import { Injectable } from '@nestjs/common';
import { PrismaService } from '../../prisma/prisma.service';
import { PermissionKey } from './permission-catalog';

interface CacheEntry {
  isActive: boolean;
  passwordChangedAt: Date | null;
  permissions: ReadonlySet<string>;
  expiresAt: number;
}

const CACHE_TTL_MS = 30_000;

/**
 * Resolves a user's effective permission set fresh from the database on
 * every request (not embedded in the JWT, so revoking a role or editing a
 * role's grants takes effect without forcing a re-login), with a short TTL
 * cache to keep that from becoming a query-per-request cost. Call
 * invalidateUser/invalidateAll after any write to Role, Permission,
 * RolePermission, User.roleId, or User.passwordChangedAt so the change is
 * visible immediately instead of waiting out the cache window.
 *
 * isTokenValid shares the same cached entry: JwtAuthGuard calls it on every
 * authenticated request (including routes with no @RequirePermission) so a
 * deactivated user's still-valid access token stops working within the
 * cache TTL instead of staying usable until the token expires, and so does
 * a token issued before the user's last password change.
 */
@Injectable()
export class PermissionResolverService {
  private readonly cache = new Map<string, CacheEntry>();

  constructor(private readonly prisma: PrismaService) {}

  async getPermissions(userId: string): Promise<ReadonlySet<string>> {
    const entry = await this.getEntry(userId);
    return entry.permissions;
  }

  /**
   * The permissions read fresh (one primary-key lookup), never from the
   * cache, and stored as the cache entry. For a process that does not hear
   * invalidateUser of the API pods (the worker): a right revoked there must
   * stop mattering at once, not after the 30 s cache window. Empty for an
   * inactive user or role.
   */
  async getFreshPermissions(userId: string): Promise<ReadonlySet<string>> {
    const entry = await this.loadEntry(userId);
    this.cache.set(userId, entry);
    return entry.permissions;
  }

  /**
   * Always read fresh (one primary-key lookup) and stored as the cache
   * entry the PermissionsGuard then uses: a deactivation, role change or
   * password change made on ANOTHER replica takes effect on the very next
   * request here, not after the cache window.
   */
  async isTokenValid(
    userId: string,
    tokenIssuedAtSeconds: number,
  ): Promise<boolean> {
    const entry = await this.loadEntry(userId);
    this.cache.set(userId, entry);
    if (!entry.isActive) {
      return false;
    }
    if (!entry.passwordChangedAt) {
      return true;
    }
    return tokenIssuedAtSeconds * 1000 >= entry.passwordChangedAt.getTime();
  }

  async hasAny(
    userId: string,
    keys: readonly PermissionKey[],
  ): Promise<boolean> {
    if (keys.length === 0) {
      return true;
    }
    const permissions = await this.getPermissions(userId);
    return keys.some((key) => permissions.has(key));
  }

  invalidateUser(userId: string): void {
    this.cache.delete(userId);
  }

  invalidateAll(): void {
    this.cache.clear();
  }

  private async getEntry(userId: string): Promise<CacheEntry> {
    const cached = this.cache.get(userId);
    if (cached && cached.expiresAt > Date.now()) {
      return cached;
    }
    const entry = await this.loadEntry(userId);
    this.cache.set(userId, entry);
    return entry;
  }

  private async loadEntry(userId: string): Promise<CacheEntry> {
    const user = await this.prisma.user.findUnique({
      where: { id: userId },
      select: {
        isActive: true,
        passwordChangedAt: true,
        role: {
          select: {
            status: true,
            permissions: {
              select: { permission: { select: { key: true } } },
            },
          },
        },
      },
    });
    const isEligible = Boolean(
      user && user.isActive && user.role.status === 'ACTIVE',
    );
    const permissions = isEligible
      ? new Set(user!.role.permissions.map((grant) => grant.permission.key))
      : new Set<string>();
    return {
      isActive: isEligible,
      passwordChangedAt: user?.passwordChangedAt ?? null,
      permissions,
      expiresAt: Date.now() + CACHE_TTL_MS,
    };
  }
}