#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_LOADI,
	OP_STORE,
	OP_STOREI,

	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;
unsigned char mem[65536];

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

inline unsigned short WORD() { vm_pc += 2; return vm_program[vm_pc - 2] + (vm_program[vm_pc - 1] << 8); }

void vm_step() {
	char val;
	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: stack_push(vm_datastack, mem[WORD()]); vm_cycles++; break;
	case OP_LOADI: stack_push(vm_datastack, mem[WORD() + stack_pop(vm_datastack)]); vm_cycles++; break;
	case OP_STORE: mem[WORD()] = stack_pop(vm_datastack); vm_cycles++; break;
	case OP_STOREI: val = stack_pop(vm_datastack); mem[WORD() + stack_pop(vm_datastack)] = val; vm_cycles++; break;
	case OP_JMP: vm_pc = WORD(); vm_cycles++; break;
	case OP_JNT: if (stack_pop(vm_datastack) == 0) { vm_pc = WORD(); } vm_cycles++; break;
	case OP_JTR: if (stack_pop(vm_datastack) != 0) { vm_pc = WORD(); } vm_cycles++; break;
	case OP_JSR: stack_push(vm_callstack, vm_pc+2); vm_pc = WORD(); vm_cycles++; break;
	case OP_RET: vm_pc = stack_pop(vm_callstack); vm_cycles++; break;
	case OP_CALL: external_calls[vm_program[vm_pc++]](vm_datastack); vm_cycles++; break;
	case OP_ADD: stack_push(vm_datastack, stack_pop(vm_datastack) + stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_SUB: stack_push(vm_datastack, stack_pop(vm_datastack) - stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_MUL: stack_push(vm_datastack, stack_pop(vm_datastack) * stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_DIV: stack_push(vm_datastack, stack_pop(vm_datastack) / stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_MOD: stack_push(vm_datastack, stack_pop(vm_datastack) % stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_AND: stack_push(vm_datastack, stack_pop(vm_datastack) & stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_OR: stack_push(vm_datastack, stack_pop(vm_datastack) | stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_NOT: stack_push(vm_datastack, !stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_NEG: stack_push(vm_datastack, -stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_INC: stack_push(vm_datastack, stack_pop(vm_datastack)+1); vm_cycles++; break;
	case OP_EQ: stack_push(vm_datastack, stack_pop(vm_datastack) == stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_NEQ: stack_push(vm_datastack, stack_pop(vm_datastack) != stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_LT: stack_push(vm_datastack, stack_pop(vm_datastack) < stack_pop(vm_datastack)); vm_cycles++; break;
	case OP_GT: stack_push(vm_datastack, stack_pop(vm_datastack) > stack_pop(vm_datastack)); vm_cycles++; break;
	}
}

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