refactor(runner): rename preprocessing to runner and update directory structure

libs/alpha_composite.js

@@ -0,0 +1,31 @@
+import sharp from "sharp";
+import path from "path";
+
+export default class AlphaComposite {
+  #config
+  #operatorName
+  #operatorSourceFolder
+
+  constructor(config, operatorName, rootDir) {
+    this.#config = config
+    this.#operatorName = operatorName
+    this.#operatorSourceFolder = path.join(rootDir, this.#config.folder.operator, this.#operatorName)
+  }
+
+  async process(filename, extractedDir) {
+    const image = sharp(path.join(extractedDir, filename))
+      .removeAlpha()
+    const imageMeta = await image.metadata()
+    const imageBuffer = await image.toBuffer()
+    const mask = await sharp(path.join(extractedDir, `${path.parse(filename).name}[alpha].png`))
+      .extractChannel("blue")
+      .resize(imageMeta.width, imageMeta.height)
+      .toBuffer();
+
+    return sharp(imageBuffer)
+      .joinChannel(mask)
+      .toBuffer()
+
+  }
+
+}