import Foundation
import IOKit

/// SMC-Zugriff **mit** Schreibpfad — nur im privilegierten Helfer.
///
/// Bewusst eine eigene Kopie und keine geteilte Bibliothek mit der App: der
/// Schreibpfad soll gar nicht erst in einem Prozess vorhanden sein, der ohne
/// Sonderrechte läuft und in dem jedes Widget Code ausführt. Was nicht da ist,
/// kann auch nicht versehentlich aufgerufen werden.
///
/// Byte-Reihenfolge und Struktur stammen aus `docs/spikes/A-smc.md`.
final class SMCAccess {

    private struct Version { var major: UInt8 = 0; var minor: UInt8 = 0
                             var build: UInt8 = 0; var reserved: UInt8 = 0
                             var release: UInt16 = 0 }
    private struct PLimitData { var version: UInt16 = 0; var length: UInt16 = 0
                                var cpuPLimit: UInt32 = 0; var gpuPLimit: UInt32 = 0
                                var memPLimit: UInt32 = 0 }
    private struct KeyInfo { var dataSize: UInt32 = 0; var dataType: UInt32 = 0
                             var dataAttributes: UInt8 = 0 }

    private struct Param {
        var key: UInt32 = 0
        var vers = Version()
        var pLimitData = PLimitData()
        var keyInfo = KeyInfo()
        var padding: UInt16 = 0
        var result: UInt8 = 0
        var status: UInt8 = 0
        var data8: UInt8 = 0
        var data32: UInt32 = 0
        var bytes: (UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8,
                    UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8,
                    UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8,
                    UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8) =
            (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
             0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
    }

    private static let handleYPCEvent: UInt32 = 2
    private static let readKey: UInt8 = 5
    private static let writeKey: UInt8 = 6
    private static let getKeyFromIndex: UInt8 = 8
    private static let getKeyInfo: UInt8 = 9

    private var connection: io_connect_t = 0
    private var keyInfoCache: [String: KeyInfo] = [:]

    init?() {
        let service = IOServiceGetMatchingService(kIOMainPortDefault,
                                                  IOServiceMatching("AppleSMC"))
        guard service != 0 else { return nil }
        defer { IOObjectRelease(service) }
        guard IOServiceOpen(service, mach_task_self_, 0, &connection) == kIOReturnSuccess
        else { return nil }
    }

    deinit { if connection != 0 { IOServiceClose(connection) } }

    // MARK: - Lesen

    func float(_ key: String) -> Double? {
        guard let value = read(key), value.bytes.count >= 4 else { return nil }
        let bits = UInt32(value.bytes[3]) << 24 | UInt32(value.bytes[2]) << 16
                 | UInt32(value.bytes[1]) << 8 | UInt32(value.bytes[0])
        return Double(Float(bitPattern: bits))
    }

    func uint8(_ key: String) -> UInt8? { read(key)?.bytes.first }

    func keys(withPrefix prefix: String) -> [String] {
        guard let value = read("#KEY"), value.bytes.count >= 4 else { return [] }
        // Big-endian, anders als die Messwerte — siehe Spike A.
        let total = UInt32(value.bytes[0]) << 24 | UInt32(value.bytes[1]) << 16
                  | UInt32(value.bytes[2]) << 8 | UInt32(value.bytes[3])
        guard total > 0, total < 100_000 else { return [] }

        var found: [String] = []
        for index in 0..<total {
            var command = Param()
            command.data8 = Self.getKeyFromIndex
            command.data32 = index
            guard let output = call(command) else { continue }
            let name = Self.fourCCString(output.key)
            if name.hasPrefix(prefix) { found.append(name) }
        }
        return found
    }

    // MARK: - Schreiben

    /// Schreibt einen `flt`-Wert (Zieldrehzahl).
    @discardableResult
    func writeFloat(_ key: String, _ value: Double) -> Bool {
        let bits = Float(value).bitPattern
        return write(key, bytes: [UInt8(bits & 0xFF), UInt8((bits >> 8) & 0xFF),
                                  UInt8((bits >> 16) & 0xFF), UInt8((bits >> 24) & 0xFF)])
    }

    /// Schreibt ein einzelnes Byte (Betriebsart).
    @discardableResult
    func writeUInt8(_ key: String, _ value: UInt8) -> Bool {
        write(key, bytes: [value])
    }

    private func write(_ key: String, bytes: [UInt8]) -> Bool {
        guard let info = keyInfo(for: key) else { return false }
        // Nur schreiben, wenn die Größe zur Firmware passt. Ein zu kurzer oder
        // zu langer Schreibvorgang landet sonst in benachbarten Feldern.
        guard Int(info.dataSize) == bytes.count else { return false }

        var command = Param()
        command.key = Self.fourCC(key)
        command.keyInfo = info
        command.data8 = Self.writeKey
        withUnsafeMutableBytes(of: &command.bytes) { raw in
            for (index, byte) in bytes.enumerated() { raw[index] = byte }
        }
        return call(command) != nil
    }

    // MARK: - Innereien

    private struct Value { let bytes: [UInt8] }

    private func keyInfo(for key: String) -> KeyInfo? {
        if let cached = keyInfoCache[key] { return cached }
        var command = Param()
        command.key = Self.fourCC(key)
        command.data8 = Self.getKeyInfo
        guard let output = call(command) else { return nil }
        keyInfoCache[key] = output.keyInfo
        return output.keyInfo
    }

    private func read(_ key: String) -> Value? {
        guard let info = keyInfo(for: key) else { return nil }
        var command = Param()
        command.key = Self.fourCC(key)
        command.keyInfo = info
        command.data8 = Self.readKey
        guard let output = call(command) else { return nil }
        let all = withUnsafeBytes(of: output.bytes) { Array($0) }
        return Value(bytes: Array(all.prefix(Int(min(info.dataSize, 32)))))
    }

    private func call(_ input: Param) -> Param? {
        var input = input
        var output = Param()
        var size = MemoryLayout<Param>.stride
        let result = IOConnectCallStructMethod(connection, Self.handleYPCEvent,
                                               &input, MemoryLayout<Param>.stride,
                                               &output, &size)
        guard result == kIOReturnSuccess, output.result == 0 else { return nil }
        return output
    }

    private static func fourCC(_ string: String) -> UInt32 {
        var value: UInt32 = 0
        for character in string.utf8.prefix(4) { value = value << 8 | UInt32(character) }
        return value
    }

    private static func fourCCString(_ value: UInt32) -> String {
        let bytes = [UInt8((value >> 24) & 0xFF), UInt8((value >> 16) & 0xFF),
                     UInt8((value >> 8) & 0xFF), UInt8(value & 0xFF)]
        return String(bytes: bytes, encoding: .ascii) ?? "????"
    }
}