refactor: replace CanvasToolkit instantiation with singleton access

Author: snowfluke

README.md

@@ -77,7 +77,7 @@ import { CanvasToolkit, ImageProcessor, cv } from "ppu-ocv";
 const file = Bun.file("./assets/receipt.jpg");
 const image = await file.arrayBuffer();
 
-const canvasToolkit = new CanvasToolkit();
+const canvasToolkit = CanvasToolkit.getInstance();
 const canvas = await ImageProcessor.prepareCanvas(image);
 await ImageProcessor.initRuntime();
 

examples/perspective-correction-with-debug.ts

@@ -8,7 +8,7 @@ const DEBUG_FOLDER = "out";
 const canvas = await ImageProcessor.prepareCanvas(image);
 await ImageProcessor.initRuntime();
 
-const canvasToolkit = new CanvasToolkit();
+const canvasToolkit = CanvasToolkit.getInstance();
 const processor = new ImageProcessor(canvas);
 canvasToolkit.clearOutput(DEBUG_FOLDER);
 

src/canvas-toolkit.ts

@@ -10,17 +10,39 @@ import {
 } from "fs";
 import { join } from "path";
 
+/**
+ * Singleton class for canvas manipulation utilities
+ */
 export class CanvasToolkit {
+  private static instance: CanvasToolkit | null = null;
   private step: number = 0;
 
+  /**
+   * Private constructor to prevent direct instantiation
+   */
+  private constructor() {}
+
+  /**
+   * Get the singleton instance of CanvasToolkit
+   * @returns The singleton instance
+   * @example
+   * const canvasToolkit = CanvasToolkit.getInstance();
+   */
+  public static getInstance(): CanvasToolkit {
+    if (!CanvasToolkit.instance) {
+      CanvasToolkit.instance = new CanvasToolkit();
+    }
+    return CanvasToolkit.instance;
+  }
+
   /**
    * Crop a part of source canvas and return a new canvas of the cropped part
    * @param options
    * @param options.bbox Bounding box of the cropped part
    * @param options.canvas Source canvas
    * @returns A new canvas of the cropped part
    * @example
-   * const croppedCanvas = canvasToolkit.crop({
+   * const croppedCanvas = CanvasToolkit.getInstance().crop({
    *   bbox: { x0: 10, y0: 10, x1: 100, y1: 100 },
    *   canvas: sourceCanvas,
    * });
@@ -54,7 +76,7 @@ export class CanvasToolkit {
    * @param options.majorColorThreshold Major color threshold (default: 0.97)
    * @returns true if the canvas is dirty, false otherwise
    * @example
-   * const isDirty = canvasToolkit.isDirty({
+   * const isDirty = CanvasToolkit.getInstance().isDirty({
    *   canvas: sourceCanvas,
    *   threshold: 127.5,
    *   majorColorThreshold: 0.97,
@@ -115,7 +137,7 @@ export class CanvasToolkit {
    * @param options.path Path to save the image file (default: "out")
    * @returns A promise that resolves when the image is saved
    * @example
-   * await canvasToolkit.saveImage({
+   * await CanvasToolkit.getInstance().saveImage({
    *   canvas: sourceCanvas,
    *   filename: "output.png",
    * });

tests/canvas-toolkit.test.ts

@@ -27,7 +27,7 @@ test("crop returns correct sub-canvas", () => {
   ctx.fillStyle = "red";
   ctx.fillRect(2, 3, 4, 5);
 
-  const toolkit = new CanvasToolkit();
+  const toolkit = CanvasToolkit.getInstance();
   const cropped = toolkit.crop({
     bbox: { x0: 2, y0: 3, x1: 6, y1: 8 },
     canvas,
@@ -51,7 +51,7 @@ test("isDirty returns false for uniform canvas and true for checkerboard", () =>
   ctx1.fillStyle = "white";
   ctx1.fillRect(0, 0, size, size);
 
-  const toolkit = new CanvasToolkit();
+  const toolkit = CanvasToolkit.getInstance();
   expect(toolkit.isDirty({ canvas: canvas1 })).toBe(false);
 
   const canvas2 = createCanvas(10, 10);
@@ -74,7 +74,7 @@ test("saveImage and clearOutput manage files correctly", async () => {
   ctx.fillStyle = "green";
   ctx.fillRect(0, 0, 4, 4);
 
-  const toolkit = new CanvasToolkit();
+  const toolkit = CanvasToolkit.getInstance();
 
   await toolkit.saveImage({
     canvas,
@@ -102,7 +102,7 @@ test("saveImage and clearOutput manage files correctly", async () => {
 test("drawLine draws a rectangle stroke on canvas", () => {
   const canvas = createCanvas(10, 10);
   const ctx = canvas.getContext("2d");
-  const toolkit = new CanvasToolkit();
+  const toolkit = CanvasToolkit.getInstance();
 
   toolkit.drawLine({
     ctx,
@@ -133,7 +133,7 @@ test("drawContour draws given contour", () => {
   const canvas = createCanvas(6, 6);
 
   const ctx = canvas.getContext("2d");
-  const toolkit = new CanvasToolkit();
+  const toolkit = CanvasToolkit.getInstance();
 
   toolkit.drawContour({ ctx, contour, strokeStyle: "red", lineWidth: 1 });