/*	Copyright (C) 2020 Gentoo-libre Install

	This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

	This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

	You should have received a copy of the GNU General Public License along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

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

int main(int argc, char *argv[])
{
	if (argc < 2){fprintf(stderr,"Usage: %s <codes.txt>\n", argv[0]); exit(1);}

	FILE *output = fopen("output.gct","wb");
	if (!output){fprintf(stderr,"Could not open output file!\n"); exit(1);}

	/* Header */
	char header[] = {0x00,0xd0,0xc0,0xde,0x00,0xd0,0xc0,0xde};
	fwrite(header, 1, 8, output);


	FILE *input = fopen(argv[1],"r");
	if (!input){fprintf(stderr,"Could not open: %s\n",argv[1]); exit(1);}

	/* check that the given file isn't empty */
	fseek(input, 0L, SEEK_END);
	if (!ftell(input)){fprintf(stderr,"File %s is empty.\n", argv[1]); exit(1);}
	rewind(input);

	char code[18];
	size_t result;

	/* convert each ASCII encoded hex line into the byte values and write that to the gct file */
	while ((result = fread(code, 1, 18, input)))
		{
		if (result < 18){fprintf(stderr, "Invalid code length.\n"); exit(1);}

		/* remove space in middle of code line */
		for (int i = 8; i < 17; ++i)
			{
			code[i] = code[i+1];
			}

		/* convert ASCII encoded hex to byte values */
		for (int i = 0, j = 0; i < 8; ++i, j += 2)
			{
			int amount0;
			int amount1;

			/* check if first number is decimal or hex */
			if (code[j] >= '0' && code[j] <= '9'){amount0 = '0';}
			else if (code[j] >= 'A' && code[j] <= 'F') {amount0 = 55;}
			else {fprintf(stderr,"Invalid code character: %c\n", code[j]); exit(1);}

			/* check if second number is decimal or hex */
			if (code[j+1] >= '0' && code[j+1] <= '9'){amount1 = '0';}
			else if (code[j+1] >= 'A' && code[j+1] <= 'F') {amount1 = 55;}
			else {fprintf(stderr,"Invalid code character: %c\n", code[j+1]); exit(1);}

			/* extract the two characters and place them into one byte */
			code[i] = ((code[j] - amount0) << 4) | (code[j+1] - amount1);
			}

		/* write the code to the gct file */
		fwrite(code, 1, 8, output);
		}


	/* Footer */
	char footer[] = {0xf0,0,0,0,0,0,0,0};
	fwrite(footer, 1, 8, output);

	fclose(output);
	fclose(input);
	return 0;
}