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

import SwiftUI
import Pachyderm
import Combine

struct ComposeView: View {
    @ObservedObject var draft: Draft
    @EnvironmentObject var mastodonController: MastodonController
    @EnvironmentObject var uiState: ComposeUIState
    
    @State private var isPosting = false
    @State private var postProgress: Double = 0
    @State private var postTotalProgress: Double = 0
    @State private var isShowingPostErrorAlert = false
    @State private var postError: PostError?
    
    private let stackPadding: CGFloat = 8
    
    init(draft: Draft) {
        self.draft = draft
    }
    
    var charactersRemaining: Int {
        let limit = mastodonController.instance?.maxStatusCharacters ?? 500
        let cwCount = draft.contentWarningEnabled ? draft.contentWarning.count : 0
        return limit - (cwCount + CharacterCounter.count(text: draft.text))
    }
    
    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
    }
    
    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)
                }
            }
            
            // can't use SwiftUI.ProgressView because there's no UIProgressView.Style.bar equivalent, see FB8587149
            WrappedProgressView(value: postProgress, total: postTotalProgress)
            
            autocompleteSuggestions
        }
        .onAppear(perform: self.didAppear)
        .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)
    }
    
    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 {
                ComposeContentWarningTextField(text: $draft.contentWarning)
            }
            
            MainComposeTextView(
                draft: draft,
                placeholder: Text("What's on your mind?")
            )
            
            ComposeAttachmentsList(
                draft: draft
            )
            // the list rows provide their own padding, so we cancel out the extra spacing from the VStack
            .padding([.top, .bottom], -8)
        }
        .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(action: self.postStatus) {
            Text("Post")
        }
        .disabled(!postButtonEnabled)
    }
    
    private func didAppear() {
        let proxy = UIScrollView.appearance(whenContainedInInstancesOf: [ComposeHostingController.self])
        proxy.keyboardDismissMode = .interactive
    }
    
    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() {
        guard draft.hasContent else { return }
        
        isPosting = true
        
        // save before posting, so if a crash occurs during network request, the status won't be lost
        DraftsManager.save()
        
        let contentWarning = draft.contentWarningEnabled ? draft.contentWarning : nil
        let sensitive = contentWarning != nil
        
        // 2 steps (request data, then upload) for each attachment
        postTotalProgress = Double(2 + (draft.attachments.count * 2))
        postProgress = 1
        
        uploadAttachments { (result) in
            switch result {
            case let .failure(error):
                self.isShowingPostErrorAlert = true
                self.postError = error
                self.postProgress = 0
                self.postTotalProgress = 0
                self.isPosting = false
            
            case let .success(uploadedAttachments):
                let request = Client.createStatus(text: draft.textForPosting,
                                                  contentType: Preferences.shared.statusContentType,
                                                  inReplyTo: draft.inReplyToID,
                                                  media: uploadedAttachments,
                                                  sensitive: sensitive,
                                                  spoilerText: contentWarning,
                                                  visibility: draft.visibility,
                                                  language: nil)
                self.mastodonController.run(request) { (response) in
                    switch response {
                    case let .failure(error):
                        self.isShowingPostErrorAlert = true
                        self.postError = error

                    case .success(_, _):
                        self.postProgress += 1
                        
                        DraftsManager.shared.remove(self.draft)
                        
                        // wait .25 seconds so the user can see the progress bar has completed
                        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(250)) {
                            self.uiState.delegate?.dismissCompose(mode: .post)
                        }
                    }
                }
            }
        }
    }
    
    private func uploadAttachments(_ completion: @escaping (Result<[Attachment], AttachmentUploadError>) -> Void) {
        let group = DispatchGroup()
        
        var attachmentDatas = [(Data, String)?]()
        
        for (index, compAttachment) in draft.attachments.enumerated() {
            group.enter()
            
            attachmentDatas.append(nil)
            
            compAttachment.data.getData { (data, mimeType) in
                postProgress += 1
                
                attachmentDatas[index] = (data, mimeType)
                group.leave()
            }
        }
        
        group.notify(queue: .global(qos: .userInitiated)) {
            
            var anyFailed = false
            var uploadedAttachments = [Result<Attachment, Error>?]()
        
            // Mastodon does not respect the order of the `media_ids` parameter in the create post request,
            // it determines attachment order by which was uploaded first. Since the upload attachment request
            // does not include any timestamp data, and requests may arrive at the server out-of-order,
            // attachments need to be uploaded serially in order to ensure the order of attachments in the
            // posted status reflects order the user set.
            // Pleroma does respect the order of the `media_ids` parameter.
            
            for (index, (data, mimeType)) in attachmentDatas.map(\.unsafelyUnwrapped).enumerated() {
                group.enter()
                
                let compAttachment = draft.attachments[index]
                let formAttachment = FormAttachment(mimeType: mimeType, data: data, fileName: "file")
                let request = Client.upload(attachment: formAttachment, description: compAttachment.attachmentDescription)
                self.mastodonController.run(request) { (response) in
                    switch response {
                    case let .failure(error):
                        uploadedAttachments.append(.failure(error))
                        anyFailed = true
                        
                    case let .success(attachment, _):
                        self.postProgress += 1
                        uploadedAttachments.append(.success(attachment))
                    }
                    
                    group.leave()
                }
                
                group.wait()
            }
            
            
            if anyFailed {
                let errors = uploadedAttachments.map { (result) -> Error? in
                    if case let .failure(error) = result {
                        return error
                    } else {
                        return nil
                    }
                }
                completion(.failure(AttachmentUploadError(errors: errors)))
            } else {
                let uploadedAttachments = uploadedAttachments.map {
                    try! $0!.get()
                }
                completion(.success(uploadedAttachments))
            }

        }
    }
}

fileprivate protocol PostError: LocalizedError {}

extension PostError {
    var localizedDescription: String {
        if let self = self as? Client.Error {
            return self.localizedDescription
        } else if let self = self as? AttachmentUploadError {
            return self.localizedDescription
        } else {
            return "Unknown Error"
        }
    }
}

extension Client.Error: PostError {}

fileprivate struct AttachmentUploadError: PostError {
    let errors: [Error?]
    
    var localizedDescription: String {
        return errors.enumerated().compactMap { (index, error) -> String? in
            guard let error = error else { return nil }
            let description: String
            // need to downcast to use more specific localizedDescription impl from Pachyderm
            if let error = error as? Client.Error {
                description = error.localizedDescription
            } else {
                description = error.localizedDescription
            }
            return "Attachment \(index + 1): \(description)"
        }.joined(separator: ",\n")
    }
}

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