feat: add bidirectional ICO image converter

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/converters/ico.js

@@ -0,0 +1,45 @@
+import fs from 'node:fs/promises';
+import sharp from 'sharp';
+import { decodeIco, encodeIco } from 'icojs';
+import { register } from './registry.js';
+import { sharpFormatName, buildFormatOptions } from './image.js';
+
+const IMAGE_FORMATS = ['jpg', 'jpeg', 'png', 'webp', 'gif', 'tiff', 'avif'];
+export const DEFAULT_ICON_SIZE = 256;
+
+export async function encodeIcoFromInput(input, size = DEFAULT_ICON_SIZE) {
+  const pngBuffer = await sharp(input).resize(size, size, { fit: 'contain' }).png().toBuffer();
+  return Buffer.from(await encodeIco([{ buffer: pngBuffer }]));
+}
+
+async function decodeIcoLargestImage(inputPath) {
+  const buffer = await fs.readFile(inputPath);
+  const images = await decodeIco(buffer, 'image/png');
+  return images.reduce((a, b) => (a.width * a.height >= b.width * b.height ? a : b));
+}
+
+export function registerIcoConverter() {
+  for (const format of IMAGE_FORMATS) {
+    register({
+      family: 'image',
+      sourceFormat: 'ico',
+      targetFormat: format,
+      convert: async (inputPath, outputPath, { quality } = {}) => {
+        const largest = await decodeIcoLargestImage(inputPath);
+        await sharp(Buffer.from(largest.buffer))
+          .toFormat(sharpFormatName(format), buildFormatOptions(format, quality))
+          .toFile(outputPath);
+      },
+    });
+
+    register({
+      family: 'image',
+      sourceFormat: format,
+      targetFormat: 'ico',
+      convert: async (inputPath, outputPath, { iconSize } = {}) => {
+        const icoBuffer = await encodeIcoFromInput(inputPath, iconSize ?? DEFAULT_ICON_SIZE);
+        await fs.writeFile(outputPath, icoBuffer);
+      },
+    });
+  }
+}

src/converters/image.js

@@ -3,7 +3,7 @@ import { register } from './registry.js';
 
 const IMAGE_FORMATS = ['jpg', 'jpeg', 'png', 'webp', 'gif', 'tiff', 'avif'];
 
-function sharpFormatName(format) {
+export function sharpFormatName(format) {
   return format === 'jpg' ? 'jpeg' : format;
 }