import { existsSync, readFileSync, statSync, writeFileSync } from 'node:fs';
import { join } from 'node:path';
import { CronExpressionParser } from 'cron-parser';
import { type CronJob, CronJobSchema, CronStoreSchema } from './types.ts';

export type OnJobCallback = (job: CronJob) => Promise<void>;

export class CronService {
  private _filePath: string;
  private _jobs: Map<string, CronJob> = new Map();
  private _timers: Map<string, ReturnType<typeof setTimeout>> = new Map();
  private _onJob: OnJobCallback;
  private _lastMtime = 0;

  constructor(workspacePath: string, onJob: OnJobCallback) {
    this._filePath = join(workspacePath, 'cron', 'jobs.json');
    this._onJob = onJob;
    this._load();
  }

  // ---------------------------------------------------------------------------
  // Persistence
  // ---------------------------------------------------------------------------

  private _load(): void {
    if (!existsSync(this._filePath)) return;
    try {
      const raw = readFileSync(this._filePath, 'utf8');
      const store = CronStoreSchema.parse(JSON.parse(raw));
      this._jobs = new Map(store.jobs.map((j) => [j.id, j]));
      this._lastMtime = statSync(this._filePath).mtimeMs;
    } catch {
      // start fresh on corrupt file
    }
  }

  private _save(): void {
    const store = CronStoreSchema.parse({ jobs: [...this._jobs.values()] });
    const dir = this._filePath.replace(/\/[^/]+$/, '');
    require('node:fs').mkdirSync(dir, { recursive: true });
    writeFileSync(this._filePath, JSON.stringify(store, null, 2), 'utf8');
    this._lastMtime = statSync(this._filePath).mtimeMs;
  }

  private _reloadIfChanged(): void {
    if (!existsSync(this._filePath)) return;
    const mtime = statSync(this._filePath).mtimeMs;
    if (mtime !== this._lastMtime) this._load();
  }

  // ---------------------------------------------------------------------------
  // Public API
  // ---------------------------------------------------------------------------

  listJobs(): CronJob[] {
    this._reloadIfChanged();
    return [...this._jobs.values()];
  }

  addJob(job: Omit<CronJob, 'state' | 'createdAtMs' | 'updatedAtMs'>): CronJob {
    const now = Date.now();
    const full = CronJobSchema.parse({ ...job, state: {}, createdAtMs: now, updatedAtMs: now });
    this._jobs.set(full.id, full);
    this._save();
    this._arm(full);
    return full;
  }

  removeJob(id: string): boolean {
    if (!this._jobs.has(id)) return false;
    this._clearTimer(id);
    this._jobs.delete(id);
    this._save();
    return true;
  }

  enableJob(id: string, enabled: boolean): boolean {
    const job = this._jobs.get(id);
    if (!job) return false;
    this._jobs.set(id, { ...job, enabled, updatedAtMs: Date.now() });
    this._save();
    if (enabled) this._arm(this._jobs.get(id)!);
    else this._clearTimer(id);
    return true;
  }

  async runJob(id: string): Promise<string> {
    const job = this._jobs.get(id);
    if (!job) return `Error: job ${id} not found`;
    await this._execute(job);
    return `Job ${id} executed.`;
  }

  status(): string {
    const jobs = this.listJobs();
    if (jobs.length === 0) return 'No cron jobs configured.';
    return jobs
      .map((j) => {
        const next = j.state.nextRunAtMs ? new Date(j.state.nextRunAtMs).toISOString() : 'N/A';
        return `[${j.enabled ? 'ON' : 'OFF'}] ${j.id} "${j.name}" next=${next}`;
      })
      .join('\n');
  }

  /** Arm all loaded jobs. Call once after construction. */
  start(): void {
    for (const job of this._jobs.values()) {
      if (job.enabled) this._arm(job);
    }
  }

  stop(): void {
    for (const id of this._timers.keys()) this._clearTimer(id);
  }

  // ---------------------------------------------------------------------------
  // Scheduling internals
  // ---------------------------------------------------------------------------

  private _arm(job: CronJob): void {
    this._clearTimer(job.id);
    if (!job.enabled) return;

    const delayMs = this._nextDelayMs(job);
    if (delayMs === null) return;

    const nextRunAtMs = Date.now() + delayMs;
    const updated: CronJob = { ...job, state: { ...job.state, nextRunAtMs }, updatedAtMs: Date.now() };
    this._jobs.set(job.id, updated);
    this._save();

    const timer = setTimeout(() => void this._tick(job.id), delayMs);
    this._timers.set(job.id, timer);
  }

  private async _tick(id: string): Promise<void> {
    this._timers.delete(id);
    const job = this._jobs.get(id);
    if (!job || !job.enabled) return;
    await this._execute(job);
    // Re-arm unless it was deleted or is a one-shot
    const current = this._jobs.get(id);
    if (current && !current.deleteAfterRun) this._arm(current);
  }

  private async _execute(job: CronJob): Promise<void> {
    try {
      await this._onJob(job);
      const updated: CronJob = {
        ...job,
        state: { ...job.state, lastRunAtMs: Date.now(), lastStatus: 'ok', lastError: null },
        updatedAtMs: Date.now(),
      };
      this._jobs.set(job.id, updated);
      if (job.deleteAfterRun) {
        this._jobs.delete(job.id);
      }
      this._save();
    } catch (err) {
      const updated: CronJob = {
        ...job,
        state: { ...job.state, lastRunAtMs: Date.now(), lastStatus: 'error', lastError: String(err) },
        updatedAtMs: Date.now(),
      };
      this._jobs.set(job.id, updated);
      this._save();
    }
  }

  private _nextDelayMs(job: CronJob): number | null {
    const { schedule } = job;
    const now = Date.now();

    if (schedule.kind === 'at') {
      const delay = schedule.atMs - now;
      return delay > 0 ? delay : null;
    }

    if (schedule.kind === 'every') {
      const lastRun = job.state.lastRunAtMs ?? 0;
      const elapsed = now - lastRun;
      const delay = Math.max(0, schedule.everyMs - elapsed);
      return delay;
    }

    if (schedule.kind === 'cron') {
      try {
        const interval = CronExpressionParser.parse(schedule.expr, { tz: schedule.tz });
        const next = interval.next();
        return next.getTime() - now;
      } catch {
        console.error(`[cron] Failed to parse expression for job ${job.id}: ${schedule.expr}`);
        return null;
      }
    }

    return null;
  }

  private _clearTimer(id: string): void {
    const timer = this._timers.get(id);
    if (timer !== undefined) {
      clearTimeout(timer);
      this._timers.delete(id);
    }
  }
}