import Foundation
import IOKit
import SMC

/// 功耗与 CPU 频率
public struct PowerReading: Sendable, Equatable {
    /// 整机功耗（SMC PSTR）
    public var system: Double?
    /// 电源适配器输入（SMC PDTR），使用电池时为 nil
    public var adapter: Double?
    /// 电池充放电功率（SMC PPBR）
    public var battery: Double?
    /// GPU 功耗（IOReport Energy Model，两次采样之间的平均值）
    public var gpu: Double?
    /// 各类核心在工作时的平均频率（MHz），键为 perflevel，0 为最高性能档
    public var clusterFrequency: [Int: Double] = [:]

    public init(system: Double? = nil, adapter: Double? = nil, battery: Double? = nil, gpu: Double? = nil,
                clusterFrequency: [Int: Double] = [:]) {
        self.system = system
        self.adapter = adapter
        self.battery = battery
        self.gpu = gpu
        self.clusterFrequency = clusterFrequency
    }
}

/// 功耗读 SMC，CPU 频率与 GPU 能耗读 IOReport，都不需要 root。
/// 注：新款芯片上 IOReport 的 CPU 能耗计数器（mJ）长时间不更新，因此不显示 CPU 功耗。
public final class PowerSampler: @unchecked Sendable {
    private let smc = try? SMCConnection()
    private var energy: Subscription?
    private var cpuStates: Subscription?
    private var lastEnergy: (date: Date, sample: CFDictionary)?
    private var lastStates: (date: Date, sample: CFDictionary)?
    private lazy var frequencyTables: [[Double]] = Self.readFrequencyTables()

    public init() {}

    /// SMC 读数几乎没有开销；IOReport 每次采样约 5 毫秒 CPU，GPU 功耗与 CPU 频率只在界面需要时读
    public func sample(gpu includeGPU: Bool = true, frequency includeFrequency: Bool = true, now: Date = Date()) -> PowerReading {
        var reading = PowerReading()
        reading.system = positive(smc?.double(SMCKey("PSTR")))
        reading.adapter = positive(smc?.double(SMCKey("PDTR")))
        reading.battery = smc?.double(SMCKey("PPBR")).flatMap { $0.isFinite && abs($0) >= 0.01 ? $0 : nil }
        if includeGPU { reading.gpu = sampleGPU(now: now) }
        if includeFrequency { reading.clusterFrequency = sampleFrequencies(now: now) }
        return reading
    }

    private func positive(_ value: Double?) -> Double? {
        guard let value, value.isFinite, value > 0.05, value < 1000 else { return nil }
        return value
    }

    // MARK: GPU

    private func sampleGPU(now: Date) -> Double? {
        if energy == nil { energy = Subscription(group: "Energy Model", subgroup: nil) }
        guard let energy, let current = energy.sample() else { return nil }
        defer { lastEnergy = (now, current) }
        // 间隔太短噪声大；太长（界面关闭过一段时间）的平均值没有意义
        guard let last = lastEnergy, (0.2...15).contains(now.timeIntervalSince(last.date)),
              let delta = IOReportCreateSamplesDelta(last.sample, current, nil)?.takeRetainedValue() else {
            return nil
        }
        let seconds = now.timeIntervalSince(last.date)
        for channel in Subscription.channels(in: delta) where Subscription.name(channel) == "GPU Energy" {
            let value = Double(IOReportSimpleGetIntegerValue(channel, 0))
            let joules = value * Self.joulesPerUnit(Subscription.unit(channel))
            return joules / seconds
        }
        return nil
    }

    static func joulesPerUnit(_ unit: String) -> Double {
        switch unit {
        case "nJ": 1e-9
        case "uJ", "µJ": 1e-6
        case "mJ": 1e-3
        default: 1
        }
    }

    // MARK: CPU 频率

    private func sampleFrequencies(now: Date) -> [Int: Double] {
        if cpuStates == nil { cpuStates = Subscription(group: "CPU Stats", subgroup: "CPU Complex Performance States") }
        guard let cpuStates, let current = cpuStates.sample() else { return [:] }
        defer { lastStates = (now, current) }
        guard let last = lastStates, now.timeIntervalSince(last.date) <= 15,
              let delta = IOReportCreateSamplesDelta(last.sample, current, nil)?.takeRetainedValue() else { return [:] }

        var complexes: [ComplexResidency] = []
        for channel in Subscription.channels(in: delta) {
            let name = Subscription.name(channel)
            guard let letter = Self.complexLetter(name) else { continue }
            var states: [(String, Int64)] = []
            for index in 0..<IOReportStateGetCount(channel) {
                let stateName = IOReportStateGetNameForIndex(channel, index)?.takeUnretainedValue() as String? ?? ""
                states.append((stateName, IOReportStateGetResidency(channel, index)))
            }
            complexes.append(ComplexResidency(letter: letter, states: states))
        }
        let levels = Sysctl.int("hw.nperflevels") ?? 1
        return Self.clusterFrequencies(complexes, tables: frequencyTables, perfLevels: levels)
    }

    struct ComplexResidency {
        let letter: Character
        let states: [(name: String, residency: Int64)]
    }

    /// “ECPU”“PCPU”“MCPU0” 这类核心组通道；“PCPM”“MCPM0_IDLE” 是电源管理通道，不计入
    static func complexLetter(_ name: String) -> Character? {
        guard name.count >= 4, let first = name.first, first.isUppercase,
              name.dropFirst().hasPrefix("CPU"), name.dropFirst(4).allSatisfy(\.isNumber) else { return nil }
        return first
    }

