import fs from "fs";
import path from "path";
import bcrypt from "bcryptjs";

const DATA_DIR = path.join(process.cwd(), "data");
const USERS_FILE = path.join(DATA_DIR, "users.json");

export interface UserRow {
  id: number;
  username: string;
  email: string;
  password_hash: string;
  created_at: string;
}

export interface UserPublic {
  id: number;
  username: string;
  email: string;
  created_at: string;
}

function ensureDataDir() {
  if (!fs.existsSync(DATA_DIR)) {
    fs.mkdirSync(DATA_DIR, { recursive: true });
  }
}

function readUsers(): UserRow[] {
  ensureDataDir();
  if (!fs.existsSync(USERS_FILE)) {
    return [];
  }
  try {
    const raw = fs.readFileSync(USERS_FILE, "utf-8");
    return JSON.parse(raw);
  } catch {
    return [];
  }
}

function writeUsers(users: UserRow[]) {
  ensureDataDir();
  fs.writeFileSync(USERS_FILE, JSON.stringify(users, null, 2), "utf-8");
}

let nextId = 0;
function getNextId(): number {
  if (nextId === 0) {
    const users = readUsers();
    nextId = users.reduce((max, u) => Math.max(max, u.id), 0) + 1;
  }
  return nextId++;
}

export function createUser(username: string, email: string, password: string): UserPublic {
  const users = readUsers();

  if (users.find((u) => u.email === email || u.username === username)) {
    throw new Error("A user with that email or username already exists.");
  }

  const password_hash = bcrypt.hashSync(password, 10);
  const newUser: UserRow = {
    id: getNextId(),
    username,
    email,
    password_hash,
    created_at: new Date().toISOString(),
  };

  users.push(newUser);
  writeUsers(users);

  return {
    id: newUser.id,
    username: newUser.username,
    email: newUser.email,
    created_at: newUser.created_at,
  };
}

export function authenticateUser(email: string, password: string): UserPublic {
  const users = readUsers();
  const user = users.find((u) => u.email === email);

  if (!user) {
    throw new Error("Invalid email or password.");
  }

  if (!bcrypt.compareSync(password, user.password_hash)) {
    throw new Error("Invalid email or password.");
  }

  return {
    id: user.id,
    username: user.username,
    email: user.email,
    created_at: user.created_at,
  };
}

export function getUserById(id: number): UserPublic | null {
  const users = readUsers();
  const user = users.find((u) => u.id === id);
  if (!user) return null;
  return {
    id: user.id,
    username: user.username,
    email: user.email,
    created_at: user.created_at,
  };
}