feat: add image watermark

image-watermark/main_test.ts

@@ -0,0 +1,49 @@
+import { assertEquals } from "@std/assert";
+import { addWatermark } from "./main.ts";
+
+Deno.test("addWatermark - should add watermark to image", async () => {
+  const { default: sharp } = await import("sharp");
+  
+  // 创建测试图片 (200x200 红色方块)
+  const testImagePath = "/tmp/test_image.png";
+  await sharp({
+    create: {
+      width: 200,
+      height: 200,
+      channels: 3,
+      background: { r: 255, g: 0, b: 0 },
+    },
+  }).png().toFile(testImagePath);
+  
+  const outputPath = "/tmp/test_image_watermarked.png";
+  
+  try {
+    // 添加水印（带背景色）
+    await addWatermark(testImagePath, {
+      text: "Test Watermark",
+      fontSize: 16,
+      color: "white",
+      backgroundColor: "#80000000",
+      backgroundPadding: 5,
+      marginRight: 10,
+      marginBottom: 10,
+      outputPath,
+    });
+    
+    // 验证输出文件存在
+    const stat = await Deno.stat(outputPath);
+    assertEquals(stat.isFile, true);
+  } finally {
+    // 清理
+    try {
+      await Deno.remove(testImagePath);
+    } catch {
+      // Ignore
+    }
+    try {
+      await Deno.remove(outputPath);
+    } catch {
+      // Ignore
+    }
+  }
+});