#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>

/*
   0000 0000 0000 0000 0000 0000 0000 0000
   rc         topscore  botflag. botscore.
     topflag x         x

   0000 0000 0000 0000 0000 0000 0000 0000
   xd4. d3.d 2.d1 .d0. prng state.... ....
*/

typedef struct {
	uint8_t topflag_w_roll;
	uint8_t topscore;
	uint8_t botflag;
	uint8_t botscore;
	uint16_t dice;
	uint16_t seed;
} ytz_state;

/* ROLLS */
#define GET_ROLL(s) ((uint8_t)((s & 0xC0) >> 6))  /* top 2 bits */
#define SET_ROLL(s, x) (s & 0x3F | ((uint8_t)x << 6))

/* TOP NUMBERS */
#define GET_NUM(s, x) ((uint8_t)((s & (1 << x)) >> x))
#define GET_ACE(s) (GET_NUM(s, 0))
#define GET_TWO(s) (GET_NUM(s, 1))
#define GET_THREE(s) (GET_NUM(s, 2))
#define GET_FOUR(s) (GET_NUM(s, 3))
#define GET_FIVE(s) (GET_NUM(s, 4))
#define GET_SIX(s) (GET_NUM(s, 5))

#define SET_NUM(s, x) (s | (1 << x))
#define SET_ACE(s) (SET_NUM(s, 0))
#define SET_TWO(s) (SET_NUM(s, 1))
#define SET_THREE(s) (SET_NUM(s, 2))
#define SET_FOUR(s) (SET_NUM(s, 3))
#define SET_FIVE(s) (SET_NUM(s, 4))
#define SET_SIX(s) (SET_NUM(s, 5))

/* DICE */
#define GET_D(s, x) ((uint8_t)((s & (0x07 << (3 * x))) >> (3 * x)))
#define GET_D0(s) (GET_D(s, 0))
#define GET_D1(s) (GET_D(s, 1))
#define GET_D2(s) (GET_D(s, 2))
#define GET_D3(s) (GET_D(s, 3))
#define GET_D4(s) (GET_D(s, 4))

#define SET_D(s, x, y) (s & (0xFFFF ^ (0x0007 << (3 * x))) | (y << (3 * x)))
#define SET_D0(s, y) (SET_D(s, 0, y))
#define SET_D1(s, y) (SET_D(s, 1, y))
#define SET_D2(s, y) (SET_D(s, 2, y))
#define SET_D3(s, y) (SET_D(s, 3, y))
#define SET_D4(s, y) (SET_D(s, 4, y))

/* 16-bit prng, with thanks/apologies to Dr. Lemire (https://lemire.me/blog/2019/07/03/a-fast-16-bit-random-number-generator/) */
uint32_t hash16(uint32_t input, uint32_t key) {
	uint32_t hash = input * key;
	return ((hash >> 16) ^ hash) & 0xFFFF;
}

uint16_t wyhash16(uint16_t* seed) {
	*seed += 0xfc15;
	return hash16(*seed, 0x2ab);
}

uint16_t roll_die(uint16_t* seed) {
	const uint16_t s = 6;  /* generating in the range of [0,6) */
	uint16_t x = wyhash16(seed);
	uint32_t m = (uint32_t)x * (uint32_t)s;  
	uint32_t l = (uint16_t)m;
	if (l < s) {
		uint16_t t = -s % s;
		while (l < t) {
			x = wyhash16(seed);
			m = (uint32_t)x * (uint32_t)s;
			l = (uint16_t)m;
		}
	}
	return (m >> 16) + 1;  /* we ultimately want [1,7) */
}

void print_dice(ytz_state* state) {
	char* label = "die %d ";
	char* top = ",---,";
	char* mid = "| %d | ";
	char* bot = "'---'";

	for (int i = 0; i < 5; i++)
		printf(label, i);
	printf("\n%s %s %s %s %s\n", top, top, top, top, top);
	for (int i = 0; i < 5; i++)
		printf(mid, GET_D(state->dice, i));
	printf("\n%s %s %s %s %s\n", bot, bot, bot, bot, bot);
}

void ask_for_rerolls(ytz_state* state) {
	char buf[10];
	printf("which dice should be re-rolled? ");
	fgets(buf, sizeof(buf), stdin);

	int dice[6] = { -1, -1, -1, -1, -1, -1 }; /* we only ever look for 5 dice, so should always hit -1 at some point */
	sscanf(buf, "%d %d %d %d %d", &dice[0], &dice[1], &dice[2], &dice[3], &dice[4]);

	for (int i = 0; i < 5; i++) {
		if (dice[i] == -1)
			break;
		state->dice = SET_D(state->dice, dice[i], 0);
	}
}

void do_turn(ytz_state* state) {
	int roll = GET_ROLL(state->topflag_w_roll);
	bool reset = false;

	// if we're out of rolls, reset
	if (roll == 3) {
		reset = true;
		roll = 0;
	}

	for (int i = 0; i < 5; i++) {
		if (reset || (GET_D(state->dice, i) == 0)) {
			state->dice = SET_D(state->dice, i, roll_die(&(state->seed)));
		}
	}
	state->topflag_w_roll = SET_ROLL(state->topflag_w_roll, ++roll);
}

void init_ytz_state(ytz_state* state) {
	state->topflag_w_roll = 0;
	state->topscore = 0;
	state->botflag = 0;
	state->botscore = 0;
	state->dice = 0;
	state->seed = 13;  /* TODO this isn't random */
}

void main() {
	ytz_state y;
	init_ytz_state(&y);

	/*
	 * until the win condition is met
	 *  - roll all dice
	 *  - up to 2 times, ask user which dice to reroll
	 *  - ask user which category to mark it in
	 *  - validate and update state
	 *
	 *
	 */

	do_turn(&y);

	printf("new roll: %d\n", GET_ROLL(y.topflag_w_roll));
	printf("new d1: %d\n", GET_D0(y.dice));
	printf("new d2: %d\n", GET_D1(y.dice));
	printf("new d3: %d\n", GET_D2(y.dice));
	printf("new d4: %d\n", GET_D3(y.dice));
	printf("new d5: %d\n", GET_D4(y.dice));

	print_dice(&y);
	
	ask_for_rerolls(&y);
	do_turn(&y);
	printf("newer roll: %d\n", GET_ROLL(y.topflag_w_roll));
	printf("newer d1: %d\n", GET_D0(y.dice));
	printf("newer d2: %d\n", GET_D1(y.dice));
	printf("newer d3: %d\n", GET_D2(y.dice));
	printf("newer d4: %d\n", GET_D3(y.dice));
	printf("newer d5: %d\n", GET_D4(y.dice));
}