// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "lib/jxl/exif.h"

namespace jxl {

constexpr uint16_t kExifOrientationTag = 274;

// Checks if a blob looks like Exif, and if so, sets bigendian
// according to the tiff endianness
bool IsExif(const std::vector<uint8_t>& exif, bool* bigendian) {
  if (exif.size() < 12) return false;  // not enough bytes for a valid exif blob
  const uint8_t* t = exif.data();
  if (LoadLE32(t) == 0x2A004D4D) {
    *bigendian = true;
    return true;
  } else if (LoadLE32(t) == 0x002A4949) {
    *bigendian = false;
    return true;
  }
  return false;  // not a valid tiff header
}

// Finds the position of an Exif tag, or 0 if it is not found
size_t FindExifTagPosition(const std::vector<uint8_t>& exif, uint16_t tagname) {
  bool bigendian;
  if (!IsExif(exif, &bigendian)) return 0;
  const uint8_t* t = exif.data() + 4;
  uint32_t offset = (bigendian ? LoadBE32(t) : LoadLE32(t));
  if (exif.size() < 12 + offset + 2 || offset < 8) return 0;
  t += offset - 4;
  uint16_t nb_tags = (bigendian ? LoadBE16(t) : LoadLE16(t));
  t += 2;
  while (nb_tags > 0) {
    if (t + 12 >= exif.data() + exif.size()) return 0;
    uint16_t tag = (bigendian ? LoadBE16(t) : LoadLE16(t));
    t += 2;
    if (tag == tagname) return static_cast<size_t>(t - exif.data());
    t += 10;
    nb_tags--;
  }
  return 0;
}

// TODO (jon): tag 1 can be used to represent Adobe RGB 1998 if it has value
// "R03"
// TODO (jon): set intrinsic dimensions according to
// https://discourse.wicg.io/t/proposal-exif-image-resolution-auto-and-from-image/4326/24
void InterpretExif(const std::vector<uint8_t>& exif, CodecMetadata* metadata) {
  bool bigendian;
  if (!IsExif(exif, &bigendian)) return;
  size_t o_pos = FindExifTagPosition(exif, kExifOrientationTag);
  if (o_pos) {
    const uint8_t* t = exif.data() + o_pos;
    uint16_t type = (bigendian ? LoadBE16(t) : LoadLE16(t));
    t += 2;
    uint32_t count = (bigendian ? LoadBE32(t) : LoadLE32(t));
    t += 4;
    uint16_t value = (bigendian ? LoadBE16(t) : LoadLE16(t));
    t += 4;
    if (type == 3 && count == 1 && value >= 1 && value <= 8) {
      metadata->m.orientation = value;
    }
  }
}

void ResetExifOrientation(std::vector<uint8_t>& exif) {
  bool bigendian;
  if (!IsExif(exif, &bigendian)) return;
  size_t o_pos = FindExifTagPosition(exif, kExifOrientationTag);
  if (o_pos) {
    uint8_t* t = exif.data() + o_pos;
    uint16_t type = (bigendian ? LoadBE16(t) : LoadLE16(t));
    t += 2;
    uint32_t count = (bigendian ? LoadBE32(t) : LoadLE32(t));
    t += 4;
    if (type == 3 && count == 1) {
      if (bigendian)
        StoreBE16(1, t);
      else
        StoreLE16(1, t);
    }
  }
}

}  // namespace jxl