Merge pull request #1 from happo/dynamic-drift

Apply drift for lcs algorithm dynamically (based on image height)

.circleci/config.yml

@@ -0,0 +1,10 @@
+version: 2
+jobs:
+  build:
+    docker:
+      - image: circleci/node:10
+    working_directory: ~/repo
+    steps:
+      - checkout
+      - run: yarn install
+      - run: yarn test

src/__tests__/snapshots-test.js

@@ -0,0 +1,58 @@
+const crypto = require('crypto');
+const childProcess = require('child_process');
+const fs = require('fs');
+const path = require('path');
+
+const Jimp = require('jimp');
+
+const imageDiff = require('../');
+
+function hashFunction(data) {
+  return crypto
+    .createHash('md5')
+    .update(data)
+    .digest('hex');
+}
+
+const snapshots = childProcess
+  .execSync('ls snapshots', { encoding: 'utf-8' })
+  .split(/\n/)
+  .filter(Boolean);
+
+jest.setTimeout(60000);
+
+describe('snapshot tests', () => {
+  snapshots.forEach(snapshot => {
+    it(snapshot, async () => {
+      console.log('Starting', snapshot);
+      const [image1, image2] = await Promise.all([
+        Jimp.read(path.resolve('snapshots', snapshot, 'before.png')),
+        Jimp.read(path.resolve('snapshots', snapshot, 'after.png')),
+      ]);
+      console.log('Images ready', snapshot);
+      const diffImage = imageDiff(image1.bitmap, image2.bitmap, {
+        hashFunction,
+      });
+
+      console.log('Created diff image', snapshot);
+      const pathToDiff = path.resolve('snapshots', snapshot, 'diff.png');
+
+      if (!fs.existsSync(pathToDiff)) {
+        console.log(
+          `No previous diff image for ${snapshot} found -- saving diff.png.`,
+        );
+        const newDiffImage = await new Jimp(diffImage);
+        await newDiffImage.write(pathToDiff);
+      }
+      const expectedDiffImage = (await Jimp.read(pathToDiff)).bitmap;
+      const diffHash = hashFunction(diffImage.data);
+      const expectedHash = hashFunction(expectedDiffImage.data);
+      if (diffHash !== expectedHash) {
+        console.log(
+          `Diff image did not match existing diff image. Remove this image and run again to re-generate:\n${pathToDiff}`,
+        );
+      }
+      expect(diffHash).toEqual(expectedHash);
+    });
+  });
+});

src/alignArrays.js

@@ -6,7 +6,7 @@ const MOVEMENT = {
 };
 
 const PLACEHOLDER = '+';
-const DRIFT_RANGE = 200;
+const MIN_DRIFT_RANGE = 200;
 
 /**
  * Creates a 2d matrix of a certain size.
@@ -38,11 +38,15 @@ function longestCommonSubsequence(a, b) {
   const memo = initMatrix(aLength + 1, bLength + 1);
   const solution = initMatrix(aLength + 1, bLength + 1);
 
+  const usedDriftRange = Math.abs(
+    Math.max(Math.max(aLength, bLength) / 10, MIN_DRIFT_RANGE),
+  );
+
   // Loop and find the solution
   for (let i = 1; i <= aLength; i += 1) {
     for (
-      let j = Math.max(1, i - (DRIFT_RANGE / 2));
-      j <= Math.min(bLength, i + (DRIFT_RANGE / 2));
+      let j = Math.max(1, i - usedDriftRange / 2);
+      j <= Math.min(bLength, i + usedDriftRange / 2);
       j += 1
     ) {
       if (a[i - 1] === b[j - 1]) {