/**
 * src/managers/FirebaseManager.ts
 *
 * Singleton wrapper around the Firebase Admin SDK.
 * Responsibilities:
 *   - Initialize the Admin SDK once from env (service account JSON string)
 *   - Real-time Firestore listener for `titan_transpiler_jobs`
 *   - Atomic job claiming via Firestore transactions (prevents duplicate processing
 *     if multiple workers are ever running)
 *   - Firebase Storage upload / download helpers
 */

import admin from 'firebase-admin';
import axios from 'axios';
import fs from 'fs';
import { pipeline } from 'stream/promises';
import type { Firestore } from 'firebase-admin/firestore';
import { logger } from '../utils/logger';
import { ENV } from '../config/env';

// ─── Job Document Types ───────────────────────────────────────────────────────

export type JobStatus =
  | 'pending'
  | 'processing'
  | 'transpiling'
  | 'auditing'
  | 'completed'
  | 'failed';

export interface TranspilerJob {
  /** Firestore document ID */
  id: string;
  /** gs:// or https:// URL of the uploaded Website.zip in Firebase Storage */
  zipUrl: string;
  status: JobStatus;
  appName?: string;
  createdAt: admin.firestore.Timestamp;
  updatedAt?: admin.firestore.Timestamp;
  /** Signed download URL for the generated Flutter_Code.zip */
  outputUrl?: string;
  /** Human-readable error message when status === 'failed' */
  errorMessage?: string;
  /** 0–100 overall progress indicator */
  progress?: number;
  /** Per-file Dart confidence scores */
  confidenceScores?: Record<string, number>;
  /** Per-file audit pass/fail */
  auditResults?: Record<string, boolean>;
}

export interface JobUpdate {
  status?: JobStatus;
  outputUrl?: string;
  errorMessage?: string;
  progress?: number;
  confidenceScores?: Record<string, number>;
  auditResults?: Record<string, boolean>;
}

// ─── FirebaseManager (Singleton) ─────────────────────────────────────────────

export class FirebaseManager {
  private static instance: FirebaseManager | null = null;

  private readonly db: Firestore;
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  private readonly bucket: any; // admin.storage().bucket() — type varies by firebase-admin version
  private unsubscribeListener: (() => void) | null = null;

  // ─── Initialization ──────────────────────────────────────────────────────

  private constructor() {
    // Guard: only call initializeApp once (important for hot-reload in dev)
    if (!admin.apps.length) {
      const serviceAccount = JSON.parse(ENV.FIREBASE_SERVICE_ACCOUNT) as admin.ServiceAccount;
      admin.initializeApp({
        credential: admin.credential.cert(serviceAccount),
        storageBucket: ENV.FIREBASE_STORAGE_BUCKET,
      });
    }

    this.db = admin.firestore();
    this.bucket = admin.storage().bucket();

    logger.info('FirebaseManager: Admin SDK initialized');
    logger.info(`FirebaseManager: bucket="${ENV.FIREBASE_STORAGE_BUCKET}"`);
  }

  static getInstance(): FirebaseManager {
    if (!FirebaseManager.instance) {
      FirebaseManager.instance = new FirebaseManager();
    }
    return FirebaseManager.instance;
  }

  // ─── Firestore Job Operations ────────────────────────────────────────────

  /**
   * Fetches a single job document by its Firestore document ID.
   * Returns null if the document does not exist.
   */
  async getJob(jobId: string): Promise<TranspilerJob | null> {
    const snap = await this.db
      .collection(ENV.FIRESTORE_JOBS_COLLECTION)
      .doc(jobId)
      .get();

    if (!snap.exists) return null;
    return { id: snap.id, ...(snap.data() as Omit<TranspilerJob, 'id'>) };
  }

