#import <mach/mach.h>
#import <mach/mach_host.h>

natural_t  freeMemory(void) {
    mach_port_t           host_port = mach_host_self();
    mach_msg_type_number_t   host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
    vm_size_t               pagesize;
    vm_statistics_data_t     vm_stat;

    host_page_size(host_port, &pagesize);

    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) NSLog(@"Failed to fetch vm statistics");

    natural_t   mem_used = (vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize;
    natural_t   mem_free = vm_stat.free_count * pagesize;
    natural_t   mem_total = mem_used + mem_free;

    return mem_free;
}

func systemFreeMemorySize() -> UInt?
{
    let HOST_VM_INFO_COUNT: mach_msg_type_number_t = mach_msg_type_number_t(sizeof(vm_statistics_data_t) / sizeof(integer_t))

    let host: host_t = mach_host_self()

    var pageSize: vm_size_t = vm_size_t()
    let hostPageSizeKernStatus: kern_return_t = host_page_size(host, &pageSize)
    guard hostPageSizeKernStatus == KERN_SUCCESS else {
        NSLog("Error with host_page_size():" + (String.fromCString(mach_error_string(hostPageSizeKernStatus)) ??"unknown error"))
        return nil
    }

    var stats: vm_statistics_data_t = vm_statistics_data_t()
    var count: mach_msg_type_number_t = HOST_VM_INFO_COUNT

    let kernStatus: kern_return_t = withUnsafeMutablePointer(&stats) {
        return host_statistics(host, HOST_VM_INFO, host_info_t($0), &count)
    }

    guard kernStatus == KERN_SUCCESS else {
        NSLog("Error with host_statistics():" + (String.fromCString(mach_error_string(kernStatus)) ??"unknown error"))
        return nil
    }

    return UInt(stats.free_count) * UInt(pageSize)
}