enhance rag retrieval + summary

backend/src/main/java/com/aiteacher/retrieval/CitationValidatorService.java

@@ -0,0 +1,59 @@
+package com.aiteacher.retrieval;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Service;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Post-processes generated answers to strip citation labels that do not
+ * correspond to any passage retrieved for the current query, preventing
+ * hallucinated source references from reaching the user.
+ */
+@Service
+public class CitationValidatorService {
+
+    private static final Logger log = LoggerFactory.getLogger(CitationValidatorService.class);
+
+    /** Matches citation labels of the form [S1], [F2], [S12], etc. */
+    private static final Pattern CITATION_PATTERN = Pattern.compile("\\[(S|F)\\d+\\]");
+
+    /**
+     * Removes any {@code [Sx]} / {@code [Fx]} citation in {@code generatedAnswer}
+     * whose label is not contained in {@code validLabels}.
+     *
+     * @param generatedAnswer raw model output
+     * @param validLabels     set of labels present in the retrieved context
+     * @return cleaned answer text with hallucinated citations removed
+     */
+    public String validate(String generatedAnswer, Set<String> validLabels) {
+        if (generatedAnswer == null) return "";
+
+        Matcher matcher = CITATION_PATTERN.matcher(generatedAnswer);
+        List<String> removed = new ArrayList<>();
+        StringBuffer sb = new StringBuffer();
+
+        while (matcher.find()) {
+            String label = matcher.group();
+            String inner = label.substring(1, label.length() - 1); // strip [ ]
+            if (validLabels.contains(inner)) {
+                matcher.appendReplacement(sb, Matcher.quoteReplacement(label));
+            } else {
+                removed.add(inner);
+                matcher.appendReplacement(sb, "");
+            }
+        }
+        matcher.appendTail(sb);
+
+        if (!removed.isEmpty()) {
+            log.warn("Stripped hallucinated citations: {}", removed);
+        }
+
+        return sb.toString();
+    }
+}