/**
 * OpenRouter OAuth PKCE flow.
 *
 * OpenRouter exchanges an authorization code for a permanent, user-controlled
 * API key rather than an expiring access/refresh token pair. The callback is
 * handled by a one-shot loopback server on an ephemeral port, raced against a
 * manual prompt so remote/headless sessions can paste the redirect URL when
 * the browser cannot reach the loopback server.
 *
 * NOTE: This module uses Node.js http.createServer for the OAuth callback server.
 * It is only intended for CLI use, not browser environments.
 */

import { createServer, type Server, type ServerResponse } from "node:http";
import { getProviderEnvValue } from "../../utils/provider-env.ts";
import type { OAuthAuth, OAuthCredential, ProviderAuthInteraction } from "../types.ts";
import { oauthErrorHtml, oauthSuccessHtml } from "./oauth-page.ts";
import { generatePKCE } from "./pkce.ts";

const AUTHORIZE_URL = "https://openrouter.ai/auth";
const TOKEN_URL = "https://openrouter.ai/api/v1/auth/keys";
const LOGIN_TIMEOUT_MS = 5 * 60 * 1000;
const TOKEN_EXCHANGE_TIMEOUT_MS = 30_000;

function getCallbackHost(): string {
	return getProviderEnvValue("PI_OAUTH_CALLBACK_HOST") || "127.0.0.1";
}

type JsonObject = Record<string, unknown>;

type OpenRouterCallbackServer = {
	callbackUrl: string;
	/** Stop listening and release timers without settling `waitForCredential`. */
	close: () => void;
	/** Hand the login over to manual code entry unless a callback already claimed the exchange. */
	cancelWait: () => void;
	/**
	 * Resolves with the credential once a browser callback completes the key
	 * exchange, or with null once `cancelWait` hands the login over to manual
	 * code entry. Rejects on timeout, cancellation, or a failed exchange.
	 */
	waitForCredential: () => Promise<OAuthCredential | null>;
};

function sendHtml(response: ServerResponse, status: number, html: string): void {
	response.statusCode = status;
	response.setHeader("content-type", "text/html; charset=utf-8");
	response.setHeader("cache-control", "no-store");
	response.end(html);
}

function parseAuthorizationInput(input: string): string | undefined {
	const value = input.trim();
	if (!value) return undefined;

	try {
		return new URL(value).searchParams.get("code") ?? undefined;
	} catch {
		// not a URL
	}

	if (value.includes("code=")) {
		return new URLSearchParams(value).get("code") ?? undefined;
	}

	return value;
}

function errorDetail(body: JsonObject): string | undefined {
	if (typeof body.error_description === "string") return body.error_description;
	if (typeof body.message === "string") return body.message;
	if (typeof body.error === "string") return body.error;
	if (body.error && typeof body.error === "object" && !Array.isArray(body.error)) {
		const message = (body.error as JsonObject).message;
		if (typeof message === "string") return message;
	}
	return undefined;
}

async function exchangeAuthorizationCode(
	code: string,
	verifier: string,
	signal: AbortSignal,
): Promise<OAuthCredential> {
	if (signal.aborted) throw new Error("Login cancelled");
	const controller = new AbortController();
	const onAbort = () => controller.abort(signal.reason);
	signal.addEventListener("abort", onAbort, { once: true });
	const timeout = setTimeout(
		() => controller.abort(new Error("OpenRouter OAuth token exchange timed out")),
		TOKEN_EXCHANGE_TIMEOUT_MS,
	);

	let response: Response;
	let body: JsonObject = {};
	try {
		response = await fetch(TOKEN_URL, {
			method: "POST",
			headers: { accept: "application/json", "content-type": "application/json" },
			body: JSON.stringify({ code, code_verifier: verifier, code_challenge_method: "S256" }),
			signal: controller.signal,
		});
		try {
			const parsed = (await response.json()) as unknown;
			if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) body = parsed as JsonObject;
		} catch {
			if (response.ok) throw new Error("OpenRouter OAuth returned invalid JSON");
		}
	} catch (error) {
		if (signal.aborted) throw new Error("Login cancelled");
		if (controller.signal.aborted) throw new Error("OpenRouter OAuth token exchange timed out");
		throw error;
	} finally {
		clearTimeout(timeout);
		signal.removeEventListener("abort", onAbort);
	}

	if (!response.ok) {
		const detail = errorDetail(body);
		throw new Error(`OpenRouter OAuth key exchange failed (HTTP ${response.status})${detail ? `: ${detail}` : ""}`);
	}

	if (typeof body.key !== "string" || body.key.length === 0) {
		throw new Error('OpenRouter OAuth response carries no "key"');
	}

	return {
		type: "oauth",
		access: body.key,
		refresh: "",
		expires: Number.MAX_SAFE_INTEGER,
	};
}

async function startCallbackServer(
	callbackPath: string,
	verifier: string,
	signal: AbortSignal,
): Promise<OpenRouterCallbackServer> {
	if (signal.aborted) throw new Error("Login cancelled");
	const callbackHost = getCallbackHost();
	let resolveCredential: (credential: OAuthCredential | null) => void = () => {};
	let rejectCredential: (error: Error) => void = () => {};
	const credential = new Promise<OAuthCredential | null>((resolve, reject) => {
		resolveCredential = resolve;
		rejectCredential = reject;
	});

