import { createHash, randomBytes, timingSafeEqual } from "node:crypto";
import type { Context, Hono } from "hono";
import { deleteCookie, getCookie, setCookie } from "hono/cookie";
import { html } from "../pages/html.ts";
import { type PageContext, page } from "../pages/layout.ts";
import { clientIp } from "./client.ts";

const SESSION_SECONDS = 30 * 86400;
const SESSION_COOKIE = "kepr_session";
const SIGN_IN_COOKIE = "kepr_sign_in";
// Readable by kepr.js, and saying only that someone signed in here: public pages stay the same
// cacheable HTML for everyone, and the script asks the admin routes for the editing controls.
const EDITOR_COOKIE = "kepr_editor";
const COOKIE = { httpOnly: true, secure: true, sameSite: "Strict", path: "/" } as const;
const HEX64 = /^[0-9a-f]{64}$/;
const FAILURE_WINDOW_MS = 15 * 60 * 1000;
const FAILURES_PER_ADDRESS = 5;

// Failed sign-ins, oldest first, in memory: a restart forgets them, but an attacker can't cause one.
const failures: { at: number; address: string }[] = [];
// Addresses are keyed hashes even in memory, as issue filings store them (§23).
const addressKey = randomBytes(32);

const nowSeconds = () => Math.floor(Date.now() / 1000);
const sha256 = (text: string) => createHash("sha256").update(text).digest("hex");

function sameText(a: string, b: string): boolean {
	const [x, y] = [Buffer.from(a), Buffer.from(b)];
	return x.length === y.length && timingSafeEqual(x, y);
}

/** The session cookie's token when it names a live session in kepr.db, else null. */
function sessionToken(ctx: PageContext, c: Context): string | null {
	const token = getCookie(c, SESSION_COOKIE);
	if (!token || !HEX64.test(token)) return null;
	const row = ctx.kepr
		.query<{ n: number }, [string, number]>(
			"SELECT 1 AS n FROM sessions WHERE token_hash = ? AND expires_at > ?",
		)
		.get(sha256(token), nowSeconds());
	return row ? token : null;
}

export function signedIn(ctx: PageContext, c: Context): boolean {
	return sessionToken(ctx, c) !== null;
}

/** How many sessions are live, this one included. */
export function liveSessions(ctx: PageContext): number {
	return (
		ctx.kepr
			.query<{ n: number }, [number]>("SELECT COUNT(*) AS n FROM sessions WHERE expires_at > ?")
			.get(nowSeconds())?.n ?? 0
	);
}

/** Revokes every session but the one making this request. */
export function endOtherSessions(ctx: PageContext, c: Context): void {
	const token = sessionToken(ctx, c) ?? "";
	ctx.kepr.query("DELETE FROM sessions WHERE token_hash != ?").run(sha256(token));
}

/**
 * Whether a request came from this site. A localhost domain also accepts plain http, since a
 * local run has no TLS in front of it; browsers keep Secure cookies on http://localhost.
 */
function fromSite(c: Context, domain: string): boolean {
	const origin = c.req.header("origin");
	if (origin === `https://${domain}`) return true;
	return origin === `http://${domain}` && /^localhost(:\d+)?$/.test(domain);
}

export async function adminPostRefusal(ctx: PageContext, c: Context): Promise<string> {
	if (!fromSite(c, ctx.domain)) return "Refused: wrong origin.";
	const form = (await c.req.parseBody()).form;
	return typeof form !== "string" || !sameText(form, formToken(c))
		? "Refused: this form expired. Reload and try again."
		: "";
}

/**
 * The same-site token every admin form carries (§25): derived from the session's secret token, so
 * a page on another site can neither read nor guess it, and it dies with the session.
 */
export function formToken(c: Context): string {
	return formTokenOf(getCookie(c, SESSION_COOKIE) ?? "");
}

function formTokenOf(session: string): string {
	return sha256(`form:${session}`);
}

// The readable mark beside the session: its form token, so the navbar can offer log out without
// asking the server (nav.js). Readable by the site's own scripts only, as any page's form is.
function setEditorCookie(c: Context, session: string): void {
	setCookie(c, EDITOR_COOKIE, formTokenOf(session), {
		...COOKIE,
		httpOnly: false,
		maxAge: SESSION_SECONDS,
	});
}

/**
 * The refusal page behind every admin entry point, `/connect` included: one answer for a missing
 * session, a foreign origin, an expired form token or too many attempts, wherever it arrives.
 */
export function adminRefusal(
	c: Context,
	ctx: PageContext,
	status: 401 | 403 | 429,
	text: string,
): Response {
	c.header("Cache-Control", "no-store");
	const body = html`<h1 class="file-page-title">${text}</h1>`;
	return c.html(page(ctx, { title: "admin", description: "", path: c.req.path, body }), status);
}

