import { getWebSearchConfigPath } from "../config/path.ts";

interface ApiBaseUrlOptions {
	configKey: string;
	configuredValue: unknown;
	defaultValue: string;
	environmentKey: string;
	environmentValue: string | undefined;
}

export function resolveApiBaseUrl(options: ApiBaseUrlOptions): string {
	const fromEnvironment = options.environmentValue !== undefined;
	const value = fromEnvironment ? options.environmentValue : options.configuredValue;
	if (value === undefined) return options.defaultValue;
	const source = fromEnvironment ? options.environmentKey : `${options.configKey} in ${getWebSearchConfigPath()}`;
	if (typeof value !== "string" || !value.trim()) throw new Error(`${source} must be an absolute HTTP(S) URL`);
	let url: URL;
	try {
		url = new URL(value.trim());
	} catch {
		throw new Error(`${source} must be an absolute HTTP(S) URL`);
	}
	if (url.protocol !== "https:") throw new Error(`${source} must be an absolute HTTPS URL`);
	if (url.username || url.password) throw new Error(`${source} must not include credentials`);
	if (url.search || url.hash) throw new Error(`${source} must not include query parameters or fragments`);
	url.pathname = url.pathname.replace(/\/+$/, "");
	return url.toString().replace(/\/+$/, "");
}

const REDIRECT_STATUSES = new Set([301, 302, 303, 307, 308]);
const BODY_HEADERS = ["Content-Encoding", "Content-Language", "Content-Location", "Content-Type"];
const MAX_REDIRECTS = 5;

export async function fetchWithCredentialRedirects(url: string, init: RequestInit, credentialHeaders: readonly string[]): Promise<Response> {
	let current = new URL(url);
	let requestInit = init;
	for (let redirects = 0; ; redirects++) {
		const response = await fetch(current, { ...requestInit, redirect: "manual" });
		if (!REDIRECT_STATUSES.has(response.status)) return response;
		const location = response.headers.get("location");
		if (!location) return response;
		if (redirects === MAX_REDIRECTS) throw new Error(`Too many API redirects from ${url}`);
		const next = new URL(location, current);
		if (next.protocol !== "http:" && next.protocol !== "https:") throw new Error(`API redirect from ${current.origin} must use HTTP(S)`);
		const method = requestInit.method?.toUpperCase() ?? "GET";
		if (((response.status === 301 || response.status === 302) && method === "POST") || (response.status === 303 && method !== "GET" && method !== "HEAD")) {
			const headers = new Headers(requestInit.headers);
			for (const name of BODY_HEADERS) headers.delete(name);
			const { body: _body, ...withoutBody } = requestInit;
			requestInit = { ...withoutBody, method: "GET", headers };
		}
		if (next.origin !== current.origin) {
			const headers = new Headers(requestInit.headers);
			for (const name of credentialHeaders) headers.delete(name);
			requestInit = { ...requestInit, headers };
		}
		current = next;
	}
}