// Storage abstraction
//
// All backup artifacts (repo CARs, blobs) go through this interface, so
// swapping the backend (local FS today, S3/WebDAV tomorrow) is a drop-in.
//
// Paths are forward-slash logical paths (e.g. "repos/did:plc:abc/2026-04-18.car").
// Backends are responsible for any on-disk encoding they need.

import { env } from '../env';
import { LocalStorage } from './local';

export interface StorageUsage {
	// Bytes currently occupied by our stored artifacts.
	usedBytes: number;
	// Bytes free on the backing device, or null for backends where this is
	// not well-defined (e.g. S3).
	freeBytes: number | null;
	// Total bytes on the backing device, or null where not well-defined.
	totalBytes: number | null;
}

export interface StorageEntry {
	path: string;
	size: number;
	mtime: Date;
}

export interface Storage {
	put(
		path: string,
		data: Uint8Array | ReadableStream<Uint8Array>
	): Promise<void>;

	get(path: string): Promise<ReadableStream<Uint8Array> | null>;

	exists(path: string): Promise<boolean>;

	delete(path: string): Promise<void>;

	stat(path: string): Promise<{ size: number; mtime: Date } | null>;

	// Recursive listing. Yields every object under the prefix.
	list(prefix: string): AsyncIterable<StorageEntry>;

	// Aggregate size under a prefix. Implementations may cache / optimise.
	sizeOf(prefix: string): Promise<number>;

	// Overall backing-device usage stats.
	usage(): Promise<StorageUsage>;
}

let _storage: Storage | null = null;

export function storage(): Storage {
	if (_storage) return _storage;
	switch (env.STORAGE_BACKEND) {
		case 'local':
			_storage = new LocalStorage(env.STORAGE_LOCAL_ROOT);
			return _storage;
		default: {
			const _exhaustive: never = env.STORAGE_BACKEND;
			throw new Error(`Unknown storage backend: ${_exhaustive}`);
		}
	}
}