week') next = addDays(startOfWeek(today), 7)
  else {
    const [y, m] = today.split('-').map(Number)
    const nm = new Date(Date.UTC(y, m, 1))
    next = nm.toISOString().slice(0, 10)
  }
  // 本地零点转北京时间零点: 用 Date 构造 "next 00:00 +08:00"
  const target = new Date(next + 'T00:00:00+08:00').getTime()
  return Math.max(1000, target - now.getTime())
}