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


#define MATH_OP(vmblState, operation)                                                                                                                             \
	do {                                                                                                												          \
		if ((vmblState)->stackSize < 2) {						 																					         	  \
			return (VMBL_Exception){ EXCEPTION_STACK_UNDERFLOW };	                                                                                              \
		 }										  													   										   								  													  						  													   								  													   								  													   								  													   \
		(vmblState)->stack[(vmblState)->stackSize - 2] = (vmblState)->stack[(vmblState)->stackSize - 2] operation (vmblState)->stack[(vmblState)->stackSize - 1]; \
		(vmblState)->stackSize--;                                                                     													          \
	} while (0);



VMBL_Exception VBML_ExecuteInstruction(VMBL_State *vmblState, VMBL_Instruction instruction) {
	switch (instruction.type)
	{
	case INSTRUCTION_PUSH:
		if (vmblState->stackSize >= VMBL_STACK_SIZE) {
			return (VMBL_Exception){ EXCEPTION_STACK_OVERFLOW };
		}

		vmblState->stack[vmblState->stackSize++] = instruction.opperands[0];
		break;
	
	case INSTRUCTION_ADD:
		MATH_OP(vmblState, +);
		break;
	case INSTRUCTION_SUB:
		MATH_OP(vmblState, -);
		break;
	case INSTRUCTION_MUL:
		MATH_OP(vmblState, *);
		break;
	case INSTRUCTION_DIV:
		if (vmblState->stack[vmblState->stackSize-1] == 0) {
			return (VMBL_Exception){ EXCEPTION_DIVIDE_BY_ZERO };
		}

		MATH_OP(vmblState, /);
		break;

	case INSTRUCTION_DUPLICATE:
		if (vmblState->stackSize - instruction.opperands[0] <= 0) {
			return (VMBL_Exception){ EXCEPTION_STACK_UNDERFLOW };
		}

		if (vmblState->stackSize >= VMBL_STACK_SIZE) {
			return (VMBL_Exception){ EXCEPTION_STACK_OVERFLOW };
		}
		
		if (instruction.opperands[0] < 0) {
			return (VMBL_Exception) { EXCEPTION_INVALID_OPPERAND };
		}
		
		vmblState->stack[vmblState->stackSize++] = vmblState->stack[vmblState->stackSize - 1 - instruction.opperands[0]];

		break;

	case INSTRUCTION_JUMP:

		vmblState->ip = instruction.opperands[0];

		break;

	case INSTRUCTION_HALT:
		vmblState->halted = true;
		break;

	case INSTRUCTION_EQUAL:
		MATH_OP(vmblState, ==);
		break;

	case INSTRUCTION_JUMP_CONDITIONAL:
		if (instruction.opperands[0] < 0) {
			return (VMBL_Exception) { EXCEPTION_INVALID_OPPERAND };
		}

		if (vmblState->stack[vmblState->stackSize--]) {
			vmblState->ip = instruction.opperands[0];
		}
		break;

	case INSTRUCTION_DROP:
		if (vmblState->stackSize <= 0) {
			return (VMBL_Exception){ EXCEPTION_STACK_UNDERFLOW };
		}

		vmblState->stackSize--;

		break;

	default:
		return (VMBL_Exception) { EXCEPTION_INVALID_OPCODE };
		break;
	}

	return (VMBL_Exception) { EXCEPTION_NONE };
}

void VMBL_Dump(VMBL_State vmblState, VMBL_Exception exception) {
	fprintf(stderr, "EXCEPTION: %s\n\n", exceptionAsCString(exception));
	fprintf(stderr, "Stack:\n");

	if (vmblState.stackSize > 0) {
		for (size_t i = 0; i < vmblState.stackSize; i++) {
				fprintf(stderr, "    0x%lX: %ld\n", i, vmblState.stack[i]);
		}
	} else {
		fprintf(stderr, "    [empty]\n");
	}
	
}

void VMBL_StartVM(VMBL_State *vmblState) {
	for (;;)
	{
		// fetch next instruction
		if (vmblState->ip >= VMBL_PROGRAM_SIZE) {
			VMBL_Dump(*vmblState, (VMBL_Exception){ EXCEPTION_INVALID_INSTRUCTION_ACCESS});
			return;
		}

		
		VMBL_Instruction instruction = vmblState->program[vmblState->ip++];
		printf("%s 0x%lx, 0x%lx, 0x%lx\n", instructionTypeToCStr(instruction.type), instruction.opperands[0], instruction.opperands[1], instruction.opperands[2]);
		
		VMBL_Exception exception = VBML_ExecuteInstruction(vmblState, instruction);

		if (exception.type != EXCEPTION_NONE) {
			VMBL_Dump(*vmblState, exception);
			return;
		}

		if (vmblState->halted) {
			return;
		}
		 
	}
	
}


// executable operations
void VMBL_LoadExecutable(VMBL_State *vmblState, VMBL_Instruction *program, size_t programSize) {
	if (programSize > VMBL_PROGRAM_SIZE) {
		fprintf(stderr, "VMBL: failed to load program from memory because it is %ld words in size, while the max size is %d.", programSize, VMBL_PROGRAM_SIZE);
		exit(1);
	}

	memcpy(&vmblState->program, program, programSize);

	vmblState->programSize = programSize;
}

void VMBL_LoadExecutableFromFile(VMBL_State *vmblState, const char* filePath) {
	FILE *file = fopen(filePath, "rb");

	if (file == NULL) {
		perror("VMBL: Failed to open file");
		exit(1);
	}

	fseek(file, 0, SEEK_END);
	long size = ftell(file);
	rewind(file);

	size_t programSize = size / sizeof(vmblState->program[0]);
	VMBL_Instruction program[programSize];
	fread(program, sizeof(program[0]), programSize, file);

	VMBL_LoadExecutable(vmblState, program, programSize);

	fclose(file);
	
}

void VMBL_SaveExecutable(const char* filePath, VMBL_Instruction *program, size_t programSize) {
	FILE *file = fopen(filePath, "wb");

	if (file == NULL) {
		perror("VMBL: Failed to open file");
		exit(1);
	}

	fwrite(program, sizeof(program), programSize, file);
	fclose(file);
}

char *instructionTypeToCStr(InstructionType type) {
	printf("%x\n", type);
	switch (type)
	{

	case INSTRUCTION_PUSH:
		return "PUSH";
		break;

	case INSTRUCTION_ADD:
		return "ADD ";
		break;
	case INSTRUCTION_SUB:
		return "SUB ";
		break;
	case INSTRUCTION_MUL:
		return "MUL ";
		break;
	case INSTRUCTION_DIV:
		return "DIV ";
		break;

	case INSTRUCTION_DUPLICATE:
		return "DUP ";
		break;
		
	case INSTRUCTION_JUMP:
		return "JMP ";
		break;

	case INSTRUCTION_HALT:
		return "HALT";
		break;

	case INSTRUCTION_EQUAL:
		return "EQ  ";
		break;
	case INSTRUCTION_NOT_EQUAL:
		return "NEQ  ";
		break;
	case INSTRUCTION_GREATER_THAN:
		return "GT  ";
		break;
	case INSTRUCTION_GREATER_THAN_EQUAL:
		return "GTE ";
		break;
	case INSTRUCTION_LESS_THAN:
		return "LT  ";
		break;
	case INSTRUCTION_LESS_THAN_EQUAL:
		return "LTE ";
		break;

	case INSTRUCTION_JUMP_CONDITIONAL:
		return "JC  ";
		break;
	
	default:
		return "??? ";
		break;
	}
}