  /**
   * Partially updates a job document. Always stamps `updatedAt`.
   */
  async updateJob(jobId: string, update: JobUpdate): Promise<void> {
    const payload: Record<string, unknown> = {
      ...update,
      updatedAt: admin.firestore.Timestamp.now(),
    };

    await this.db
      .collection(ENV.FIRESTORE_JOBS_COLLECTION)
      .doc(jobId)
      .update(payload);

    logger.info(
      `FirebaseManager: job ${jobId} updated` +
      (update.status ? ` → status="${update.status}"` : '') +
      (update.progress !== undefined ? ` progress=${update.progress}%` : '')
    );
  }

  /**
   * Starts a Firestore real-time listener on the jobs collection.
   * When a document is added with status === "pending", it:
   *   1. Runs a Firestore transaction to atomically claim the job
   *      (sets status → "processing"), preventing races.
   *   2. Calls `onNewJob(job)` asynchronously.
   *
   * @returns An unsubscribe function that stops the listener.
   */
  listenForPendingJobs(
    onNewJob: (job: TranspilerJob) => Promise<void>
  ): () => void {
    const col = this.db.collection(ENV.FIRESTORE_JOBS_COLLECTION);
    const query = col
      .where('status', '==', 'pending')
      .orderBy('createdAt', 'asc');

    const unsubscribe = query.onSnapshot(
      async (snapshot) => {
        for (const change of snapshot.docChanges()) {
          // We only care about documents that just became 'pending'
          if (change.type !== 'added') continue;

          const docRef = change.doc.ref;
          const rawData = change.doc.data() as Omit<TranspilerJob, 'id'>;
          const job: TranspilerJob = { id: change.doc.id, ...rawData };

          logger.info(`FirebaseManager: new pending job → id=${job.id}`);

          // ── Atomic claim via transaction ─────────────────────────────────
          let claimed = false;
          try {
            await this.db.runTransaction(async (tx) => {
              const freshSnap = await tx.get(docRef);
              if (!freshSnap.exists) throw new Error('Job document disappeared');

              const freshStatus = (freshSnap.data() as Omit<TranspilerJob, 'id'>).status;
              if (freshStatus !== 'pending') {
                // Another worker claimed it first — abort silently
                throw new Error(`Job ${job.id} already claimed (status="${freshStatus}")`);
              }

              tx.update(docRef, {
                status: 'processing',
                updatedAt: admin.firestore.Timestamp.now(),
              });
            });
            claimed = true;
          } catch (txErr) {
            logger.warn(`FirebaseManager: job ${job.id} claim failed — ${String(txErr)}`);
          }

          if (!claimed) continue;

          // ── Dispatch to orchestrator (non-blocking) ──────────────────────
          onNewJob(job).catch((err: unknown) => {
            logger.error(`FirebaseManager: uncaught error in onNewJob for ${job.id}`, err);
          });
        }
      },
      (err) => {
        logger.error('FirebaseManager: Firestore listener error', err);
      }
    );

    this.unsubscribeListener = unsubscribe;
    logger.info(
      `FirebaseManager: listening on collection "${ENV.FIRESTORE_JOBS_COLLECTION}"`
    );
    return unsubscribe;
  }

  /** Stops the active Firestore listener, if any. */
  stopListening(): void {
    this.unsubscribeListener?.();
    this.unsubscribeListener = null;
    logger.info('FirebaseManager: listener stopped');
  }

  // ─── Queue Operations (titan_builder_queue) ──────────────────────────────
  //
  // These methods target titan_builder_queue exclusively.
  // No existing method above is touched or modified.

  /**
   * Writes a partial update to a document in `titan_builder_queue`.
   * Uses set({ merge: true }) so it is safe even if the doc is brand-new,
   * and always stamps updatedAt.
   */
  async updateQueueDoc(docId: string, update: QueueDocUpdate): Promise<void> {
    const payload: Record<string, unknown> = {
      ...update,
      updatedAt: admin.firestore.Timestamp.now(),
    };
    await this.db
      .collection(QUEUE_COLLECTION)
      .doc(docId)
      .set(payload, { merge: true });

    logger.info(
      `FirebaseManager[queue]: ${docId} updated` +
      (update.status ? ` → "${update.status}"` : '')
    );
  }

