/*
 CPU.swift
 Menubar RunCat

 Created by Takuto Nakamura on 2019/08/06.
 Copyright © 2019 Takuto Nakamura. All rights reserved.
*/

import Darwin

typealias CPUInfo = (value: Double, description: String)

final class CPU {
    static let `default` = CPUInfo(0.0, " 0.0% ")

    private let loadInfoCount: mach_msg_type_number_t!
    private var loadPrevious = host_cpu_load_info()
    
    init() {
        loadInfoCount = UInt32(MemoryLayout<host_cpu_load_info_data_t>.size / MemoryLayout<integer_t>.size)
    }
    
    private func hostCPULoadInfo() -> host_cpu_load_info {
        var size: mach_msg_type_number_t = loadInfoCount
        let hostInfo = host_cpu_load_info_t.allocate(capacity: 1)
        let _ = hostInfo.withMemoryRebound(to: integer_t.self, capacity: Int(size)) { (pointer) -> kern_return_t in
            return host_statistics(mach_host_self(), HOST_CPU_LOAD_INFO, pointer, &size)
        }
        let data = hostInfo.move()
        hostInfo.deallocate()
        return data
    }
    
    func currentUsage() -> CPUInfo {
        let load = hostCPULoadInfo()
        let userDiff = Double(load.cpu_ticks.0 - loadPrevious.cpu_ticks.0)
        let sysDiff  = Double(load.cpu_ticks.1 - loadPrevious.cpu_ticks.1)
        let idleDiff = Double(load.cpu_ticks.2 - loadPrevious.cpu_ticks.2)
        let niceDiff = Double(load.cpu_ticks.3 - loadPrevious.cpu_ticks.3)
        loadPrevious = load
        
        let totalTicks = sysDiff + userDiff + idleDiff + niceDiff
        let sys  = 100.0 * sysDiff / totalTicks
        let user = 100.0 * userDiff / totalTicks

        let value = min(99.9, (10.0 * (sys + user)).rounded() / 10.0)
        let description = String(format: "%4.1f%%", value)
        
        return CPUInfo(value, description)
    }
}