import SwiftUI
import Combine

public extension View {
    /// Applies the given change effect to this view while a condition is `true`.
    ///
    /// - Parameters:
    ///   - effect: The effect to apply.
    ///   - condition: A boolean that indicates whether the effect is active.
    ///
    /// - Returns: A view that applies the effect to this view when `isActive` is `true`.
    @ViewBuilder
    func conditionalEffect(_ effect: AnyConditionalEffect, condition: Bool) -> some View {
        switch effect.guts {
        case .continuous(let effect):
            modifier(ContinuousEffectModifier(effect: effect, isActive: condition))
                .environment(\.isConditionalEffect, true)
        case .repeating(let effect, let interval):
            modifier(RepeatingChangeEffectModifier(effect: effect, interval: interval, isActive: condition))
                .environment(\.isConditionalEffect, true)
        }
    }
}

public struct AnyConditionalEffect {
    internal enum Guts {
        case continuous(AnyContinuousEffect)
        case repeating(AnyChangeEffect, TimeInterval)
    }

    internal var guts: Guts

    private init(guts: Guts) {
        self.guts = guts
    }

    internal static func continuous(_ effect: AnyContinuousEffect) -> AnyConditionalEffect {
        AnyConditionalEffect(guts: .continuous(effect))
    }

    /// Repeats a change effect at the specified interval while a condition is true.
    ///
    /// - Parameters:
    ///   - effect: The change effect to repeat.
    ///   - interval: The number of seconds between each change effect.
    public static func `repeat`(_ effect: AnyChangeEffect, every interval: TimeInterval) -> AnyConditionalEffect {
        AnyConditionalEffect(guts: .repeating(effect, interval))
    }

    /// Repeats a change effect at the specified interval while a condition is true.
    ///
    /// - Parameters:
    ///   - effect: The change effect to repeat.
    ///   - interval: The duration between each change effect.
    @available(iOS 16.0, *)
    @available(macOS 13.0, *)
    public static func `repeat`(_ effect: AnyChangeEffect, every interval: Duration) -> AnyConditionalEffect {
        AnyConditionalEffect(guts: .repeating(effect, interval.timeInterval))
    }
}

private struct ContinuousEffectModifier: ViewModifier {

    var effect: AnyContinuousEffect

    var isActive: Bool

    @State
    private var changeCount: Int = 0

    @State
    private var startDate: Date = .distantPast

    func body(content: Content) -> some View {
        content
            .modifier(effect.viewModifier(isActive))
    }
}

private struct RepeatingChangeEffectModifier: ViewModifier {
    private final class RepeatingTimer: ObservableObject {
        @Published
        var count: Int = 0

        var timer: Timer? {
            willSet {
                timer?.invalidate()
            }
        }

        init() {}

        func resume(interval: TimeInterval, delay: TimeInterval = 0) {
            if delay != 0 {
                timer = Timer.scheduledTimer(withTimeInterval: delay, repeats: false) { [weak self] t in
                    self?.resume(interval: interval)
                }
            } else {
                count += 1

                reschedule(interval: interval)
            }
        }

        private func reschedule(interval: TimeInterval) {
            timer = Timer.scheduledTimer(withTimeInterval: interval, repeats: false) { [weak self] t in
                self?.resume(interval: interval)
            }
        }

        func pause() {
            timer = nil
        }
    }

    var effect: AnyChangeEffect

    var interval: TimeInterval

    @StateObject
    private var timer = RepeatingTimer()

    private var isEnabled: Bool

    init(effect: AnyChangeEffect, interval: TimeInterval, isActive: Bool) {
        self.effect = effect
        self.interval = clamp(1 / 15, interval, .infinity)
        self.isEnabled = isActive && interval > 0
    }

    func body(content: Content) -> some View {
        content
            .modifier(effect.viewModifier(changeCount: timer.count))
            .onAppear {
                if isEnabled {
                    timer.resume(interval: interval, delay: effect.delay)
                }
            }
            .onChange(of: isEnabled) { isEnabled in
                if isEnabled {
                    timer.resume(interval: interval, delay: effect.delay)
                } else {
                    timer.pause()
                }
            }
            .onChange(of: interval) { interval in
                if isEnabled {
                    timer.resume(interval: interval, delay: effect.delay)
                }
            }
    }
}

internal extension EnvironmentValues {
    private struct IsConditionalEffectKey: EnvironmentKey {
        static var defaultValue: Bool = false
    }

    var isConditionalEffect: Bool {
        get { self[IsConditionalEffectKey.self] }
        set { self[IsConditionalEffectKey.self] = newValue }
    }
}

#if os(iOS) && DEBUG
struct WhileEffectPreview_Previews: PreviewProvider {
    private struct Preview: View {
        @State
        private var isEnabled: Bool = false

        var body: some View {
            GroupBox("iOS 15") {
                VStack {
                    Toggle("Enabled", isOn: $isEnabled)

                    Button {

                    } label: {
                        Label("Answer", systemImage: "phone.fill")
                    }
                    .tint(.green)
                    .buttonStyle(.borderedProminent)
                    .controlSize(.large)
                    .conditionalEffect(.repeat(.shake(rate: .fast), every: 1), condition: isEnabled)
                }
            }
            .padding()
        }
    }

    @available(iOS 16.0, *)
    private struct Preview16: View {
        @State
        private var isEnabled: Bool = false

        var body: some View {
            GroupBox("iOS 16") {
                VStack {
                    Toggle("Enabled", isOn: $isEnabled)

                    Button {

                    } label: {
                        Label("Answer", systemImage: "phone.fill")
                    }
                    .tint(.green)
                    .buttonStyle(.borderedProminent)
                    .controlSize(.large)
                    .conditionalEffect(.repeat(.wiggle(rate: .fast), every: .seconds(1.5)), condition: isEnabled)

                    Button {

                    } label: {
                        Label("Alert", systemImage: "light.beacon.max.fill")
                    }
                    .tint(.red)
                    .buttonStyle(.borderedProminent)
                    .controlSize(.large)
                    .conditionalEffect(.repeat(.glow(color: .red, radius: 50), every: .seconds(1)), condition: isEnabled)

                    Button {

                    } label: {
                        Label("Press", systemImage: "hand.raised.fingers.spread.fill")
                    }
                    .tint(.blue)
                    .buttonStyle(.borderedProminent)
                    .controlSize(.large)
                    .conditionalEffect(.pushDown, condition: isEnabled)

                    Button {

                    } label: {
                        Label("Burn", systemImage: "opticaldisc")
                    }
                    .tint(.gray)
                    .buttonStyle(.borderedProminent)
                    .controlSize(.large)
                    .conditionalEffect(.smoke, condition: isEnabled)
                }
            }
            .padding()
        }
    }

    static var previews: some View {
        if #available(iOS 16.0, *) {
            Preview16()
                .preferredColorScheme(.dark)
        } else {
            Preview()
        }
    }
}
#endif