first (part 3: src directory)

src/common/interceptors/response.interceptor.ts

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+import {
+  Injectable,
+  NestInterceptor,
+  ExecutionContext,
+  CallHandler,
+} from '@nestjs/common';
+import { Observable } from 'rxjs';
+import { map } from 'rxjs/operators';
+import { ApiResponse, createSuccessResponse } from '../types/api-response.type';
+
+/**
+ * Response interceptor that wraps all successful responses
+ * in the standard ApiResponse format
+ */
+import { I18nService, I18nContext } from 'nestjs-i18n';
+
+@Injectable()
+export class ResponseInterceptor<T> implements NestInterceptor<
+  T,
+  ApiResponse<T>
+> {
+  constructor(private readonly i18n: I18nService) {}
+
+  intercept(
+    context: ExecutionContext,
+    next: CallHandler,
+  ): Observable<ApiResponse<T>> {
+    return next.handle().pipe(
+      map((data: unknown) => {
+        const request = context.switchToHttp().getRequest();
+
+        // Determine language
+        const i18nContext = I18nContext.current();
+        let lang = i18nContext?.lang;
+
+        if (!lang) {
+          const acceptLanguage = request.headers['accept-language'];
+          const xLang = request.headers['x-lang'];
+
+          if (xLang) {
+            lang = Array.isArray(xLang) ? xLang[0] : xLang;
+          } else if (acceptLanguage) {
+            lang = acceptLanguage.split(',')[0].split(';')[0].split('-')[0];
+          }
+        }
+
+        lang = lang || 'en';
+
+        // If data is already an ApiResponse, we should still translate its 'data' property
+        // But first let's just do it directly on 'data' below before returning
+        if (this.isApiResponse(data)) {
+          if (data !== null) {
+            try {
+              this.translateReasons(data, lang);
+            } catch {
+              // Ignore if object is not extensible
+            }
+          }
+          return data as ApiResponse<T>;
+        }
+
+        // Recursively translate reasons arrays in the response body
+        if (data !== null) {
+          try {
+            this.translateReasons(data, lang);
+          } catch {
+            // Ignore if object is not extensible
+          }
+        }
+
+        const message = this.i18n.translate('common.success', {
+          lang,
+        });
+
+        // Wrap in success response
+        return createSuccessResponse(data as T, message);
+      }),
+    );
+  }
+
+  private translateReasons(data: any, lang: string) {
+    if (!data || typeof data !== 'object') {
+      return;
+    }
+
+    if (Array.isArray(data)) {
+      data.forEach((item) => this.translateReasons(item, lang));
+      return;
+    }
+
+    Object.keys(data).forEach((key) => {
+      const val = data[key];
+      if (
+        (key === 'reasons' ||
+          key === 'decision_reasons' ||
+          key === 'reasoning_factors') &&
+        Array.isArray(val)
+      ) {
+        data[key] = val.map((r: any) => {
+          if (typeof r !== 'string') return r;
+          const translationKey = `predictions.reasons.${r}`;
+          const translated = this.i18n.translate(translationKey, {
+            lang,
+          });
+          return translated === translationKey ? r : translated;
+        });
+      } else if (key === 'reason' && typeof val === 'string') {
+        const translationKey = `predictions.reasons.${val}`;
+        const translated = this.i18n.translate(translationKey, {
+          lang,
+        });
+        data[key] = translated === translationKey ? val : translated;
+      } else if (key === 'flags' && Array.isArray(val)) {
+        data[key] = val.map((r: any) => {
+          if (typeof r !== 'string') return r;
+          const translationKey = `predictions.flags.${r}`;
+          const translated = this.i18n.translate(translationKey, {
+            lang,
+          });
+          return translated === translationKey ? r : translated;
+        });
+      } else if (key === 'warnings' && Array.isArray(val)) {
+        data[key] = val.map((r: any) => {
+          if (typeof r !== 'string') return r;
+          const translationKey = `predictions.warnings.${r}`;
+          const translated = this.i18n.translate(translationKey, {
+            lang,
+          });
+          return translated === translationKey ? r : translated;
+        });
+      } else if (typeof val === 'object' && val !== null) {
+        this.translateReasons(val, lang);
+      }
+    });
+  }
+
+  private isApiResponse(data: unknown): boolean {
+    return (
+      data !== null &&
+      typeof data === 'object' &&
+      'success' in data &&
+      'status' in data &&
+      'message' in data &&
+      'data' in data
+    );
+  }
+}