feature: Move ML prediction logic to PredictionUtils class

- Refactored the predictReadingLevel method from core class into PredictionUtils to enhance reusability and separation of concerns.
- The utility class no longer includes logging statements, adhering to best practices.
- Added a ReadingLevelConstants class responsible for containing all constants related to the Reading Level ML model.
- Added unit test cases for ReadingLevelUtil class.

Issue elimu-ai#1825

Author: Aryant-Tripathi

src/main/java/ai/elimu/util/ReadingLevelConstants.java

@@ -1,12 +1,32 @@
 package ai.elimu.util;
 
-public class AppConstants {
+public class ReadingLevelConstants {
 
     public static class READING_LEVEL_CONSTANTS {
+
+        /**
+         * Key for the number of chapters in a book
+         */
         public static final String CHAPTER_COUNT_KEY = "chapter_count";
+
+        /**
+         * Key for the number of paragraphs in a book
+         */
         public static final String PARAGRAPH_COUNT_KEY = "paragraph_count";
+
+        /**
+         * Key for the total word count in a book
+         */
         public static final String WORD_COUNT_KEY = "word_count";
-        public static final String LEVEL = "LEVEL";
-    }
 
+        /**
+         * Key for the predicted reading level output
+         */
+        public static final String READING_LEVEL_KEY = "LEVEL";
+
+        /**
+         * Reading level file pmml path key
+         */
+        public static final String READING_LEVEL_MODEL_FILE_PATH_KEY = "src/main/resources/ai/elimu/web/content/storybook/step2_2_model.pmml";
+    }
 }

src/main/java/ai/elimu/util/ml/ReadingLevelUtil.java

@@ -6,18 +6,41 @@
 import java.util.Arrays;
 import java.util.Map;
 
-import static ai.elimu.util.AppConstants.READING_LEVEL_CONSTANTS.*;
+import static ai.elimu.util.ReadingLevelConstants.READING_LEVEL_CONSTANTS.*;
 
 public class ReadingLevelUtil {
 
+    /**
+     * Predicts the reading level based on chapter count, paragraph count, and word count using a machine learning model.
+     *
+     * <p>This method loads a pre-trained machine learning model and predicts the reading level by passing the
+     * given chapter count, paragraph count, and word count as input features. The model returns a numeric
+     * prediction, which is then converted into a corresponding {@link ReadingLevel} enum.</p>
+     *
+     * @param chapterCount    The number of chapters in the text. Must be an integer value.
+     * @param paragraphCount  The number of paragraphs in the text. Must be an integer value.
+     * @param wordCount       The number of words in the text. Must be an integer value.
+     *
+     * @return The predicted {@link ReadingLevel} based on the input features.
+     *
+     * <p>Example usage:</p>
+     * <pre>
+     * {@code
+     * int chapterCount = 10;
+     * int paragraphCount = 50;
+     * int wordCount = 300;
+     * ReadingLevel readingLevel = PredictionUtils.predictReadingLevel(chapterCount, paragraphCount, wordCount);
+     * System.out.println("Predicted Reading Level: " + readingLevel);
+     * }
+     * </pre>
+     */
     public static ReadingLevel predictReadingLevel(
             int chapterCount,
             int paragraphCount,
-            int wordCount,
-            String modelFilePath
+            int wordCount
     ) {
 
-        Model model = Model.fromFile(modelFilePath);
+        Model model = Model.fromFile(READING_LEVEL_MODEL_FILE_PATH_KEY);
         Map<String, Double> features = Map.of(
                 CHAPTER_COUNT_KEY, (double) chapterCount,
                 PARAGRAPH_COUNT_KEY, (double) paragraphCount,
@@ -34,7 +57,7 @@ public static ReadingLevel predictReadingLevel(
         Double resultAsDouble = (Double) result;
         int resultAsInteger = resultAsDouble.intValue();
 