/**
 * §24's login at `/sign-in`, sessions, sign-out, and the guard in front of every
 * `/admin` route: a live session, and for anything but GET a matching `Origin` and form token.
 */
export function registerLogin(
	app: Hono,
	ctx: PageContext,
	// The live config, so a password changed in the console works at once.
	config: { adminPasswordHash: string },
): void {
	const refuse = (c: Context, status: 401 | 403 | 429, text: string) =>
		adminRefusal(c, ctx, status, text);

	app.use("/admin/*", async (c, next) => {
		const token = sessionToken(ctx, c);
		if (!token) return refuse(c, 401, "Sign in first.");
		// A mark set before it carried the token is brought up to date.
		if (getCookie(c, EDITOR_COOKIE) !== formTokenOf(token)) setEditorCookie(c, token);
		if (c.req.method !== "GET") {
			const error = await adminPostRefusal(ctx, c);
			if (error) return refuse(c, 403, error);
		}
		await next();
		c.header("Cache-Control", "no-store");
	});

	app.get("/sign-in", (c) => signInPage(c, ctx, "", 200, nextPath(c.req.query("next"))));

	app.post("/sign-in", async (c) => {
		const fields = await c.req.parseBody();
		const next = nextPath(fields.next);
		const cookie = getCookie(c, SIGN_IN_COOKIE) ?? "";
		const form = typeof fields.form === "string" ? fields.form : "";
		if (!fromSite(c, ctx.domain) || !HEX64.test(cookie) || !sameText(form, cookie)) {
			return refuse(c, 403, "Refused: this form expired. Reload and try again.");
		}
		const now = Date.now();
		while (failures[0] && failures[0].at <= now - FAILURE_WINDOW_MS) failures.shift();
		const address = createHash("sha256").update(addressKey).update(clientIp(c)).digest("hex");
		const mine = failures.filter((failure) => failure.address === address).length;
		if (mine >= FAILURES_PER_ADDRESS) {
			c.header("Retry-After", String(FAILURE_WINDOW_MS / 1000));
			return signInPage(c, ctx, "Too many attempts. Try again later.", 429, next);
		}
		const password = typeof fields.password === "string" ? fields.password : "";
		if (!(await Bun.password.verify(password, config.adminPasswordHash))) {
			failures.push({ at: now, address });
			return signInPage(c, ctx, "That password is not right.", 401, next);
		}
		const token = randomBytes(32).toString("hex");
		const at = nowSeconds();
		ctx.kepr.query("DELETE FROM sessions WHERE expires_at <= ?").run(at);
		ctx.kepr
			.query("INSERT INTO sessions (token_hash, expires_at) VALUES (?, ?)")
			.run(sha256(token), at + SESSION_SECONDS);
		setCookie(c, SESSION_COOKIE, token, { ...COOKIE, maxAge: SESSION_SECONDS });
		setEditorCookie(c, token);
		deleteCookie(c, SIGN_IN_COOKIE, COOKIE);
		return c.redirect(next, 303);
	});

	app.post("/admin/sign-out", (c) => {
		ctx.kepr
			.query("DELETE FROM sessions WHERE token_hash = ?")
			.run(sha256(getCookie(c, SESSION_COOKIE) ?? ""));
		deleteCookie(c, SESSION_COOKIE, COOKIE);
		deleteCookie(c, EDITOR_COOKIE, { ...COOKIE, httpOnly: false });
		return c.redirect("/", 303);
	});
}

/**
 * Where a sign-in goes on to: a path on this site, or `/admin`. `//host` and `/\host` are other
 * sites to a browser, and a control character could split the Location header.
 */
function nextPath(value: unknown): string {
	if (typeof value !== "string" || !value.startsWith("/")) return "/admin";
	if (value.startsWith("//") || value.startsWith("/\\")) return "/admin";
	if ([...value].some((char) => char.charCodeAt(0) <= 31 || char.charCodeAt(0) === 127))
		return "/admin";
	return value;
}

// A double-submit token repeats a SameSite=Strict cookie that a cross-site post never has.
function signInPage(
	c: Context,
	ctx: PageContext,
	error: string,
	status: 200 | 401 | 429,
	next: string,
) {
	let cookie = getCookie(c, SIGN_IN_COOKIE) ?? "";
	if (!HEX64.test(cookie)) {
		cookie = randomBytes(32).toString("hex");
		setCookie(c, SIGN_IN_COOKIE, cookie, COOKIE);
	}
	c.header("Cache-Control", "no-store");
	const body = html`<h1 class="file-page-title">sign in</h1>
${error && html`<p class="issues-error mono" role="alert">${error}</p>`}
<form class="issues-form" method="post" action="/sign-in">
<input type="hidden" name="form" value="${cookie}">
<input type="hidden" name="next" value="${next}">
<label class="issues-label" for="password">password</label>
<input class="issues-input" id="password" name="password" type="password" required autocomplete="current-password" autofocus>
<button class="issues-submit" type="submit">sign in</button>
</form>`;
	return c.html(page(ctx, { title: "sign in", description: "", path: "/sign-in", body }), status);
}