#ifndef LAIKA_VM_H
#define LAIKA_VM_H

/* Laika VM:
        This is an obfuscation technique where vital code can be executed in a
    stack-based VM, inlined into the function. The VM instruction-set is fairly
    simple, see the OP_* enum for avaliable opcodes and their expected arguments.
    The VM is turing-complete, however the instruction-set has been curated to
    fit this specific use case.
*/

#include "core/lerror.h"
#include "laika.h"

#include <inttypes.h>

#define LAIKA_VM_STACKSIZE 64
#define LAIKA_VM_CONSTSIZE 32

struct sLaikaV_vm_val
{
    union
    {
        uint8_t i;
        uint8_t *ptr;
    };
};

struct sLaikaV_vm
{
    struct sLaikaV_vm_val stack[LAIKA_VM_STACKSIZE];
    struct sLaikaV_vm_val constList[LAIKA_VM_CONSTSIZE];
    uint8_t code[LAIKA_VM_CODESIZE];
    int pc;
};

#define LAIKA_MAKE_VM(_consts, _code)                                                              \
    {                                                                                              \
        .constList = _consts, .code = _code, .pc = 0, .stack = { 0 }                               \
    }

/* constants */
#define LAIKA_MAKE_VM_INT(_i)                                                                      \
    {                                                                                              \
        .i = _i                                                                                    \
    }
#define LAIKA_MAKE_VM_PTR(_ptr)                                                                    \
    {                                                                                              \
        .ptr = _ptr                                                                                \
    }
/* instructions */
#define LAIKA_MAKE_VM_IA(opcode, a)         opcode, a
#define LAIKA_MAKE_VM_IAB(opcode, a, b)     opcode, a, b
#define LAIKA_MAKE_VM_IABC(opcode, a, b, c) opcode, a, b, c

enum
{
    OP_EXIT,
    OP_LOADCONST, /* stk_indx[uint8_t] = const_indx[uint8_t] */
    OP_PUSHLIT,   /* stk_indx[uint8_t].i = uint8_t */
    OP_READ,      /* stk_indx[uint8_t].i = *(int8_t*)stk_indx[uint8_t] */
    OP_WRITE,     /* *(uint8_t*)stk_indx[uint8_t].ptr = stk_indx[uint8_t].i */
    OP_INCPTR,    /* stk_indx[uint8_t].ptr++ */
    OP_DECPTR,    /* stk_indx[uint8_t].ptr-- */

    /* arithmetic */
    OP_ADD, /* stk_indx[uint8_t] = stk_indx[uint8_t] + stk_indx[uint8_t] */
    OP_SUB, /* stk_indx[uint8_t] = stk_indx[uint8_t] - stk_indx[uint8_t] */
    OP_MUL, /* stk_indx[uint8_t] = stk_indx[uint8_t] * stk_indx[uint8_t] */
    OP_DIV, /* stk_indx[uint8_t] = stk_indx[uint8_t] / stk_indx[uint8_t] */
    OP_AND, /* stk_indx[uint8_t] = stk_indx[uint8_t] & stk_indx[uint8_t] */
    OP_OR,  /* stk_indx[uint8_t] = stk_indx[uint8_t] | stk_indx[uint8_t] */
    OP_XOR, /* stk_indx[uint8_t] = stk_indx[uint8_t] ^ stk_indx[uint8_t] */

    /* control-flow */
    OP_TESTJMP, /* if stk_indx[uint8_t] != 0, pc += [int8_t] */

    /* misc. */
#ifdef DEBUG
    OP_DEBUG
#endif
};

LAIKA_FORCEINLINE void laikaV_execute(struct sLaikaV_vm *vm)
{

#define READBYTE (vm->code[vm->pc++])
#define BINOP(x)                                                                                   \
    {                                                                                              \
        uint8_t a = READBYTE;                                                                      \
        uint8_t b = READBYTE;                                                                      \
        uint8_t c = READBYTE;                                                                      \
        vm->stack[a].i = vm->stack[b].i x vm->stack[c].i;                                          \
        break;                                                                                     \
    }

    while (vm->code[vm->pc]) {
        switch (vm->code[vm->pc++]) {
        case OP_LOADCONST: {
            uint8_t indx = READBYTE;
            uint8_t constIndx = READBYTE;
            vm->stack[indx] = vm->constList[constIndx];
            break;
        }
        case OP_PUSHLIT: {
            uint8_t indx = READBYTE;
            uint8_t lit = READBYTE;
            vm->stack[indx].i = lit;
            break;
        }
        case OP_READ: {
            uint8_t indx = READBYTE;
            uint8_t ptr = READBYTE;
            vm->stack[indx].i = *vm->stack[ptr].ptr;
            break;
        }
        case OP_WRITE: {
            uint8_t ptr = READBYTE;
            uint8_t indx = READBYTE;
            *vm->stack[ptr].ptr = vm->stack[indx].i;
            break;
        }
        case OP_INCPTR: {
            uint8_t ptr = READBYTE;
            vm->stack[ptr].ptr++;
            break;
        }
        case OP_DECPTR: {
            uint8_t ptr = READBYTE;
            vm->stack[ptr].ptr--;
            break;
        }
        case OP_ADD:
            BINOP(+);
        case OP_SUB:
            BINOP(-);
        case OP_MUL:
            BINOP(*);
        case OP_DIV:
            BINOP(/);
        case OP_AND:
            BINOP(&);
        case OP_OR:
            BINOP(|);
        case OP_XOR:
            BINOP(^);
        case OP_TESTJMP: {
            uint8_t indx = READBYTE;
            int8_t jmp = READBYTE;

            /* if stack indx is true, jump by jmp (signed 8-bit int) */
            if (vm->stack[indx].i)
                vm->pc += jmp;

            break;
        }
#ifdef DEBUG
        case OP_DEBUG: {
            int i;

            /* print stack info */
            for (i = 0; i < LAIKA_VM_STACKSIZE; i++)
                printf("[%03d] - 0x%02x\n", i, vm->stack[i].i);

            break;
        }
#endif
        default:
            LAIKA_ERROR("laikaV_execute: unknown opcode [0x%02x]! pc: %d\n", vm->code[vm->pc],
                        vm->pc);
        }
    }

#undef READBYTE
#undef BINOP
}

#endif