note2any/src/exif-orientation.ts

/*
 * Lightweight EXIF orientation reader + conditional JPEG -> PNG converter.
 * We only care about orientation values 3,6,8 (rotations). Others return as-is.
 */

export async function readOrientation(blob: Blob): Promise<number | null> {
  try {
    console.log(`[readOrientation] Blob type: ${blob.type}, size: ${blob.size}`);
    if (blob.type !== 'image/jpeg' && blob.type !== 'image/jpg') {
      console.log(`[readOrientation] Not a JPEG, blob type: ${blob.type}`);
      return null;
    }
    const buf = await blob.arrayBuffer();
    const view = new DataView(buf);
    console.log(`[readOrientation] ArrayBuffer length: ${buf.byteLength}`);
    // JPEG starts with 0xFFD8
    if (view.getUint16(0) !== 0xFFD8) {
      console.log(`[readOrientation] Not a valid JPEG, header: ${view.getUint16(0).toString(16)}`);
      return null;
    }
    console.log(`[readOrientation] Valid JPEG detected`);
    let offset = 2;
    const length = view.byteLength;
    while (offset < length) {
      if (view.getUint8(offset) !== 0xFF) break;
      const marker = view.getUint8(offset + 1);
      console.log(`[readOrientation] Processing marker: 0xFF${marker.toString(16).padStart(2, '0')} at offset ${offset}`);
      if (marker === 0xE1) { // APP1 EXIF
        const size = view.getUint16(offset + 2, false);
        const exifHeader = offset + 4;
        console.log(`[readOrientation] Found APP1 segment, size: ${size}`);
        if (view.getUint32(exifHeader, false) === 0x45786966) { // 'Exif'
          console.log(`[readOrientation] Found EXIF header`);
          const tiff = exifHeader + 6;
          const endian = view.getUint16(tiff, false);
          const little = endian === 0x4949; // 'II'
          console.log(`[readOrientation] Endian: ${little ? 'little' : 'big'} (${endian.toString(16)})`);
          const getU16 = (p:number) => view.getUint16(p, little);
          const getU32 = (p:number) => view.getUint32(p, little);
          if (getU16(tiff + 2) !== 0x002A) {
            console.log(`[readOrientation] Invalid TIFF magic: ${getU16(tiff + 2).toString(16)}`);
            return null;
          }
          const ifdOffset = getU32(tiff + 4);
          let dir = tiff + ifdOffset;
          const entries = getU16(dir); 
          console.log(`[readOrientation] IFD has ${entries} entries`);
          dir += 2;
          for (let i=0;i<entries;i++) {
            const entry = dir + i*12;
            const tag = getU16(entry);
            if (tag === 0x0112) { // Orientation
              const orientationValue = getU16(entry + 8);
              console.log(`[readOrientation] Found Orientation tag: ${orientationValue}`);
              return orientationValue;
            }
          }
          console.log(`[readOrientation] No Orientation tag found, returning 1`);
          return 1; // treat as normal
        }
        offset += 2 + size;
      } else if (marker === 0xDA) { // SOS
        console.log(`[readOrientation] Reached SOS marker, stopping`);
        break;
      } else {
        const size = view.getUint16(offset + 2, false);
        offset += 2 + size;
      }
    }
  } catch (e) {
    console.error(`[readOrientation] Error reading orientation:`, e);
  }
  console.log(`[readOrientation] No orientation found, returning null`);
  return null;
}

/**
 * Converts JPEG to PNG without rotation, regardless of orientation.
 * Returns a PNG blob + suggested filename.
 */
export async function convertJpegIfNeeded(blob: Blob, filename: string): Promise<{blob: Blob; filename: string; changed: boolean; orientation: number | null}> {
    console.log(`[exif-orientation] Processing ${filename}, blob type: ${blob.type}, size: ${blob.size}`);
    const ori = await readOrientation(blob);
    console.log(`[exif-orientation] Detected orientation for ${filename}: ${ori}`);
    return new Promise((resolve) => {
        const url = URL.createObjectURL(blob);
        const img = new Image();
        img.onload = () => {
            const w = img.naturalWidth;
            const h = img.naturalHeight;
            const canvas = document.createElement('canvas');
            const ctx = canvas.getContext('2d');
            if (!ctx) {
                URL.revokeObjectURL(url);
                resolve({ blob, filename, changed: false, orientation: ori });
                return;
            }
            canvas.width = w;
            canvas.height = h;
            ctx.drawImage(img, 0, 0);
            canvas.toBlob(b => {
                URL.revokeObjectURL(url);
                if (!b) {
                    resolve({ blob, filename, changed: false, orientation: ori });
                    return;
                }
                const pngName = filename.replace(/\.(jpe?g)$/i, '') + '_converted.png';
                resolve({ blob: b, filename: pngName, changed: true, orientation: ori });
            }, 'image/png');
        };
        img.onerror = () => {
            URL.revokeObjectURL(url);
            resolve({ blob, filename, changed: false, orientation: ori });
        };
        img.src = url;
    });
}