import type { GitHubAccount, GitHubKey, GitHubRepo } from "$lib/github";
import { type GitHubEnv, hostOf } from "./env";

export class GitHubUpstreamError extends Error {
	constructor(public status: number) {
		super("github upstream");
	}
}

const malformed = () => new Error("github malformed response");

type Json = Record<string, unknown>;
const object = (value: unknown): Json | null =>
	value !== null && typeof value === "object" && !Array.isArray(value) ? (value as Json) : null;
const text = (o: Json, key: string) => (typeof o[key] === "string" ? o[key] : null);
const integer = (o: Json, key: string) =>
	typeof o[key] === "number" && Number.isInteger(o[key]) ? o[key] : null;

interface GitHubCaller {
	env: GitHubEnv;
	token: string;
	fetch: typeof fetch;
}

const send = async (call: GitHubCaller, url: string) => {
	const response = await call.fetch(url, {
		redirect: "error",
		headers: {
			accept: "application/vnd.github+json",
			authorization: `Bearer ${call.token}`,
			"user-agent": "tangled"
		}
	});
	if (!response.ok) throw new GitHubUpstreamError(response.status);
	return { body: (await response.json()) as unknown, link: response.headers.get("link") };
};

const one = async (call: GitHubCaller, path: string): Promise<Json> => {
	const { body } = await send(call, `${call.env.apiOrigin}${path}`);
	const value = object(body);
	if (!value) throw malformed();
	return value;
};

const NEXT = /<([^>]+)>;\s*rel="next"/;
// preserve configured origin to prevent pagination SSRF
const nextPage = (link: string | null, origin: string) => {
	const raw = link
		?.split(",")
		.map((part) => NEXT.exec(part.trim())?.[1])
		.find((href): href is string => href !== undefined);
	if (!raw) return null;
	const next = URL.parse(raw);
	if (!next || next.origin !== origin) throw malformed();
	return next.toString();
};

const PAGE_LIMIT = 100;
const all = async (
	call: GitHubCaller,
	path: string,
	rows: (body: unknown) => unknown = (body) => body
): Promise<Json[]> => {
	const out: Json[] = [];
	let url: string | null =
		`${call.env.apiOrigin}${path}${path.includes("?") ? "&" : "?"}per_page=100`;
	for (let page = 0; page < PAGE_LIMIT; page++) {
		const { body, link } = await send(call, url);
		const value = rows(body);
		if (!Array.isArray(value)) throw malformed();
		for (const row of value) {
			const item = object(row);
			if (!item) throw malformed();
			out.push(item);
		}
		url = nextPage(link, call.env.apiOrigin);
		if (!url) return out;
	}
	throw new Error("github pagination limit exceeded");
};

const inside = (key: string) => (body: unknown) => object(body)?.[key];

const sameHost = (value: string, host: string) => {
	const url = URL.parse(value);
	return (
		url !== null &&
		url.protocol === "https:" &&
		url.hostname === host &&
		!url.username &&
		!url.password
	);
};

const repo = (env: GitHubEnv, row: Json, installationId?: number): GitHubRepo | null => {
	const host = hostOf(env.publicOrigin);
	const id = integer(row, "id"),
		name = text(row, "name"),
		fullName = text(row, "full_name"),
		cloneUrl = text(row, "clone_url"),
		htmlUrl = text(row, "html_url"),
		visibility = text(row, "visibility"),
		privateFlag = row.private;
	if (
		id === null ||
		name === null ||
		fullName === null ||
		cloneUrl === null ||
		htmlUrl === null ||
		!sameHost(cloneUrl, host) ||
		!sameHost(htmlUrl, host) ||
		(privateFlag !== undefined && typeof privateFlag !== "boolean")
	)
		return null;
	const isPrivate = privateFlag === true || visibility === "private" || visibility === "internal";
	const language = text(row, "language"),
		stars = integer(row, "stargazers_count"),
		issues = integer(row, "open_issues_count"),
		forks = integer(row, "forks_count"),
		sizeKb = integer(row, "size"),
		updatedAt = text(row, "pushed_at") ?? text(row, "updated_at");
	return {
		id,
		name,
		fullName,
		description: text(row, "description"),
		cloneUrl,
		htmlUrl,
		defaultBranch: text(row, "default_branch") ?? "",
		visibility:
			visibility === "public" || visibility === "private" || visibility === "internal"
				? visibility
				: isPrivate
					? "private"
					: "public",
		private: isPrivate,
		installationId,
		language,
		stars,
		issues,
		forks,
		updatedAt,
		sizeKb
	};
};