  /**
   * Creates a seed document in `titan_transpiler_jobs` via .set().
   *
   * WHY THIS EXISTS:
   *   updateJob() uses .update() which throws NOT_FOUND if the doc is absent.
   *   JobQueue calls this BEFORE LLMOrchestrator.processJob() so that the
   *   orchestrators internal updateJob() calls have a real document to land on.
   */
  async createTranspilerJobDoc(job: TranspilerJob): Promise<void> {
    const { id, ...data } = job;
    await this.db
      .collection(ENV.FIRESTORE_JOBS_COLLECTION)
      .doc(id)
      .set({
        ...data,
        createdAt: data.createdAt ?? admin.firestore.Timestamp.now(),
        updatedAt:  admin.firestore.Timestamp.now(),
      });
    logger.info(`FirebaseManager: transpiler job seeded → id=${id}`);
  }

  /**
   * Downloads a Firebase Storage object entirely into a Node.js Buffer.
   *
   * Use-case: the build queue handler needs the reviewed Dart ZIP as bytes
   * to pass directly to GitHubActionsService.triggerBuild().
   *
   * Memory note: keep payloads under ~50 MB — fully buffered in RAM.
   */
  async downloadToBuffer(storageUrl: string): Promise<Buffer> {
    const storagePath = this.parseStoragePath(storageUrl);
    logger.info(`FirebaseManager: downloading to buffer — "${storagePath}"`);
    const [contents] = await this.bucket.file(storagePath).download();
    const buf = Buffer.isBuffer(contents) ? contents : Buffer.from(contents as Uint8Array);
    logger.info(`FirebaseManager: buffer ready — ${buf.length} bytes`);
    return buf;
  }


  // ─── Firebase Storage Operations ─────────────────────────────────────────

  /**
   * Downloads a file from Firebase Storage to a local path.
   * Accepts gs://, public storage URLs, or firebasestorage.googleapis.com URLs.
   */
  async downloadFile(storageUrl: string, localPath: string): Promise<void> {
    const storagePath = this.parseStoragePath(storageUrl);
    logger.info(`FirebaseManager: downloading "${storagePath}" → "${localPath}"`);
    await this.bucket.file(storagePath).download({ destination: localPath });
    logger.info(`FirebaseManager: download complete`);
  }

  /**
   * Downloads a file from any HTTPS URL (HF Dataset, etc.) to a local path.
   * Used when zipUrl is an HF Dataset URL instead of a Firebase Storage URL.
   */
  async downloadFileFromUrl(url: string, localPath: string): Promise<void> {
    // If it's a Firebase Storage URL, use the old method
    if (url.startsWith('gs://') || url.includes('firebasestorage') || url.includes('storage.googleapis')) {
      return this.downloadFile(url, localPath);
    }
    // Otherwise download via HTTP (HF Dataset, file.io, etc.)
    logger.info(`FirebaseManager: downloading "${url}" → "${localPath}"`);
    const response = await axios.get<NodeJS.ReadableStream>(url, {
      responseType: 'stream',
      timeout: 120_000,
    });
    const writer = fs.createWriteStream(localPath);
    await pipeline(response.data, writer);
    logger.info(`FirebaseManager: download complete`);
  }

  /**
   * Uploads a local file to Firebase Storage.
   * @returns A signed URL valid for 7 days.
   */
  async uploadFile(
    localPath: string,
    destinationPath: string,
    contentType = 'application/zip'
  ): Promise<string> {
    logger.info(`FirebaseManager: uploading "${localPath}" → "${destinationPath}"`);

    await this.bucket.upload(localPath, {
      destination: destinationPath,
      metadata: { contentType },
    });

    return this.getSignedUrl(destinationPath);
  }

  /**
   * Uploads a Buffer directly to Firebase Storage without touching disk.
   * @returns A signed URL valid for 7 days.
   */
  async uploadBuffer(
    buffer: Buffer,
    destinationPath: string,
    contentType = 'application/zip'
  ): Promise<string> {
    logger.info(`FirebaseManager: uploading buffer (${buffer.length} bytes) → "${destinationPath}"`);
    const file = this.bucket.file(destinationPath);

