import { createReadStream } from 'node:fs';
import { access, mkdir, rm, writeFile } from 'node:fs/promises';
import { join } from 'node:path';
import type { Readable } from 'node:stream';

import { Injectable } from '@nestjs/common';

import { AppConfig } from '../config/app-config.service';

/**
 * Filesystem binding for uploaded files (ADR 0011, issue #27): opaque
 * layout `<uploadsDir>/<pondId>/<fileId>`, original filenames and metadata
 * live in the database, not on disk. Kept behind this interface so an S3
 * binding stays possible later without touching callers.
 */
@Injectable()
export class FileStorageService {
  constructor(private readonly config: AppConfig) {}

  private pathFor(pondId: string, fileId: string): string {
    return join(this.config.env.UPLOADS_DIR, pondId, fileId);
  }

  async save(pondId: string, fileId: string, data: Buffer): Promise<void> {
    await mkdir(join(this.config.env.UPLOADS_DIR, pondId), { recursive: true });
    await writeFile(this.pathFor(pondId, fileId), data);
  }

  createReadStream(pondId: string, fileId: string): Readable {
    return createReadStream(this.pathFor(pondId, fileId));
  }

  /** Whether the file's bytes are actually on disk. Used by the pond export to
   * skip an attachment whose bytes are missing (data drift) rather than crash
   * the archive stream (issue #65). */
  async exists(pondId: string, fileId: string): Promise<boolean> {
    try {
      await access(this.pathFor(pondId, fileId));
      return true;
    } catch {
      return false;
    }
  }

  /** Idempotent — removing an already-absent file is not an error. */
  async delete(pondId: string, fileId: string): Promise<void> {
    await rm(this.pathFor(pondId, fileId), { force: true });
  }
}