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

enum overture_mode {
	IMMEDIATE,
	CALCULATE,
	COPY,
	CONDITION
};

enum overture_calculate_mode {
	OR,
	NAND,
	NOR,
	AND,
	ADD,
	SUB
};

enum overture_condition_mode {
	NEVER,
	EQZ,
	LTZ,
	LTEQZ,
	ALWAYS,
	NEQZ,
	GTEQZ,
	GTZ
};

enum overture_registers {
	R0,
	R1,
	R2,
	R3,
	R4,
	R5,
	INPUT_OUTPUT
};

void overture_immediate(uint8_t immediate, uint8_t* r0) {
	*r0 = immediate;
}

void overture_alu_calculate(enum overture_calculate_mode mode, uint8_t r1, uint8_t r2, uint8_t* r3) {
	switch (mode) {
		case OR:	
			*r3 = r1 | r2;
			break;
		case NAND:
			*r3 = ~(r1 & r2);
			break;
		case NOR:
			*r3 = ~(r1 | r2);	
			break;
		case AND:
			*r3 = r1 & r2;	
			break;
		case ADD:
			*r3 = r1 + r2;
			break;
		case SUB:
			*r3 = r1 - r2;	
			break;
	}
};

void overture_register_copy(uint8_t* source, uint8_t* destination) {
	*destination = *source;
};

void overture_condition_jump(enum overture_condition_mode mode, uint8_t r0, uint8_t r3, uint8_t* program_counter) {
	switch (mode) {
		case NEVER:
			return;
		case EQZ:
			if (r3 == 0)
				*program_counter = r0;
			break;
		case LTZ:
			if (r3 < 0)
				*program_counter = r0;
			break;
		case LTEQZ:
			if (r3 <= 0)
				*program_counter = r0;
			break;
		case ALWAYS:
			*program_counter = r0;
			break;
		case NEQZ:
			if (r3 != 0)
				*program_counter = r0;
			break;
		case GTEQZ:
			if (r3 >= 0)
				*program_counter = r0;
			break;
		case GTZ:
			if (r3 > 0)
				*program_counter = r0;
			break;
	};
}

typedef union overture_instruction {
	uint8_t instruction;
	union {
		struct {
			uint8_t combined_immediate : 6;
			uint8_t overture_mode : 2;
		};
		struct {
			uint8_t right_operand : 3;
			uint8_t left_operand : 3;
		};
	};
} overture_instruction;

void overture_fetch_instruction(uint8_t program_counter, uint8_t* current_instruction, uint8_t rom[256]) {
	*current_instruction = rom[program_counter - 1];
}

typedef struct overture {
	bool step_mode;
	int clock_speed_hz;
	uint8_t program_counter;

	uint8_t r0;
	uint8_t r1;
	uint8_t r2;
	uint8_t r3;
	uint8_t r4;
	uint8_t r5;

	uint8_t input;
	uint8_t output;
	bool output_enable;

	overture_instruction current_instruction;
} overture;

void sleep_hz(int hz) {
	usleep(1000000 / hz);
};

uint8_t* multiplex_source(uint8_t operand, overture* cpu) {
	uint8_t* source;

	switch (operand) {
		case R0:
			source = &(cpu->r0);
			break;
		case R1:
			source = &(cpu->r1);
			break;
		case R2:
			source = &(cpu->r2);
			break;
		case R3:
			source = &(cpu->r3);
			break;
		case R4:
			source = &(cpu->r4);
			break;
		case R5:
			source = &(cpu->r5);
			break;
		case INPUT_OUTPUT:
			source = &(cpu->input);
			break;
	}

	return source;
}

uint8_t* multiplex_destination(uint8_t operand, overture* cpu) {
	uint8_t* destination;

	switch (operand) {
		case R0:
			destination = &(cpu->r0);
			break;
		case R1:
			destination = &(cpu->r1);
			break;
		case R2:
			destination = &(cpu->r2);
			break;
		case R3:
			destination = &(cpu->r3);
			break;
		case R4:
			destination = &(cpu->r4);
			break;
		case R5:
			destination = &(cpu->r5);
			break;
		case INPUT_OUTPUT:
			destination = &(cpu->output);
			break;
	}

	return destination;
}

void overture_execute_instruction(overture_instruction instruction, overture* cpu) {
	uint8_t* source_register = multiplex_source(instruction.left_operand, cpu);
	uint8_t* destination_register = multiplex_destination(instruction.right_operand, cpu);

	switch (instruction.overture_mode) {
		case IMMEDIATE:
			overture_immediate(instruction.combined_immediate, &(cpu->r0));
			break;
		case CALCULATE:
			overture_alu_calculate(instruction.right_operand, cpu->r1, cpu->r2, &(cpu->r3));
			break;
		case COPY:
			overture_register_copy(source_register, destination_register);

			if (instruction.right_operand == INPUT_OUTPUT) {
				cpu->output_enable = true;
			}
			break;
		case CONDITION:
			overture_condition_jump(instruction.right_operand, cpu->r0, cpu->r3, &(cpu->program_counter));
			break;
	};
}

void cpu_diagnostics(overture* cpu) {
	if (cpu->step_mode) {
		printf("Step mode\n");
	} else {
		printf("Clock speed: %dhz\n", cpu->clock_speed_hz);
	}
	printf("Program counter: %d\n\n", cpu->program_counter);

	printf("r0: %d\n", cpu->r0);
	printf("r1: %d\n", cpu->r1);
	printf("r2: %d\n", cpu->r2);
	printf("r3: %d\n", cpu->r3);
	printf("r4: %d\n", cpu->r4);
	printf("r5: %d\n\n", cpu->r5);

	printf("input: %d\n", cpu->input);
	printf("output: %d\n", cpu->output);
	printf("Output enabled?: %d\n\n", cpu->output_enable);

	printf("Current instruction: %d\n", cpu->current_instruction.instruction);
	printf("Mode: %d\n", cpu->current_instruction.overture_mode);
	printf("Left Operand: %d\n", cpu->current_instruction.left_operand);
	printf("Right Operand: %d\n", cpu->current_instruction.right_operand);
	printf("Combined Immediate: %d\n\n", cpu->current_instruction.combined_immediate);
}

void overture_cycle(overture* cpu, uint8_t rom[256]) {
	if (cpu->program_counter == 255) {
		cpu->program_counter = 0;
	};
	cpu->program_counter += 1;
	cpu->output_enable = false;
	overture_fetch_instruction(cpu->program_counter, &(cpu->current_instruction.instruction), rom);

	overture_execute_instruction(cpu->current_instruction, cpu);

	cpu_diagnostics(cpu);
}

void overture_start_clock(overture* cpu, uint8_t rom[256]) {
	while (true) {
		if (cpu->step_mode) {
			getchar();
		} else {
			sleep_hz(cpu->clock_speed_hz);
		}

		overture_cycle(cpu, rom);
	};
}

int main() {
	uint8_t rom[256] = { 63, 129, 7, 130, 68 , 158 };
	overture cpu = {
		.step_mode = true,
		.clock_speed_hz = 1,
		.program_counter = 0,

		.r0 = 0,
		.r1 = 0,
		.r2 = 0,
		.r3 = 0,
		.r4 = 0,
		.r5 = 0,

		.input = 0,
		.output = 0,
		.output_enable = true,

		.current_instruction.instruction = 0
	};

	overture_start_clock(&cpu, rom);

	return 0;
}