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

void fail(char *error) {
	fprintf(stderr, "%s\n", error);
	exit(1);
}

int main(int argc, char **argv) {
	FILE *f;
	unsigned char buffer[1024];
	long int sample_size[31];
	int num_samples;
	int num_channels;
	int num_patterns;
	int total_sample = 0;
	long int expected_size;
	int i, n;

	if (argc < 2) {
		fprintf(stderr, "usage: conv4-8 <file>\n");
		exit(1);
	}

	f = fopen(argv[1], "rb");
	if (!f)
		fail("can't open file");

	fprintf(stderr, "converting module...\n");
	fseek(f, 1080, SEEK_SET);
	if (fread(buffer, 1, 4, f) < 4)
		fail("seek failed");
	buffer[4] = '\0';
	if(!strcmp(buffer, "M.K.") || !strcmp(buffer, "M!K!")) {
		num_samples = 31;
	} else {
		num_samples = 15;
	}
	num_channels = 4;
	fprintf(stderr, "number of samples     : %i\n", num_samples);
	fprintf(stderr, "number of channels    : %i\n", num_channels);

	fseek(f, 0, SEEK_SET);
	if (fread(buffer, 1, 20, f) < 20)
		fail("seek failed : song name");
	fwrite(buffer, 1, 20, stdout);
	for (i = 0; i < num_samples; i++) {
		if (fread(buffer, 1, 30, f) < 30)
			fail("read error : sample info");
		sample_size[i] = (buffer[22] << 8) | buffer[23];
		total_sample += sample_size[i];
		fwrite(buffer, 1, 30, stdout);
	}

	fprintf(stderr, "total sample size     : %i (%i)\n", total_sample, total_sample*2);

	i = 130 + ((num_channels > 15) ? 4 : 0);
	if (fread(buffer, 1, i, f) < i)
		fail("read error : song info");
	fwrite(buffer, 1, i, stdout);
	
	num_patterns = buffer[2];
	for (i = 3; i < 130; i++) {
		if (buffer[i] > num_patterns) {
			num_patterns = buffer[i];
		}
	}
	num_patterns++;

	fprintf(stderr, "number of patterns    : %i\n", num_patterns);

	expected_size = 20 + (30*num_samples) + 130 + (num_samples>15?4:0) + (num_patterns*64*4*num_channels) + total_sample;
	fprintf(stderr, "expected size (4-bit) : %li\n", expected_size);
	expected_size = 20 + (30*num_samples) + 130 + (num_samples>15?4:0) + (num_patterns*64*4*num_channels) + total_sample*2;
	fprintf(stderr, "expected size (8-bit) : %li\n", expected_size);

	for (i = 0; i < num_patterns; i++) {
		int j = 64 * 4 * num_channels;
		while (j > 0) {
			int k = j > 1024 ? 1024 : j;
			if (fread(buffer, 1, k, f) < k)
				fail("read error : pattern data");
			fwrite(buffer, 1, k, stdout);
			j -= k;
		}
	}

	/* first half of the sample data */
	n = ftell(f);
	while(!feof(f)) {
		int j = fread(buffer, 1, 1024, f);
		for(i = 0; i < j; i++)
			buffer[i] = buffer[i] & 0xf0;
		fwrite(buffer, 1, j, stdout);
	}

	/* second half */
	fseek(f, n, SEEK_SET);
	while(!feof(f)) {
		int j = fread(buffer, 1, 1024, f);
		for(i = 0; i < j; i++)
			buffer[i] = (buffer[i] & 0x0f) << 4;
		fwrite(buffer, 1, j, stdout);
	}

	fprintf(stderr, "actual size (input)   : %li\n", ftell(f));
	fprintf(stderr, "actual size (output)  : %li\n", ftell(stdout));
	fprintf(stderr, "done\n");
	fclose(f);
	return 0;
}