import { z } from "zod";
import bcrypt from "bcryptjs";
import { prisma } from "./prisma";

// Minimal internal auth accounts — see prisma/schema.prisma's User model
// comment and CLAUDE.md's auth decision notes. A handful of trusted IT
// staff accounts, created by hand via scripts/create-user.ts. No
// self-registration, no `role` field (flat permission model: any logged-in
// user can do anything), no public list/CRUD API route — just enough to
// support login + account creation.

// bcryptjs cost factor for hashing. 10 is bcrypt's long-standing default
// and a reasonable balance of hashing cost vs. login latency for this use
// case (a handful of staff logins, not a high-value target).
const BCRYPT_SALT_ROUNDS = 10;

// Deliberately chosen minimum — long enough to rule out trivially weak
// passwords for a handful of trusted IT staff accounts, not a full password
// policy (no complexity rules, no breach-list check). Revisit if this ever
// grows into employee self-service.
const MIN_PASSWORD_LENGTH = 8;

// Precomputed bcrypt hash of a fixed dummy password, hashed with the same
// cost factor (BCRYPT_SALT_ROUNDS) used for real user passwords. Used as a
// timing-safety decoy in verifyUserCredentials() below: when the looked-up
// email doesn't exist, we still run a bcrypt.compare() against this hash
// (whose result is always discarded) so that the "unknown email" code path
// takes roughly the same time as the "wrong password" path — otherwise the
// early return would let an attacker distinguish "email doesn't exist" from
// "email exists, password wrong" purely by response latency (bcrypt.compare
// dominates request time). Computed once at module load via hashSync (not
// per-request) since hashing itself is deliberately expensive.
const DUMMY_PASSWORD_HASH = bcrypt.hashSync(
  "dummy-password-for-timing-safety",
  BCRYPT_SALT_ROUNDS
);

export interface UserRecord {
  id: string;
  email: string;
  name: string;
  created_at: string;
}

export interface CreateUserInput {
  email: string;
  name: string;
  password: string;
}

export type ValidationResult =
  | { ok: true; value: CreateUserInput }
  | { ok: false; error: string };

// A string field that must be present and not just whitespace. Mirrors the
// same helper in src/lib/requests.ts (not shared/exported from there since
// that file doesn't export it — small enough to duplicate rather than
// introduce a shared-helpers module for one function).
function nonEmptyString(message: string) {
  return z.string({ required_error: message, invalid_type_error: message }).refine(
    (value) => value.trim() !== "",
    { message }
  );
}

const createUserSchema = z.object({
  email: z
    .string({ required_error: "email is required", invalid_type_error: "email is required" })
    .email("email must be a valid email address"),
  name: nonEmptyString("name is required and must be a non-empty string"),
  password: z
    .string({
      required_error: `password is required and must be at least ${MIN_PASSWORD_LENGTH} characters`,
      invalid_type_error: `password is required and must be at least ${MIN_PASSWORD_LENGTH} characters`,
    })
    .min(
      MIN_PASSWORD_LENGTH,
      `password is required and must be at least ${MIN_PASSWORD_LENGTH} characters`
    ),
});

/**
 * Validates raw (untyped) user-creation input. email must be a valid email
 * address, name must be a non-empty string, password must be at least
 * MIN_PASSWORD_LENGTH characters. The password is validated here in its
 * plaintext form — hashing happens separately in createUser().
 */
export function validateCreateUserInput(input: {
  email?: unknown;
  name?: unknown;
  password?: unknown;
}): ValidationResult {
  const result = createUserSchema.safeParse(input);
  if (!result.success) {
    const message = result.error.issues[0]?.message ?? "Invalid input";
    return { ok: false, error: message };
  }
  return { ok: true, value: result.data };
}

function toRecord(row: {
  id: string;
  email: string;
  name: string;
  createdAt: Date;
}): UserRecord {
  return {
    id: row.id,
    email: row.email,
    name: row.name,
    created_at: row.createdAt.toISOString(),
  };
}

/**
 * Hashes the given plaintext password with bcryptjs and inserts a new User
 * row. Caller is expected to have already validated the input via
 * validateCreateUserInput() — this does not re-validate.
 */
export async function createUser(input: CreateUserInput): Promise<UserRecord> {
  const passwordHash = await bcrypt.hash(input.password, BCRYPT_SALT_ROUNDS);
  const created = await prisma.user.create({
    data: {
      email: input.email,
      name: input.name,
      passwordHash,
    },
  });
  return toRecord(created);
}

/**
 * Looks up a user by email and compares the given plaintext password
 * against the stored bcrypt hash. Returns the user record (never the
 * password hash) on success, or null if the email doesn't exist or the
 * password doesn't match — callers should treat both failure cases
 * identically (don't leak which one it was).
 *
 * Accepts `unknown` for email/password since this is also the core logic
 * behind the Credentials provider's authorize() callback, whose input
 * comes from unvalidated form/request data — see src/auth.ts.
 */
export async function verifyUserCredentials(
  email: unknown,
  password: unknown
): Promise<UserRecord | null> {
  if (typeof email !== "string" || typeof password !== "string") {
    return null;
  }
  if (email.trim() === "" || password === "") {
    return null;
  }

  const user = await prisma.user.findUnique({ where: { email } });
  if (!user) {
    // Run a dummy compare against a fixed decoy hash and discard the result
    // — see DUMMY_PASSWORD_HASH comment above. This keeps timing consistent
    // with the "email exists, password wrong" branch below instead of
    // returning early.
    await bcrypt.compare(password, DUMMY_PASSWORD_HASH);
    return null;
  }

  const passwordMatches = await bcrypt.compare(password, user.passwordHash);
  if (!passwordMatches) {
    return null;
  }

  return toRecord(user);
}