implement rotation via injecting exif headers (#19)

exif.ts

@@ -0,0 +1,28 @@
+// Create a minimal EXIF segment with orientation
+export const createExifOrientation = (orientation: number) => {
+  const tiffHeader = Buffer.from("49492A0008000000", "hex");
+  const ifdEntry = Buffer.concat([
+    Buffer.from("0100", "hex"), // Number of IFD entries
+    Buffer.from("1201030001000000", "hex"), // Tag, Type, Count
+    Buffer.from(orientation.toString(16).padStart(2, "0"), "hex"), // Orientation value
+    Buffer.from("0000", "hex"), // No more IFDs
+    Buffer.from("0000000000", "hex"), // padding??
+  ]);
+
+  const exifData = Buffer.concat([Buffer.from("457869660000", "hex"), tiffHeader, ifdEntry]);
+  const segmentLength = Buffer.from([(exifData.length + 2) >> 8, (exifData.length + 2) & 0xff]);
+  const exifHeader = Buffer.concat([Buffer.from("FFE1", "hex"), segmentLength]);
+
+  return Buffer.concat([exifHeader, exifData]);
+};
+
+export const addExifToJpeg = (jpegData: Buffer, exifSegment: Buffer) => {
+  // Check for existing EXIF (simplified check)
+  if (jpegData.includes(Buffer.from("FFE1", "hex"))) {
+    throw new Error("JPEG already contains EXIF segment");
+  }
+
+  const soiEnd = 2; // After FFD8
+  const modifiedJpeg = Buffer.concat([jpegData.subarray(0, soiEnd), exifSegment, jpegData.subarray(soiEnd)]);
+  return modifiedJpeg;
+};