/*
	Compile with:
	g++ -std=c++11 get_seed.c -o get_seed
*/

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <random>
#include <string>

const char *g_charSet = "ABCDEFGHJKLMNPQRSTWXYZ01234V6789";
unsigned char g_charLookup[256];

void initCharLookup() {
	memset(g_charLookup, 0xFF, sizeof(g_charLookup));

	int i = 0;
	for (const char *p = g_charSet; *p; ++p, ++i) {
		g_charLookup[*p] = i;
	}
}

unsigned int string2seed(const std::string &str) {
	int n = str.size();

	// Must be 9 character long
	if (n != 9) {
		return 0;
	}

	// 5th character must be a whitespace
	if (str[4] != ' ') {
		return 0;
	}

	// Convert into a 64-bit seed
	unsigned char bytes[8];
	for(int i = 0; i < 9; ++i) {
		if (i == 4) {
			continue;
		}

		int j;
		if (i > 4) {
			j = i - 1;
		} else {
			j = i;
		}
		unsigned char b = g_charLookup[(unsigned char)str[i]];

		// Invalid character
		if (b == 0xFF) {
			return 0;
		}

		bytes[j] = b;
	}

	// Reduce to 32 bits
	unsigned int r0 = bytes[0];
	r0 = (r0 << 5) | bytes[1];
	r0 = (r0 << 5) | bytes[2];
	r0 = (r0 << 5) | bytes[3];
	r0 = (r0 << 5) | bytes[4];
	r0 = (r0 << 5) | bytes[5];
	r0 = (r0 << 2) | (bytes[6] >> 3);
	r0 ^= 0xFEF7FFD;

	unsigned int r = r0;
	unsigned int d = 0;

	while (r != 0) {
		d = (r + d) & 0xFF;
		d = ((d >> 7) + (d << 1)) & 0xFF;
		r >>= 5;
	}

	if (d == (bytes[7] | ((bytes[6] << 5) & 0xFF))) {
		return r0;
	} else {
		return 0;
	}
}

std::string seed2string(unsigned int seed) {
	// Expand to 64 bits
	unsigned int r = seed;
	unsigned int d = 0;
	while(r != 0) {
		d = (r + d) & 0xFF;
		d = ((d >> 7) + (d << 1)) & 0xFF;
		r >>= 5;
	}

	unsigned char bytes[8];
	seed ^= 0xFEF7FFD;
	bytes[0] = (seed >> 27) & 0x1F;
	bytes[1] = (seed >> 22) & 0x1F;
	bytes[2] = (seed >> 17) & 0x1F;
	bytes[3] = (seed >> 12) & 0x1F;
	bytes[4] = (seed >> 7 ) & 0x1F;
	bytes[5] = (seed >> 2 ) & 0x1F;
	bytes[6] = ((d | (seed << 8)) >> 5) & 0x1F;
	bytes[7] = d & 0x1F;

	// Convert into valid seed characters
	std::string out = "0000 0000";

	for (int i = 0; i < 9; ++i) {
		if (i == 4) {
			continue;
		}

		int j;
		if (i > 4) {
			j = i - 1;
		} else {
			j = i;
		}
		out[i] = g_charSet[bytes[j]];
	}

	return out;
}

int main(int argc, char *argv[]) {
	initCharLookup();

	std::default_random_engine gen(time(NULL));
	std::uniform_int_distribution<unsigned int> dist;

	unsigned int seed = dist(gen);
	printf("%s\n", seed2string(seed).c_str());

	return 0;
}