import Dexie from 'dexie';
import { BackupError, buildBackup, EXPORT_FORMAT, EXPORT_VERSION, parseBackup } from './backup.js';
import { DAY, HOUR, localDateKey } from './time.js';

/**
 * A single working day. `plannedStartTs` / `plannedEndTs` are snapshotted from the
 * settings in force when the day was created, so editing settings later never
 * rewrites history.
 *
 * @typedef {object} DayRecord
 * @property {string} date               local 'YYYY-MM-DD', primary key
 * @property {'active'|'closed'} status
 * @property {number} plannedStartTs
 * @property {number} plannedEndTs
 * @property {number} startedTs
 * @property {number|null} endedTs
 * @property {'panier'|'restaurant'|null} lunchType
 * @property {string|null} restaurant
 * @property {number|null} closePromptedTs
 * @property {boolean} [autoLunchHandled]
 * @property {number|null} [autoLunchEndTs]
 * @property {boolean} [lunchManual]
 */

/**
 * One stretch of the day. `endTs === null` marks the single running entry; every
 * other entry has a finite end; imported histories may contain gaps.
 *
 * @typedef {object} EntryRecord
 * @property {number} [id]
 * @property {string} date
 * @property {number} seq                position within the day, dense from 0
 * @property {'travel'|'work'|'lunch'|'break'} kind
 * @property {string} task
 * @property {string|null} client
 * @property {number} startTs
 * @property {number|null} endTs
 * @property {boolean} [automatic] true only for unconfirmed automatic entries
 */

/**
 * @typedef {object} SettingsRecord
 * @property {string} key
 * @property {any} value
 */

/**
 * @typedef {Dexie & {
 *   days: import('dexie').Table<DayRecord, string>,
 *   entries: import('dexie').Table<EntryRecord, number>,
 *   settings: import('dexie').Table<SettingsRecord, string>,
 *   syncState: import('dexie').Table<any, string>,
 *   syncObjects: import('dexie').Table<any, string>,
 *   syncVersions: import('dexie').Table<any, string>,
 *   syncOutbox: import('dexie').Table<any, string>,
 *   syncConflicts: import('dexie').Table<any, string>,
 * }} TimeLogDB
 */

export const db = /** @type {TimeLogDB} */ (new Dexie('TimeLogDB'));

// v1 was the throwaway prototype schema; declared so Dexie has an upgrade path.
db.version(1).stores({
  timeLogs: '++id, date, startTime, endTime, taskName, clientName',
  settings: 'key',
});

db.version(2).stores({
  timeLogs: null, // drop the prototype table
  days: 'date, status',
  entries: '++id, date, [date+seq], startTs',
  settings: 'key',
});

db.version(3).stores({
  syncState: 'key', syncObjects: 'key', syncVersions: 'id, key',
  syncOutbox: 'id', syncConflicts: 'key',
});

// Journal every local mutation in its native IndexedDB transaction, including
// direct writes by editing, automation, import and purge. The durable source
// rows + last captured values are the outbox until revisions are materialised.
db.use({
  stack: 'dbcore', name: 'sync-dirty-journal',
  create(core) {
    return {
      ...core,
      transaction(stores, mode, options) {
        const names = mode === 'readwrite' && stores.some(s => ['days', 'entries', 'settings'].includes(s))
          ? [...new Set([...stores, 'syncState'])] : stores;
        return core.transaction(names, mode, options);
      },
      table(name) {
        const table = core.table(name);
        if (!['days', 'entries', 'settings'].includes(name)) return table;
        return { ...table, async mutate(req) {
          const result = await table.mutate(req);
          const marker = await core.table('syncState').mutate({ type: 'put', trans: req.trans, values: [{ key: 'dirty', value: true }] });
          if (marker.numFailures) throw marker.failures[0];
          return result;
        } };
      },
    };
  },
});

/* ------------------------------------------------------------------ settings */

export async function readSettings() {
  const rec = await db.settings.get('app');
  return rec?.value ?? null;
}

export async function writeSettings(value) {
  await db.settings.put({ key: 'app', value });
}

