import type { ActorIdentifier, Did } from "@atcute/lexicons/syntax";
import {
	OAuthUserAgent,
	createAuthorizationUrl,
	deleteStoredSession,
	finalizeAuthorization,
	getSession,
	type Session
} from "@atcute/oauth-browser-client";
import { markOrgDid, orgControllerFor } from "#lib/auth/accounts.ts";
import { mintServiceAuth, serviceDidForHost } from "#lib/auth/agent.ts";
import { isDeadSessionError } from "#lib/auth/session.ts";
import { nsidOf } from "#lib/api/syntax.ts";

interface ConsentScope {
	scope: string;
	restricted?: boolean;
}

interface ConsentPermissionSet {
	include_scope: string;
	restricted?: boolean;
}

interface ConsentData {
	scopes: ConsentScope[];
	permission_sets?: ConsentPermissionSet[];
}

interface ApprovalData {
	redirect_uri?: string;
	error?: string;
	error_description?: string;
}

type AccessTokenClaims = {
	act?: { sub?: unknown };
};

export const delegatedSessionController = (session: Pick<Session, "token">): Did | null => {
	try {
		const encodedPayload = session.token.access.split(".")[1];
		if (!encodedPayload) return null;
		const base64 = encodedPayload.replace(/-/g, "+").replace(/_/g, "/");
		const padded = base64.padEnd(Math.ceil(base64.length / 4) * 4, "=");
		const claims = JSON.parse(atob(padded)) as AccessTokenClaims;
		const controller = claims.act?.sub;
		return typeof controller === "string" && controller.startsWith("did:")
			? (controller as Did)
			: null;
	} catch {
		return null;
	}
};

const approvedScopesOf = (consent: ConsentData): string[] => {
	const scopes = new Set([
		...consent.scopes.filter((s) => !s.restricted).map((s) => s.scope),
		...(consent.permission_sets ?? []).filter((s) => !s.restricted).map((s) => s.include_scope)
	]);
	if (consent.scopes.some((s) => s.scope === "atproto")) {
		scopes.add("atproto");
	}
	return scopes.size > 0 ? [...scopes] : ["atproto"];
};

const createAuthorizationRequest = async (
	controllerAgent: OAuthUserAgent,
	delegatedDid: Did
): Promise<URL> => {
	const authorizationUrl = await createAuthorizationUrl({
		target: { type: "account", identifier: delegatedDid as ActorIdentifier },
		scope: controllerAgent.session.token.scope
	});
	const requestUri = authorizationUrl.searchParams.get("request_uri");
	if (!requestUri) throw new Error("tranquil did not return a request_uri for the org account.");
	return authorizationUrl;
};

const bindAuthorizationRequest = async (
	controllerAgent: OAuthUserAgent,
	delegatedDid: Did,
	requestUri: string,
	pds: URL
): Promise<void> => {
	const token = await mintServiceAuth(controllerAgent, {
		aud: serviceDidForHost(pds.host),
		lxm: nsidOf("farm.tranquil.delegation.authorize")
	});
	const response = await fetch(new URL("/oauth/delegation/auth-token", pds), {
		method: "POST",
		headers: { "content-type": "application/json", authorization: `Bearer ${token}` },
		body: JSON.stringify({ request_uri: requestUri, delegated_did: delegatedDid })
	});
	const fallback = "Could not bind the org account's authorization request.";
	// error bodies may not be json (proxy pages, timeouts), so parse leniently
	const data: { success?: boolean; error?: string } = await response.json().catch(() => ({}));
	if (!response.ok || !data.success) throw new Error(data.error || fallback);
};

const consentEndpoint = (pds: URL): URL => new URL("/oauth/authorize/consent", pds);

const loadConsent = async (pds: URL, requestUri: string): Promise<ConsentData> => {
	const url = consentEndpoint(pds);
	url.searchParams.set("request_uri", requestUri);
	const response = await fetch(url);
	if (!response.ok) throw new Error("Could not load the org account's authorization request.");
	return response.json();
};

const approveConsent = async (
	pds: URL,
	requestUri: string,
	consent: ConsentData
): Promise<string> => {
	const response = await fetch(consentEndpoint(pds), {
		method: "POST",
		headers: { "content-type": "application/json" },
		body: JSON.stringify({
			request_uri: requestUri,
			approved_scopes: approvedScopesOf(consent),
			remember: false
		})
	});
	const data: ApprovalData = await response.json();
	if (!data.redirect_uri) {
		throw new Error(
			data.error_description || data.error || "Authorizing the org account failed."
		);
	}
	return data.redirect_uri;
};

const callbackParams = (intermediateRedirect: string, issuer: string): URLSearchParams => {
	const intermediate = new URL(intermediateRedirect);
	const code = intermediate.searchParams.get("code");
	if (!code) throw new Error("tranquil did not return an authorization code.");

	const params = new URLSearchParams({ iss: new URL(issuer).origin, code });
	const state = intermediate.searchParams.get("state");
	if (state) params.set("state", state);
	return params;
};

export const createDelegatedSession = async (
	controllerAgent: OAuthUserAgent,
	delegatedDid: Did
): Promise<OAuthUserAgent> => {
	const authorizationUrl = await createAuthorizationRequest(controllerAgent, delegatedDid);
	const requestUri = authorizationUrl.searchParams.get("request_uri")!;
	await bindAuthorizationRequest(controllerAgent, delegatedDid, requestUri, authorizationUrl);
	const consent = await loadConsent(authorizationUrl, requestUri);
	const redirect = await approveConsent(authorizationUrl, requestUri, consent);
	const params = callbackParams(redirect, authorizationUrl.origin);
	const { session } = await finalizeAuthorization(params);
	if (
		session.info.sub !== delegatedDid ||
		delegatedSessionController(session) !== controllerAgent.sub
	) {
		deleteStoredSession(session.info.sub);
		throw new Error("The authorized organization or controller did not match the request.");
	}
	return new OAuthUserAgent(session);
};

const storedDelegatedSession = async (
	controllerDid: Did,
	delegatedDid: Did
): Promise<Session | null> => {
	const recordedController = orgControllerFor(delegatedDid);
	if (recordedController && recordedController !== controllerDid) {
		deleteStoredSession(delegatedDid);
		return null;
	}
	try {
		const session = await getSession(delegatedDid);
		if (delegatedSessionController(session) !== controllerDid) {
			deleteStoredSession(delegatedDid);
			return null;
		}
		return session;
	} catch (cause) {
		if (!isDeadSessionError(cause)) throw cause;
		return null;
	}
};

// prefer this over createDelegatedSession directly
export const getOrCreateDelegatedSession = async (
	controllerAgent: OAuthUserAgent,
	delegatedDid: Did
): Promise<OAuthUserAgent> => {
	const controllerDid = controllerAgent.sub as Did;
	if (delegatedDid === controllerDid) return controllerAgent;
	const stored = await storedDelegatedSession(controllerDid, delegatedDid);
	const agent = stored
		? new OAuthUserAgent(stored)
		: await createDelegatedSession(controllerAgent, delegatedDid);
	markOrgDid(delegatedDid, controllerDid);
	return agent;
};

export const agentActingAs = async (
	agent: OAuthUserAgent | null,
	actAs: Did | null | undefined
): Promise<OAuthUserAgent | null> =>
	agent && actAs ? getOrCreateDelegatedSession(agent, actAs) : agent;