import { chmod, rename, writeFile } from "node:fs/promises";

export type BucketSource =
	| {
			kind: "s3";
			endpoint: string;
			name: string;
			region: string;
			accessKeyId: string;
			secretAccessKey: string;
			write?: { accessKeyId: string; secretAccessKey: string };
	  }
	// A directory laid out exactly like the bucket (Koh 3's folder remote), for development and tests.
	| { kind: "folder"; path: string };

export type Config = {
	domain: string;
	dataDir: string;
	adminPasswordHash: string;
	bucket: BucketSource;
};

export class ConfigError extends Error {}

const HOSTNAME = new RegExp(
	String.raw`^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)*` +
		String.raw`(:([1-9]\d{0,3}|[1-5]\d{4}|6[0-4]\d{3}|65[0-4]\d{2}|655[0-2]\d|6553[0-5]))?$`,
	"i",
);

export function parseConfig(text: string): Config {
	let raw: unknown;
	try {
		raw = Bun.TOML.parse(text);
	} catch (cause) {
		throw new ConfigError(`kepr.toml is not valid TOML: ${(cause as Error).message}`);
	}
	const top = asTable(raw, "kepr.toml");
	const bucket = asTable(top.bucket, "[bucket]");
	const adminPasswordHash = requireString(top, "admin_password_hash");
	if (!adminPasswordHash.startsWith("$argon2id$")) {
		throw new ConfigError("admin_password_hash must be an Argon2id hash ($argon2id$...)");
	}
	const domain = requireString(top, "domain");
	// Pages, feeds and install.sh put it in URLs and a shell script as is.
	if (!HOSTNAME.test(domain))
		throw new ConfigError("domain must be a bare hostname, with an optional :port");
	return {
		domain,
		dataDir: requireString(top, "data_dir"),
		adminPasswordHash,
		bucket: parseBucket(bucket),
	};
}

/** Where `main` reads the config, and where the console's Bucket section writes it back (§19). */
export const CONFIG_FILE = "kepr.toml";

/**
 * Replaces the config file with `config` in one rename, owner-only since it holds keys (§19).
 * Comments in the old file are not kept. What would not parse back is never written.
 */
export async function saveConfig(path: string, config: Config): Promise<void> {
	// A JSON string is a valid TOML basic string for everything the parse-back below accepts.
	const str = JSON.stringify;
	const { bucket } = config;
	const lines = [
		`domain = ${str(config.domain)}`,
		`data_dir = ${str(config.dataDir)}`,
		`admin_password_hash = ${str(config.adminPasswordHash)}`,
		"",
		"[bucket]",
	];
	if (bucket.kind === "folder") lines.push(`folder = ${str(bucket.path)}`);
	else {
		lines.push(
			`endpoint = ${str(bucket.endpoint)}`,
			`name = ${str(bucket.name)}`,
			`region = ${str(bucket.region)}`,
			`access_key_id = ${str(bucket.accessKeyId)}`,
			`secret_access_key = ${str(bucket.secretAccessKey)}`,
		);
		if (bucket.write) {
			lines.push(
				"",
				"[bucket.write]",
				`access_key_id = ${str(bucket.write.accessKeyId)}`,
				`secret_access_key = ${str(bucket.write.secretAccessKey)}`,
			);
		}
	}
	const text = `${lines.join("\n")}\n`;
	parseConfig(text);
	const next = `${path}.new`;
	await writeFile(next, text, { mode: 0o600 });
	// `mode` applies only to a new file, and a crash may have left an older one behind.
	await chmod(next, 0o600);
	await rename(next, path);
}

export async function loadConfig(path: string): Promise<Config> {
	const file = Bun.file(path);
	if (!(await file.exists())) throw new ConfigError(`${path} not found`);
	return parseConfig(await file.text());
}

function parseBucket(bucket: Record<string, unknown>): BucketSource {
	if (bucket.folder !== undefined) {
		if (bucket.write !== undefined)
			throw new ConfigError("[bucket] write cannot be combined with folder");
		const s3Keys = ["endpoint", "name", "region", "access_key_id", "secret_access_key"];
		const mixed = s3Keys.filter((key) => bucket[key] !== undefined);
		if (mixed.length > 0) {
			throw new ConfigError(`[bucket] folder cannot be combined with ${mixed.join(", ")}`);
		}
		return { kind: "folder", path: requireString(bucket, "folder", "[bucket] ") };
	}
	const endpoint = requireString(bucket, "endpoint", "[bucket] ");
	if (!URL.canParse(endpoint)) throw new ConfigError("[bucket] endpoint must be a URL");
	const write = bucket.write === undefined ? undefined : asTable(bucket.write, "[bucket.write]");
	return {
		kind: "s3",
		endpoint,
		name: requireString(bucket, "name", "[bucket] "),
		region: requireString(bucket, "region", "[bucket] "),
		accessKeyId: requireString(bucket, "access_key_id", "[bucket] "),
		secretAccessKey: requireString(bucket, "secret_access_key", "[bucket] "),
		...(write
			? {
					write: {
						accessKeyId: requireString(write, "access_key_id", "[bucket.write] "),
						secretAccessKey: requireString(write, "secret_access_key", "[bucket.write] "),
					},
				}
			: {}),
	};
}

function asTable(value: unknown, name: string): Record<string, unknown> {
	if (typeof value !== "object" || value === null || Array.isArray(value)) {
		throw new ConfigError(`${name} is missing or not a table`);
	}
	return value as Record<string, unknown>;
}

function requireString(table: Record<string, unknown>, key: string, section = ""): string {
	const value = table[key];
	if (typeof value !== "string" || value.trim() === "") {
		throw new ConfigError(`${section}${key} is required and must be a non-empty string`);
	}
	return value;
}