#include <stdio.h>
#include <jpeglib.h>
#include <stdlib.h>

/* we will be using this uninitialized pointer later to store raw, uncompressd image */
unsigned char *raw_image = NULL;

/* dimensions of the image we want to write */
int width = 1600;
int height = 1200;
int bytes_per_pixel = 3;   /* or 1 for GRACYSCALE images */
J_COLOR_SPACE color_space = JCS_RGB; /* or JCS_GRAYSCALE for grayscale images */

/**
 * read_jpeg_file Reads from a jpeg file on disk specified by filename and saves into the
 * raw_image buffer in an uncompressed format.
 *
 * \returns positive integer if successful, -1 otherwise
 * \param *filename char string specifying the file name to read from
 *
 */

int read_jpeg_file( char *filename )
{
	/* these are standard libjpeg structures for reading(decompression) */
	struct jpeg_decompress_struct cinfo;
	struct jpeg_error_mgr jerr;
	/* libjpeg data structure for storing one row, that is, scanline of an image */
	JSAMPROW row_pointer[1];

	FILE *infile = fopen( filename, "rb" );
	unsigned long location = 0;
	int i = 0;

	if ( !infile )
	{
		printf("Error opening jpeg file %s\n!", filename );
		return -1;
	}
	/* here we set up the standard libjpeg error handler */
	cinfo.err = jpeg_std_error( &jerr );
	/* setup decompression process and source, then read JPEG header */
	jpeg_create_decompress( &cinfo );
	/* this makes the library read from infile */
	jpeg_stdio_src( &cinfo, infile );
	/* reading the image header which contains image information */
	jpeg_read_header( &cinfo, TRUE );
	/* Uncomment the following to output image information, if needed. */
	/*--
	printf( "JPEG File Information: \n" );
	printf( "Image width and height: %d pixels and %d pixels.\n", cinfo.image_width, cinfo.image_height );
	printf( "Color components per pixel: %d.\n", cinfo.num_components );
	printf( "Color space: %d.\n", cinfo.jpeg_color_space );
	--*/
	/* Start decompression jpeg here */
	jpeg_start_decompress( &cinfo );

	/* allocate memory to hold the uncompressed image */
	raw_image = (unsigned char*)malloc( cinfo.output_width*cinfo.output_height*cinfo.num_components );
	/* now actually read the jpeg into the raw buffer */
	row_pointer[0] = (unsigned char *)malloc( cinfo.output_width*cinfo.num_components );
	/* read one scan line at a time */
	while( cinfo.output_scanline < cinfo.image_height )
	{
		jpeg_read_scanlines( &cinfo, row_pointer, 1 );
		for( i=0; i<cinfo.image_width*cinfo.num_components;i++)
			raw_image[location++] = row_pointer[0][i];
	}
	/* wrap up decompression, destroy objects, free pointers and close open files */
	jpeg_finish_decompress( &cinfo );
	jpeg_destroy_decompress( &cinfo );
	free( row_pointer[0] );
	fclose( infile );
	/* yup, we succeeded! */
	return 1;
}

/**
 * write_jpeg_file Writes the raw image data stored in the raw_image buffer
 * to a jpeg image with default compression and smoothing options in the file
 * specified by *filename.
 *
 * \returns positive integer if successful, -1 otherwise
 * \param *filename char string specifying the file name to save to
 *
 */
int write_jpeg_file( char *filename )
{
	struct jpeg_compress_struct cinfo;
	struct jpeg_error_mgr jerr;

	/* this is a pointer to one row of image data */
	JSAMPROW row_pointer[1];
	FILE *outfile = fopen( filename, "wb" );

	if ( !outfile )
	{
		printf("Error opening output jpeg file %s\n!", filename );
		return -1;
	}
	cinfo.err = jpeg_std_error( &jerr );
	jpeg_create_compress(&cinfo);
	jpeg_stdio_dest(&cinfo, outfile);

	/* Setting the parameters of the output file here */
	cinfo.image_width = width;
	cinfo.image_height = height;
	cinfo.input_components = bytes_per_pixel;
	cinfo.in_color_space = color_space;
    /* default compression parameters, we shouldn't be worried about these */
	jpeg_set_defaults( &cinfo );
	/* Now do the compression .. */
	jpeg_start_compress( &cinfo, TRUE );
	/* like reading a file, this time write one row at a time */
	while( cinfo.next_scanline < cinfo.image_height )
	{
		row_pointer[0] = &raw_image[ cinfo.next_scanline * cinfo.image_width *  cinfo.input_components];
		jpeg_write_scanlines( &cinfo, row_pointer, 1 );
	}
	/* similar to read file, clean up after we're done compressing */
	jpeg_finish_compress( &cinfo );
	jpeg_destroy_compress( &cinfo );
	fclose( outfile );
	/* success code is 1! */
	return 1;
}

int main()
{
	char *infilename = "test.jpg", *outfilename = "test_out.jpg";

	/* Try opening a jpeg*/
	if( read_jpeg_file( infilename ) > 0 )
	{
		/* then copy it to another file */
		if( write_jpeg_file( outfilename ) < 0 ) return -1;
	}
	else return -1;
	return 0;
}