//
// Copyright © 2022 osy. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

import SwiftUI
import SwiftUIVisualEffects

struct VMWindowView: View {
    let id: VMSessionState.WindowID

    @State var isInteractive = true
    @State private var state: VMWindowState
    @EnvironmentObject private var session: VMSessionState
    @Environment(\.scenePhase) private var scenePhase
    
    private let keyboardDidShowNotification = NotificationCenter.default.publisher(for: UIResponder.keyboardDidShowNotification)
    private let keyboardDidHideNotification = NotificationCenter.default.publisher(for: UIResponder.keyboardDidHideNotification)
    private let didReceiveMemoryWarningNotification = NotificationCenter.default.publisher(for: UIApplication.didReceiveMemoryWarningNotification)

    init(id: VMSessionState.WindowID, isInteractive: Bool = true) {
        self.id = id
        self._isInteractive = State<Bool>(initialValue: isInteractive)
        self._state = State<VMWindowState>(initialValue: VMWindowState(id: id))
    }

    private func withOptionalAnimation<Result>(_ animation: Animation? = .default, _ body: () throws -> Result) rethrows -> Result {
        if UIAccessibility.isReduceMotionEnabled {
            return try body()
        } else {
            return try withAnimation(animation, body)
        }
    }
    
    var body: some View {
        ZStack {
            ZStack {
                if let device = state.device {
                    switch device {
                    case .display(_, _):
                        VMDisplayHostedView(vm: session.vm, device: device, state: $state)
                    case .serial(_, _):
                        VMDisplayHostedView(vm: session.vm, device: device, state: $state)
                    }
                } else if !state.isBusy && state.isRunning {
                    // headless
                    HeadlessView()
                }
                if state.isBusy || !state.isRunning {
                    BlurEffect().blurEffectStyle(.light)
                    VStack {
                        Spacer()
                        HStack {
                            Spacer()
                            if state.isBusy {
                                Spinner(size: .large)
                            } else if session.vmState == .paused {
                                Button {
                                    session.vm.requestVmResume()
                                } label: {
                                    if #available(iOS 16, *) {
                                        Label("Resume", systemImage: "playpause.circle.fill")
                                    } else {
                                        Label("Resume", systemImage: "play.circle.fill")
                                    }
                                }
                            } else {
                                Button {
                                    session.vm.requestVmStart()
                                } label: {
                                    Label("Start", systemImage: "play.circle.fill")
                                }
                            }
                            Spacer()
                        }
                        Spacer()
                    }.labelStyle(.iconOnly)
                        .font(.system(size: 128))
                        .vibrancyEffect()
                        .vibrancyEffectStyle(.label)
                }
            }.background(Color.black)
            .ignoresSafeArea()
            #if !os(visionOS)
            if isInteractive && state.isRunning {
                VMToolbarView(state: $state)
            }
            #endif
        }
        .modifier(VMToolbarOrnamentModifier(state: $state))
        .statusBarHidden(true)
        .alert(item: $state.alert, content: { type in
            switch type {
            case .powerDown:
                return Alert(title: Text("Are you sure you want to stop this VM and exit? Any unsaved changes will be lost."), primaryButton: .destructive(Text("Yes")) {
                    session.powerDown()
                }, secondaryButton: .cancel(Text("No")))
            case .terminateApp:
                return Alert(title: Text("Are you sure you want to exit UTM?"), primaryButton: .destructive(Text("Yes")) {
                    session.stop()
                }, secondaryButton: .cancel(Text("No")))
            case .restart:
                return Alert(title: Text("Are you sure you want to reset this VM? Any unsaved changes will be lost."), primaryButton: .destructive(Text("Yes")) {
                    session.reset()
                }, secondaryButton: .cancel(Text("No")))
            #if WITH_USB
            case .deviceConnected(let device):
                return Alert(title: Text("Would you like to connect '\(device.name ?? device.description)' to this virtual machine?"), primaryButton: .default(Text("Yes")) {
                    session.mostRecentConnectedDevice = nil
                    session.connectDevice(device)
                }, secondaryButton: .cancel(Text("No")) {
                    session.mostRecentConnectedDevice = nil
                })
            #endif
            case .nonfatalError(let message), .fatalError(let message):
                return Alert(title: Text(message), dismissButton: .cancel(Text("OK")) {
                    if case .fatalError(_) = type {
                        session.stop()
                    } else {
                        session.nonfatalError = nil
                    }
                })
            case .memoryWarning:
                return Alert(title: Text("Running low on memory! UTM might soon be killed by iOS. You can prevent this by decreasing the amount of memory and/or JIT cache assigned to this VM"), dismissButton: .cancel(Text("OK")) {
                    session.didReceiveMemoryWarning()
                })
            }
        })
        .onChange(of: session.windowDeviceMap) { windowDeviceMap in
            if let device = windowDeviceMap[state.id] {
                state.device = device
            } else {
                state.device = nil
            }
        }
        .onChange(of: state.device) { [oldDevice = state.device] newDevice in
            if session.windowDeviceMap[state.id] != newDevice {
                session.windowDeviceMap[state.id] = newDevice
            }
            state.saveWindow(to: session.vm.registryEntry, device: oldDevice)
            state.restoreWindow(from: session.vm.registryEntry, device: newDevice)
        }
        #if WITH_USB
        .onChange(of: session.mostRecentConnectedDevice) { newValue in
            if session.activeWindow == state.id, let device = newValue {
                state.alert = .deviceConnected(device)
            }
        }
        #endif
        .onChange(of: session.nonfatalError) { newValue in
            if session.activeWindow == state.id, let message = newValue {
                state.alert = .nonfatalError(message)
            }
        }
        .onChange(of: session.fatalError) { newValue in
            if session.activeWindow == state.id, let message = newValue {
                state.alert = .fatalError(message)
            }
        }
        .onChange(of: session.vmState) { [oldValue = session.vmState] newValue in
            vmStateUpdated(from: oldValue, to: newValue)
        }
        .onReceive(keyboardDidShowNotification) { _ in
            state.isKeyboardShown = true
            state.isKeyboardRequested = true
        }
        .onReceive(keyboardDidHideNotification) { _ in
            state.isKeyboardShown = false
            state.isKeyboardRequested = false
        }
        .onReceive(didReceiveMemoryWarningNotification) { _ in
            if session.activeWindow == state.id && !session.hasShownMemoryWarning {
                session.hasShownMemoryWarning = true
                state.alert = .memoryWarning
            }
        }
        .onChange(of: scenePhase) { newValue in
            guard session.activeWindow == state.id else {
                return
            }
            if newValue == .background {
                saveWindow()
                session.didEnterBackground()
            } else if newValue == .active {
                session.didEnterForeground()
            }
        }
        .onAppear {
            vmStateUpdated(from: nil, to: session.vmState)
            session.registerWindow(state.id, isExternal: !isInteractive)
            if !isInteractive {
                session.externalWindowBinding = $state
            }
        }
        .onDisappear {
            session.removeWindow(state.id)
            if !isInteractive {
                session.externalWindowBinding = nil
            }
        }
    }
    
