(#307) Implement image writer

Author: s1hofmann

Diff for: lib/provider/io/jimp-image-writer.class.spec.ts

@@ -0,0 +1,19 @@
+import ImageWriter from "./jimp-image-writer.class";
+import ImageReader from "./jimp-image-reader.class";
+import {join} from "path";
+
+describe('Jimp image writer', () => {
+    it('should reject on writing failures', async () => {
+        // GIVEN
+        const inputFilename = join(__dirname, '__mocks__', 'calculator.png');
+        const outputFile = await (new ImageReader().load(inputFilename));
+        const outputFileName = "/does/not/compute.png"
+        const SUT = new ImageWriter();
+
+        // WHEN
+        const func = () => SUT.store({data: outputFile, path: outputFileName});
+
+        // THEN
+        await expect(func).rejects.toThrowError()
+    });
+});

Diff for: lib/provider/io/jimp-image-writer.class.ts

@@ -0,0 +1,24 @@
+import Jimp from 'jimp';
+import {ImageWriter, ImageWriterParameters} from "../image-writer.type";
+
+export default class implements ImageWriter {
+    store(parameters: ImageWriterParameters): Promise<void> {
+        return new Promise((resolve, reject) => {
+            const jimpImage = new Jimp({
+                data: parameters.data.data,
+                width: parameters.data.width,
+                height: parameters.data.height
+            });
+            // libnut returns data in BGR format, so we have to switch red and blue color channels
+            jimpImage.scan(0, 0, jimpImage.bitmap.width, jimpImage.bitmap.height, function(_, __, idx) {
+                const red = this.bitmap.data[idx];
+                this.bitmap.data[idx] = this.bitmap.data[idx + 2];
+                this.bitmap.data[idx + 2] = red;
+            });
+            return jimpImage
+                .writeAsync(parameters.path)
+                .then(_ => resolve())
+                .catch(err => reject(err));
+        });
+    }
+}