/****************************************************************************
 Copyright (c) 2010-2012 cocos2d-x.org
 Copyright (c) 2013-2016 Chukong Technologies Inc.
 Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.
 
 http://www.cocos2d-x.org
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ****************************************************************************/

#include "base/etc2.h"
#include <stdint.h>
#include <string.h>

static const char kMagic[] = { 'P', 'K', 'M', ' ', '2', '0' };

static const etc2_uint32 ETC2_PKM_FORMAT_OFFSET = 6;
static const etc2_uint32 ETC2_PKM_ENCODED_WIDTH_OFFSET = 8;
static const etc2_uint32 ETC2_PKM_ENCODED_HEIGHT_OFFSET = 10;
static const etc2_uint32 ETC2_PKM_WIDTH_OFFSET = 12;
static const etc2_uint32 ETC2_PKM_HEIGHT_OFFSET = 14;

static void writeBEUint16(etc2_byte* pOut, etc2_uint32 data) {
    pOut[0] = (etc2_byte) (data >> 8);
    pOut[1] = (etc2_byte) data;
}

static etc2_uint32 readBEUint16(const etc2_byte* pIn) {
    return (pIn[0] << 8) | pIn[1];
}

// Check if a PKM header is correctly formatted.

etc2_bool etc2_pkm_is_valid(const etc2_byte* pHeader) {
    if (memcmp(pHeader, kMagic, sizeof(kMagic))) {
        return false;
    }
    etc2_uint32 format = readBEUint16(pHeader + ETC2_PKM_FORMAT_OFFSET);
    etc2_uint32 encodedWidth = readBEUint16(pHeader + ETC2_PKM_ENCODED_WIDTH_OFFSET);
    etc2_uint32 encodedHeight = readBEUint16(pHeader + ETC2_PKM_ENCODED_HEIGHT_OFFSET);
    etc2_uint32 width = readBEUint16(pHeader + ETC2_PKM_WIDTH_OFFSET);
    etc2_uint32 height = readBEUint16(pHeader + ETC2_PKM_HEIGHT_OFFSET);
    return (format == ETC2_RGB_NO_MIPMAPS || format == ETC2_RGBA_NO_MIPMAPS) &&
            encodedWidth >= width && encodedWidth - width < 4 &&
            encodedHeight >= height && encodedHeight - height < 4;
}

// Read the image width from a PKM header

etc2_uint32 etc2_pkm_get_width(const etc2_byte* pHeader) {
    return readBEUint16(pHeader + ETC2_PKM_WIDTH_OFFSET);
}

// Read the image height from a PKM header

etc2_uint32 etc2_pkm_get_height(const etc2_byte* pHeader){
    return readBEUint16(pHeader + ETC2_PKM_HEIGHT_OFFSET);
}

etc2_uint32 etc2_pkm_get_format(const uint8_t* pHeader) {
    return readBEUint16(pHeader + ETC2_PKM_FORMAT_OFFSET);
}