updated design

packages/diff-engine/__tests__/myers.test.ts

@@ -0,0 +1,73 @@
+import { describe, it, expect } from 'vitest';
+import { computeEditScript } from '../src/myers.js';
+
+describe('computeEditScript', () => {
+  it('returns empty for two empty arrays', () => {
+    expect(computeEditScript([], [])).toEqual([]);
+  });
+
+  it('returns all-insert for empty before', () => {
+    const ops = computeEditScript([], ['a', 'b']);
+    expect(ops).toEqual([{ type: 'insert', lines: ['a', 'b'] }]);
+  });
+
+  it('returns all-delete for empty after', () => {
+    const ops = computeEditScript(['a', 'b'], []);
+    expect(ops).toEqual([{ type: 'delete', lines: ['a', 'b'] }]);
+  });
+
+  it('returns all-equal for identical arrays', () => {
+    const ops = computeEditScript(['a', 'b', 'c'], ['a', 'b', 'c']);
+    expect(ops).toEqual([{ type: 'equal', lines: ['a', 'b', 'c'] }]);
+  });
+
+  it('detects a single changed line', () => {
+    const ops = computeEditScript(['a', 'b', 'c'], ['a', 'X', 'c']);
+    const types = ops.map(o => o.type);
+    expect(types).toContain('delete');
+    expect(types).toContain('insert');
+    const deleted = ops.filter(o => o.type === 'delete').flatMap(o => o.lines);
+    const inserted = ops.filter(o => o.type === 'insert').flatMap(o => o.lines);
+    expect(deleted).toContain('b');
+    expect(inserted).toContain('X');
+  });
+
+  it('detects inserted lines at end', () => {
+    const ops = computeEditScript(['a'], ['a', 'b', 'c']);
+    const inserted = ops.filter(o => o.type === 'insert').flatMap(o => o.lines);
+    expect(inserted).toEqual(['b', 'c']);
+  });
+
+  it('detects deleted lines at start', () => {
+    const ops = computeEditScript(['x', 'y', 'a'], ['a']);
+    const deleted = ops.filter(o => o.type === 'delete').flatMap(o => o.lines);
+    expect(deleted).toEqual(['x', 'y']);
+  });
+
+  it('merges consecutive ops of same type', () => {
+    const ops = computeEditScript(['a', 'b'], ['c', 'd']);
+    // Should have merged deletes and inserts, not one-op-per-line
+    const delOp = ops.find(o => o.type === 'delete');
+    const insOp = ops.find(o => o.type === 'insert');
+    expect(delOp?.lines.length).toBeGreaterThanOrEqual(1);
+    expect(insOp?.lines.length).toBeGreaterThanOrEqual(1);
+  });
+
+  it('round-trip: applying ops to before yields after', () => {
+    const before = ['prop: 1', 'style: red', 'size: md'];
+    const after = ['prop: 1', 'style: blue', 'size: lg', 'weight: 600'];
+    const ops = computeEditScript(before, after);
+
+    const result: string[] = [];
+    for (const op of ops) {
+      if (op.type === 'equal' || op.type === 'insert') result.push(...op.lines);
+    }
+    expect(result).toEqual(after);
+  });
+
+  it('handles single-element change', () => {
+    const ops = computeEditScript(['x'], ['y']);
+    expect(ops.some(o => o.type === 'delete' && o.lines.includes('x'))).toBe(true);
+    expect(ops.some(o => o.type === 'insert' && o.lines.includes('y'))).toBe(true);
+  });
+});