first implementation

backend/src/main/java/com/aiteacher/config/GlobalExceptionHandler.java

@@ -0,0 +1,56 @@
+package com.aiteacher.config;
+
+import com.aiteacher.book.NoKnowledgeSourceException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.multipart.MaxUploadSizeExceededException;
+
+import java.util.Map;
+import java.util.NoSuchElementException;
+
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);
+
+    @ExceptionHandler(NoKnowledgeSourceException.class)
+    public ResponseEntity<Map<String, String>> handleNoKnowledgeSource(NoKnowledgeSourceException ex) {
+        return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE)
+            .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(NoSuchElementException.class)
+    public ResponseEntity<Map<String, String>> handleNotFound(NoSuchElementException ex) {
+        return ResponseEntity.status(HttpStatus.NOT_FOUND)
+            .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(IllegalArgumentException.class)
+    public ResponseEntity<Map<String, String>> handleBadRequest(IllegalArgumentException ex) {
+        return ResponseEntity.status(HttpStatus.BAD_REQUEST)
+            .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(IllegalStateException.class)
+    public ResponseEntity<Map<String, String>> handleConflict(IllegalStateException ex) {
+        return ResponseEntity.status(HttpStatus.CONFLICT)
+            .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(MaxUploadSizeExceededException.class)
+    public ResponseEntity<Map<String, String>> handleMaxUploadSize(MaxUploadSizeExceededException ex) {
+        return ResponseEntity.status(HttpStatus.PAYLOAD_TOO_LARGE)
+            .body(Map.of("error", "File exceeds maximum size of 100 MB."));
+    }
+
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<Map<String, String>> handleGeneric(Exception ex) {
+        log.error("Unhandled exception", ex);
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+            .body(Map.of("error", "An unexpected error occurred."));
+    }
+}