    await new Promise<void>((resolve, reject) => {
      const stream = file.createWriteStream({ metadata: { contentType } });
      stream.on('error', reject);
      stream.on('finish', resolve);
      stream.end(buffer);
    });

    return this.getSignedUrl(destinationPath);
  }

  // ─── Private Helpers ─────────────────────────────────────────────────────

  /** Generates a 7-day signed download URL for a storage path. */
  private async getSignedUrl(storagePath: string): Promise<string> {
    const [url] = await this.bucket.file(storagePath).getSignedUrl({
      action: 'read',
      expires: Date.now() + 7 * 24 * 60 * 60 * 1000, // 7 days
    });
    return url;
  }

  /**
   * Normalises various Firebase Storage URL formats to a raw storage path.
   *
   * Handles:
   *   gs://bucket-name/path/to/file.zip
   *   https://storage.googleapis.com/bucket/path/to/file.zip
   *   https://firebasestorage.googleapis.com/v0/b/bucket/o/path%2Fto%2Ffile.zip?token=…
   */
  private parseStoragePath(url: string): string {
    // gs:// protocol
    if (url.startsWith('gs://')) {
      const withoutScheme = url.slice(5); // strip "gs://"
      const firstSlash = withoutScheme.indexOf('/');
      return firstSlash === -1 ? withoutScheme : withoutScheme.slice(firstSlash + 1);
    }

    // Public Google Storage CDN URL
    if (url.includes('storage.googleapis.com/')) {
      const u = new URL(url);
      // pathname = /bucket-name/path/to/file — drop first two segments
      const parts = u.pathname.split('/').filter(Boolean);
      return parts.slice(1).join('/');
    }

    // Firebase Storage REST URL
    if (url.includes('firebasestorage.googleapis.com')) {
      const u = new URL(url);
      const oSegment = u.pathname.split('/o/')[1];
      if (oSegment) return decodeURIComponent(oSegment.split('?')[0]);
    }

    // Fallback: treat as a raw storage path
    return url;
  }
}

// ═══════════════════════════════════════════════════════════════════════════
//  QUEUE TYPES  (added for titan_builder_queue — existing types unchanged)
// ═══════════════════════════════════════════════════════════════════════════

/** The Firestore collection that acts as the job message broker. */
export const QUEUE_COLLECTION = 'titan_builder_queue';

export type QueueStatus =
  | 'pending'
  | 'processing'
  | 'building'
  | 'completed'
  | 'failed';

export type QueueJobType = 'transpile' | 'build' | 'webview';

/**
 * Shape of a document in `titan_builder_queue`.
 * Clients (mobile app, web dashboard) write this; the worker reads it.
 */
export interface QueueDoc {
  id: string;
  type: QueueJobType;
  status: QueueStatus;

  // ── 'transpile' fields ─────────────────────────────────────────────────
  /** HF Dataset URL or HTTPS URL pointing to the ZIP */
  zipUrl?: string;
  appName?: string;

  // ── 'build' fields ─────────────────────────────────────────────────────
  /** Flutter ZIP as base64 string */
  zipBase64?: string;

  // ── 'webview' fields ───────────────────────────────────────────────────
  url?: string;
  iconUrl?: string;
  iconBase64?: string;
  iconMime?: string;
  enableCamera?: boolean;
  enableStorage?: boolean;
  enableLocation?: boolean;
  enableNotifications?: boolean;
  buildType?: string;
  manifestUrl?: string;
  templateType?: string;

  // ── Result fields (set by the worker) ──────────────────────────────────
  /** HF Dataset public download URL for the output ZIP */
  resultZipUrl?: string;
  errorMessage?: string;
  createdAt: admin.firestore.Timestamp;
  updatedAt?: admin.firestore.Timestamp;
}

export interface QueueDocUpdate {
  status?: QueueStatus;
  resultZipUrl?: string;
  errorMessage?: string;
}