#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>


int main(int argc, char **argv) {
	if (argc < 2) {
		printf("Usage: vaxcheck <filename.rom> [<output.rom>]\n");
		return -1;
	}

	if (argc > 3) {
		printf("Usage: vaxcheck <filename.rom> [<output.rom>]\n");
		return -1;
	}

	int f = open(argv[1], O_RDONLY);

	if (!f) {
		printf("Unable to open %s for reading\n", argv[1]);
		return -1;
	}

	lseek(f, 3, SEEK_SET);

	uint8_t v[5];
	read(f, v, 5);
	if ((v[1] != 0x55) ||
		(v[2] != 0xAA) ||
		(v[3] != 0x33)) {
		printf("File is not a VAX ROM image\n");
		return -1;
	}

	uint32_t romsize = v[4] << 10;

	printf("ROM is a %d byte VAX ROM image, with rom ID of %d\n", romsize, v[0]);

	lseek(f, 0, SEEK_SET);

	int out = -1;
	if (argc == 3) {
		out = open(argv[2], O_RDWR | O_TRUNC | O_CREAT, 0644);
		if (!out) {
			printf("Unable to open %s for writing\n", argv[2]);
		}
	}

	uint32_t r2 = 0;
	uint8_t r3 = 0; // Accumulator
	uint8_t r4 = 0; // Test byte
	for (r2 = 0; r2 < (romsize-1); r2++) {
		read(f, &r4, 1);
		if (out) {
			write(out, &r4, 1);
		}
		uint8_t tmp = r3 >> 7;
		r3 = (r3 << 1) | tmp;
		r3 = r3 + r4;
	}

	uint8_t cs;
	read(f, &cs, 1);

	printf("Current checksum:    0x%02x\n", cs);
	printf("Calculated checksum: 0x%02x\n", r3);

	if (out) {
		write(out, &r3, 1);
		close(out);
	}
	close(f);

	return !(r3 == cs);
}