import { readdir } from "node:fs/promises";
import { join, relative } from "node:path";
import type { BucketSource } from "../server/config.ts";

/** Read-only view of a Koh 3 remote (§9.1): Kepr needs only these two of its five operations. */
export type BucketReader = {
	get(key: string): Promise<Uint8Array | null>;
	list(prefix: string): Promise<string[]>;
};

export function openBucket(source: BucketSource): BucketReader {
	return source.kind === "s3" ? s3Reader(source) : folderReader(source.path);
}

function s3Reader(source: Extract<BucketSource, { kind: "s3" }>): BucketReader {
	const client = new Bun.S3Client({
		endpoint: source.endpoint,
		bucket: source.name,
		region: source.region,
		accessKeyId: source.accessKeyId,
		secretAccessKey: source.secretAccessKey,
	});
	return {
		async get(key) {
			try {
				return await client.file(key).bytes();
			} catch (error) {
				if ((error as { code?: string }).code === "NoSuchKey") return null;
				throw error;
			}
		},
		async list(prefix) {
			const keys: string[] = [];
			let continuationToken: string | undefined;
			do {
				const page = await client.list({ prefix, continuationToken });
				for (const object of page.contents ?? []) keys.push(object.key);
				continuationToken = page.isTruncated ? page.nextContinuationToken : undefined;
			} while (continuationToken);
			return keys;
		},
	};
}

function folderReader(root: string): BucketReader {
	return {
		async get(key) {
			if (key.split("/").includes("..")) throw new Error(`bucket key escapes the folder: ${key}`);
			const file = Bun.file(join(root, key));
			return (await file.exists()) ? await file.bytes() : null;
		},
		async list(prefix) {
			const entries = await readdir(root, { recursive: true, withFileTypes: true });
			return entries
				.filter((entry) => entry.isFile())
				.map((entry) => relative(root, join(entry.parentPath, entry.name)))
				.filter((key) => key.startsWith(prefix))
				.sort();
		},
	};
}