export const APP_COOKIE = "app_session";
export const APP_SESSION_MAX_AGE = 60 * 60 * 24 * 7;
export const DEFAULT_APP_USERNAME = "student";
export const DEFAULT_APP_PASSWORD = "password";

const encoder = new TextEncoder();

export function appUsername() {
  return process.env.APP_USERNAME || DEFAULT_APP_USERNAME;
}

export function appPassword() {
  return process.env.APP_PASSWORD || DEFAULT_APP_PASSWORD;
}

function safeEqual(a: string, b: string) {
  if (a.length !== b.length) return false;
  let diff = 0;
  for (let i = 0; i < a.length; i += 1) {
    diff |= a.charCodeAt(i) ^ b.charCodeAt(i);
  }
  return diff === 0;
}

async function sha256Hex(value: string) {
  const digest = await crypto.subtle.digest("SHA-256", encoder.encode(value));
  return [...new Uint8Array(digest)]
    .map((byte) => byte.toString(16).padStart(2, "0"))
    .join("");
}

export async function appSessionToken() {
  return sha256Hex(`${appUsername()}:${appPassword()}`);
}

export async function verifyAppCredentials(username: string, password: string) {
  return safeEqual(username, appUsername()) && safeEqual(password, appPassword());
}

export async function isValidAppSession(value: string | undefined) {
  if (!value) return false;
  return safeEqual(value, await appSessionToken());
}

function attributes(isHttps: boolean, maxAge: number) {
  const parts = [`Path=/`, `Max-Age=${maxAge}`, "HttpOnly"];
  if (isHttps) {
    parts.push("Secure", "SameSite=None", "Partitioned");
  } else {
    parts.push("SameSite=Lax");
  }
  return parts.join("; ");
}

export function setAppSessionCookie(headers: Headers, value: string, isHttps: boolean) {
  headers.append(
    "set-cookie",
    `${APP_COOKIE}=${encodeURIComponent(value)}; ${attributes(isHttps, APP_SESSION_MAX_AGE)}`
  );
}

export function clearAppSessionCookie(headers: Headers, isHttps: boolean) {
  headers.append("set-cookie", `${APP_COOKIE}=; ${attributes(isHttps, 0)}`);
}