feat: build failure message from invalid hunks (#90)

* test: add failing stub and test for building the failure message

* fix: implement message building

* fix: use original line numbers in error message

* docs: add docstring

* docs: add note about empty input returning empty string

src/github-handler/comment-handler/invalid-hunk-handler/index.ts

@@ -0,0 +1,40 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import {Hunk} from '../../../types';
+
+function hunkErrorMessage(hunk: Hunk): string {
+  return `  * lines ${hunk.oldStart}-${hunk.oldEnd}`;
+}
+
+function fileErrorMessage(filename: string, hunks: Hunk[]): string {
+  return `* ${filename}\n` + hunks.map(hunkErrorMessage).join('\n');
+}
+
+/**
+ * Build an error message based on invalid hunks.
+ * Returns an empty string if the provided hunks are empty.
+ * @param invalidHunks a map of filename to hunks that are not suggestable
+ */
+export function buildErrorMessage(invalidHunks: Map<string, Hunk[]>): string {
+  if (invalidHunks.size === 0) {
+    return '';
+  }
+  return (
+    'Some suggestions could not be made:\n' +
+    Array.from(invalidHunks, ([filename, hunks]) =>
+      fileErrorMessage(filename, hunks)
+    ).join('\n')
+  );
+}

test/invalid-hunks.ts

@@ -0,0 +1,65 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import {expect} from 'chai';
+import {describe, it, before} from 'mocha';
+import {setup} from './util';
+import {buildErrorMessage} from '../src/github-handler/comment-handler/invalid-hunk-handler';
+
+before(() => {
+  setup();
+});
+
+describe('buildErrorMessage', () => {
+  it('should handle an empty list of failures', () => {
+    const invalidHunks = new Map();
+    const expectedMessage = '';
+
+    const errorMessage = buildErrorMessage(invalidHunks);
+    expect(errorMessage).to.be.equal(expectedMessage);
+  });
+
+  it('should handle multiple file entries', () => {
+    const invalidHunks = new Map();
+    invalidHunks.set('foo.txt', [
+      {oldStart: 1, oldEnd: 2, newStart: 1, newEnd: 2},
+    ]);
+    invalidHunks.set('bar.txt', [
+      {oldStart: 3, oldEnd: 4, newStart: 3, newEnd: 4},
+    ]);
+    const expectedMessage = `Some suggestions could not be made:
+* foo.txt
+  * lines 1-2
+* bar.txt
+  * lines 3-4`;
+
+    const errorMessage = buildErrorMessage(invalidHunks);
+    expect(errorMessage).to.be.equal(expectedMessage);
+  });
+
+  it('should handle multiple entries for a file', () => {
+    const invalidHunks = new Map();
+    invalidHunks.set('foo.txt', [
+      {oldStart: 1, oldEnd: 2, newStart: 1, newEnd: 2},
+      {oldStart: 3, oldEnd: 4, newStart: 3, newEnd: 4},
+    ]);
+    const expectedMessage = `Some suggestions could not be made:
+* foo.txt
+  * lines 1-2
+  * lines 3-4`;
+
+    const errorMessage = buildErrorMessage(invalidHunks);
+    expect(errorMessage).to.be.equal(expectedMessage);
+  });
+});