import { reactive, computed } from 'vue'
import { parseICS, serializeICS } from '../lib/ical-io.js'
import { organize as organizeEvents } from '../lib/organize.js'
import { createEvent, cloneEvent } from '../lib/event-factory.js'
import { splitRecurringEvent } from '../lib/split.js'
import { todayISO, addDays, startOfMonth, parseISODate, pad2 } from '../lib/date.js'

const MAX_HISTORY = 50

// 单例响应式状态
const state = reactive({
  meta: null,
  events: [],
  selectedUid: null,
  history: [],
  fileName: null,
  dirty: false,
  viewMode: 'edit',        // 'edit' | 'month' | 'week'
  previewDate: todayISO(),  // 预览锚定日期 (月预览取当月, 周预览取当周)
})

// ------------------------------------------------------------------ //
// 快照 / 撤销
// ------------------------------------------------------------------ //
function snapshot() {
  return {
    meta: state.meta ? cloneEvent(state.meta) : null,
    events: state.events.map(cloneEvent),
    selectedUid: state.selectedUid,
  }
}

function pushHistory() {
  state.history.push(snapshot())
  if (state.history.length > MAX_HISTORY) state.history.shift()
}

function restore(snap) {
  state.meta = snap.meta ? cloneEvent(snap.meta) : null
  state.events = snap.events.map(cloneEvent)
  state.selectedUid = snap.selectedUid
}

// ------------------------------------------------------------------ //
// 文件加载
// ------------------------------------------------------------------ //
function loadFile(file) {
  return file.text().then((text) => {
    const parsed = parseICS(text)
    state.meta = parsed.meta
    state.events = parsed.events
    state.selectedUid = null
    state.history = []
    state.fileName = file.name
    state.dirty = false
  })
}

// ------------------------------------------------------------------ //
// 事件操作
// ------------------------------------------------------------------ //
function selectEvent(uid) {
  state.selectedUid = uid
}

function organize() {
  if (state.events.length === 0) return
  pushHistory()
  const result = organizeEvents(state.events)
  state.events = result.events
  state.dirty = true
  return result.stats
}

/**
 * 更新指定事件的字段 (自动记录历史)。
 * 供 EventDetail 的自动应用 (watch) 调用。
 */
function updateEvent(uid, patch) {
  pushHistory()
  const ev = state.events.find((e) => e.uid === uid)
  if (ev) {
    Object.assign(ev, patch)
    state.dirty = true
  }
}

function deleteEvent(uid) {
  pushHistory()
  state.events = state.events.filter((e) => e.uid !== uid)
  if (state.selectedUid === uid) state.selectedUid = null
  state.dirty = true
}

function addEvent() {
  pushHistory()
  const ev = createEvent()
  state.events.push(ev)
  state.selectedUid = ev.uid
  state.dirty = true
}

function splitEvent(uid, splitDate) {
  const ev = state.events.find((e) => e.uid === uid)
  if (!ev || !ev.rrule) return

  const parts = splitRecurringEvent(ev, splitDate)
  if (!parts) return

  pushHistory()
  const [partA, partB] = parts
  const idx = state.events.findIndex((e) => e.uid === uid)
  state.events.splice(idx, 1, partA, partB)
  state.selectedUid = partB.uid
  state.dirty = true
}

function toggleOccurrence(uid, date) {
  pushHistory()
  const ev = state.events.find((e) => e.uid === uid)
  if (!ev) return
  const i = ev.exdates.indexOf(date)
  if (i >= 0) {
    ev.exdates.splice(i, 1)
  } else {
    ev.exdates.push(date)
    ev.exdates.sort()
  }
  state.dirty = true
}

function undo() {
  if (state.history.length === 0) return
  restore(state.history.pop())
}

// ------------------------------------------------------------------ //
// 序列化
// ------------------------------------------------------------------ //
function serialize() {
  return serializeICS({ meta: state.meta, events: state.events })
}

function markSaved() {
  state.dirty = false
}

// ------------------------------------------------------------------ //
// 视图切换 / 预览导航
// ------------------------------------------------------------------ //
function setViewMode(mode) {
  state.viewMode = mode
}

function shiftMonth(delta) {
  const { year, month } = parseISODate(startOfMonth(state.previewDate))
  const d = new Date(year, month - 1 + delta, 1)
  state.previewDate = `${d.getFullYear()}-${pad2(d.getMonth() + 1)}-01`
}

function prevMonth() {
  shiftMonth(-1)
}

function nextMonth() {
  shiftMonth(1)
}

function prevWeek() {
  state.previewDate = addDays(state.previewDate, -7)
}

function nextWeek() {
  state.previewDate = addDays(state.previewDate, 7)
}

// ------------------------------------------------------------------ //
// 计算属性
// ------------------------------------------------------------------ //
const selectedEvent = computed(() =>
  state.events.find((e) => e.uid === state.selectedUid) || null,
)

const canUndo = computed(() => state.history.length > 0)
const isLoaded = computed(() => state.events.length > 0)
const stats = computed(() => {
  const nRecur = state.events.filter((e) => e.rrule !== null).length
  return { total: state.events.length, recurring: nRecur, single: state.events.length - nRecur }
})

export function useCalendar() {
  return {
    state,
    selectedEvent,
    canUndo,
    isLoaded,
    stats,
    loadFile,
    selectEvent,
    organize,
    updateEvent,
    deleteEvent,
    addEvent,
    splitEvent,
    toggleOccurrence,
    undo,
    serialize,
    markSaved,
    setViewMode,
    prevMonth,
    nextMonth,
    prevWeek,
    nextWeek,
  }
}