// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//


#if os(OSX) || os(iOS)
import Darwin
#elseif os(Linux) || CYGWIN
import Glibc
#endif
import CoreFoundation

internal class NSThreadSpecific<T: NSObject> {
    private var key = _CFThreadSpecificKeyCreate()

    internal func get(_ generator: () -> T) -> T {
        if let specific = _CFThreadSpecificGet(key) {
            return specific as! T
        } else {
            let value = generator()
            _CThreadSpecificSet(key, value)
            return value
        }
    }

    internal func set(_ value: T) {
        _CThreadSpecificSet(key, value)
    }
}

internal enum _NSThreadStatus {
    case initialized
    case starting
    case executing
    case finished
}

private func NSThreadStart(_ context: UnsafeMutableRawPointer?) -> UnsafeMutableRawPointer? {
    let thread: Thread = NSObject.unretainedReference(context!)
    Thread._currentThread.set(thread)
    thread._status = .executing
    thread.main()
    thread._status = .finished
    Thread.releaseReference(context!)
    return nil
}

open class Thread : NSObject {

    static internal var _currentThread = NSThreadSpecific<Thread>()
    open class var current: Thread {
        return Thread._currentThread.get() {
            if Thread.isMainThread {
                return mainThread
            } else {
                return Thread(thread: pthread_self())
            }
        }
    }

    open class var isMainThread: Bool {
        return _CFIsMainThread()
    }

    // !!! NSThread's mainThread property is incorrectly exported as "main", which conflicts with its "main" method.
    private static let _mainThread: Thread = {
        var thread = Thread(thread: _CFMainPThread)
        thread._status = .executing
        return thread
    }()

    open class var mainThread: Thread {
        return _mainThread
    }


    /// Alternative API for detached thread creation
    /// - Experiment: This is a draft API currently under consideration for official import into Foundation as a suitable alternative to creation via selector
    /// - Note: Since this API is under consideration it may be either removed or revised in the near future
    open class func detachNewThread(_ block: @escaping () -> Swift.Void) {
        let t = Thread(block: block)
        t.start()
    }

    open class func isMultiThreaded() -> Bool {
        return true
    }

    open class func sleep(until date: Date) {
        let start_ut = CFGetSystemUptime()
        let start_at = CFAbsoluteTimeGetCurrent()
        let end_at = date.timeIntervalSinceReferenceDate
        var ti = end_at - start_at
        let end_ut = start_ut + ti
        while (0.0 < ti) {
            var __ts__ = timespec(tv_sec: Int.max, tv_nsec: 0)
            if ti < Double(Int.max) {
                var integ = 0.0
                let frac: Double = withUnsafeMutablePointer(to: &integ) { integp in
                    return modf(ti, integp)
                }
                __ts__.tv_sec = Int(integ)
                __ts__.tv_nsec = Int(frac * 1000000000.0)
            }
            let _ = withUnsafePointer(to: &__ts__) { ts in
                nanosleep(ts, nil)
            }
            ti = end_ut - CFGetSystemUptime()
        }
    }

    open class func sleep(forTimeInterval interval: TimeInterval) {
        var ti = interval
        let start_ut = CFGetSystemUptime()
        let end_ut = start_ut + ti
        while 0.0 < ti {
            var __ts__ = timespec(tv_sec: Int.max, tv_nsec: 0)
            if ti < Double(Int.max) {
                var integ = 0.0
                let frac: Double = withUnsafeMutablePointer(to: &integ) { integp in
                    return modf(ti, integp)
                }
                __ts__.tv_sec = Int(integ)
                __ts__.tv_nsec = Int(frac * 1000000000.0)
            }
            let _ = withUnsafePointer(to: &__ts__) { ts in
                nanosleep(ts, nil)
            }
            ti = end_ut - CFGetSystemUptime()
        }
    }

    open class func exit() {
        Thread.current._status = .finished
        pthread_exit(nil)
    }

    internal var _main: () -> Void = {}
#if os(OSX) || os(iOS) || CYGWIN
    private var _thread: pthread_t? = nil
#elseif os(Linux) || os(Android)
    private var _thread = pthread_t()
#endif
#if CYGWIN
    internal var _attr : pthread_attr_t? = nil
#else
    internal var _attr = pthread_attr_t()
#endif
    internal var _status = _NSThreadStatus.initialized
    internal var _cancelled = false
    /// - Note: this differs from the Darwin implementation in that the keys must be Strings
    open var threadDictionary = [String : Any]()

