import type { Database } from "bun:sqlite";
import { createHmac, randomBytes, timingSafeEqual } from "node:crypto";
import type { Context } from "hono";
import { getCookie, setCookie } from "hono/cookie";
import { clientIp } from "../server/client.ts";
import { setting } from "../server/db.ts";

// §23's spam defenses, all server-side: nothing here trusts a clock or a value from the browser.
export const MIN_SECONDS_ON_PAGE = 3;
const STAMP_MAX_AGE = 86400;
export const FILINGS_PER_HOUR = 5;
export const MAX_CHARS = 20_000;
const FORM_COOKIE = "kepr_form";
const HEX = /^[0-9a-f]{32,64}$/;

/** One random key, made on first use and kept in kepr.db, for the IP hash and the form stamps. */
function secret(db: Database): string {
	db.query("INSERT OR IGNORE INTO settings (key, value) VALUES ('issue_secret', ?)").run(
		randomBytes(32).toString("hex"),
	);
	return setting(db, "issue_secret") as string;
}

function mac(db: Database, message: string): string {
	return createHmac("sha256", secret(db)).update(message).digest("hex");
}

/** A keyed hash, so the stored value can't be reversed by hashing every IPv4 address. */
export function ipHash(db: Database, c: Context): string {
	return mac(db, `ip:${clientIp(c)}`);
}

/**
 * SameSite=Strict so a cross-site post arrives without it, and a form stamp
 * `<unix time>.<HMAC(time, cookie)>`.
 */
export function formStamp(db: Database, c: Context, now: number): string {
	let cookie = getCookie(c, FORM_COOKIE);
	if (!cookie || !HEX.test(cookie)) {
		cookie = randomBytes(16).toString("hex");
		setCookie(c, FORM_COOKIE, cookie, {
			httpOnly: true,
			secure: true,
			sameSite: "Strict",
			path: "/",
		});
	}
	return `${now}.${mac(db, `form:${now}:${cookie}`)}`;
}

export type StampCheck = "ok" | "invalid" | "too-fast";

export function checkStamp(db: Database, c: Context, stamp: string, now: number): StampCheck {
	const cookie = getCookie(c, FORM_COOKIE);
	const [time, signature] = stamp.split(".");
	if (!cookie || !time || !signature || !/^\d{1,12}$/.test(time)) return "invalid";
	const expected = Buffer.from(mac(db, `form:${time}:${cookie}`));
	const given = Buffer.from(signature);
	if (given.length !== expected.length || !timingSafeEqual(given, expected)) return "invalid";
	const age = now - Number(time);
	if (age > STAMP_MAX_AGE || age < 0) return "invalid";
	return age < MIN_SECONDS_ON_PAGE ? "too-fast" : "ok";
}