//
//  ComposeView.swift
//  Tusker
//
//  Created by Shadowfacts on 8/18/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import SwiftUI
import Pachyderm
import Combine

@propertyWrapper struct OptionalStateObject<T: ObservableObject>: DynamicProperty {
    private class Republisher: ObservableObject {
        var cancellable: AnyCancellable?
        var wrapped: T? {
            didSet {
                cancellable?.cancel()
                cancellable = wrapped?.objectWillChange
                    .receive(on: RunLoop.main)
                    .sink { [unowned self] _ in
                        self.objectWillChange.send()
                    }
            }
        }
    }
    
    @StateObject private var republisher = Republisher()
    @State private var object: T?
    var wrappedValue: T? {
        get {
            object
        }
        nonmutating set {
            object = newValue
        }
    }
    
    func update() {
        republisher.wrapped = wrappedValue
    }
}

struct ComposeView: View {
    @ObservedObject var draft: Draft
    @EnvironmentObject var mastodonController: MastodonController
    @EnvironmentObject var uiState: ComposeUIState
    
    @OptionalStateObject private var poster: PostService?
    @State private var isShowingPostErrorAlert = false
    @State private var postError: PostService.Error?
    
    private var isPosting: Bool {
        poster != nil
    }
    
    private let stackPadding: CGFloat = 8
    
    init(draft: Draft) {
        self.draft = draft
    }
    
    var charactersRemaining: Int {
        let limit = mastodonController.instanceFeatures.maxStatusChars
        let cwCount = draft.contentWarningEnabled ? draft.contentWarning.count : 0
        return limit - (cwCount + CharacterCounter.count(text: draft.text, for: mastodonController.instance))
    }
    
    var requiresAttachmentDescriptions: Bool {
        guard Preferences.shared.requireAttachmentDescriptions else { return false }
        let attachmentIds = draft.attachments.map(\.id)
        return attachmentIds.contains { uiState.attachmentsMissingDescriptions.contains($0) }
    }
    
    var postButtonEnabled: Bool {
        draft.hasContent && charactersRemaining >= 0 && !isPosting && !requiresAttachmentDescriptions && (draft.poll == nil || draft.poll!.options.allSatisfy { !$0.text.isEmpty })
    }
    
    var body: some View {
        mostOfTheBody.toolbar {
            ToolbarItem(placement: .cancellationAction) { cancelButton }
            ToolbarItem(placement: .confirmationAction) { postButton }
        }
    }
    
    var mostOfTheBody: some View {
        ZStack(alignment: .top) {
            GeometryReader { (outer) in
                ScrollView(.vertical) {
                    mainStack(outerMinY: outer.frame(in: .global).minY)
                }
                .scrollDismissesKeyboardInteractivelyIfAvailable()
            }
            
            if let poster = poster {
                // can't use SwiftUI.ProgressView because there's no UIProgressView.Style.bar equivalent, see FB8587149
                WrappedProgressView(value: poster.currentStep, total: poster.totalSteps)
            }
            
            autocompleteSuggestions
        }
        .navigationBarTitle("Compose")
        .actionSheet(isPresented: $uiState.isShowingSaveDraftSheet, content: self.saveAndCloseSheet)
        .alert(isPresented: $isShowingPostErrorAlert) {
            Alert(
                title: Text("Error Posting Status"),
                message: Text(postError?.localizedDescription ?? ""),
                dismissButton: .default(Text("OK"))
            )
        }
    }
    
    @ViewBuilder
    var autocompleteSuggestions: some View {
        VStack(spacing: 0) {
            Spacer()
            if let state = uiState.autocompleteState {
                ComposeAutocompleteView(autocompleteState: state)
            }
        }
        .transition(.move(edge: .bottom))
        .animation(.default, value: uiState.autocompleteState)
    }
    
    func mainStack(outerMinY: CGFloat) -> some View {
        VStack(alignment: .leading, spacing: 8) {
            if let id = draft.inReplyToID,
               let status = mastodonController.persistentContainer.status(for: id) {
                ComposeReplyView(
                    status: status,
                    stackPadding: stackPadding,
                    outerMinY: outerMinY
                )
            }
            
            header
            
            if draft.contentWarningEnabled {
                ComposeEmojiTextField(text: $draft.contentWarning, placeholder: "Write your warning here")
            }
            
