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#ifndef BDL_VM_H
#define BDL_VM_H

#include "types.h"
#include "errors.h"
#include "chunk.h"
#include "ops.h"
#include "debug.h"

#define VM_STACK_CAP 1024

typedef struct VM {
    // Program code.
    Chunk *chunk;
    // Program counter.
    u8 *pc;
    // Stack.
    Object *stack;
} VM;

void vm_init(VM *vm);
void vm_free(VM *vm);
void vm_reset(VM *vm);
void vm_interpret(VM *vm, Chunk *chunk);

void
vm_init(VM *vm) {
    *vm = (VM){0};
    array_init(vm->stack, VM_STACK_CAP);
}

void
vm_free(VM *vm) {
    array_free(vm->stack);
}

void
vm_reset(VM *vm) {
    vm_free(vm);
    vm_init(vm);
}

void
vm_interpret(VM *vm, Chunk *chunk) {
    vm->chunk = chunk;
    vm->pc = vm->chunk->code;

    if (vm->chunk->code == NULL || array_size(vm->chunk->code) == 0) {
        error_push((Error){
            .type = ERR_TYPE_RUNTIME,
            .value = ERR_EMPTY_CHUNK,
        });
        return;
    }

    u8 *last = vm->chunk->code + array_size(vm->chunk->code);
    while (vm->pc < last) {
#ifdef DEBUG_TRACE_EXECUTION
        printf("stack:  [ ");
        for (size_t i = 0; i < array_size(vm->stack); i++) {
            display(vm->stack[i]);
            if (i < array_size(vm->stack) - 1) {
                printf(" | ");
            }
        }
        printf(" ]\nop: ");
        disassemble_instruction(vm->chunk, (vm->pc - vm->chunk->code));
#endif
        u8 instruction = *vm->pc++;
        switch (instruction) {
            case OP_CONSTANT: {
                u8 constant = *vm->pc++;
                Object obj = vm->chunk->constants[constant];
                array_push(vm->stack, obj);
            } break;
            case OP_SUM: {
                ssize_t a = AS_FIXNUM(array_pop(vm->stack));
                ssize_t b = AS_FIXNUM(array_pop(vm->stack));
                array_push(vm->stack, FIXNUM_VAL(a + b));
            } break;
            case OP_SUB: {
                ssize_t a = AS_FIXNUM(array_pop(vm->stack));
                ssize_t b = AS_FIXNUM(array_pop(vm->stack));
                array_push(vm->stack, FIXNUM_VAL(b - a));
            } break;
            case OP_MUL: {
                ssize_t a = AS_FIXNUM(array_pop(vm->stack));
                ssize_t b = AS_FIXNUM(array_pop(vm->stack));
                array_push(vm->stack, FIXNUM_VAL(a * b));
            } break;
            case OP_DIV: {
                ssize_t a = AS_FIXNUM(array_pop(vm->stack));
                ssize_t b = AS_FIXNUM(array_pop(vm->stack));
                array_push(vm->stack, FIXNUM_VAL(b / a));
            } break;
            case OP_MOD: {
                ssize_t a = AS_FIXNUM(array_pop(vm->stack));
                ssize_t b = AS_FIXNUM(array_pop(vm->stack));
                array_push(vm->stack, FIXNUM_VAL(a % b));
            } break;
            case OP_RETURN: {
                display(array_pop(vm->stack));
                printf("\n");
                return;
            } break;
            default: {
                error_push((Error){
                    .type = ERR_TYPE_RUNTIME,
                    .value = ERR_NOT_IMPLEMENTED,
                    .line = vm->chunk->lines[(vm->pc - vm->chunk->code) - 1].line,
                    .col = vm->chunk->lines[(vm->pc - vm->chunk->code) - 1].col,
                });
                return;
            } break;
        }
    }

    error_push((Error){
        .type = ERR_TYPE_RUNTIME,
        .value = ERR_PC_OOB,
        .line = vm->chunk->lines[0].line,
        .col = vm->chunk->lines[0].col,
    });
}

#endif // BDL_VM_H