/* ---------------------------------------------------------------------- days */

export function getDay(dateKey) {
  return db.days.get(dateKey);
}

export function putDay(day) {
  return db.days.put(day);
}

export function patchDay(dateKey, patch) {
  return db.days.update(dateKey, patch);
}

/** Create once. Automatic callers supply exclusions, checked again under lock. */
export function createDay(day, first, nonWorkingDates = null) {
  return db.transaction('rw', db.days, db.entries, db.settings, async () => {
    if (nonWorkingDates != null) {
      const stored = await readSettings();
      if ((stored?.nonWorkingDates ?? nonWorkingDates).includes(day.date)) return false;
    }
    if (await getDay(day.date) || await getActiveDay()) return false;
    await db.days.add(day);
    await closeAndStart(day.date, day.startedTs, first);
    return true;
  });
}

/** Close the day and its last entry at the same authoritative timestamp. */
export function closeDay(date, ts, stale = false) {
  return db.transaction('rw', db.days, db.entries, async () => {
    const day = await getDay(date);
    if (!day || day.status !== 'active') return false;
    const entries = await getEntries(date);
    const lastActivity = entries.reduce((max, e) => Math.max(max, e.startTs, e.endTs ?? e.startTs), day.startedTs);
    const endedTs = Math.max(stale ? day.plannedEndTs : ts, lastActivity);
    await closeAndStart(date, endedTs, null);
    await patchDay(date, { status: 'closed', endedTs });
    return true;
  });
}

/** Confirmed same-day reopening; status and all resumed slots commit together. */
export function reopenDay(date, now, mode = 'continue', expected = null) {
  return db.transaction('rw', db.days, db.entries, async () => {
    const day = await getDay(date);
    if (!['continue', 'break'].includes(mode)) throw new Error('Choix de reprise invalide.');
    if (!day || date !== localDateKey(now) || day.status !== 'closed' || await getActiveDay()) return false;
    const entries = await getEntries(date);
    const last = entries.at(-1);
    if (!last) return false;
    if (expected && (day.endedTs !== expected.endedTs ||
      ['id', 'kind', 'task', 'client', 'startTs', 'endTs'].some(key => last[key] !== expected.last[key]))) {
      throw new Error('La clôture ou le dernier poste a changé. Fermez puis ouvrez la confirmation de reprise.');
    }
    const boundary = day.endedTs;
    if (!Number.isFinite(boundary) || now < boundary) return false;
    if (mode === 'continue' && ['work', 'travel'].includes(last.kind)) {
      await db.entries.update(last.id, { endTs: null, automatic: false });
    } else {
      let seq = last.seq + 1;
      if (now > boundary) {
        if (mode === 'continue') await db.entries.update(last.id, { endTs: now, automatic: false });
        else await db.entries.add({ date, seq: seq++, kind: 'break', task: 'Pause', client: null, startTs: boundary, endTs: now });
      }
      const history = await db.entries.toArray();
      const work = history.filter((e) => e.kind === 'work' && e.date <= date)
        .sort((a, b) => b.date.localeCompare(a.date) || b.seq - a.seq)[0];
      await db.entries.add({ date, seq, kind: 'work', task: work?.task || 'Travaux sur site', client: work?.client ?? null, startTs: now, endTs: null });
    }
    await patchDay(date, {
      status: 'active', endedTs: null, closePromptedTs: null,
      plannedEndTs: Math.max(day.plannedEndTs, now + HOUR),
    });
    return true;
  });
}

/** Conditional day updates cannot resurrect or modify a concurrently closed day. */
export function patchActiveDay(date, makePatch) {
  return db.transaction('rw', db.days, async () => {
    const day = await getDay(date);
    if (day?.status !== 'active') return false;
    const patch = makePatch(day);
    if (!patch) return false;
    await patchDay(date, patch);
    return true;
  });
}

/** The one day still running, if any — including a stale one from a past date. */
export function getActiveDay() {
  return db.days.where('status').equals('active').first();
}

