Implemented function to compute minimal delta of two texts

lib/utility.dart

@@ -0,0 +1,108 @@
+class Word {
+  final int start;
+  final int end;
+  final String text;
+
+  Word({required this.start, required this.end, required this.text});
+}
+
+class WordDelta {
+  Word? old;
+  Word? modified;
+
+  WordDelta({this.old, this.modified});
+}
+
+class TextDelta {
+  final List<WordDelta> wordDeltas = [];
+}
+
+class Utility {
+  static List<Word> splitToWords(String text) {
+    List<Word> words = [];
+    String currentWord = "";
+    for (int i = 0; i < text.length; i++) {
+      if (text[i] == " " ||
+          text[i] == "\n" ||
+          text[i] == "\r" ||
+          text[i] == "\t") {
+        if (currentWord.isNotEmpty) {
+          words.add(
+              Word(start: i - currentWord.length, end: i, text: currentWord));
+          currentWord = "";
+        }
+      } else {
+        currentWord += text[i];
+      }
+    }
+    if (currentWord.isNotEmpty) {
+      words.add(Word(
+          start: text.length - currentWord.length,
+          end: text.length,
+          text: currentWord));
+    }
+    return words;
+  }
+
+  static List<TextDelta> compare(String oldText, String newText) {
+    var oldWords = splitToWords(oldText);
+    var newWords = splitToWords(newText);
+
+    int oldIndex = 0;
+    int newIndex = 0;
+
+    List<TextDelta> textDeltas = [];
+    while ((oldIndex < oldWords.length) && (newIndex < newWords.length)) {
+      var oldWord = oldWords[oldIndex];
+      var newWord = newWords[newIndex];
+      if (oldWord.text == newWord.text) {
+        oldIndex++;
+        newIndex++;
+      } else {
+        var delta = TextDelta();
+        delta.wordDeltas.add(WordDelta(old: oldWord, modified: newWord));
+        textDeltas.add(delta);
+        oldIndex++;
+        newIndex++;
+
+        if (oldIndex < oldWords.length && newIndex < newWords.length) {
+          var nextOldWord = oldWords[oldIndex];
+          var newSubIndex = newIndex;
+          var oldSubIndex = oldIndex;
+          while (newSubIndex < newWords.length &&
+              newWords[newSubIndex].text != nextOldWord.text) {
+            WordDelta wordDelta =
+                WordDelta(old: nextOldWord, modified: newWords[newSubIndex]);
+            delta.wordDeltas.add(wordDelta);
+            newSubIndex++;
+            oldSubIndex++;
+          }
+          if (newIndex != newSubIndex) {
+            newIndex = newSubIndex;
+            oldIndex = oldSubIndex;
+          }
+        }
+      }
+    }
+
+    if (newIndex < newWords.length) {
+      var delta = TextDelta();
+      while (newIndex < newWords.length) {
+        delta.wordDeltas.add(WordDelta(modified: newWords[newIndex]));
+        newIndex++;
+      }
+      textDeltas.add(delta);
+    }
+
+    if (oldIndex < oldWords.length) {
+      var delta = TextDelta();
+      while (oldIndex < oldWords.length) {
+        delta.wordDeltas.add(WordDelta(old: oldWords[oldIndex]));
+        oldIndex++;
+      }
+      textDeltas.add(delta);
+    }
+
+    return textDeltas;
+  }
+}

test/utlity_test.dart

@@ -0,0 +1,89 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fitlien_common/utility.dart';
+
+void main() {
+  test('Test splitToWords function 1', () {
+    List<Word> words = Utility.splitToWords("This is a test sentence.");
+    expect(words.length, 5);
+    expect(words[0].text, "This");
+    expect(words[1].text, "is");
+    expect(words[2].text, "a");
+    expect(words[3].text, "test");
+    expect(words[4].text, "sentence.");
+  });
+
+  test('Test splitToWords function 2', () {
+    List<Word> words = Utility.splitToWords("This is a another sentence.");
+    expect(words.length, 5);
+    expect(words[0].text, "This");
+    expect(words[1].text, "is");
+    expect(words[2].text, "a");
+    expect(words[3].text, "another");
+    expect(words[4].text, "sentence.");
+  });
+
+  test('Comparison test 1', () {
+    var text1 = "ab bc cd";
+    var text2 = "ab cb cd";
+    var deltas = Utility.compare(text1, text2);
+    expect(deltas.length, 1);
+    expect(deltas[0].wordDeltas.length, 1);
+    expect(deltas[0].wordDeltas[0].old!.text, "bc");
+    expect(deltas[0].wordDeltas[0].modified!.text, "cb");
+  });
+
+  test('Comparison test 2', () {
+    var text1 = "ab bc cd";
+    var text2 = "ab cb dc";
+    var deltas = Utility.compare(text1, text2);
+    expect(deltas.length, 1);
+    expect(deltas[0].wordDeltas.length, 2);
+    expect(deltas[0].wordDeltas[0].old!.text, "bc");
+    expect(deltas[0].wordDeltas[0].modified!.text, "cb");
+    expect(deltas[0].wordDeltas[1].old!.text, "cd");
+    expect(deltas[0].wordDeltas[1].modified!.text, "dc");
+  });
+
+  test('Comparison test 3', () {
+    var text1 = "ab bc cd fe";
+    var text2 = "ab cb cd ef";
+    var deltas = Utility.compare(text1, text2);
+    expect(deltas.length, 2);
+    expect(deltas[0].wordDeltas.length, 1);
+    expect(deltas[0].wordDeltas[0].old!.text, "bc");
+    expect(deltas[0].wordDeltas[0].modified!.text, "cb");
+    expect(deltas[1].wordDeltas.length, 1);
+    expect(deltas[1].wordDeltas[0].old!.text, "fe");
+    expect(deltas[1].wordDeltas[0].modified!.text, "ef");
+  });
+
+  test('Comparison test 4', () {
+    var text1 = "ab bc";
+    var text2 = "ab cb cd ef";
+    var deltas = Utility.compare(text1, text2);
+    expect(deltas.length, 2);
+    expect(deltas[0].wordDeltas.length, 1);
+    expect(deltas[0].wordDeltas[0].old!.text, "bc");
+    expect(deltas[0].wordDeltas[0].modified!.text, "cb");
+    expect(deltas[1].wordDeltas.length, 2);
+    expect(deltas[1].wordDeltas[0].old, null);
+    expect(deltas[1].wordDeltas[0].modified!.text, "cd");
+    expect(deltas[1].wordDeltas[1].old, null);
+    expect(deltas[1].wordDeltas[1].modified!.text, "ef");
+  });
+
+  test('Comparison test 5', () {
+    var text1 = "ab bc cd ef";
+    var text2 = "ab cb";
+    var deltas = Utility.compare(text1, text2);
+    expect(deltas.length, 2);
+    expect(deltas[0].wordDeltas.length, 1);
+    expect(deltas[0].wordDeltas[0].old!.text, "bc");
+    expect(deltas[0].wordDeltas[0].modified!.text, "cb");
+    expect(deltas[1].wordDeltas.length, 2);
+    expect(deltas[1].wordDeltas[0].old!.text, "cd");
+    expect(deltas[1].wordDeltas[0].modified, null);
+    expect(deltas[1].wordDeltas[1].old!.text, "ef");
+    expect(deltas[1].wordDeltas[1].modified, null);
+  });
+}