import {
  ConflictException,
  Injectable,
  UnauthorizedException,
} from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';
import * as bcrypt from 'bcrypt';
import { createHash, randomUUID } from 'crypto';
import { Session, User } from '../../../../generated/prisma/client';
import { PrismaService } from '../../../prisma/prisma.service';
import { AuthUser, RefreshPayload } from './auth.types';

const PASSWORD_HASH_ROUNDS = 12;
const REFRESH_TTL_MS = 604_800_000;

const ACCESS_TTL = '15m';
const REFRESH_TTL = '7d';
const DUMMY_PASSWORD_HASH =
  '$2b$12$Z49BwJsyiUqY0ZozFzt9IeYvjhV4kbeLw9KdxOguT5bfhA1RvPCx6';

@Injectable()
export class AuthService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly jwt: JwtService,
  ) {}

  async register(
    email: string,
    password: string,
  ): Promise<{ user: AuthUser; accessToken: string; refreshToken: string }> {
    const normalizedEmail = this.normalizeEmail(email);
    const existing = await this.prisma.user.findUnique({
      where: { email: normalizedEmail },
    });
    if (existing)
      throw new ConflictException({ code: 'EMAIL_ALREADY_REGISTERED' });

    let user: User;
    try {
      user = await this.prisma.user.create({
        data: {
          id: randomUUID(),
          email: normalizedEmail,
          passwordHash: await bcrypt.hash(password, PASSWORD_HASH_ROUNDS),
        },
      });
    } catch (error) {
      if (isUniqueConstraintError(error))
        throw new ConflictException({ code: 'EMAIL_ALREADY_REGISTERED' });
      throw error;
    }
    return this.createSession(user);
  }

  async login(
    email: string,
    password: string,
  ): Promise<{ user: AuthUser; accessToken: string; refreshToken: string }> {
    const user = await this.prisma.user.findUnique({
      where: { email: this.normalizeEmail(email) },
    });
    const valid = await bcrypt.compare(
      password,
      user?.passwordHash ?? DUMMY_PASSWORD_HASH,
    );
    if (!user || !valid)
      throw new UnauthorizedException({ code: 'INVALID_CREDENTIALS' });
    return this.createSession(user);
  }

  async refresh(
    token: string,
  ): Promise<{ user: AuthUser; accessToken: string; refreshToken: string }> {
    let payload: RefreshPayload;
    try {
      payload = await this.jwt.verifyAsync<RefreshPayload>(token, {
        algorithms: ['HS256'],
      });
    } catch {
      throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    }
    if (payload.type !== 'refresh')
      throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    const session = await this.prisma.session.findUnique({
      where: { id: payload.sid },
      include: { user: true },
    });
    if (
      !session ||
      session.userId !== payload.sub ||
      session.revokedAt ||
      session.expiresAt <= new Date()
    ) {
      if (session && !session.revokedAt)
        await this.prisma.session.delete({ where: { id: session.id } });
      throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    }
    if (session.refreshTokenHash !== this.hash(token))
      throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    return this.rotateSession(session, session.refreshTokenHash);
  }

  async logout(token?: string): Promise<void> {
    if (!token) return;
    try {
      const payload = await this.jwt.verifyAsync<RefreshPayload>(token, {
        algorithms: ['HS256'],
      });
      if (payload.type !== 'refresh') return;
      const session = await this.prisma.session.findUnique({
        where: { id: payload.sid },
      });
      if (
        session &&
        !session.revokedAt &&
        session.refreshTokenHash === this.hash(token)
      ) {
        await this.prisma.session.update({
          where: { id: session.id },
          data: { revokedAt: new Date() },
        });
      }
    } catch {
      // Logout is intentionally idempotent.
    }
  }

  toUser(user: User): AuthUser {
    return { id: user.id, email: user.email };
  }

  async userById(id: string): Promise<User> {
    const user = await this.prisma.user.findUnique({ where: { id } });
    if (!user) throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    return user;
  }

  private async createSession(
    user: User,
  ): Promise<{ user: AuthUser; accessToken: string; refreshToken: string }> {
    const session = await this.prisma.session.create({
      data: {
        id: randomUUID(),
        userId: user.id,
        refreshTokenHash: '',
        expiresAt: new Date(),
      },
    });
    return this.rotateSession({ ...session, user });
  }

  private async rotateSession(
    session: Session & { user: User },
    expectedRefreshTokenHash?: string,
  ): Promise<{ user: AuthUser; accessToken: string; refreshToken: string }> {
    const refreshToken = await this.jwt.signAsync(
      {
        sub: session.userId,
        sid: session.id,
        type: 'refresh',
        jti: randomUUID(),
      },
      { expiresIn: REFRESH_TTL, algorithm: 'HS256' },
    );
    const data = {
      refreshTokenHash: this.hash(refreshToken),
      expiresAt: new Date(Date.now() + REFRESH_TTL_MS),
    };
    if (expectedRefreshTokenHash) {
      const updated = await this.prisma.session.updateMany({
        where: { id: session.id, refreshTokenHash: expectedRefreshTokenHash },
        data,
      });
      if (updated.count !== 1)
        throw new UnauthorizedException({ code: 'UNAUTHORIZED' });
    } else {
      await this.prisma.session.update({ where: { id: session.id }, data });
    }
    return {
      user: this.toUser(session.user),
      accessToken: await this.jwt.signAsync(
        { sub: session.userId, sid: session.id, type: 'access' },
        { expiresIn: ACCESS_TTL, algorithm: 'HS256' },
      ),
      refreshToken,
    };
  }

  private normalizeEmail(email: string): string {
    return email;
  }

  private hash(token: string): string {
    return createHash('sha256').update(token).digest('hex');
  }
}

function isUniqueConstraintError(error: unknown): boolean {
  return (
    typeof error === 'object' &&
    error !== null &&
    'code' in error &&
    (error as { code?: unknown }).code === 'P2002'
  );
}