#include "impl_macros.h"

FILE* NULLABLE(fileFromN)(VM* vm, u32 file_n){
    FILE* f = NULL;
    switch(file_n){
        case 0: f = stdin; break;
        case 1: f = stdout; break;
        case 2: f = stderr; break;
        default:
            VM_setError(vm, "invalid file_n (%x) ", file_n);
            break;
    }

    return f;
}

// sys_read
// bx - file n
// cx - buffer ptr
// dx - buffer size
i32 SYS_read(VM* vm){
    const u32 file_n = vm->bx.u32v;
    u8* const buf = vm->data + vm->cx.u32v;
    const u32 size = vm->dx.u32v;

    if(buf + size > vm->data + vm->data_size)
        return 40;
    
    FILE* f = fileFromN(vm, file_n);
    return fread(buf, 1, size, f);
}

// sys_write
// bx - file n
// cx - buffer ptr
// dx - buffer size
i32 SYS_write(VM* vm){
    const u32 file_n = vm->bx.u32v;
    u8* const buf = vm->data + vm->cx.u32v;
    const u32 size = vm->dx.u32v;

    if(buf + size > vm->data + vm->data_size)
        return 41;
    
    FILE* f = fileFromN(vm, file_n);
    return fwrite(buf, 1, size, f);
}

/// SYS
/// before call: ax - func code
/// after  call: ax - result code
i32 SYS_impl(VM* vm){
    u8 func_code = vm->ax.u8v0;
    u32 result_code = 0;
    switch(func_code){
        case 0:
            result_code = SYS_read(vm);
            break;
        case 1:;
            result_code = SYS_write(vm);
            break;
        default:
            VM_setError(vm, "invalid system call (%x) ", func_code);
            return -1;
    }

    vm->ax.u32v = result_code;
    return 0;
}