Import source: app/backend/src/lib/storage

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

app/backend/src/lib/storage.ts

@@ -0,0 +1,72 @@
+// Storage abstraction layer.
+// Switch between local disk and S3-compatible storage via STORAGE_BACKEND env var.
+// Required env vars for S3: S3_ENDPOINT, S3_BUCKET, S3_ACCESS_KEY, S3_SECRET_KEY
+// Default: LocalStorageAdapter (STORAGE_BACKEND=local or unset)
+
+import fs from 'node:fs/promises';
+import path from 'node:path';
+import { config } from '../config.js';
+
+export interface StorageAdapter {
+  /** Write file buffer at the given key, return the public URL */
+  upload(file: Buffer, key: string, mimeType?: string): Promise<string>;
+  /** Delete the object at the given key */
+  delete(key: string): Promise<void>;
+  /** Return the public URL for a key (without writing) */
+  url(key: string): string;
+}
+
+class LocalStorageAdapter implements StorageAdapter {
+  async upload(file: Buffer, key: string): Promise<string> {
+    const dest = path.join(config.UPLOAD_DIR, key);
+    await fs.mkdir(path.dirname(dest), { recursive: true });
+    await fs.writeFile(dest, file);
+    return this.url(key);
+  }
+
+  async delete(key: string): Promise<void> {
+    await fs.unlink(path.join(config.UPLOAD_DIR, key)).catch(() => undefined);
+  }
+
+  url(key: string): string {
+    return `/uploads/${key}`;
+  }
+}
+
+class S3StorageAdapter implements StorageAdapter {
+  private endpoint: string;
+  private bucket: string;
+  private accessKey: string;
+  private secretKey: string;
+
+  constructor() {
+    this.endpoint = process.env.S3_ENDPOINT ?? '';
+    this.bucket = process.env.S3_BUCKET ?? '';
+    this.accessKey = process.env.S3_ACCESS_KEY ?? '';
+    this.secretKey = process.env.S3_SECRET_KEY ?? '';
+    if (!this.endpoint || !this.bucket || !this.accessKey || !this.secretKey) {
+      throw new Error('S3 storage requires S3_ENDPOINT, S3_BUCKET, S3_ACCESS_KEY, S3_SECRET_KEY');
+    }
+  }
+
+  async upload(_file: Buffer, _key: string, _mimeType?: string): Promise<string> {
+    // Wire a real S3 client (e.g. @aws-sdk/client-s3 or minio SDK) in Phase 12
+    throw new Error('S3StorageAdapter.upload: not yet implemented');
+  }
+
+  async delete(_key: string): Promise<void> {
+    throw new Error('S3StorageAdapter.delete: not yet implemented');
+  }
+
+  url(key: string): string {
+    return `${this.endpoint}/${this.bucket}/${key}`;
+  }
+}
+
+function createStorageAdapter(): StorageAdapter {
+  const backend = process.env.STORAGE_BACKEND ?? 'local';
+  if (backend === 's3') return new S3StorageAdapter();
+  return new LocalStorageAdapter();
+}
+
+export const storage: StorageAdapter = createStorageAdapter();