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

/**
 * A Koh 3 remote as Kepr uses it (§9.1): read-only on Koh's data, which needs two of its five
 * operations, plus a short-lived download URL so Kepr never streams release files itself (§22.2).
 * Kepr's own files (uploads) live under `KEPR_PREFIX` (June, 2026-09-29); no Koh repo can have
 * that name, since Kepr and Koh both need a `head` for one. Beyond it Kepr touches only builds,
 * which Koh has no way to delete (June, 2026-09-30): it deletes a version's files, rewrites its
 * record without a deleted one, and moves `releases/latest`.
 */
export type Bucket = {
	get(key: string): Promise<Uint8Array | null>;
	list(prefix: string): Promise<string[]>;
	/** Every key under `prefix` with its size in bytes, for the console's storage view. */
	sizes(prefix: string): Promise<Map<string, number>>;
	/** A URL that serves `key` for five minutes, as an attachment with this filename and content type. */
	downloadUrl(key: string, filename: string, type: string): string;
	/** A five-minute URL that shows `key` in the page, or null when Kepr must serve the bytes itself. */
	viewUrl(key: string, type: string): string | null;
	/**
	 * Writes one of Kepr's own files, a repo's `releases/latest`, or a version's `release.json` when
	 * one of its files is deleted; any other key is refused.
	 */
	put(key: string, bytes: Uint8Array, type: string): Promise<void>;
	/** Deletes one of Kepr's own files, a release's file or `releases/latest`; nothing else. */
	remove(key: string): Promise<void>;
};

export const KEPR_PREFIX = ".kepr/";

/** A write Kepr can't make: outside its folder, or without the `[bucket.write]` key. */
export class BucketWriteError extends Error {}

const DOWNLOAD_SECONDS = 5 * 60;

const RELEASE_WRITE = /^[^/]+\/releases\/(latest|[^/]+\/release\.json)$/;
const RELEASE_FILE = /^[^/]+\/releases\/(latest|[^/]+\/.+)$/;

function requireWritable(key: string, releaseKey: RegExp): void {
	const allowed = key.startsWith(KEPR_PREFIX) || releaseKey.test(key);
	if (!allowed || key.split("/").some((part) => part === ".." || part === "")) {
		throw new BucketWriteError(`Kepr writes only under ${KEPR_PREFIX} and builds, not "${key}"`);
	}
}

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

type S3Source = Extract<BucketSource, { kind: "s3" }>;

/**
 * The console's connection test (§24), made before settings are saved: the read key must list the
 * bucket, and a write key must write Kepr's own test file. Returns what failed, or null.
 */
export async function checkS3Access(source: S3Source): Promise<string | null> {
	const reason = (error: unknown) => (error instanceof Error ? error.message : String(error));
	try {
		// One key is proof enough; listing the whole bucket could take minutes.
		await s3Client(source).list({ maxKeys: 1 });
	} catch (error) {
		return `The read key cannot list the bucket: ${reason(error)}`;
	}
	if (!source.write) return null;
	try {
		const stamp = new TextEncoder().encode(new Date().toISOString());
		await s3Reader(source).put(`${KEPR_PREFIX}connection-test`, stamp, "text/plain");
	} catch (error) {
		return `The write key cannot write ${KEPR_PREFIX}connection-test: ${reason(error)}`;
	}
	return null;
}

function s3Client(
	source: S3Source,
	keys: { accessKeyId: string; secretAccessKey: string } = source,
): Bun.S3Client {
	return new Bun.S3Client({
		endpoint: source.endpoint,
		bucket: source.name,
		region: source.region,
		accessKeyId: keys.accessKeyId,
		secretAccessKey: keys.secretAccessKey,
	});
}

function s3Reader(source: S3Source): Bucket {
	const client = s3Client(source);
	// Reads keep the read-only key; only Kepr's own writes use the write key, when there is one.
	const writer = source.write && s3Client(source, source.write);
	const requireWriter = () => {
		if (!writer) {
			throw new BucketWriteError("Writing needs the bucket's write key: add [bucket.write].");
		}
		return writer;
	};
	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;
		},
		async sizes(prefix) {
			const sizes = new Map<string, number>();
			let continuationToken: string | undefined;
			do {
				const page = await client.list({ prefix, continuationToken });
				for (const object of page.contents ?? []) sizes.set(object.key, object.size ?? 0);
				continuationToken = page.isTruncated ? page.nextContinuationToken : undefined;
			} while (continuationToken);
			return sizes;
		},
		downloadUrl(key, filename, type) {
			// Bun signs these as response-content-disposition and response-content-type (verified, v1.3.14).
			return client.presign(key, {
				method: "GET",
				expiresIn: DOWNLOAD_SECONDS,
				contentDisposition: `attachment; filename="${filename}"`,
				type,
			});
		},
		viewUrl(key, type) {
			return client.presign(key, { method: "GET", expiresIn: DOWNLOAD_SECONDS, type });
		},
		async put(key, bytes, type) {
			requireWritable(key, RELEASE_WRITE);
			await requireWriter().file(key).write(bytes, { type });
		},
		async remove(key) {
			requireWritable(key, RELEASE_FILE);
			await requireWriter().file(key).delete();
		},
	};
}

function folderReader(root: string): Bucket {
	const list = async (prefix: string) => {
		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();
	};
	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;
		},
		list,
		async sizes(prefix) {
			return new Map((await list(prefix)).map((key) => [key, Bun.file(join(root, key)).size]));
		},
		// Development and tests only: a file:// URL can't carry a filename, a type or an expiry.
		downloadUrl(key) {
			if (key.split("/").includes("..")) throw new Error(`bucket key escapes the folder: ${key}`);
			return pathToFileURL(join(root, key)).href;
		},
		viewUrl: () => null,
		async put(key, bytes) {
			requireWritable(key, RELEASE_WRITE);
			await Bun.write(join(root, key), bytes);
		},
		async remove(key) {
			requireWritable(key, RELEASE_FILE);
			await unlink(join(root, key)).catch((error: NodeJS.ErrnoException) => {
				if (error.code !== "ENOENT") throw error;
			});
		},
	};
}