// Custom lightweight undo/redo specifically for calendar store with Map support
// Adds store.$history = { undo(), redo(), canUndo, canRedo, clear(), pushManual() }
// Wraps action calls to create history entries only for meaningful mutations.

function deepCloneCalendarState(raw) {
  // We only need to snapshot keys we care about; omit volatile fields
  const { today, events, config, weekend } = raw
  return {
    today,
    weekend: Array.isArray(weekend) ? [...weekend] : weekend,
    config: JSON.parse(JSON.stringify(config)),
    events: new Map([...events].map(([k, v]) => [k, { ...v }])),
  }
}

function restoreCalendarState(store, snap) {
  store.today = snap.today
  store.weekend = Array.isArray(snap.weekend) ? [...snap.weekend] : snap.weekend
  store.config = JSON.parse(JSON.stringify(snap.config))
  store.events = new Map([...snap.events].map(([k, v]) => [k, { ...v }]))
  store.eventsMutation = (store.eventsMutation + 1) % 1_000_000_000
}

export function calendarHistory({ store }) {
  if (store.$id !== 'calendar') return

  const max = 100 // history depth limit
  const history = [] // past states
  let pointer = -1 // index of current state in history
  let isRestoring = false
  let lastSerialized = null
  // Compound editing session (e.g. event dialog) flags
  let compoundActive = false
  let compoundBaseSig = null
  let compoundChanged = false

  function serializeForComparison() {
    const evCount = store.events instanceof Map ? store.events.size : 0
    const em = store.eventsMutation || 0
    return `${em}|${evCount}|${store.today}|${JSON.stringify(store.config)}`
  }

  function pushSnapshot() {
    if (isRestoring) return
    const sig = serializeForComparison()
    if (sig === lastSerialized) return
    // Drop any redo branch
    if (pointer < history.length - 1) history.splice(pointer + 1)
    history.push(deepCloneCalendarState(store))
    if (history.length > max) history.shift()
    pointer = history.length - 1
    lastSerialized = sig
    bumpIndicators()
    // console.log('[history] pushed', pointer, sig)
  }

  function bumpIndicators() {
    if (typeof store.historyTick === 'number') {
      store.historyTick = (store.historyTick + 1) % 1_000_000_000
    }
    if (typeof store.historyCanUndo === 'boolean') {
      store.historyCanUndo = pointer > 0
    }
    if (typeof store.historyCanRedo === 'boolean') {
      store.historyCanRedo = pointer >= 0 && pointer < history.length - 1
    }
  }

  function markPotentialChange() {
    if (isRestoring) return
    if (compoundActive) {
      const sig = serializeForComparison()
      if (sig !== compoundBaseSig) compoundChanged = true
      return
    }
    pushSnapshot()
  }

  function beginCompound() {
    if (compoundActive) return
    compoundActive = true
    compoundBaseSig = serializeForComparison()
    compoundChanged = false
  }
  function endCompound() {
    if (!compoundActive) return
    const finalSig = serializeForComparison()
    const changed = compoundChanged || finalSig !== compoundBaseSig
    compoundActive = false
    compoundBaseSig = null
    if (changed) pushSnapshot()
    else bumpIndicators() // session ended without change – still refresh flags
  }

  function undo() {
    // Ensure any active compound changes are finalized before moving back
    if (compoundActive) endCompound()
    else {
      // If current state differs from last snapshot, push it so redo can restore it
      const curSig = serializeForComparison()
      if (curSig !== lastSerialized) pushSnapshot()
    }
    if (pointer <= 0) return
    pointer--
    isRestoring = true
    try {
      restoreCalendarState(store, history[pointer])
      lastSerialized = serializeForComparison()
    } finally {
      isRestoring = false
    }
    bumpIndicators()
  }

  function redo() {
    if (compoundActive) endCompound()
    else {
      const curSig = serializeForComparison()
      if (curSig !== lastSerialized) pushSnapshot()
    }
    if (pointer >= history.length - 1) return
    pointer++
    isRestoring = true
    try {
      restoreCalendarState(store, history[pointer])
      lastSerialized = serializeForComparison()
    } finally {
      isRestoring = false
    }
    bumpIndicators()
  }

  function clear() {
    history.length = 0
    pointer = -1
    lastSerialized = null
    bumpIndicators()
  }

  // Wrap selected mutating actions to push snapshot AFTER they run if state changed.
  const actionNames = [
    'createEvent',
    'deleteEvent',
    'deleteFirstOccurrence',
    'deleteSingleOccurrence',
    'deleteFromOccurrence',
    'setEventRange',
    'splitMoveVirtualOccurrence',
    'splitRepeatSeries',
    '_terminateRepeatSeriesAtIndex',
    'toggleHolidays',
    'initializeHolidays',
  ]

  for (const name of actionNames) {
    if (typeof store[name] === 'function') {
      const original = store[name].bind(store)
      store[name] = (...args) => {
        const beforeSig = serializeForComparison()
        const result = original(...args)
        const afterSig = serializeForComparison()
        if (afterSig !== beforeSig) markPotentialChange()
        return result
      }
    }
  }

  // Capture direct property edits (e.g., deep field edits signaled via touchEvents())
  store.$subscribe((mutation, _state) => {
    if (mutation.storeId !== 'calendar') return
    markPotentialChange()
  })

  // Initial snapshot after hydration (next microtask to let persistence load)
  Promise.resolve().then(() => pushSnapshot())

  store.$history = {
    undo,
    redo,
    clear,
    pushManual: pushSnapshot,
    beginCompound,
    endCompound,
    flush() {
      pushSnapshot()
    },
    get canUndo() {
      return pointer > 0
    },
    get canRedo() {
      return pointer >= 0 && pointer < history.length - 1
    },
    get compoundActive() {
      return compoundActive
    },
    _debug() {
      return { pointer, length: history.length }
    },
  }
}