#include "gif.h"
#include <stdio.h>   // for NULL, fprintf, stderr
#include <stdlib.h>  // for malloc, realloc, exit, calloc, free

void uncompress( int code_length,
               const unsigned char *input,
               int input_length,
               unsigned char *out )
{
    //int maxbits;
    int i, bit;
    int code, prev = -1;
    dictionary_entry_t *dictionary;
    int dictionary_ind;
    unsigned int mask = 0x01;
    int reset_code_length;
    int clear_code; // This varies depending on code_length
    int stop_code;  // one more than clear code
    int match_len;

    clear_code = 1 << ( code_length );
    stop_code = clear_code + 1;
    // To handle clear codes
    reset_code_length = code_length;

    // Create a dictionary large enough to hold "code_length" entries.
    // Once the dictionary overflows, code_length increases
    dictionary = ( dictionary_entry_t * )
    malloc( sizeof( dictionary_entry_t ) * ( 1 << ( code_length + 1 ) ) );

    // Initialize the first 2^code_len entries of the dictionary with their
    // indices.  The rest of the entries will be built up dynamically.

    // Technically, it shouldn't be necessary to initialize the
    // dictionary.  The spec says that the encoder "should output a
    // clear code as the first code in the image data stream".  It doesn't
    // say must, though...
    for ( dictionary_ind = 0;
         dictionary_ind < ( 1 << code_length );
         dictionary_ind++ )
    {
        dictionary[ dictionary_ind ].byte = dictionary_ind;
        // XXX this only works because prev is a 32-bit int (> 12 bits)
        dictionary[ dictionary_ind ].prev = -1;
        dictionary[ dictionary_ind ].len = 1;
    }

    // 2^code_len + 1 is the special "end" code; don't give it an entry here
    dictionary_ind++;
    dictionary_ind++;

    // TODO verify that the very last byte is clear_code + 1
    while ( input_length )
    {
        code = 0x0;
        // Always read one more bit than the code length
        for ( i = 0; i < ( code_length + 1 ); i++ )
        {
            // This is different than in the file read example; that
            // was a call to "next_bit"
            bit = ( *input & mask ) ? 1 : 0;
            mask <<= 1;

            if ( mask == 0x100 )
            {
                mask = 0x01;
                input++;
                input_length--;
            }

            code = code | ( bit << i );
        }

        if ( code == clear_code )
        {
            code_length = reset_code_length;
            dictionary = ( dictionary_entry_t * ) realloc( dictionary,
                                                          sizeof( dictionary_entry_t ) * ( 1 << ( code_length + 1 ) ) );

            for ( dictionary_ind = 0;
                 dictionary_ind < ( 1 << code_length );
                 dictionary_ind++ )
            {
                dictionary[ dictionary_ind ].byte = dictionary_ind;
                // XXX this only works because prev is a 32-bit int (> 12 bits)
                dictionary[ dictionary_ind ].prev = -1;
                dictionary[ dictionary_ind ].len = 1;
            }
            dictionary_ind++;
            dictionary_ind++;
            prev = -1;
            continue;
        }
        else if ( code == stop_code )
        {
            /*if ( input_length > 1 )
            {
                fprintf( stderr, "Malformed GIF (early stop code)\n" );
                exit( 0 );
            }*/
            break;
        }

        // Update the dictionary with this character plus the _entry_
        // (character or string) that came before it
        if ( ( prev > -1 ) && ( code_length < 12 ) )
        {
            if ( code > dictionary_ind )
            {
                fprintf( stderr, "code = %.02x, but dictionary_ind = %.02x\n",
                        code, dictionary_ind );
                exit( 0 );
            }

            // Special handling for KwKwK
            if ( code == dictionary_ind )
            {
                int ptr = prev;

                while ( dictionary[ ptr ].prev != -1 )
                {
                    ptr = dictionary[ ptr ].prev;
                }
                dictionary[ dictionary_ind ].byte = dictionary[ ptr ].byte;
            }
            else
            {
                int ptr = code;
                while ( dictionary[ ptr ].prev != -1 )
                {
                    ptr = dictionary[ ptr ].prev;
                }
                dictionary[ dictionary_ind ].byte = dictionary[ ptr ].byte;
            }

            dictionary[ dictionary_ind ].prev = prev;

            dictionary[ dictionary_ind ].len = dictionary[ prev ].len + 1;

            dictionary_ind++;

            // GIF89a mandates that this stops at 12 bits
            if ( ( dictionary_ind == ( 1 << ( code_length + 1 ) ) ) &&
                ( code_length < 11 ) )
            {
                code_length++;

                dictionary = ( dictionary_entry_t * ) realloc( dictionary,
                                                              sizeof( dictionary_entry_t ) * ( 1 << ( code_length + 1 ) ) );
            }
        }

        prev = code;

        // Now copy the dictionary entry backwards into "out"
        match_len = dictionary[ code ].len;
        while ( code != -1 )
        {
            out[ dictionary[ code ].len - 1 ] = dictionary[ code ].byte;
            if ( dictionary[ code ].prev == code )
            {
                fprintf( stderr, "Internal error; self-reference." );
                exit( 0 );
            }
            code = dictionary[ code ].prev;
        }

        out += match_len;
    }
}

static int read_sub_blocks( unsigned char* buffer, unsigned char **data )
{
    int data_length;
    int index;
    unsigned char block_size;

    // Everything following are data sub-blocks, until a 0-sized block is
    // encountered.
    data_length = 0;
    *data = NULL;
    index = 0;

    while ( 1 )
    {
		READ(&block_size, 1);

        if ( block_size == 0 )  // end of sub-blocks
        {
            break;
        }

        data_length += block_size;
        *data = (unsigned char*)realloc( *data, data_length );

