import {
  ConflictException,
  ForbiddenException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import * as bcrypt from 'bcryptjs';
import { PrismaService } from '../prisma/prisma.service';
import { AuditLogService } from '../audit/audit-log.service';
import { assertPasswordNotBreached } from '../common/password/password-policy';
import { PermissionResolverService } from '../auth/permissions/permission-resolver.service';
import { Prisma } from '../../generated/prisma';
import { CreateUserDto } from './dto/create-user.dto';
import { UpdateUserDto } from './dto/update-user.dto';
import { ResetUserPasswordDto } from './dto/reset-user-password.dto';

const BCRYPT_SALT_ROUNDS = 12;

const USER_WITH_ROLE = {
  include: { role: true },
} satisfies { include: Prisma.UserInclude };

type UserWithRole = Prisma.UserGetPayload<typeof USER_WITH_ROLE>;

export interface UserSummary {
  id: string;
  email: string;
  name: string;
  roleId: string;
  roleKey: string;
  roleName: string;
  isActive: boolean;
  createdAt: Date;
  deactivatedAt: Date | null;
  mfaEnabled: boolean;
}

@Injectable()
export class UsersService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly auditLog: AuditLogService,
    private readonly permissionResolver: PermissionResolverService,
  ) {}

  private toSummary(user: UserWithRole): UserSummary {
    return {
      id: user.id,
      email: user.email,
      name: user.name,
      roleId: user.roleId,
      roleKey: user.role.key,
      roleName: user.role.name,
      isActive: user.isActive,
      createdAt: user.createdAt,
      deactivatedAt: user.deactivatedAt,
      mfaEnabled: user.mfaEnabled,
    };
  }

  /**
   * Assigning a role is gated by its own permission, separate from
   * users:create/users:update - otherwise any role holding those (e.g. a
   * minimal "user manager" role) could hand out any role, including a
   * system/admin one, to itself or a colluding account. actingUserId is
   * only absent for non-HTTP callers (there are none today, and tests that
   * exercise the service directly without an actor), where there is no
   * caller to check permissions against.
   */
  private async assertCanAssignRole(actingUserId?: string): Promise<void> {
    if (!actingUserId) {
      return;
    }
    const allowed = await this.permissionResolver.hasAny(actingUserId, [
      'users:assign-role',
    ]);
    if (!allowed) {
      throw new ForbiddenException('Missing permission to assign roles');
    }
  }

  /**
   * Nobody may act on - or hand out - more than they can do themselves: a
   * limited "user manager" holding users:update could otherwise reset an
   * administrator's password or MFA, change their email to one they control,
   * or give a colluding account the ADMIN role, and so become admin. Same
   * rule as RolesService.assertCanGrantPermissions. Reads the role's grants
   * directly (not the cached effective set), so a deactivated admin counts
   * as an admin too.
   */
  private async assertWithinCallerPermissions(
    roleId: string,
    actingUserId?: string,
  ): Promise<void> {
    if (!actingUserId) {
      return;
    }
    const grants = await this.prisma.rolePermission.findMany({
      where: { roleId },
      select: { permission: { select: { key: true } } },
    });
    const callerPermissions =
      await this.permissionResolver.getPermissions(actingUserId);
    const exceeds = grants.some(
      (grant) => !callerPermissions.has(grant.permission.key),
    );
    if (exceeds) {
      throw new ForbiddenException(
        'Dieses Konto hat mehr Rechte als Sie selbst und kann von Ihnen nicht verwaltet werden',
      );
    }
  }

  private async assertActiveRole(roleId: string): Promise<void> {
    const role = await this.prisma.role.findUnique({ where: { id: roleId } });
    if (!role) {
      throw new NotFoundException('Role not found');
    }
    if (role.status !== 'ACTIVE') {
      throw new ConflictException('Role is not active');
    }
  }

