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

typedef struct {
    unsigned int width;
    unsigned int height;
    unsigned char* data;
} Image;

static int
readPGM( Image* pgm, FILE* fp )
{
    int headerNumbersRead = 0;
    int inNumber = 0;
    int number = 0;
    int inHeader = 1;
    int ch;

    if ( fp == 0 ) {
	return __LINE__;
    }

    if ( ( ch = fgetc( fp ) ) != 'P' || ( ch = fgetc( fp ) ) != '5' ) {
	fprintf( stderr, "Not a valid raw pgm file\n" );
	return __LINE__;
    }

    while ( inHeader && ( ch = fgetc( fp ) ) != EOF ) {
	if ( isdigit( ch ) ) {
	    if ( !inNumber ) {
		number = 0;
		inNumber = 1;
	    }

	    number *= 10;
	    number += ( ch - '0' );
	} else {
	    if ( inNumber ) {
		switch ( ++headerNumbersRead ) {
		case 1:
		    pgm->width = number;
		    break;
		case 2:
		    pgm->height = number;
		    break;
		case 3:
		    inHeader = 0;
		    break;
		}
		inNumber = 0;
	    }

	    if ( ch == '#' ) {
		while ( ( ch = fgetc( fp ) ) != EOF && ch != '\n' ) {
		    /* do nothing */;
		}
	    } else if ( !isspace( ch ) ) {
		fprintf( stderr, "Illegal header character <%c>\n", ch );
	    }
	}
    }

    if ( ch != '\n' ) {
	while ( ( ch = fgetc( fp ) ) != EOF && ch != '\n' ) {
	    /* do nothing */;
	}
    }

    if ( pgm->width == 0 || pgm->height == 0 ) {
	fprintf( stderr, "Invalid width or height\n" );
	fclose( fp );
	return __LINE__;
    }

    pgm->data = (unsigned char*)malloc( pgm->width * pgm->height );
    if ( pgm->data == 0 ) {
	fprintf( stderr, "Out of memory\n" );
	fclose( fp );
	return __LINE__;
    }

    fread( pgm->data, 1, pgm->width * pgm->height, fp );

    return 0;
}

static void
offsetImage( Image* image, unsigned int offset )
{
    if ( offset != 0 ) {
	unsigned char* buf
	    = (unsigned char*)malloc( image->width * image->height );

	if ( buf != 0 ) {
	    unsigned int preSize = offset * image->width; 
	    unsigned int postSize = ( image->height - offset ) * image->width; 

	    memcpy( buf, &image->data[ preSize ], postSize );
	    memcpy( &buf[ postSize ], image->data, preSize );

	    free( image->data );
	    image->data = buf;
	}
    }
}

int
main( int argc, const char* argv[] )
{
    unsigned int help = 0;
    const char* fileName = 0;
    FILE* fp = stdin;
    unsigned int reps = 0;
    unsigned int offset = 0;
    unsigned int ii;
    Image pgm;

    for ( ii=1; ii < argc; ++ii ) {
	if ( !strcmp( argv[ ii ], "-file" ) ) {
	    fileName = argv[ ++ii ];
	} else if ( !strcmp( argv[ ii ], "-reps" ) ) {
	    reps = strtol( argv[ ++ii ], 0, 0 );
	} else if ( !strcmp( argv[ ii ], "-offset" ) ) {
	    offset = strtol( argv[ ++ii ], 0, 0 );
	} else {
	    help = 1;
	}
    }

    if ( help ) {
	fprintf( stderr, "Usage: %s\n", argv[0] );
	fprintf( stderr, "\t[-file fileName]\n" );
	fprintf( stderr, "\t[-reps repetitions]\n" );
	fprintf( stderr, "\t[-offset starting line number]\n" );
	return __LINE__;
    }

    if ( fileName != 0 ) {
	fp = fopen( fileName, "rb" );
    }

    if ( readPGM( &pgm, fp ) != 0 ) {
	fprintf( stderr, "Couldn't read pgm: %s\n", fileName );
	if ( fp != 0 ) {
	    fclose( fp );
	}
	return __LINE__;
    }

    if ( fp != 0 ) {
	fclose( fp );
    }

    offsetImage( &pgm, offset % pgm.height );

    fprintf( stdout, "%d # %s\n", pgm.width, argv[0] );

    for ( ii=0; ( reps == 0 ) || ii < reps; ++ii ) {
	if ( fwrite( pgm.data, 1, pgm.width * pgm.height, stdout ) !=
	pgm.width * pgm.height ) {
	    fprintf( stderr, "Didn't write a full chunk\n" );
	    return __LINE__;
	}
    }

    return 0;
}