-        String readingLevelAsString = LEVEL + resultAsInteger;
+        String readingLevelAsString = READING_LEVEL_KEY + resultAsInteger;
         return ReadingLevel.valueOf(readingLevelAsString);
 
     }

src/main/java/ai/elimu/web/content/storybook/StoryBookCreateFromEPubController.java

@@ -542,14 +542,12 @@ private ReadingLevel predictReadingLevel(int chapterCount, int paragraphCount, i
 
         // Load the machine learning model (https://github.com/elimu-ai/ml-storybook-reading-level)
 
-        String modelFilePath = Objects.requireNonNull(getClass().getResource("step2_2_model.pmml")).getFile();
-
         logger.info(
-                "Predicting reading level for chapter: {}, paragraph: {}, word: {}, modelPath: {} ",
-                chapterCount, paragraphCount, wordCount, modelFilePath
+                "Predicting reading level for chapter: {}, paragraph: {}, word: {} ",
+                chapterCount, paragraphCount, wordCount
         );
 
-        ReadingLevel readingLevel = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount, modelFilePath);
+        ReadingLevel readingLevel = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount);
         logger.info("Predicted reading level: {}", readingLevel);
 
         return readingLevel;

src/test/java/ai/elimu/util/ml/ReadingLevelUtilTest.java

@@ -3,57 +3,55 @@
 import ai.elimu.model.v2.enums.ReadingLevel;
 import org.junit.jupiter.api.Test;
 
-import java.io.IOException;
-
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 
 public class ReadingLevelUtilTest {
 
     @Test
     public void testPredictReadingLevel_Level1() {
 
-        String modelFilePath = "src/test/resources/ai/elimu/util/reading_level/model1.pmml";
-        int chapterCount = 5;
-        int paragraphCount = 20;
-        int wordCount = 100;
+        int chapterCount = 12;
+        int paragraphCount = 18;
+        int wordCount = 150;
 
-        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount, modelFilePath);
+        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount);
         assertEquals(ReadingLevel.LEVEL1, result, "Expected ReadingLevel to be LEVEL1, but got: " + result);
 
     }
 
     @Test
     public void testPredictReadingLevel_Level2() {
 
-        String modelFilePath = "src/test/resources/ai/elimu/util/reading_level/model1.pmml";
-        int chapterCount = 12;
-        int paragraphCount = 22;
-        int wordCount = 250;
+        int chapterCount = 20;
+        int paragraphCount = 30;
+        int wordCount = 300;
 
-        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount, modelFilePath);
+        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount);
         assertEquals(ReadingLevel.LEVEL2, result, "Expected ReadingLevel to be LEVEL2, but got: " + result);
 
     }
 
     @Test
     public void testPredictReadingLevel_Level3() {
 
-        String modelFilePath = "src/test/resources/ai/elimu/util/reading_level/model1.pmml";
-        int chapterCount = 12;
-        int paragraphCount = 25;
+        int chapterCount = 25;
+        int paragraphCount = 40;
         int wordCount = 350;
 
-        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount, modelFilePath);
+        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount);
         assertEquals(ReadingLevel.LEVEL3, result, "Expected ReadingLevel to be LEVEL3, but got: " + result);
 
     }
 
     @Test
-    public void testPredictReadingLevel_InvalidModelFile() {
+    public void testPredictReadingLevel_Level4() {
+
+        int chapterCount = 15;
+        int paragraphCount = 45;
+        int wordCount = 559;
+
+        ReadingLevel result = ReadingLevelUtil.predictReadingLevel(chapterCount, paragraphCount, wordCount);
+        assertEquals(ReadingLevel.LEVEL4, result, "Expected ReadingLevel to be LEVEL4, but got: " + result);
 
-        assertThrows(IOException.class, () -> {
-            ReadingLevelUtil.predictReadingLevel(1, 1, 1, "invalidPath");
-        }, "Expected IOException when loading an invalid model file path");
     }
 }