/** Most recent closed day: the one the resume screen shows. */
export async function getLastClosedDay() {
  const closed = await db.days.where('status').equals('closed').toArray();
  if (!closed.length) return null;
  closed.sort((a, b) => a.date.localeCompare(b.date));
  return closed[closed.length - 1];
}

/* ------------------------------------------------------------------- entries */

export function getEntries(dateKey) {
  return db.entries.where('date').equals(dateKey).sortBy('seq');
}

/**
 * The single place the chain invariant is enforced: closing the running entry and
 * opening the next one share one timestamp, in one transaction, so entry N's end
 * can never drift from entry N+1's start.
 *
 * @param {string} dateKey
 * @param {number} ts
 * @param {(Pick<EntryRecord, 'kind'|'task'|'client'> & {automatic?: boolean})|null} next
 *        Pass null to only close the running entry (end of day).
 * @param {number|null} [expectedId] running entry observed by the action's caller
 * @returns {Promise<number|null>} id of the new entry
 */
export function closeAndStart(dateKey, ts, next, expectedId) {
  return db.transaction('rw', db.days, db.entries, async () => {
    if ((await getDay(dateKey))?.status !== 'active') return null;
    const list = await db.entries.where('date').equals(dateKey).sortBy('seq');
    const running = list.find((e) => e.endTs == null);
    // Two taps/tabs acting on the same entry may advance it only once.
    if (expectedId !== undefined && (running?.id ?? null) !== expectedId) return null;

    let boundary = ts;
    if (running) {
      // A tap can never produce an entry that ends before it started.
      boundary = Math.max(ts, running.startTs);
      await db.entries.update(running.id, { endTs: boundary });
    }
    if (!next) return null;

    const seq = list.length ? list[list.length - 1].seq + 1 : 0;
    return db.entries.add({
      date: dateKey,
      seq,
      startTs: boundary,
      endTs: null,
      ...next,
    });
  });
}

export function patchEntry(id, patch) {
  return db.entries.update(id, { ...patch, automatic: false });
}

/**
 * Move the boundary at the start of an entry. Because that instant is shared with
 * the previous entry's end, both sides move together and the chain stays gapless.
 * For the first entry of a day there is no predecessor, so the day's start moves
 * instead — that is what makes the auto-captured start time correctable.
 *
 * The value is clamped between the previous entry's start and this entry's own
 * end (or now, while it is still running), so no edit can invert the timeline.
 *
 * @returns {Promise<number|undefined>} the timestamp actually stored
 */
export function setEntryStart(id, ts, now = Date.now()) {
  return db.transaction('rw', db.entries, db.days, async () => {
    const entry = await db.entries.get(id);
    if (!entry) return undefined;

    const list = await db.entries.where('date').equals(entry.date).sortBy('seq');
    const prev = list[list.findIndex((e) => e.id === id) - 1];

    const lower = prev ? (prev.endTs === entry.startTs ? prev.startTs : prev.endTs) : Number.NEGATIVE_INFINITY;
    const upper = entry.endTs ?? now;
    const stored = Math.min(Math.max(ts, lower), upper);

    await db.entries.update(entry.id, { startTs: stored, ...(entry.automatic ? { automatic: false } : {}) });
    if (prev && prev.endTs === entry.startTs) await db.entries.update(prev.id, { endTs: stored, ...(prev.automatic ? { automatic: false } : {}) });
    else if (!prev) await db.days.update(entry.date, { startedTs: stored });

    return stored;
  });
}

/**
 * Remove an entry and re-stitch the chain: the previous entry absorbs the gap by
 * extending to the next entry's start. Keeps the timeline contiguous after a
 * mis-tap, which is the whole point of allowing deletes.
 */
export function deleteEntry(id) {
  return db.transaction('rw', db.entries, async () => {
    const victim = await db.entries.get(id);
    if (!victim) return;
    const list = await db.entries.where('date').equals(victim.date).sortBy('seq');
    const i = list.findIndex((e) => e.id === id);
    const prev = list[i - 1];
    const next = list[i + 1];

