import {
  CallHandler,
  ExecutionContext,
  Injectable,
  NestInterceptor,
  StreamableFile,
} from '@nestjs/common';
import { Reflector } from '@nestjs/core';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { PAGINATION_RESPONSE, RAW_RESPONSE } from './constants';
import {
  createPaginationResponse,
  resolvePaginationQuery,
} from './pagination-meta.helper';

/**
 * Applies pagination enveloping when a handler is marked with `@Pagination()`.
 *
 * Non-paginated handlers pass through unchanged. `@RawResponse()`, empty
 * bodies, and `StreamableFile` downloads are never wrapped.
 */
@Injectable()
export class TransformInterceptor implements NestInterceptor {
  constructor(private readonly reflector: Reflector) {}

  intercept(context: ExecutionContext, next: CallHandler): Observable<unknown> {
    const isRaw = this.reflector.getAllAndOverride<boolean>(RAW_RESPONSE, [
      context.getHandler(),
      context.getClass(),
    ]);
    if (isRaw) {
      return next.handle();
    }

    const isPagination = this.reflector.getAllAndOverride<boolean>(
      PAGINATION_RESPONSE,
      [context.getHandler(), context.getClass()],
    );
    if (!isPagination) {
      return next.handle();
    }

    const request = context.switchToHttp().getRequest<{
      query: Record<string, unknown>;
    }>();
    const { page, limit } = resolvePaginationQuery(request.query);

    return next.handle().pipe(
      map((payload: unknown): unknown => {
        if (payload == null || payload instanceof StreamableFile) {
          return payload;
        }
        return createPaginationResponse(payload, page, limit);
      }),
    );
  }
}