#include <png.h>
#include <stdlib.h>
#include <string.h>

#include "shader_helpers.h"
#include "shader_platform.h"

static void gl_error_callback( GLenum source,
                                GLenum type,
                                GLuint id,
                                GLenum severity,
                                GLsizei length,
                                const GLchar* message,
                                const void* userParam )
{
    if (type== GL_DEBUG_TYPE_ERROR)
    {
        fprintf( stderr, "GL: %s type = 0x%x, severity = 0x%x, \n %s\n",
             (type == GL_DEBUG_TYPE_ERROR ? "*ERROR*" : ""),
             type, severity, message );
    }
    else
    {
        fprintf( stderr, "GL type = 0x%x, severity = 0x%x, \n %s\n",
                 type, severity, message);
    }

    return;
}

bool gl_version_at_least (int maj, int min)
{
    static int major_version = -1;
    static int minor_version = -1;

    if (major_version < 0 || minor_version < 0)
    {
        const char *version_string = (const char *) glGetString (GL_VERSION);
        sscanf (version_string, "%d.%d", &major_version, &minor_version);
    }

    if (major_version > maj)
        return true;

    if (maj == major_version && minor_version >= min)
        return true;

    return false;
}

bool srgb_available (void)
{
    if (gl_version_at_least (3, 0))
        return true;

    const char *extensions = (const char *) glGetString (GL_EXTENSIONS);

    if (strstr (extensions, "texture_sRGB") &&
        strstr (extensions, "framebuffer_sRGB"))
        return true;

    return false;
}

bool float_texture_available (void)
{
    if (gl_version_at_least (3, 2))
        return true;

    const char *extensions = (const char *) glGetString (GL_EXTENSIONS);

    if (strstr (extensions, "texture_float"))
        return true;

    return false;
}

void glLogErrors (void)
{
    glEnable (GL_DEBUG_OUTPUT);
    glDebugMessageCallback ((GLDEBUGPROC) gl_error_callback, 0);
}

bool loadPngImage(const char* name,
    int& outWidth,
    int& outHeight,
    bool& outHasAlpha,
    GLubyte** outData)
{
    png_structp png_ptr;
    png_infop info_ptr;
    unsigned int sig_read = 0;
    FILE* fp;

    if ((fp = fopen(name, "rb")) == NULL)
        return false;

    /* Create and initialize the png_struct
   * with the desired error handler
   * functions.  If you want to use the
   * default stderr and longjump method,
   * you can supply NULL for the last
   * three parameters.  We also supply the
   * the compiler header file version, so
   * that we know if the application
   * was compiled with a compatible version
   * of the library.  REQUIRED
   */
    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);

    if (png_ptr == NULL) {
        fclose(fp);
        return false;
    }

    /* Allocate/initialize the memory
   * for image information.  REQUIRED. */
    info_ptr = png_create_info_struct(png_ptr);
    if (info_ptr == NULL) {
        fclose(fp);
        png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
        return false;
    }

    /* Set error handling if you are
   * using the setjmp/longjmp method
   * (this is the normal method of
   * doing things with libpng).
   * REQUIRED unless you  set up
   * your own error handlers in
   * the png_create_read_struct()
   * earlier.
   */
    if (setjmp(png_jmpbuf(png_ptr))) {
        /* Free all of the memory associated
     * with the png_ptr and info_ptr */
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
        fclose(fp);
        /* If we get here, we had a
     * problem reading the file */
        return false;
    }

    /* Set up the output control if
   * you are using standard C streams */
    png_init_io(png_ptr, fp);

    /* If we have already
   * read some of the signature */
    png_set_sig_bytes(png_ptr, sig_read);

    /*
   * If you have enough memory to read
   * in the entire image at once, and
   * you need to specify only
   * transforms that can be controlled
   * with one of the PNG_TRANSFORM_*
   * bits (this presently excludes
   * dithering, filling, setting
   * background, and doing gamma
   * adjustment), then you can read the
   * entire image (including pixels)
   * into the info structure with this
   * call
   *
   * PNG_TRANSFORM_STRIP_16 |
   * PNG_TRANSFORM_PACKING  forces 8 bit
   * PNG_TRANSFORM_EXPAND forces to
   *  expand a palette into RGB
   */
    png_read_png(png_ptr,
        info_ptr,
        PNG_TRANSFORM_STRIP_16 | PNG_TRANSFORM_PACKING | PNG_TRANSFORM_EXPAND,
        (png_voidp)NULL);

    outWidth = png_get_image_width(png_ptr, info_ptr);
    outHeight = png_get_image_height(png_ptr, info_ptr);
    switch (png_get_color_type(png_ptr, info_ptr)) {
    case PNG_COLOR_TYPE_RGBA:
        outHasAlpha = true;
        break;
    case PNG_COLOR_TYPE_RGB:
        outHasAlpha = false;
        break;
    default:
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        fclose(fp);
        return false;
    }
    unsigned int row_bytes = png_get_rowbytes(png_ptr, info_ptr);
    *outData = (unsigned char*)malloc(row_bytes * outHeight);

    png_bytepp row_pointers = png_get_rows(png_ptr, info_ptr);

    for (int i = 0; i < outHeight; i++) {
        memcpy(*outData + (row_bytes * i), row_pointers[i], row_bytes);
    }

    /* Clean up after the read,
   * and free any memory allocated */
    png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);

    /* Close the file */
    fclose(fp);

    /* That's it */
    return true;
}

bool loadTGA(const char* filename, STGA& tgaFile)
{
    FILE* file;
    unsigned char type[4];
    unsigned char info[6];

    file = fopen(filename, "rb");

    if (!file)
        return false;

    fread(&type, sizeof(char), 3, file);
    fseek(file, 12, SEEK_SET);
    fread(&info, sizeof(char), 6, file);

    // image type either 2 (color) or 3 (greyscale)
    if (type[1] != 0 || (type[2] != 2 && type[2] != 3)) {
        fclose(file);
        return false;
    }

    tgaFile.width = info[0] + info[1] * 256;
    tgaFile.height = info[2] + info[3] * 256;
    tgaFile.byteCount = info[4] / 8;

    if (tgaFile.byteCount != 3 && tgaFile.byteCount != 4) {
        fclose(file);
        return false;
    }

    long imageSize = tgaFile.width * tgaFile.height * tgaFile.byteCount;

    // allocate memory for image data
    unsigned char* tempBuf = new unsigned char[imageSize];
    tgaFile.data = new unsigned char[tgaFile.width * tgaFile.height * 4];

    // read in image data
    fread(tempBuf, sizeof(unsigned char), imageSize, file);

    // swap line order and convert to RBGA
    for (int i = 0; i < tgaFile.height; i++) {
        unsigned char* source = tempBuf + tgaFile.width * (tgaFile.height - 1 - i) * tgaFile.byteCount;
        unsigned char* destination = tgaFile.data + tgaFile.width * i * 4;
        for (int j = 0; j < tgaFile.width; j++) {
            destination[0] = source[2];
            destination[1] = source[1];
            destination[2] = source[0];
            destination[3] = tgaFile.byteCount == 4 ? source[3] : 0xff;
            source += tgaFile.byteCount;
            destination += 4;
        }
    }
    delete[] tempBuf;
    tgaFile.byteCount = 4;

    // close file
    fclose(file);

    return true;
}