	let server: Server;
	let claimed = false;
	let settled = false;
	let timeout: ReturnType<typeof setTimeout> | undefined;
	let onAbort: (() => void) | undefined;

	const close = (): void => {
		if (timeout) clearTimeout(timeout);
		if (onAbort) signal.removeEventListener("abort", onAbort);
		server.close();
	};

	const finish = (result: { credential: OAuthCredential | null } | { error: Error }): void => {
		if (settled) return;
		settled = true;
		close();
		if ("credential" in result) resolveCredential(result.credential);
		else rejectCredential(result.error);
	};

	server = createServer((request, response) => {
		void (async () => {
			const requestUrl = new URL(request.url ?? "/", `http://${callbackHost}`);
			if (request.method !== "GET" || requestUrl.pathname !== callbackPath) {
				sendHtml(response, 404, oauthErrorHtml("OAuth callback route not found."));
				return;
			}
			if (claimed || settled) {
				sendHtml(response, 409, oauthErrorHtml("This OAuth callback has already been used."));
				return;
			}

			const oauthError = requestUrl.searchParams.get("error");
			if (oauthError) {
				const description = requestUrl.searchParams.get("error_description") ?? oauthError;
				sendHtml(response, 400, oauthErrorHtml("OpenRouter authorization was denied.", description));
				finish({ error: new Error(`OpenRouter authorization failed: ${description}`) });
				return;
			}

			const code = requestUrl.searchParams.get("code");
			if (!code) {
				sendHtml(response, 400, oauthErrorHtml("OpenRouter returned no authorization code."));
				return;
			}
			claimed = true;

			try {
				const result = await exchangeAuthorizationCode(code, verifier, signal);
				sendHtml(response, 200, oauthSuccessHtml("Signed in to OpenRouter. You may now close this page."));
				finish({ credential: result });
			} catch (error) {
				const message = error instanceof Error ? error.message : "Unknown token exchange error";
				sendHtml(response, 502, oauthErrorHtml("OpenRouter key exchange failed.", message));
				finish({ error: error instanceof Error ? error : new Error(message) });
			}
		})();
	});

	await new Promise<void>((resolve, reject) => {
		server.once("error", reject);
		server.listen(0, callbackHost, () => {
			server.removeListener("error", reject);
			resolve();
		});
	});

	server.on("error", (error) => finish({ error }));
	onAbort = () => finish({ error: new Error("Login cancelled") });
	signal.addEventListener("abort", onAbort, { once: true });
	if (signal.aborted) {
		close();
		throw new Error("Login cancelled");
	}
	timeout = setTimeout(() => finish({ error: new Error("OpenRouter OAuth login timed out") }), LOGIN_TIMEOUT_MS);

	const address = server.address();
	if (!address || typeof address === "string") {
		close();
		throw new Error("Could not determine the OpenRouter OAuth callback port");
	}

	return {
		callbackUrl: `http://${callbackHost}:${address.port}${callbackPath}`,
		close,
		// A claimed callback is already exchanging its code; let that exchange settle the login.
		cancelWait: () => {
			if (!claimed) finish({ credential: null });
		},
		waitForCredential: () => credential,
	};
}

async function loginOpenRouter(interaction: ProviderAuthInteraction): Promise<OAuthCredential> {
	const { verifier, challenge } = await generatePKCE();
	const callbackPath = `/oauth/callback/${crypto.randomUUID()}`;
	const callback = await startCallbackServer(callbackPath, verifier, interaction.signal);
	const manualAbort = new AbortController();
	let manualInput: string | undefined;
	let manualError: Error | undefined;

	try {
		const authorizeUrl = new URL(AUTHORIZE_URL);
		authorizeUrl.search = new URLSearchParams({
			callback_url: callback.callbackUrl,
			code_challenge: challenge,
			code_challenge_method: "S256",
		}).toString();

		interaction.notify({
			type: "progress",
			message: `Listening for OpenRouter OAuth callback on ${callback.callbackUrl}`,
		});
		interaction.notify({
			type: "auth_url",
			url: authorizeUrl.toString(),
			instructions:
				"Complete sign-in in your browser. If the browser is on another machine, paste the final redirect URL here.",
		});

		const manualPromise = interaction
			.prompt({
				type: "manual_code",
				message: "Complete sign-in in your browser, or paste the authorization code / redirect URL here:",
				placeholder: callback.callbackUrl,
				signal: manualAbort.signal,
			})
			.then((input) => {
				manualInput = input;
				callback.cancelWait();
			})
			.catch((error) => {
				manualError = error instanceof Error ? error : new Error(String(error));
				callback.cancelWait();
			});

		const credential = await callback.waitForCredential();
		if (manualError) throw manualError;
		if (credential) return credential;

		await manualPromise;
		if (manualError) throw manualError;
		const code = manualInput ? parseAuthorizationInput(manualInput) : undefined;
		if (!code) throw new Error("Missing authorization code");
		interaction.notify({ type: "progress", message: "Exchanging authorization code for an API key..." });
		return await exchangeAuthorizationCode(code, verifier, interaction.signal);
	} finally {
		manualAbort.abort();
		callback.close();
	}
}

export const openRouterOAuth: OAuthAuth = {
	name: "OpenRouter OAuth",
	loginLabel: "Sign in with OpenRouter",
	login: loginOpenRouter,
	async refresh(credential, _signal) {
		return credential;
	},
	async toAuth(credential) {
		return { apiKey: credential.access };
	},
};