    /// 按工作状态（V{n}P{m}）的驻留时间加权平均频率。同一字母的核心组合并；
    /// 各组按频率表的最高频率从高到低对应 perflevel 0、1、2
    static func clusterFrequencies(_ complexes: [ComplexResidency], tables: [[Double]], perfLevels: Int) -> [Int: Double] {
        var weighted: [Character: (sum: Double, time: Double, top: Double)] = [:]
        for complex in complexes {
            let active = complex.states.filter { $0.name.hasPrefix("V") && $0.name.contains("P") }
            guard let table = table(forStateCount: active.count, letter: complex.letter, in: tables) else { continue }
            var entry = weighted[complex.letter] ?? (0, 0, table.max() ?? 0)
            for (index, state) in active.enumerated() where index < table.count {
                entry.sum += table[index] * Double(state.residency)
                entry.time += Double(state.residency)
            }
            weighted[complex.letter] = entry
        }
        let ordered = weighted.sorted { $0.value.top > $1.value.top }
        guard ordered.count == perfLevels else { return [:] }
        var result: [Int: Double] = [:]
        for (level, item) in ordered.enumerated() where item.value.time > 0 {
            result[level] = item.value.sum / item.value.time
        }
        return result
    }

    /// 状态数与频率表项数一致的表；有多张时能效核（E）取最低、其他取最高
    static func table(forStateCount count: Int, letter: Character, in tables: [[Double]]) -> [Double]? {
        let candidates = tables.filter { $0.count == count }
        return letter == "E" ? candidates.min { ($0.max() ?? 0) < ($1.max() ?? 0) }
                             : candidates.max { ($0.max() ?? 0) < ($1.max() ?? 0) }
    }

    /// pmgr 的 voltage-states*-sram 属性：每项 8 字节（频率、电压，小端 UInt32）。
    /// 旧芯片单位是 Hz，新芯片直接是 MHz；第一项为 0 的是 GPU 等其他模块的表
    static func parseFrequencyTable(_ data: Data) -> [Double]? {
        guard data.count >= 16, data.count % 8 == 0 else { return nil }
        let values = stride(from: 0, to: data.count, by: 8).map { offset -> Double in
            let raw = data.subdata(in: offset..<offset + 4).withUnsafeBytes { $0.loadUnaligned(as: UInt32.self) }
            return Double(UInt32(littleEndian: raw))
        }
        guard let first = values.first, first > 0, let top = values.max() else { return nil }
        let scale = top > 100_000_000 ? 1e-6 : top > 100_000 ? 1e-3 : 1
        let megahertz = values.map { $0 * scale }
        // 合理的 CPU 频率范围
        guard (200...10_000).contains(megahertz.max() ?? 0) else { return nil }
        return megahertz
    }

    private static func readFrequencyTables() -> [[Double]] {
        var iterator: io_iterator_t = 0
        guard IOServiceGetMatchingServices(kIOMainPortDefault, IOServiceMatching("AppleARMIODevice"), &iterator) == KERN_SUCCESS else {
            return []
        }
        defer { IOObjectRelease(iterator) }
        var tables: [[Double]] = []
        while case let entry = IOIteratorNext(iterator), entry != 0 {
            defer { IOObjectRelease(entry) }
            var name = [CChar](repeating: 0, count: 128)
            guard IORegistryEntryGetName(entry, &name) == KERN_SUCCESS,
                  String(decoding: name.prefix { $0 != 0 }.map { UInt8(bitPattern: $0) }, as: UTF8.self) == "pmgr" else { continue }
            var properties: Unmanaged<CFMutableDictionary>?
            guard IORegistryEntryCreateCFProperties(entry, &properties, kCFAllocatorDefault, 0) == KERN_SUCCESS,
                  let dictionary = properties?.takeRetainedValue() as? [String: Any] else { continue }
            for (key, value) in dictionary where key.hasPrefix("voltage-states") && key.hasSuffix("-sram") {
                if let data = value as? Data, let table = parseFrequencyTable(data), !tables.contains(table) {
                    tables.append(table)
                }
            }
        }
        return tables
    }
}

/// IOReport 订阅：只订阅需要的分组，减少每次采样的开销
private final class Subscription {
    private let channels: CFMutableDictionary
    private let subscription: IOReportSubscriptionRef

    init?(group: String, subgroup: String?) {
        guard let channels = IOReportCopyChannelsInGroup(group as CFString, subgroup as CFString?, 0, 0, 0)?.takeRetainedValue() else {
            return nil
        }
        var subscribed: Unmanaged<CFMutableDictionary>?
        guard let subscription = IOReportCreateSubscription(nil, channels, &subscribed, 0, nil) else { return nil }
        subscribed?.release()
        self.channels = channels
        self.subscription = subscription
    }

    func sample() -> CFDictionary? {
        IOReportCreateSamples(subscription, channels, nil)?.takeRetainedValue()
    }

    static func channels(in sample: CFDictionary) -> [CFDictionary] {
        let key = "IOReportChannels" as CFString
        guard let raw = CFDictionaryGetValue(sample, Unmanaged.passUnretained(key).toOpaque()) else { return [] }
        let array = unsafeBitCast(raw, to: CFArray.self)
        return (0..<CFArrayGetCount(array)).map { unsafeBitCast(CFArrayGetValueAtIndex(array, $0), to: CFDictionary.self) }
    }

    static func name(_ channel: CFDictionary) -> String {
        IOReportChannelGetChannelName(channel)?.takeUnretainedValue() as String? ?? ""
    }

    static func unit(_ channel: CFDictionary) -> String {
        (IOReportChannelGetUnitLabel(channel)?.takeUnretainedValue() as String? ?? "").trimmingCharacters(in: .whitespaces)
    }
}