const key = (row: Json): GitHubKey | null => {
	const id = integer(row, "id"),
		value = text(row, "key");
	return id === null || value === null
		? null
		: { id, key: value, title: text(row, "title") ?? "" };
};

const emailRow = (row: Json) => {
	const address = text(row, "email");
	return address === null
		? null
		: { address, primary: row.primary === true, verified: row.verified === true };
};

// noreply addresses cannot receive deliberi verification email
const NOREPLY = /@(?:users\.)?noreply\.github\.com$/i;
const primaryEmail = (rows: Json[]) => {
	const usable = rows.flatMap((row) => {
		const parsed = emailRow(row);
		return parsed === null || !parsed.verified || NOREPLY.test(parsed.address) ? [] : [parsed];
	});
	return (usable.find((e) => e.primary) ?? usable[0])?.address ?? null;
};

export const account = async (
	env: GitHubEnv,
	token: string,
	fetcher: typeof fetch = fetch
): Promise<GitHubAccount> => {
	const call: GitHubCaller = { env, token, fetch: fetcher };
	const [me, emails, keys] = await Promise.all([
		one(call, "/user"),
		all(call, "/user/emails"),
		all(call, "/user/keys")
	]);
	const login = text(me, "login");
	const [owned, installations] = await Promise.all([
		login === null ? [] : all(call, `/users/${encodeURIComponent(login)}/repos?type=owner`),
		all(call, "/user/installations", inside("installations"))
	]);
	const granted = await Promise.all(
		installations.flatMap((row) => {
			const id = integer(row, "id");
			return id === null
				? []
				: [
						all(
							call,
							`/user/installations/${id}/repositories`,
							inside("repositories")
						).then((rows) => rows.map((r) => repo(env, r, id)))
					];
		})
	);
	const unique = new Map(
		[...owned.map((row) => repo(env, row)), ...granted.flat()].flatMap((r) =>
			r === null ? [] : [[r.id, r] as const]
		)
	);
	return {
		login: login ?? "",
		avatarUrl: text(me, "avatar_url") ?? "",
		bio: text(me, "bio"),
		blog: text(me, "blog"),
		email: primaryEmail(emails),
		emails: emails.flatMap((row) => {
			const parsed = emailRow(row);
			return parsed === null ? [] : [parsed];
		}),
		keys: keys.flatMap((row) => {
			const parsed = key(row);
			return parsed === null ? [] : [parsed];
		}),
		repos: [...unique.values()],
		publicOrigin: env.publicOrigin
	};
};

export const hasInstallations = async (
	env: GitHubEnv,
	token: string,
	fetcher: typeof fetch = fetch
) =>
	(await all({ env, token, fetch: fetcher }, "/user/installations", inside("installations")))
		.length > 0;

// pinned to avatarsOrigin to prevent SSRF
export const avatarSource = async (
	env: GitHubEnv,
	token: string,
	fetcher: typeof fetch = fetch
): Promise<URL> => {
	const me = await one({ env, token, fetch: fetcher }, "/user");
	const raw = text(me, "avatar_url");
	const avatar = raw === null ? null : URL.parse(raw);
	if (!avatar || avatar.origin !== env.avatarsOrigin || avatar.username || avatar.password)
		throw malformed();
	// default github avatar size is ~40px without explicit size parameter
	avatar.searchParams.set("s", "256");
	return avatar;
};