fix: improve word selection and passage quality filtering

- Add passage quality checks to skip texts with excessive caps/numbers
- Update AI prompt to avoid malformed words and OCR errors
- Remove hardcoded word filtering in favor of AI-driven selection
- Increase max word length from 10 to 12 characters

src/aiService.js

@@ -121,10 +121,19 @@ class OpenRouterService {
           model: this.model,
           messages: [{
             role: 'system',
-            content: 'Select words for cloze reading exercises. Choose common, everyday words that students know. Avoid proper nouns (names, places), technical terms, archaic words, and words over 8 letters. Pick words students can guess from surrounding context.'
+            content: 'You are a vocabulary selector for educational cloze exercises. Select meaningful, properly-spelled content words that appear exactly as written in the passage.'
           }, {
             role: 'user',
-            content: `Select exactly ${count} meaningful content words for a cloze exercise. Choose nouns, verbs, adjectives that are 4+ letters long and important to meaning. NEVER select: articles (a, an, the), prepositions (in, on, at, to, for, of, with, by, from), conjunctions (and, or, but), pronouns (I, you, he, she, it, they), or auxiliary verbs (is, are, was, were, have, has, had). Return ONLY a JSON array of words.
+            content: `Select exactly ${count} words from this passage for a cloze exercise.
+
+REQUIREMENTS:
+- Choose clear, properly-spelled words (no OCR errors like "andsatires")
+- Select meaningful nouns, verbs, or adjectives (4-12 letters)
+- Words must appear EXACTLY as written in the passage
+- Avoid: function words, archaic terms, proper nouns, technical jargon
+- Skip any words that look malformed or concatenated
+
+Return ONLY a JSON array of the selected words.
 
 Passage: "${passage}"`
           }],

src/clozeGameEngine.js

@@ -85,13 +85,17 @@ class ClozeGame {
     const startFromMiddle = Math.floor(textLength * 0.3); // Skip first 30%
     const endAtThreeQuarters = Math.floor(textLength * 0.8); // Stop before last 20%
     
-    // Random position in the middle section
-    const availableLength = endAtThreeQuarters - startFromMiddle;
-    const randomOffset = Math.floor(Math.random() * Math.max(0, availableLength - 1000));
-    const startIndex = startFromMiddle + randomOffset;
-    
-    // Extract longer initial passage for better sentence completion
-    let passage = text.substring(startIndex, startIndex + 1000);
+    let attempts = 0;
+    let passage = '';
+    
+    while (attempts < 5) {
+      // Random position in the middle section
+      const availableLength = endAtThreeQuarters - startFromMiddle;
+      const randomOffset = Math.floor(Math.random() * Math.max(0, availableLength - 1000));
+      const startIndex = startFromMiddle + randomOffset;
+      
+      // Extract longer initial passage for better sentence completion
+      passage = text.substring(startIndex, startIndex + 1000);
     
     // Clean up start - find first complete sentence that starts with capital letter
     const firstSentenceMatch = passage.match(/[.!?]\s+([A-Z][^.!?]*)/);
@@ -106,12 +110,36 @@ class ClozeGame {
       }
     }
     
-    // Clean up end - ensure we end at a complete sentence
-    const sentences = passage.split(/(?<=[.!?])\s+/);
-    if (sentences.length > 1) {
-      // Remove the last sentence if it might be incomplete
-      sentences.pop();
-      passage = sentences.join(' ');
+      // Clean up end - ensure we end at a complete sentence
+      const sentences = passage.split(/(?<=[.!?])\s+/);
+      if (sentences.length > 1) {
+        // Remove the last sentence if it might be incomplete
+        sentences.pop();
+        passage = sentences.join(' ');
+      }
+      
+      // Quality check: reject passages with excessive caps, numbers, or special formatting
+      const words = passage.split(/\s+/);
+      const capsCount = words.filter(w => w.length > 1 && w === w.toUpperCase()).length;
+      const numbersCount = words.filter(w => /\d/.test(w)).length;
+      const totalWords = words.length;
+      
+      // Skip if more than 10% caps or 5% numbers
+      if (capsCount / totalWords > 0.1 || numbersCount / totalWords > 0.05) {
+        console.log(`Skipping passage with ${capsCount} caps and ${numbersCount} numbers out of ${totalWords} words`);
+        attempts++;
+        continue;
+      }
+      
+      // Check for other quality issues
+      if (passage.includes('CHAPTER') || passage.includes('Section') || 
+          passage.match(/\b(Fig\.|Table|Illustration)\b/)) {
+        attempts++;
+        continue;
+      }
+      
+      // Good passage found
+      break;
     }
     
     // Ensure minimum length - if too short, return what we have rather than infinite recursion
@@ -333,7 +361,7 @@ class ClozeGame {
     const contentWordIndices = [];
     words.forEach((word, index) => {
       const cleanWord = word.toLowerCase().replace(/[^\w]/g, '');
-      if (cleanWord.length > 3 && cleanWord.length <= 10 && !functionWords.has(cleanWord)) {
+      if (cleanWord.length > 3 && cleanWord.length <= 12 && !functionWords.has(cleanWord)) {
         contentWordIndices.push({ word: cleanWord, index });
       }
     });