#include <stdio.h>
#include <gdk-pixbuf/gdk-pixbuf.h>

#define IMAGE_TYPE "ico"
#define IMAGE_FILENAME "squares.ico"

/*
 * Auxiliary function, returns numeric representation of pixel.
 * For RGB format it is rrggbb(in hex), for RGBA - rrggbbaa.
 */
guint32 get_pixel(GdkPixbuf* pixbuf, int x, int y)
{
    guchar* colors = ((guchar*)gdk_pixbuf_get_pixels(pixbuf)
                + gdk_pixbuf_get_n_channels(pixbuf) * x
                + gdk_pixbuf_get_rowstride(pixbuf) * y);
    
    guint32 pixel = (colors[0] << 16) | (colors[1] << 8) | colors[2];
    if(gdk_pixbuf_get_n_channels(pixbuf) == 4) 
        pixel = (pixel << 8) | colors[3];
                 
    return pixel;
}
/*
 * Verify, whether all pixels outside area, given via x, y, width, height,
 * have same colors in pixbuf_old and pixbuf_new.
 */
gboolean pixbuf_not_changed_outside_area(
    GdkPixbuf* pixbuf_new, GdkPixbuf* pixbuf_old,
    gint x, gint y, gint width, gint height)
{
    gint pixbuf_width = gdk_pixbuf_get_width(pixbuf_new);
    gint pixbuf_height = gdk_pixbuf_get_height(pixbuf_new);

    int x_curr, y_curr;    
    for(x_curr = 0; x_curr < pixbuf_width; x_curr++)
        for(y_curr = 0; y_curr < pixbuf_height; y_curr++)
    {
        if((x_curr >= x)
            && (x_curr < x+width)
            && (y_curr >= y)
            && (y_curr < y+height))
            continue;//inside area - doesn't compare pixels.
        if(get_pixel(pixbuf_new, x_curr, y_curr)
             != get_pixel(pixbuf_old, x_curr, y_curr))
        {
            printf("Pixel at (%d, %d) changed from %x to %x,\n",
                x_curr, y_curr,
                get_pixel(pixbuf_old, x_curr, y_curr),
                get_pixel(pixbuf_new, x_curr, y_curr));
            printf("But it is outside of area with ");
            printf("x=%d, y=%d, width=%d, height=%d\n",
            x, y, width, height);

            return FALSE;
        }
    }
    return TRUE;
}

void callback_area_updated(GdkPixbufLoader* loader, int x, int y, int width, int height,
    GdkPixbuf* pixbuf_old)
{
    static gboolean signal_correct = TRUE;
    //if(y != 0) y = gdk_pixbuf_get_height(pixbuf_old) - y; //"corrected" y
    if(!signal_correct) return;//error already found
    GdkPixbuf* pixbuf_new = gdk_pixbuf_loader_get_pixbuf(loader);

    if(!pixbuf_not_changed_outside_area(pixbuf_new, pixbuf_old, x, y, width, height))
    {
        signal_correct = FALSE;
        //expand area to cover full pixbuf - for correctly update copy
        x = 0;        
        y = 0;
        width = gdk_pixbuf_get_width(pixbuf_new);
        height = gdk_pixbuf_get_height(pixbuf_new);
    }
    //update copy of pixbuf
    gdk_pixbuf_copy_area(pixbuf_new, x, y, width, height, pixbuf_old, x, y);
}
//free copy of pixbuf used in area-updated callback.
void callback_closed(GdkPixbufLoader* loader, GdkPixbuf* pixbuf_copy)
{
    g_object_unref(pixbuf_copy);
}
//prepare copy of pixbuf and connect other callbacks
void callback_area_prepared(GdkPixbufLoader* loader)
{
    GdkPixbuf* pixbuf_copy = gdk_pixbuf_copy(gdk_pixbuf_loader_get_pixbuf(loader));
    //connect callbacks for another signals
    //for not use pointer to pointer in them.
    g_signal_connect(loader, "area-updated",
            (GCallback) callback_area_updated, (gpointer)pixbuf_copy);
    g_signal_connect(loader, "closed",
            (GCallback) callback_closed, (gpointer)pixbuf_copy);

}

/*
 * Reads count_bytes from the channel and write them to the loader.
 * Returns number of bytes written.
 * count_bytes = G_MAXSIZE means read as many bytes as possible.  
 */
gsize loader_write_from_channel(GdkPixbufLoader* loader, GIOChannel *channel, gsize count_bytes)
{
    guchar* buffer;
    gsize bytes_read;
    GIOStatus read_status;
    if(count_bytes < G_MAXSIZE)
    { 
        //read no more then 'count_bytes' bytes
        buffer = g_malloc(count_bytes);
        read_status = 
            g_io_channel_read_chars(channel, (gchar*)buffer, count_bytes, &bytes_read, NULL);
    }
    else
    {
        //read up to end
        read_status = 
            g_io_channel_read_to_end(channel, (gchar**)&buffer, &bytes_read, NULL);
    }
    if((read_status != G_IO_STATUS_NORMAL) && (read_status != G_IO_STATUS_EOF))
    {
        printf("Cannot read bytes from channel.\n");
        g_free(buffer);
        return 0;    
    }
    
    if(!gdk_pixbuf_loader_write(loader, buffer, bytes_read, NULL))
    {
        printf("gdk_pixbuf_loader_write() returned FALSE.\n");
        g_free(buffer);
        return 0;
    }
    g_free(buffer);
    return bytes_read;
}


int main()
{
    g_type_init();
    //create channel from IMAGE_FILENAME
    GIOChannel* channel = g_io_channel_new_file(IMAGE_FILENAME, "r", NULL);
    if(channel == NULL)
    {
        printf("Cannot open file '%s' for read.\n", IMAGE_FILENAME);
        return 1;
    }
    g_io_channel_set_encoding(channel, NULL, NULL);
    //create loader
    GdkPixbufLoader* loader = gdk_pixbuf_loader_new_with_type(IMAGE_TYPE, NULL);
    if(loader == NULL)
    {
        printf("Cannot create loader of type '%s'.\n", IMAGE_TYPE);
        g_io_channel_unref(channel);
        return 1;
    }

    g_signal_connect(loader, "area-prepared",
            (GCallback) callback_area_prepared, NULL);
    //callbacks for "area-prepared" and "closed" signals will be connected
    //in callback_area_prepared()
    
    //read image byte by byte    
    while(loader_write_from_channel(loader, channel, 1) == 1);
    //or read full image at once
    //loader_write_from_channel(loader, channel, G_MAXSIZE);

    //free resources
    g_io_channel_unref(channel);

    gdk_pixbuf_loader_close(loader, NULL);
    g_object_unref(loader);
 
    return 0;
}
