#include "vm.h"

#define MAX_EXTERNAL_CALLS	256
#define MAX_DATA_STACK		256
#define MAX_CALL_STACK		256

enum OPS {
	OP_NOP = 0,
	OP_PUSH,
	OP_POP,
	OP_DUP,

	OP_LOAD,
	OP_STORE,

	OP_JMP,
	OP_JNT,
	OP_JTR,
	OP_JSR,
	OP_RET,
	OP_CALL,

	OP_ADD,
	OP_SUB,
	OP_MUL,
	OP_DIV,
	OP_MOD,
	OP_AND,
	OP_OR,
	OP_NOT,
	OP_NEG,
	OP_INC,

	OP_EQ,
	OP_NEQ,
	OP_LT,
	OP_GT
};

typedef void(*t_extcall)(t_stack&);
t_extcall external_calls[MAX_EXTERNAL_CALLS];
int numcallbacks = 0;
	
const unsigned char* vm_program = nullptr;
int vm_pc = 0;
int vm_cycles = 0;
t_stack vm_datastack;
t_stack vm_callstack;

void vm_init(const unsigned char* program) {
	vm_program = program;
	vm_pc = 0;
	vm_datastack = stack_new(MAX_DATA_STACK);
	vm_callstack = stack_new(MAX_CALL_STACK);
}


void vm_step() {
	switch (vm_program[vm_pc++]) {
	case OP_NOP: vm_cycles++; break;
	case OP_PUSH: stack_push(vm_datastack, vm_program[vm_pc++]); vm_cycles++; break;
	case OP_POP: stack_pop(vm_datastack); vm_cycles++; break;
	case OP_DUP: stack_push(vm_datastack, stack_peek(vm_datastack)); vm_cycles++; break;
	case OP_LOAD: vm_cycles++; break;
	case OP_STORE: vm_cycles++; break;
	case OP_JMP: vm_pc = vm_program[vm_pc] + (vm_program[vm_pc + 1] << 8);  vm_cycles++; break;
	case OP_JNT: vm_cycles++; break;
	case OP_JTR: vm_cycles++; break;
	case OP_JSR: vm_cycles++; break;
	case OP_RET: vm_cycles++; break;
	case OP_CALL: external_calls[vm_program[vm_pc++]](vm_datastack); vm_cycles++; break;
	case OP_ADD: vm_cycles++; break;
	case OP_SUB: vm_cycles++; break;
	case OP_MUL: vm_cycles++; break;
	case OP_DIV: vm_cycles++; break;
	case OP_MOD: vm_cycles++; break;
	case OP_AND: vm_cycles++; break;
	case OP_OR: vm_cycles++; break;
	case OP_NOT: vm_cycles++; break;
	case OP_NEG: vm_cycles++; break;
	case OP_INC: vm_cycles++; break;
	case OP_EQ: vm_cycles++; break;
	case OP_NEQ: vm_cycles++; break;
	case OP_LT: vm_cycles++; break;
	case OP_GT: vm_cycles++; break;
	}
}

void vm_register_call(void(*callback)(t_stack&)) {
	external_calls[numcallbacks++] = callback;
}