Use better diff algorithm

src/views/conflicts-resolution/diff.ts

@@ -9,40 +9,75 @@ export interface DiffChunk {
 function diff(oldText: string, newText: string): DiffChunk[] {
   const oldLines = oldText.split("\n");
   const newLines = newText.split("\n");
-  const result: DiffChunk[] = [];
 
-  for (let i = 0; i < Math.max(oldLines.length, newLines.length); i++) {
-    const oldLine = oldLines[i];
-    const newLine = newLines[i];
+  let matrix = Array(oldLines.length + 1)
+    .fill(null)
+    .map(() => Array(newLines.length + 1).fill(0));
 
-    if (!oldLine && newLine) {
-      result.push({
+  for (let i = 1; i <= oldLines.length; i++) matrix[i][0] = i;
+  for (let j = 1; j <= newLines.length; j++) matrix[0][j] = j;
+
+  for (let i = 1; i <= oldLines.length; i++) {
+    for (let j = 1; j <= newLines.length; j++) {
+      if (oldLines[i - 1] === newLines[j - 1]) {
+        matrix[i][j] = matrix[i - 1][j - 1];
+      } else {
+        matrix[i][j] = Math.min(
+          matrix[i - 1][j] + 1, // deletion
+          matrix[i][j - 1] + 1, // insertion
+          matrix[i - 1][j - 1] + 1, // substitution
+        );
+      }
+    }
+  }
+
+  const chunks: DiffChunk[] = [];
+  let i = oldLines.length;
+  let j = newLines.length;
+
+  while (i > 0 || j > 0) {
+    if (i > 0 && j > 0 && oldLines[i - 1] === newLines[j - 1]) {
+      i--;
+      j--;
+      continue;
+    }
+
+    const deletion = i > 0 ? matrix[i - 1][j] : Infinity;
+    const insertion = j > 0 ? matrix[i][j - 1] : Infinity;
+    const substitution = i > 0 && j > 0 ? matrix[i - 1][j - 1] : Infinity;
+
+    if (substitution <= deletion && substitution <= insertion) {
+      chunks.unshift({
+        type: "modify",
+        startLeftLine: i,
+        endLeftLine: i + 1,
+        startRightLine: j,
+        endRightLine: j + 1,
+      });
+      i--;
+      j--;
+    } else if (deletion <= insertion) {
+      chunks.unshift({
+        type: "remove",
+        startLeftLine: i,
+        endLeftLine: i + 1,
+        startRightLine: j + 1,
+        endRightLine: j + 1,
+      });
+      i--;
+    } else {
+      chunks.unshift({
         type: "add",
         startLeftLine: i + 1,
         endLeftLine: i + 1,
-        startRightLine: i + 1,
-        endRightLine: i + 2,
-      });
-    } else if (oldLine && !newLine) {
-      result.push({
-        type: "remove",
-        startLeftLine: i + 1,
-        endLeftLine: i + 2,
-        startRightLine: i + 1,
-        endRightLine: i + 1,
-      });
-    } else if (oldLine !== newLine) {
-      result.push({
-        type: "modify",
-        startLeftLine: i + 1,
-        endLeftLine: i + 2,
-        startRightLine: i + 1,
-        endRightLine: i + 2,
+        startRightLine: j,
+        endRightLine: j + 1,
       });
+      j--;
     }
   }
-  // return result;
-  return mergeDiffs(result);
+
+  return mergeDiffs(chunks);
 }
 
 function mergeDiffs(chunks: DiffChunk[]): DiffChunk[] {