    private func vmStateUpdated(from oldState: UTMVirtualMachineState?, to vmState: UTMVirtualMachineState) {
        if oldState == .started {
            saveWindow()
        }
        switch vmState {
        case .stopped, .paused:
            withOptionalAnimation {
                state.isBusy = false
                state.isRunning = false
            }
            DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(100)) {
                if session.vmState == .stopped && session.fatalError == nil {
                    session.stop()
                }
            }
        case .pausing, .stopping, .starting, .resuming, .saving, .restoring:
            withOptionalAnimation {
                state.isBusy = true
                state.isRunning = false
            }
        case .started:
            withOptionalAnimation {
                state.isBusy = false
                state.isRunning = true
            }
        }
    }
    
    private func saveWindow() {
        state.saveWindow(to: session.vm.registryEntry, device: state.device)
    }
}

private struct HeadlessView: View {
    var body: some View {
        ZStack {
            BlurEffect().blurEffectStyle(.dark)
            VStack {
                Image(systemName: "rectangle.dashed")
                    .font(.title)
                Text("No output device is selected for this window.")
                    .foregroundColor(.white)
                    .font(.headline)
                    .multilineTextAlignment(.center)
            }.padding()
                .frame(width: 200, height: 200, alignment: .center)
                .foregroundColor(.white)
                .background(Color.gray.opacity(0.5))
                .clipShape(RoundedRectangle(cornerRadius: 25.0, style: .continuous))
                .vibrancyEffect()
                .vibrancyEffectStyle(.label)
        }
    }
}

#if !os(visionOS)
/// Stub for non-Vision platforms
fileprivate struct VMToolbarOrnamentModifier: ViewModifier {
    @Binding var state: VMWindowState
    func body(content: Content) -> some View {
        content
    }
}
#endif