    await db.entries.delete(id);
    if (prev && prev.endTs === victim.startTs && (!next || victim.endTs === next.startTs)) {
      // Extend the previous entry over the hole; if nothing follows, it inherits
      // the victim's end (including `null`, i.e. it becomes the running entry).
      await db.entries.update(prev.id, { endTs: next ? next.startTs : victim.endTs });
    } else if (!prev && next && victim.endTs === next.startTs) {
      await db.entries.update(next.id, { startTs: victim.startTs });
    }
    // Re-number so `seq` stays dense.
    const rest = list.filter((e) => e.id !== id);
    await Promise.all(
      rest.map((e, n) => (e.seq === n ? null : db.entries.update(e.id, { seq: n }))),
    );
  });
}

/* ------------------------------------------------------------------- history */

/** Everything the prediction model is built from. */
export async function getHistory() {
  return db.transaction('r', db.entries, db.days, async () => {
    const [entries, days] = await Promise.all([db.entries.toArray(), db.days.toArray()]);
    return { entries, days };
  });
}

/**
 * Drop days older than the retention window. The most recent closed day is always
 * kept — it is the app's primary output and must survive any setting.
 */
export async function cleanupOldDays(retentionDays, now = Date.now()) {
  if (!retentionDays || retentionDays <= 0) return 0;
  const cutoff = localDateKey(now - retentionDays * DAY);
  return db.transaction('rw', db.days, db.entries, async () => {
    const keep = await getLastClosedDay();
    const stale = (await db.days.toArray()).filter(
      (d) => d.status === 'closed' && d.date < cutoff && d.date !== keep?.date,
    );
    const keys = stale.map((d) => d.date);
    if (!keys.length) return 0;
    await db.days.bulkDelete(keys);
    await db.entries.where('date').anyOf(keys).delete();
    return keys.length;
  });
}

/**
 * Write an imported dataset.
 *
 * `replace` wipes the local days and entries first and adopts the file's settings.
 * `merge` adds only days the device does not already have and leaves settings
 * alone — merging two devices' settings is meaningless, and keeping the local copy
 * of a day the device already knows about never loses work that was done here.
 *
 * @param {{days: Array, entries: Array, settings: object|null}} payload
 * @param {'merge'|'replace'} mode
 * @returns {Promise<{added: number, skipped: number, entries: number}>}
 */
export function importBackup(payload, mode) {
  if (mode !== 'merge' && mode !== 'replace') {
    throw new BackupError('Mode d’import inconnu.');
  }
  // Validate again at the write boundary and turn Svelte state proxies into plain
  // records. IndexedDB cannot structured-clone a proxy (DataCloneError).
  const { days, entries, settings } = parseBackup(JSON.stringify({
    ...payload,
    format: EXPORT_FORMAT,
    version: EXPORT_VERSION,
  }));
  return db.transaction('rw', db.days, db.entries, db.settings, async () => {
    if (mode === 'replace') {
      await db.days.clear();
      await db.entries.clear();
      await db.settings.clear();
    }

    const present = new Set((await db.days.toArray()).map((d) => d.date));
    const incoming = days.filter((d) => !present.has(d.date));
    const wanted = new Set(incoming.map((d) => d.date));
    const incomingEntries = entries
      .filter((e) => wanted.has(e.date))
      .map(({ id, ...rest }) => rest);

    if (incoming.length) await db.days.bulkAdd(incoming);
    if (incomingEntries.length) await db.entries.bulkAdd(incomingEntries);

    if (mode === 'replace' && settings) {
      await db.settings.put({ key: 'app', value: settings });
    }

    return {
      added: incoming.length,
      skipped: days.length - incoming.length,
      entries: incomingEntries.length,
    };
  });
}

/** A consistent snapshot of all three stores, even while another tab writes. */
export function exportBackup() {
  return db.transaction('r', db.days, db.entries, db.settings, async () => {
    const [days, entries, settings] = await Promise.all([
      db.days.toArray(), db.entries.toArray(), readSettings(),
    ]);
    return buildBackup({ days, entries, settings });
  });
}