'use strict';

const crypto = require('node:crypto');
const { AniListStop, AniListSkip } = require('./anilist');
const { topTagsFor } = require('./anchors');

const BUDGETS = { nightly: 300, admin: 300, user: 60 };
const REFRESH_COOLDOWN_MS = 3600000;
const MAX_CONSECUTIVE_FAILURES = 5;
const CREATOR_MIN_WEIGHT = 3;

// Thrown out of a run to unwind every stage at once.
class StopRun extends Error {
  constructor(status, stopReason) { super(stopReason); this.status = status; this.stopReason = stopReason; }
}

async function runHarvest({ kind, targets, cache, client, budget }) {
  let requests = 0, failures = 0;
  const seen = new Set();
  // One request: skipped when already done this run or still fresh in the cache, otherwise awaited in turn.
  const fetchInto = async (cacheKind, key, call) => {
    const id = `${cacheKind}\n${key}`;
    if (seen.has(id)) return;
    seen.add(id);
    if (cache.isFresh(cacheKind, key)) return;
    if (requests >= budget) throw new StopRun('success', 'budget');
    requests++;
    let data;
    try { data = await call(); }
    catch (error) {
      if (error instanceof AniListStop) throw new StopRun('stopped', error.reason);
      if (!(error instanceof AniListSkip)) throw error;
      if (++failures >= MAX_CONSECUTIVE_FAILURES) throw new StopRun('stopped', 'upstream-errors');
      return;
    }
    failures = 0;
    // A null title is not a manga format: nothing worth keeping.
    if (data !== null) cache.put(cacheKind, key, data);
  };

  const anchors = targets.flatMap(target => target.anchors);
  const recordOf = id => cache.get('title', id)?.data || null;
  try {
    for (const { anilistId } of anchors) await fetchInto('title', anilistId, () => client.title(anilistId));
    for (const { anilistId } of anchors) await fetchInto('recs', anilistId, () => client.recs(anilistId));
    for (const anchor of anchors) {
      if (anchor.weight < CREATOR_MIN_WEIGHT) continue;
      for (const { staffId } of recordOf(anchor.anilistId)?.authors || [])
        await fetchInto('creator', staffId, () => client.creator(staffId));
    }
    for (const target of targets) {
      for (const tag of topTagsFor(target.anchors, recordOf, { mature: target.mature }))
        await fetchInto('tagTop', `${tag.kind}:${tag.name}`, () => client.tagTop(tag));
    }
    // With nobody to harvest for, even the global list is not worth a request.
    if (targets.length) await fetchInto('fresh', 'global', () => client.fresh());
  } catch (error) {
    // The caller records how many requests a local fault had already spent.
    if (!(error instanceof StopRun)) throw Object.assign(error, { requests });
    return { requests, budget, status: error.status, stopReason: error.stopReason };
  }
  return { requests, budget, status: 'success', stopReason: null };
}

const localDate = date => [date.getFullYear(), String(date.getMonth() + 1).padStart(2, '0'),
  String(date.getDate()).padStart(2, '0')].join('-');

function shouldRunNightly({ now, harvestAt, lastNightlyDate, enabled }) {
  if (!enabled) return false;
  const match = /^(\d{2}):(\d{2})$/.exec(harvestAt || '');
  if (!match) return false;
  if (now.getHours() * 60 + now.getMinutes() < Number(match[1]) * 60 + Number(match[2])) return false;
  return localDate(now) !== lastNightlyDate;
}

const httpError = (status, message, extra = {}) => Object.assign(new Error(message), { status }, extra);

// These reasons mean AniList pushed back: no further calls until a nightly or admin run.
const BLOCKING_REASONS = ['rate-limited', 'forbidden', 'challenge'];
const blockingReason = record => record?.status === 'stopped' && BLOCKING_REASONS.includes(record.stopReason)
  ? record.stopReason : null;

