import { describe, expect, test } from "bun:test";
import { blendFeatherPatch } from "./brushRaster";

describe("feather brush raster blending", () => {
  test("mixes blurred mask values inside the stroke and preserves pixels outside it", () => {
    const original = rgbaRow([255, 255, 255, 255, 255]);
    const blurred = rgbaRow([0, 64, 128, 192, 255]);

    blendFeatherPatch(original, blurred, 5, 1, { x: 0, y: 0 }, {
      from: { x: 2.5, y: 0.5 },
      to: { x: 2.5, y: 0.5 },
      size: 3,
      strength: 100,
    });

    expect(alphaValues(original)).toEqual([255, 64, 128, 192, 255]);
  });

  test("applies strength as a non-destructive mix", () => {
    const original = rgbaRow([255]);
    const blurred = rgbaRow([0]);

    blendFeatherPatch(original, blurred, 1, 1, { x: 0, y: 0 }, {
      from: { x: 0.5, y: 0.5 },
      to: { x: 0.5, y: 0.5 },
      size: 10,
      strength: 50,
    });

    expect(alphaValues(original)).toEqual([128]);
  });
});

function rgbaRow(alpha: number[]) {
  return new Uint8ClampedArray(alpha.flatMap((value) => [255, 255, 255, value]));
}

function alphaValues(data: Uint8ClampedArray) {
  return Array.from({ length: data.length / 4 }, (_, index) => data[index * 4 + 3]);
}