import { mkdir, readFile, rm, writeFile } from 'node:fs/promises';
import { join } from 'node:path';

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

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

/**
 * Filesystem binding for branding assets (issue #306; pond overrides #307).
 *
 * One flat directory of PNGs named by a caller-supplied key
 * (`instance-logo-light`, later `pond-<id>-favicon-32`). Flat because there
 * are a handful of files per instance and the backup archives the directory
 * as a whole — a tree would buy nothing and cost a traversal question.
 *
 * The key is constrained here rather than trusted from the route: it is the
 * only thing between a request parameter and a path.
 */
@Injectable()
export class BrandingStorageService {
  constructor(private readonly config: AppConfig) {}

  /** Lowercase, digits and dashes only — no dot, so no `..`, and no slash,
   *  so the file cannot leave the directory whatever a caller sends. */
  private pathFor(key: string): string {
    if (!/^[a-z0-9-]{1,120}$/.test(key)) throw new Error(`invalid branding key: ${key}`);
    return join(this.config.env.BRANDING_DIR, `${key}.png`);
  }

  async save(key: string, bytes: Buffer): Promise<void> {
    await mkdir(this.config.env.BRANDING_DIR, { recursive: true });
    await writeFile(this.pathFor(key), bytes);
  }

  /** The bytes, or null when the file is absent — a missing asset is a normal
   *  state here (nothing uploaded, or metadata and disk drifted after a
   *  partial restore), and every caller has a fallback. */
  async read(key: string): Promise<Buffer | null> {
    try {
      return await readFile(this.pathFor(key));
    } catch {
      return null;
    }
  }

  /** Idempotent: removing what is not there is success. */
  async remove(key: string): Promise<void> {
    await rm(this.pathFor(key), { force: true });
  }
}