#include "bf_emulator.h"

#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

void bf_emulator_init(struct bf_emulator *emulator, uint32_t cell_size, uint32_t data_len)
{
	assert(cell_size == 8 || cell_size == 16 || cell_size == 32);

	emulator->cell_size = cell_size;
	emulator->data = calloc(data_len, cell_size / 8);
	emulator->data_len = data_len;
}

void bf_emulator_deinit(struct bf_emulator *emulator)
{
	free(emulator->data);
	emulator->data = NULL;
	emulator->data_len = 0;
}

static void bf_emulator_set(struct bf_emulator *emulator, uint32_t index, uint32_t value)
{
	if (emulator->cell_size == 8) {
		((uint8_t*)emulator->data)[index] = value;
	} else if (emulator->cell_size == 16) {
		((uint16_t*)emulator->data)[index] = value;
	} else if (emulator->cell_size == 32) {
		((uint32_t*)emulator->data)[index] = value;
	}
}

static uint32_t bf_emulator_get(struct bf_emulator *emulator, uint32_t index)
{
	if (emulator->cell_size == 8) {
		return ((uint8_t*)emulator->data)[index];
	} else if (emulator->cell_size == 16) {
		return ((uint16_t*)emulator->data)[index];
	} else if (emulator->cell_size == 32) {
		return ((uint32_t*)emulator->data)[index];
	}

	return 0;
}

static void bf_emulator_inc(struct bf_emulator *emulator, uint32_t index)
{
	bf_emulator_set(emulator, index, bf_emulator_get(emulator, index) + 1);
}

static void bf_emulator_dec(struct bf_emulator *emulator, uint32_t index)
{
	bf_emulator_set(emulator, index, bf_emulator_get(emulator, index) - 1);
}

enum bf_step_result bf_emulator_step(struct bf_emulator *emulator)
{
	if (emulator->program_pointer == emulator->program_len) {
		return BF_STEP_FINISHED;
	}

	char inst = emulator->program[emulator->program_pointer];
	switch (inst) {
	case '>':
		emulator->data_pointer = (emulator->data_pointer + 1) % emulator->data_len;
		break;
	case '<':
		emulator->data_pointer = (emulator->data_pointer - 1 + emulator->data_len) % emulator->data_len;
		break;
	case '-':
		bf_emulator_dec(emulator, emulator->data_pointer);
		break;
	case '+':
		bf_emulator_inc(emulator, emulator->data_pointer);
		break;
	case '.':
		putchar(bf_emulator_get(emulator, emulator->data_pointer));
		break;
	case ',':
		bf_emulator_set(emulator, emulator->data_pointer, getchar());
		break;
	case '[':
		if (bf_emulator_get(emulator, emulator->data_pointer) == 0) {
			uint32_t open_blocks = 0;
			while (true) {
				emulator->program_pointer++;
				if (emulator->program_pointer == emulator->program_len) {
					return BF_STEP_ERROR;
				}

				if (emulator->program[emulator->program_pointer] == '[') {
					open_blocks++;
				}
				if (emulator->program[emulator->program_pointer] == ']') {
					if (open_blocks == 0) break;
					open_blocks--;
				}
			}
		}
		break;
	case ']':
		if (bf_emulator_get(emulator, emulator->data_pointer) != 0) {
			uint32_t closing_blocks = 0;
			while (true) {
				if (emulator->program_pointer == 0) {
					return BF_STEP_ERROR;
				}
				emulator->program_pointer--;

				if (emulator->program[emulator->program_pointer] == ']') {
					closing_blocks++;
				}
				if (emulator->program[emulator->program_pointer] == '[') {
					if (closing_blocks == 0) break;
					closing_blocks--;
				}
			}
		}
		break;
	default:
		break;
	};

	emulator->program_pointer++;

	return BF_STEP_OK;
}

enum bf_step_result bf_emulator_continue(struct bf_emulator *emulator)
{
	while (true) {
		enum bf_step_result result = bf_emulator_step(emulator);
		if (result != BF_STEP_OK) {
			return result;
		}
	}
}

enum bf_step_result bf_emulator_run(struct bf_emulator *emulator, const char *program, size_t program_len)
{
	emulator->data_pointer = 0;
	memset(emulator->data, 0, emulator->data_len);

	emulator->program = program;
	emulator->program_len = program_len;
	emulator->program_pointer = 0;

	return bf_emulator_continue(emulator);
}