feat(beautify): add shadow rendering (extracted from border.ts pattern)

tests/unit/beautify-shadow.test.ts

@@ -0,0 +1,87 @@
+import sharp from "sharp";
+import { describe, expect, it } from "vitest";
+import { applyShadow } from "../../apps/api/src/lib/beautify/shadow.js";
+
+describe("applyShadow", () => {
+  const makeImage = (w: number, h: number) =>
+    sharp({
+      create: {
+        width: w,
+        height: h,
+        channels: 4,
+        background: { r: 100, g: 100, b: 255, alpha: 1 },
+      },
+    })
+      .png()
+      .toBuffer();
+
+  it("returns larger buffer with shadow applied", async () => {
+    const img = await makeImage(200, 150);
+    const result = await applyShadow(img, {
+      blur: 20,
+      offsetX: 0,
+      offsetY: 10,
+      color: "#000000",
+      opacity: 30,
+    });
+    const meta = await sharp(result.buffer).metadata();
+    expect(meta.width).toBeGreaterThan(200);
+    expect(meta.height).toBeGreaterThan(150);
+    expect(result.padLeft).toBeGreaterThanOrEqual(0);
+    expect(result.padTop).toBeGreaterThanOrEqual(0);
+  });
+
+  it("returns image position within shadow canvas", async () => {
+    const img = await makeImage(200, 150);
+    const result = await applyShadow(img, {
+      blur: 20,
+      offsetX: 5,
+      offsetY: 10,
+      color: "#000000",
+      opacity: 50,
+    });
+    expect(result.imgX).toBeDefined();
+    expect(result.imgY).toBeDefined();
+  });
+
+  it("handles zero-blur shadow gracefully", async () => {
+    const img = await makeImage(100, 100);
+    const result = await applyShadow(img, {
+      blur: 0,
+      offsetX: 0,
+      offsetY: 0,
+      color: "#000000",
+      opacity: 0,
+    });
+    const meta = await sharp(result.buffer).metadata();
+    expect(meta.width).toBeGreaterThanOrEqual(100);
+  });
+
+  it("handles negative offsets", async () => {
+    const img = await makeImage(200, 150);
+    const result = await applyShadow(img, {
+      blur: 15,
+      offsetX: -10,
+      offsetY: -5,
+      color: "#ff0000",
+      opacity: 40,
+    });
+    const meta = await sharp(result.buffer).metadata();
+    expect(meta.width).toBeGreaterThan(200);
+    expect(meta.height).toBeGreaterThan(150);
+  });
+
+  it("produces RGBA output with alpha channel", async () => {
+    const img = await makeImage(100, 100);
+    const result = await applyShadow(img, {
+      blur: 10,
+      offsetX: 0,
+      offsetY: 5,
+      color: "#000000",
+      opacity: 30,
+    });
+    const meta = await sharp(result.buffer).metadata();
+    expect(meta.hasAlpha).toBe(true);
+    expect(meta.channels).toBe(4);
+  });
+});