  /**
   * Blocks removing (by deactivation or role reassignment) the last active
   * user still holding a system role (ADMIN). Without this, an operator
   * could lock the app out of user/role management entirely, with no
   * self-service recovery: prisma/seed.ts skips seeding once a user with
   * its configured email already exists, so it cannot restore access to a
   * merely demoted/deactivated account.
   */
  private async assertNotLastSystemRoleUser(userId: string): Promise<void> {
    const user = await this.prisma.user.findUnique({
      where: { id: userId },
      select: { roleId: true, role: { select: { isSystem: true } } },
    });
    if (!user || !user.role.isSystem) {
      return;
    }
    const activeCount = await this.prisma.user.count({
      where: { roleId: user.roleId, isActive: true },
    });
    if (activeCount <= 1) {
      throw new ConflictException(
        'Cannot remove the last active user holding a system role',
      );
    }
  }

  async findAll(): Promise<UserSummary[]> {
    const users = await this.prisma.user.findMany({
      ...USER_WITH_ROLE,
      orderBy: { createdAt: 'asc' },
    });
    return users.map((user) => this.toSummary(user));
  }

  async findById(id: string): Promise<UserWithRole> {
    const user = await this.prisma.user.findUnique({
      where: { id },
      ...USER_WITH_ROLE,
    });
    if (!user) {
      throw new NotFoundException('User not found');
    }
    return user;
  }

  async findSummaryById(id: string): Promise<UserSummary> {
    return this.toSummary(await this.findById(id));
  }

  /** Case-insensitive: "Imker@x.de" and "imker@x.de" are one account. */
  async findByEmail(email: string): Promise<UserWithRole | null> {
    return this.prisma.user.findFirst({
      where: { email: { equals: email.trim(), mode: 'insensitive' } },
      ...USER_WITH_ROLE,
    });
  }

  async findBySsoSubject(ssoSubject: string): Promise<UserWithRole | null> {
    return this.prisma.user.findUnique({
      where: { ssoSubject },
      ...USER_WITH_ROLE,
    });
  }

  async linkSsoSubject(userId: string, ssoSubject: string): Promise<void> {
    await this.prisma.user.update({
      where: { id: userId },
      data: { ssoSubject },
    });
    await this.auditLog.record({
      entityType: 'User',
      entityId: userId,
      action: 'UPDATE',
      userId,
      afterData: { ssoLinked: true },
    });
  }

  async create(
    dto: CreateUserDto,
    actingUserId?: string,
  ): Promise<UserSummary> {
    const existing = await this.findByEmail(dto.email);
    if (existing) {
      throw new ConflictException('Email already in use');
    }
    await this.assertActiveRole(dto.roleId);
    await this.assertCanAssignRole(actingUserId);
    await this.assertWithinCallerPermissions(dto.roleId, actingUserId);
    await assertPasswordNotBreached(dto.password);
    const passwordHash = await bcrypt.hash(dto.password, BCRYPT_SALT_ROUNDS);
    const user = await this.prisma.user.create({
      data: {
        email: dto.email,
        passwordHash,
        name: dto.name,
        roleId: dto.roleId,
      },
      ...USER_WITH_ROLE,
    });
    await this.auditLog.record({
      entityType: 'User',
      entityId: user.id,
      action: 'CREATE',
      userId: actingUserId,
      afterData: this.toSummary(user),
    });
    return this.toSummary(user);
  }

  async update(
    id: string,
    dto: UpdateUserDto,
    actingUserId?: string,
  ): Promise<UserSummary> {
    const before = await this.findById(id);
    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
    const roleChanged = Boolean(dto.roleId) && dto.roleId !== before.roleId;
    const emailChanged = dto.email !== undefined && dto.email !== before.email;
    if (dto.roleId) {
      await this.assertActiveRole(dto.roleId);
    }
    if (roleChanged) {
      // Role changes for yourself always require a second party, regardless
      // of what permission the caller holds - otherwise anyone who can
      // reach this endpoint at all could grant themselves admin.
      if (actingUserId && id === actingUserId) {
        throw new ForbiddenException('Cannot change your own role');
      }
      await this.assertCanAssignRole(actingUserId);
      await this.assertWithinCallerPermissions(dto.roleId!, actingUserId);
      await this.assertNotLastSystemRoleUser(id);
    }
    const user = await this.prisma.user.update({
      where: { id },
      data: {
        name: dto.name,
        email: dto.email,
        roleId: dto.roleId,
        // A new email is a new identity: the next Microsoft sign-in links
        // afresh instead of reusing the old account's binding.
        ...(emailChanged ? { ssoSubject: null } : {}),
      },
      ...USER_WITH_ROLE,
    });
    if (emailChanged) {
      // The email is the login name and the SSO link: sessions opened under
      // the old one end here.
      await this.prisma.refreshToken.updateMany({
        where: { userId: id, revokedAt: null },
        data: { revokedAt: new Date() },
      });
    }
    if (roleChanged || emailChanged) {
      this.permissionResolver.invalidateUser(id);
    }
    await this.auditLog.record({
      entityType: 'User',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
      beforeData: this.toSummary(before),
      afterData: this.toSummary(user),
    });
    return this.toSummary(user);
  }

