// What a native host observes of whether anyone can see the stream (native-sink §6.2): whether
// the application is shown, how much of the player's area is in view, and the viewer's input.
// The platform adapters below read the platform's own state; a host with its own notion of
// visibility, and a test, gives a `WaiAttention` of its own.
import Foundation

/// The attention state a player session reads at each observation.
public protocol WaiAttention: AnyObject {
    /// The fraction of the player's area in view, in basis points: 0 while the application is not
    /// shown, its window covered or minimised, or the display asleep.
    func visibleBasisPoints() -> Int
    /// Whether the viewer interacted since the last call (at most once a second is recorded).
    func takeInteraction() -> Bool
}

/// A fixed answer: for hosts that decide visibility themselves, and for tests.
public final class WaiFixedAttention: WaiAttention, @unchecked Sendable {
    private let lock = NSLock()
    private var bp: Int
    private var interacted = false
    public init(visibleBasisPoints: Int = 10_000) { bp = visibleBasisPoints }
    public func set(visibleBasisPoints v: Int) { lock.lock(); bp = v; lock.unlock() }
    public func noteInteraction() { lock.lock(); interacted = true; lock.unlock() }
    public func visibleBasisPoints() -> Int { lock.lock(); defer { lock.unlock() }; return bp }
    public func takeInteraction() -> Bool { lock.lock(); defer { lock.unlock() }; let i = interacted; interacted = false; return i }
}

/// The fraction of `rect` that lies inside `bounds`, in basis points.
func fraction(_ rect: CGRect, in bounds: CGRect) -> Int {
    let area = rect.width * rect.height
    guard area > 0 else { return 0 }
    let i = rect.intersection(bounds)
    guard !i.isNull else { return 0 }
    return Int((i.width * i.height / area * 10_000).rounded(.down))
}

#if canImport(UIKit)
import UIKit
import UIKit.UIGestureRecognizerSubclass

/// The phone, tablet and television adapter: the application's state, the player view's place in
/// its window, and a passive recognizer on that window for the viewer's input.
@MainActor
public final class WaiViewAttention: WaiAttention {
    private weak var view: UIView?
    private var interacted = false
    private var last: Date = .distantPast
    private var recognizer: Passive?

    public init(view: UIView) {
        self.view = view
    }

    nonisolated public func visibleBasisPoints() -> Int {
        MainActor.assumeIsolated { self.visibleNow() }
    }

    nonisolated public func takeInteraction() -> Bool {
        MainActor.assumeIsolated {
            self.install()
            let i = self.interacted
            self.interacted = false
            return i
        }
    }

    private func visibleNow() -> Int {
        guard UIApplication.shared.applicationState == .active, let v = view, let w = v.window, !v.isHidden, v.alpha > 0 else { return 0 }
        return fraction(v.convert(v.bounds, to: w), in: w.bounds)
    }

    private func install() {
        guard recognizer == nil, let w = view?.window else { return }
        let r = Passive { [weak self] in
            guard let self, Date().timeIntervalSince(self.last) >= 1 else { return }
            self.last = Date()
            self.interacted = true
        }
        w.addGestureRecognizer(r)
        recognizer = r
    }

    /// Sees every touch and press and claims none: it fails at once, so the views under it get
    /// their events as before.
    final class Passive: UIGestureRecognizer {
        let seen: () -> Void
        init(_ seen: @escaping () -> Void) {
            self.seen = seen
            super.init(target: nil, action: nil)
            cancelsTouchesInView = false
            delaysTouchesBegan = false
            delaysTouchesEnded = false
        }
        override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
            seen()
            state = .failed
        }
        override func pressesBegan(_ presses: Set<UIPress>, with event: UIPressesEvent) {
            seen()
            state = .failed
        }
    }
}
#endif

#if canImport(AppKit) && !targetEnvironment(macCatalyst)
import AppKit

/// The desktop adapter: the window's occlusion state and whether it is minimised, the player
/// view's place in it, the display's sleep, and the application's input events.
@MainActor
public final class WaiViewAttention: WaiAttention {
    private weak var view: NSView?
    private var interacted = false
    private var last: Date = .distantPast
    private var asleep = false
    private var monitor: Any?
    private var observers: [NSObjectProtocol] = []

    public init(view: NSView) {
        self.view = view
        let ws = NSWorkspace.shared.notificationCenter
        observers.append(ws.addObserver(forName: NSWorkspace.screensDidSleepNotification, object: nil, queue: .main) { [weak self] _ in
            MainActor.assumeIsolated { self?.asleep = true }
        })
        observers.append(ws.addObserver(forName: NSWorkspace.screensDidWakeNotification, object: nil, queue: .main) { [weak self] _ in
            MainActor.assumeIsolated { self?.asleep = false }
        })
        monitor = NSEvent.addLocalMonitorForEvents(matching: [.keyDown, .leftMouseDown, .rightMouseDown, .otherMouseDown, .scrollWheel]) { [weak self] e in
            MainActor.assumeIsolated {
                if let self, Date().timeIntervalSince(self.last) >= 1 {
                    self.last = Date()
                    self.interacted = true
                }
            }
            return e
        }
    }

    nonisolated public func visibleBasisPoints() -> Int {
        MainActor.assumeIsolated { self.visibleNow() }
    }

    nonisolated public func takeInteraction() -> Bool {
        MainActor.assumeIsolated {
            let i = self.interacted
            self.interacted = false
            return i
        }
    }

    private func visibleNow() -> Int {
        guard !asleep, let v = view, let w = v.window, w.isVisible, !w.isMiniaturized, w.occlusionState.contains(.visible), !v.isHiddenOrHasHiddenAncestor,
              let content = w.contentView else { return 0 }
        return fraction(v.convert(v.bounds, to: content), in: content.bounds)
    }
}
#endif