        // TODO this could be split across block size boundaries
		READ(*data + index, block_size);

        index += block_size;
    }

    return data_length;
}

unsigned char* process_image_descriptor( unsigned char* buffer,
                                    rgb *gct,
                                    int gct_size,
                                    int resolution_bits )
{
    image_descriptor_t image_descriptor;
    int compressed_data_length;
    unsigned char *compressed_data = NULL;
    unsigned char lzw_code_size;
    int uncompressed_data_length = 0;
    unsigned char *uncompressed_data = NULL;

    // TODO there could actually be lots of these
	READ(&image_descriptor, 9);

    // TODO if LCT = true, read the LCT

	READ(&lzw_code_size, 1);

    compressed_data_length = read_sub_blocks( buffer, &compressed_data );

//    width = image_descriptor.image_width;
//    height = image_descriptor.image_height;
    uncompressed_data_length = image_descriptor.image_width *
    image_descriptor.image_height;
    uncompressed_data = (unsigned char*)malloc( uncompressed_data_length );

    uncompress( lzw_code_size, compressed_data, compressed_data_length,
               uncompressed_data );

    if ( compressed_data ) free( compressed_data );

    //if ( uncompressed_data )
    //    free( uncompressed_data );

    return uncompressed_data;
}

/**
 * @param gif_file the file descriptor of a file containing a
 *  GIF-encoded file.  This should point to the first byte in
 *  the file when invoked.
 */
#define rb (*(buffer++))

uint32_t* LoadPalette(unsigned char *buffer) {
	unsigned char header[7];
	screen_descriptor_t screen_descriptor;
	//int color_resolution_bits;

	int global_color_table_size = 0;  // number of entries in global_color_table
	uint32_t *global_color_table = NULL;

	READ(header, 6);
	READ(&screen_descriptor, 7);

	//color_resolution_bits = ((screen_descriptor.fields & 0x70) >> 4) + 1;
	global_color_table = (uint32_t *)calloc(1, 1024);

	if (screen_descriptor.fields & 0x80) {
		global_color_table_size = 1 << (((screen_descriptor.fields & 0x07) + 1));

		//global_color_table = (rgb *)malloc(3 * global_color_table_size);
		//READ(global_color_table, 3 * global_color_table_size);
        for (int i=0; i<global_color_table_size;++i) {
            global_color_table[i] = (buffer[0]<<16) + (buffer[1]<<8) + buffer[2];
            buffer+=3;
        }
	}
	return global_color_table;
}

static unsigned char* process_gif_stream(unsigned char *buffer, unsigned short* w, unsigned short* h)
{
    unsigned char header[ 7 ];
    screen_descriptor_t screen_descriptor;
    int color_resolution_bits;

    int global_color_table_size =0;  // number of entries in global_color_table
    rgb *global_color_table = NULL;

    unsigned char block_type = 0x0;

    // A GIF file starts with a Header (section 17)
	READ(header, 6);
    header[ 6 ] = 0x0;

    // XXX there's another format, GIF87a, that you may still find
    // floating around.
    /*if ( strcmp( "GIF89a", (char*)header ) )
    {
        fprintf( stderr,
                "Invalid GIF file (header is '%s', should be 'GIF89a')\n",
                header );
        return NULL;
    }*/

    // Followed by a logical screen descriptor
    // Note that this works because GIFs specify little-endian order; on a
    // big-endian machine, the height & width would need to be reversed.

    // Can't use sizeof here since GCC does byte alignment;
    // sizeof( screen_descriptor_t ) = 8!
	READ(&screen_descriptor, 7);
    *w = screen_descriptor.width;
    *h = screen_descriptor.height;

    color_resolution_bits = ( ( screen_descriptor.fields & 0x70 ) >> 4 ) + 1;

    if ( screen_descriptor.fields & 0x80 )
    {
        //int i;
        // If bit 7 is set, the next block is a global color table; read it
        global_color_table_size = 1 << 
        ( ( ( screen_descriptor.fields & 0x07 ) + 1 ) );
        
        global_color_table = ( rgb * ) malloc( 3 * global_color_table_size );
        
        // XXX this could conceivably return a short count...
		READ(global_color_table, 3 * global_color_table_size);
    }
    
    while ( block_type != TRAILER )
    {
		READ(&block_type, 1);
        
        unsigned char size;
        switch ( block_type )
        {
            case IMAGE_DESCRIPTOR:
				return process_image_descriptor(buffer,
					global_color_table,
					global_color_table_size,
					color_resolution_bits);
                break;
            case EXTENSION_INTRODUCER:
                buffer++;
                size = *(buffer++);
                buffer += size;
                do {
                    size = *(buffer++);
                    buffer += size;
                } while (size != 0);

                /*if ( !process_extension( buffer ) )
                {
                    return NULL;
                }*/
                break;
            case TRAILER:
                break;
            default:
                fprintf( stderr, "Bailing on unrecognized block type %.02x\n",
                        block_type );
                return NULL;
        }
    }
	return NULL;
}


unsigned char* LoadGif(unsigned char *buffer, unsigned short* w, unsigned short* h) {
	return process_gif_stream(buffer, w, h);
}

/*int main( int argc, char *argv[] )
{
    FILE* gif_file;
    
    if ( argc < 2 )
    {
        fprintf( stderr, "Usage: %s <path-to-gif-file>\n", argv[ 0 ] );
        exit( 0 );
    }
    
    gif_file = fopen( argv[ 1 ], "rb" );
    
    if ( gif_file == NULL )
    {
        fprintf( stderr, "Unable to open file '%s'", argv[ 1 ] );
        perror( ": " );
    }
    
    process_gif_stream( gif_file );
    
    fclose( gif_file );
}*/