    internal init(thread: pthread_t) {
        // Note: even on Darwin this is a non-optional pthread_t; this is only used for valid threads, which are never null pointers.
        _thread = thread
    }

    public override init() {
        let _ = withUnsafeMutablePointer(to: &_attr) { attr in
            pthread_attr_init(attr)
            pthread_attr_setscope(attr, Int32(PTHREAD_SCOPE_SYSTEM))
            pthread_attr_setdetachstate(attr, Int32(PTHREAD_CREATE_DETACHED))
        }
    }

    public convenience init(block: @escaping () -> Swift.Void) {
        self.init()
        _main = block
    }

    open func start() {
        precondition(_status == .initialized, "attempting to start a thread that has already been started")
        _status = .starting
        if _cancelled {
            _status = .finished
            return
        }
#if CYGWIN
        if let attr = self._attr {
            _thread = self.withRetainedReference {
              return _CFThreadCreate(attr, NSThreadStart, $0)
            }
        } else {
            _thread = nil
        }
#else
        _thread = self.withRetainedReference {
            return _CFThreadCreate(self._attr, NSThreadStart, $0)
        }
#endif
    }

    open func main() {
        _main()
    }

    open var name: String? {
        didSet {
            if _thread == Thread.current._thread {
                _CFThreadSetName(name)
            }
        }
    }

    open var stackSize: Int {
        get {
            var size: Int = 0
            return withUnsafeMutablePointer(to: &_attr) { attr in
                withUnsafeMutablePointer(to: &size) { sz in
                    pthread_attr_getstacksize(attr, sz)
                    return sz.pointee
                }
            }
        }
        set {
            // just don't allow a stack size more than 1GB on any platform
            var s = newValue
            if (1 << 30) < s {
                s = 1 << 30
            }
            let _ = withUnsafeMutablePointer(to: &_attr) { attr in
                pthread_attr_setstacksize(attr, s)
            }
        }
    }

    open var isExecuting: Bool {
        return _status == .executing
    }

    open var isFinished: Bool {
        return _status == .finished
    }

    open var isCancelled: Bool {
        return _cancelled
    }

    open var isMainThread: Bool {
        return self === Thread.mainThread
    }

    open func cancel() {
        _cancelled = true
    }


    private class func backtraceAddresses<T>(_ body: (UnsafeMutablePointer<UnsafeMutableRawPointer?>, Int) -> [T]) -> [T] {
        // Same as swift/stdlib/public/runtime/Errors.cpp backtrace
        let maxSupportedStackDepth = 128;
        let addrs = UnsafeMutablePointer<UnsafeMutableRawPointer?>.allocate(capacity: maxSupportedStackDepth)
        defer { addrs.deallocate(capacity: maxSupportedStackDepth) }
        let count = backtrace(addrs, Int32(maxSupportedStackDepth))
        let addressCount = max(0, min(Int(count), maxSupportedStackDepth))
        return body(addrs, addressCount)
    }

    open class var callStackReturnAddresses: [NSNumber] {
        return backtraceAddresses({ (addrs, count) in
            UnsafeBufferPointer(start: addrs, count: count).map {
                NSNumber(value: UInt(bitPattern: $0))
            }
        })
    }

    open class var callStackSymbols: [String] {
        return backtraceAddresses({ (addrs, count) in
            var symbols: [String] = []
            if let bs = backtrace_symbols(addrs, Int32(count)) {
                symbols = UnsafeBufferPointer(start: bs, count: count).map {
                    guard let symbol = $0 else {
                        return "<null>"
                    }
                    return String(cString: symbol)
                }
                free(bs)
            }
            return symbols
        })
    }
}

extension NSNotification.Name {
    public static let NSWillBecomeMultiThreaded = NSNotification.Name(rawValue: "NSWillBecomeMultiThreadedNotification")
    public static let NSDidBecomeSingleThreaded = NSNotification.Name(rawValue: "NSDidBecomeSingleThreadedNotification")
    public static let NSThreadWillExit = NSNotification.Name(rawValue: "NSThreadWillExitNotification")
}