  async deactivate(id: string, actingUserId?: string): Promise<UserSummary> {
    const before = await this.findById(id);
    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
    await this.assertNotLastSystemRoleUser(id);
    const user = await this.prisma.user.update({
      where: { id },
      data: { isActive: false, deactivatedAt: new Date() },
      ...USER_WITH_ROLE,
    });
    this.permissionResolver.invalidateUser(id);
    await this.auditLog.record({
      entityType: 'User',
      entityId: id,
      action: 'DEACTIVATE',
      userId: actingUserId,
      beforeData: this.toSummary(before),
      afterData: this.toSummary(user),
    });
    return this.toSummary(user);
  }

  /**
   * Recovery path for a user who lost their MFA device (no email-reset flow
   * exists in this project). Deliberately blocked for the caller's own
   * account: unlike resetting someone else's MFA, self-service MFA removal
   * belongs behind a password check (POST /profile/mfa/disable) - otherwise
   * a stolen access token alone (no password) would be enough to strip the
   * victim's own MFA protection via this admin route.
   */
  /**
   * Sets a new password for another user. Mirrors ProfileService.changePassword
   * in what it invalidates: every refresh token is revoked and the permission
   * cache is cleared, so sessions opened with the old password stop working at
   * once rather than living on until their access token expires.
   *
   * Your own password goes through /profile/password, which requires the
   * current one - otherwise anyone holding users:update could silently take
   * over their own account's credentials without proving they own it.
   */
  async resetPassword(
    id: string,
    dto: ResetUserPasswordDto,
    actingUserId?: string,
  ): Promise<UserSummary> {
    if (actingUserId && id === actingUserId) {
      throw new ForbiddenException(
        'Use /profile/password to change your own password',
      );
    }
    const target = await this.findById(id);
    await this.assertWithinCallerPermissions(target.roleId, actingUserId);
    await assertPasswordNotBreached(dto.password);
    const passwordHash = await bcrypt.hash(dto.password, BCRYPT_SALT_ROUNDS);
    const user = await this.prisma.user.update({
      where: { id },
      data: { passwordHash, passwordChangedAt: new Date() },
      ...USER_WITH_ROLE,
    });
    await this.prisma.refreshToken.updateMany({
      where: { userId: id, revokedAt: null },
      data: { revokedAt: new Date() },
    });
    this.permissionResolver.invalidateUser(id);
    // The new password never reaches the audit log - only the fact that it
    // was replaced, and by whom.
    await this.auditLog.record({
      entityType: 'User',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
    });
    return this.toSummary(user);
  }

  async resetMfa(id: string, actingUserId?: string): Promise<UserSummary> {
    if (actingUserId && id === actingUserId) {
      throw new ForbiddenException(
        'Use /profile/mfa/disable to disable your own MFA',
      );
    }
    const target = await this.findById(id);
    await this.assertWithinCallerPermissions(target.roleId, actingUserId);
    const user = await this.prisma.user.update({
      where: { id },
      data: { mfaEnabled: false, mfaSecret: null },
      ...USER_WITH_ROLE,
    });
    await this.auditLog.record({
      entityType: 'User',
      entityId: id,
      action: 'MFA_DISABLED',
      userId: actingUserId,
    });
    return this.toSummary(user);
  }

  async activate(id: string, actingUserId?: string): Promise<UserSummary> {
    const before = await this.findById(id);
    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
    if (before.isActive) {
      throw new ConflictException('User is already active');
    }
    const user = await this.prisma.user.update({
      where: { id },
      data: { isActive: true, deactivatedAt: null },
      ...USER_WITH_ROLE,
    });
    this.permissionResolver.invalidateUser(id);
    await this.auditLog.record({
      entityType: 'User',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
      beforeData: this.toSummary(before),
      afterData: this.toSummary(user),
    });
    return this.toSummary(user);
  }
}