            MainComposeTextView(
                draft: draft,
                placeholder: Text("What's on your mind?")
            )
            
            if let poll = draft.poll {
                ComposePollView(draft: draft, poll: poll)
                    .transition(.opacity.combined(with: .asymmetric(insertion: .scale(scale: 0.5, anchor: .leading), removal: .scale(scale: 0.5, anchor: .trailing))))
                
            }
            
            ComposeAttachmentsList(
                draft: draft
            )
            // the list rows provide their own padding, so we cancel out the extra spacing from the VStack
            .padding([.top, .bottom], -8)
        }
        .disabled(isPosting)
        .padding(stackPadding)
        .padding(.bottom, uiState.autocompleteState != nil ? 46 : nil)
    }
    
    private var header: some View {
        HStack(alignment: .top) {
            ComposeCurrentAccount()
            Spacer()
            Text(verbatim: charactersRemaining.description)
                .foregroundColor(charactersRemaining < 0 ? .red : .secondary)
                .font(Font.body.monospacedDigit())
                .accessibility(label: Text(charactersRemaining < 0 ? "\(-charactersRemaining) characters too many" : "\(charactersRemaining) characters remaining"))
        }.frame(height: 50)
    }
    
    private var cancelButton: some View {
        Button(action: self.cancel) {
            Text("Cancel")
                // otherwise all Buttons in the nav bar are made semibold
                .font(.system(size: 17, weight: .regular))
        }
    }
    
    private var postButton: some View {
        Button {
            Task {
                await self.postStatus()
            }
        } label: {
            Text("Post")
        }
        .disabled(!postButtonEnabled)
    }
    
    private func cancel() {
        if Preferences.shared.automaticallySaveDrafts {
            // draft is already stored in drafts manager, drafts manager is saved by ComposeHostingController.viewWillDisappear
            uiState.delegate?.dismissCompose(mode: .cancel)
        } else {
            // if the draft doesn't have content, it doesn't need to be saved
            if draft.hasContent {
                uiState.isShowingSaveDraftSheet = true
            } else {
                DraftsManager.shared.remove(draft)
                uiState.delegate?.dismissCompose(mode: .cancel)
            }
        }
    }
    
    private func saveAndCloseSheet() -> ActionSheet {
        ActionSheet(title: Text("Do you want to save the current post as a draft?"), buttons: [
            .default(Text("Save Draft"), action: {
                // draft is already stored in drafts manager, drafts manager is saved by ComposeHostingController.viewWillDisappear
                uiState.isShowingSaveDraftSheet = false
                uiState.delegate?.dismissCompose(mode: .cancel)
            }),
            .destructive(Text("Delete Draft"), action: {
                DraftsManager.shared.remove(draft)
                uiState.isShowingSaveDraftSheet = false
                uiState.delegate?.dismissCompose(mode: .cancel)
            }),
            .cancel(),
        ])
    }
    
    private func postStatus() async {
        guard !isPosting,
              draft.hasContent else {
            return
        }
        
        let poster = PostService(mastodonController: mastodonController, draft: draft)
        self.poster = poster
        
        do {
            try await poster.post()
            
            // wait .25 seconds so the user can see the progress bar has completed
            try? await Task.sleep(nanoseconds: 250_000_000)
            
            uiState.delegate?.dismissCompose(mode: .post)
            
        } catch let error as PostService.Error {
            self.isShowingPostErrorAlert = true
            self.postError = error
        } catch {
            fatalError("Unreachable")
        }
        
        self.poster = nil
    }
}

private extension View {
    @available(iOS, obsoleted: 16.0)
    @ViewBuilder
    func scrollDismissesKeyboardInteractivelyIfAvailable() -> some View {
        if #available(iOS 16.0, *) {
            self.scrollDismissesKeyboard(.interactively)
        } else {
            self
        }
    }
}

//struct ComposeView_Previews: PreviewProvider {
//    static var previews: some View {
//        ComposeView()
//    }
//}