class Harvester {
  constructor({ cache, client, store, targetsFor, onDone, now = Date.now }) {
    Object.assign(this, { cache, client, store, targetsFor, onDone, now });
    this.queue = [];
    this.active = null;
    this.lastAccepted = new Map();
    // The pause outlives a restart through the persisted harvest record.
    try { this.blockedReason = blockingReason(store.load?.()?.harvest); }
    catch { this.blockedReason = null; }
  }
  nextAllowedAt(user) {
    const last = this.lastAccepted.get(user);
    if (last === undefined || this.now() - last >= REFRESH_COOLDOWN_MS) return null;
    return new Date(last + REFRESH_COOLDOWN_MS).toISOString();
  }
  jobs() { return [this.active, ...this.queue].filter(Boolean); }
  request({ kind, user }) {
    if (!Object.hasOwn(BUDGETS, kind)) throw httpError(400, `Unknown harvest kind: ${kind}`);
    if (kind === 'user') {
      if (!user) throw httpError(400, 'A user refresh needs a user');
      if (this.jobs().some(job => job.kind === 'user' && job.user === user))
        throw httpError(409, 'A refresh for this user is already queued or running');
      if (this.blockedReason)
        throw httpError(503, `AniList paused the harvest: ${this.blockedReason}`, { blockedReason: this.blockedReason });
      const nextAllowedAt = this.nextAllowedAt(user);
      if (nextAllowedAt) throw httpError(429, 'Refresh is cooling down', { nextAllowedAt });
      this.lastAccepted.set(user, this.now());
    } else if (this.jobs().length) {
      throw httpError(409, 'A harvest is already queued or running');
    } else {
      // An accepted nightly or admin run is the one allowed retry after a pause.
      this.blockedReason = null;
    }
    const job = { id: crypto.randomBytes(8).toString('hex'), kind, ...(kind === 'user' ? { user } : {}) };
    const position = this.jobs().length;
    this.queue.push(job);
    if (!this.active) this.drain();
    return { harvestId: job.id, position };
  }
  state(userName) {
    const nextAllowedAt = this.nextAllowedAt(userName);
    const extra = { ...(nextAllowedAt ? { nextAllowedAt } : {}), ...(this.blockedReason ? { blockedReason: this.blockedReason } : {}) };
    const index = this.jobs().findIndex(job => job.kind === 'user' && job.user === userName);
    if (index === 0 && this.active) return { state: 'running', ...extra };
    if (index >= 0) return { state: 'queued', position: index, ...extra };
    return { state: 'idle', ...extra };
  }
  current() {
    if (!this.active) return null;
    const { id, kind, user, startedAt } = this.active;
    return { id, kind, ...(user ? { user } : {}), startedAt };
  }
  // Queued refreshes are dropped unrun; their users get their cooldown back for after the pause.
  pause(reason) {
    this.blockedReason = reason;
    for (const job of this.queue) if (job.kind === 'user') this.lastAccepted.delete(job.user);
    this.queue = this.queue.filter(job => job.kind !== 'user');
  }
  // Runs synchronously up to the first await, so a job is active before request() returns.
  async drain() {
    while (this.queue.length) {
      const job = this.queue.shift();
      job.startedAt = new Date(this.now()).toISOString();
      this.active = job;
      try { await this.run(job); }
      catch (error) { console.error(`Discovery harvest ${job.id} failed:`, error); }
      finally { this.active = null; }
    }
  }
  async run(job) {
    const budget = BUDGETS[job.kind];
    const base = { id: job.id, kind: job.kind, user: job.user ?? null };
    await this.store.patch({ harvest: { ...base, status: 'running', startedAt: job.startedAt, requests: 0, budget } });
    let result;
    try {
      const targets = await this.targetsFor(job.kind, job.user);
      result = await runHarvest({ kind: job.kind, targets, cache: this.cache, client: this.client, budget });
    } catch (error) {
      // A local fault (cache write, bad target) must not leave the record "running" until restart.
      console.error(`Discovery harvest ${job.id} failed:`, error);
      result = { requests: error?.requests ?? 0, budget, status: 'stopped', stopReason: 'error' };
    }
    const blocked = blockingReason(result);
    if (blocked) this.pause(blocked);
    await this.store.patch({ harvest: { ...base, status: result.status, startedAt: job.startedAt,
      finishedAt: new Date(this.now()).toISOString(), requests: result.requests, budget, stopReason: result.stopReason } });
    try { await this.onDone(job, result); }
    catch (error) { console.error(`Discovery harvest ${job.id} follow-up failed:`, error); }
  }
}

module.exports = { BUDGETS, REFRESH_COOLDOWN_MS, MAX_CONSECUTIVE_FAILURES, runHarvest, shouldRunNightly, Harvester };