fix: diff now handles complicated change sequences properly

joebobmiles · Nov 10, 2022 · baa3c01 · baa3c01
1 parent b4d3d9b
commit baa3c01
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Showing 2 changed files with 47 additions and 26 deletions.
diff --git a/src/diff.spec.ts b/src/diff.spec.ts
@@ -275,7 +275,7 @@ describe("diff", () =>
   });
 });
 
-describe("diffText", () =>
+describe.only("diffText", () =>
 {
   it.each([
     [ "", "" ],
@@ -298,21 +298,43 @@ describe("diffText", () =>
     expect(diffText(a, b)).toStrictEqual(diff);
   });
 
-  it("Adjusts indices to account for previous changes.", () =>
+  it.only.each([
+    [
+      "hello",
+      "goodbye",
+      [
+        [ "add", 0, "g" ],
+        [ "add", 1, "o" ],
+        [ "add", 2, "o" ],
+        [ "add", 3, "d" ],
+        [ "add", 4, "b" ],
+        [ "add", 5, "y" ],
+        [ "delete", 6, undefined ],
+        [ "delete", 7, undefined ],
+        [ "delete", 7, undefined ],
+        [ "delete", 7, undefined ]
+      ]
+    ],
+    [
+      "hello, world!",
+      "goodbye, world.",
+      [
+        [ "add", 0, "g" ],
+        [ "add", 1, "o" ],
+        [ "add", 2, "o" ],
+        [ "add", 3, "d" ],
+        [ "add", 4, "b" ],
+        [ "add", 5, "y" ],
+        [ "delete", 6, undefined ],
+        [ "delete", 7, undefined ],
+        [ "delete", 7, undefined ],
+        [ "delete", 7, undefined ],
+        [ "add", 14, "." ],
+        [ "delete", 15, undefined ]
+      ]
+    ]
+  ])("Adjusts indices to account for previous changes.", (a, b, diff) =>
   {
-    const a = "hello", b = "goodbye";
-
-    expect(diffText(a, b)).toStrictEqual([
-      [ "add", 0, "g" ],
-      [ "add", 1, "o" ],
-      [ "add", 2, "o" ],
-      [ "add", 3, "d" ],
-      [ "add", 4, "b" ],
-      [ "add", 5, "y" ],
-      [ "delete", 6, undefined ],
-      [ "delete", 8, undefined ],
-      [ "delete", 9, undefined ],
-      [ "delete", 10, undefined ]
-    ]);
+    expect(diffText(a, b)).toStrictEqual(diff);
   });
 });
diff --git a/src/diff.ts b/src/diff.ts
@@ -155,7 +155,7 @@ export const diffText = (a: string, b: string): any =>
 };
 
 /**
- * An implementation of Wu et al. O(NP) text diff. (See docs/text-diff)
+ * An adaptation of Wu et al. O(NP) text diff. (See docs/text-diff)
  *
  * Credit to [this JavaScript implementation](https://github.com/cubicdaiya/onp/blob/master/javascript/onp.js).
  *
@@ -243,8 +243,7 @@ const _diffText = (a: string, b: string, isReversed: boolean): any =>
   }
 
   const changeList: [ "add" | "delete", number, string | undefined ][] = [];
-  let x = 0, y = 0;
-  let start = 0;
+  let x = 0, y = 0, index = -1;
 
   for (let i = editPath.length - 1; i >= 0; i--)
   {
@@ -256,19 +255,19 @@ const _diffText = (a: string, b: string, isReversed: boolean): any =>
         {
           changeList[changeList.length] = [
             "delete",
-            (y - 1) + start,
+            index,
             undefined
           ];
         }
         else
         {
           changeList[changeList.length] = [
             "add",
-            y - 1,
+            index,
             b[y - 1]
           ];
 
-          start++;
+          index++;
         }
 
         y++;
@@ -279,17 +278,17 @@ const _diffText = (a: string, b: string, isReversed: boolean): any =>
         {
           changeList[changeList.length] = [
             "add",
-            x - 1,
+            index,
             a[x - 1]
           ];
 
-          start++;
+          index++;
         }
         else
         {
           changeList[changeList.length] = [
             "delete",
-            (x - 1) + start,
+            index,
             undefined
           ];
         }
@@ -298,7 +297,7 @@ const _diffText = (a: string, b: string, isReversed: boolean): any =>
       }
       else
       {
-        x++; y++;
+        x++; y++; index++;
       }
     }
   }