Tusker/Tusker/Screens/Compose/ComposeAttachmentRow.swift

//
//  ComposeAttachmentRow.swift
//  Tusker
//
//  Created by Shadowfacts on 8/19/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import SwiftUI
import Photos
import AVFoundation
import Vision

struct ComposeAttachmentRow: View {
    @ObservedObject var draft: Draft
    @ObservedObject var attachment: CompositionAttachment
    let heightChanged: (CGFloat) -> Void
    
    @EnvironmentObject var uiState: ComposeUIState
    @State private var mode: Mode = .allowEntry
    @State private var image: UIImage? = nil
    @State private var imageContentMode: ContentMode = .fill
    @State private var imageBackgroundColor: Color = .black
    @State private var isShowingTextRecognitionFailedAlert = false
    @State private var textRecognitionErrorMessage: String? = nil
    
    @Environment(\.colorScheme) private var colorScheme: ColorScheme
    
    var body: some View {
        HStack(alignment: .center, spacing: 4) {
            imageView
                .frame(width: 80, height: 80)
                .cornerRadius(8)
                .contextMenu {
                    if case .drawing(_) = attachment.data {
                        Button(action: self.editDrawing) {
                            Label("Edit Drawing", systemImage: "hand.draw")
                        }
                    } else if attachment.data.type == .image {
                        Button(action: self.recognizeText) {
                            Label("Recognize Text", systemImage: "doc.text.viewfinder")
                        }
                    }
                }
            
            switch mode {
            case .allowEntry:
                ComposeTextView(text: $attachment.attachmentDescription, placeholder: Text("Describe for the visually impaired…"), minHeight: 80)
                    .heightDidChange(self.heightChanged)
                    .backgroundColor(.clear)
                    .fontSize(17)
                
            case .recognizingText:
                ProgressView()
            }
            
            
            // todo: find a way to make this button not activated when the list row is selected, see FB8595628
//            Button(action: self.removeAttachment) {
//                Image(systemName: "xmark.circle.fill")
//                    .foregroundColor(.blue)
//            }
        }
        .onAppear(perform: self.loadImage)
        .onReceive(attachment.$attachmentDescription) { (newDesc) in
            if newDesc.isEmpty {
                uiState.attachmentsMissingDescriptions.insert(attachment.id)
            } else {
                uiState.attachmentsMissingDescriptions.remove(attachment.id)
            }
        }
        .alert(isPresented: $isShowingTextRecognitionFailedAlert) {
            Alert(
                title: Text("Text Recognition Failed"),
                message: Text(self.textRecognitionErrorMessage ?? ""),
                dismissButton: .default(Text("OK"))
            )
        }
    }
    
    @ViewBuilder
    private var imageView: some View {
        if let image = image {
            Image(uiImage: image)
                .resizable()
                .aspectRatio(contentMode: imageContentMode)
                .background(imageBackgroundColor)
        } else {
            Image(systemName: placeholderImageName)
        }
    }
    
    private var placeholderImageName: String {
        switch colorScheme {
        case .dark:
            return "photo.fill"
        case .light:
            return "photo"
        @unknown default:
            return "photo"
        }
    }
    
    private func loadImage() {
        switch attachment.data {
        case let .image(image):
            self.image = image
        case let .asset(asset):
            let size = CGSize(width: 80, height: 80)
            PHImageManager.default().requestImage(for: asset, targetSize: size, contentMode: .aspectFill, options: nil) { (image, _) in
                DispatchQueue.main.async {
                    self.image = image
                }
            }
        case let .video(url):
            let asset = AVURLAsset(url: url)
            let imageGenerator = AVAssetImageGenerator(asset: asset)
            if let cgImage = try? imageGenerator.copyCGImage(at: .zero, actualTime: nil) {
                self.image = UIImage(cgImage: cgImage)
            }
        case let .drawing(drawing):
            image = drawing.imageInLightMode(from: drawing.bounds)
            imageContentMode = .fit
            imageBackgroundColor = .white
        }
    }
    
    private func removeAttachment() {
        draft.attachments.removeAll { $0.id == attachment.id }
    }
    
    private func editDrawing() {
        uiState.composeDrawingMode = .edit(id: attachment.id)
        uiState.delegate?.presentComposeDrawing()
    }
    
    private func recognizeText() {
        mode = .recognizingText
        
        DispatchQueue.global(qos: .userInitiated).async {
            self.attachment.data.getData { (data, mimeType) in
                let handler = VNImageRequestHandler(data: data, options: [:])
                let request = VNRecognizeTextRequest { (request, error) in
                    DispatchQueue.main.async {
                        if let results = request.results as? [VNRecognizedTextObservation] {
                            var text = ""
                            for observation in results {
                                let result = observation.topCandidates(1).first!
                                text.append(result.string)
                                text.append("\n")
                            }
                            self.attachment.attachmentDescription = text
                        }
                        
                        self.mode = .allowEntry
                    }
                }
                request.recognitionLevel = .accurate
                request.usesLanguageCorrection = true
                DispatchQueue.global(qos: .userInitiated).async {
                    do {
                        try handler.perform([request])
                    } catch {
                        // The perform call throws an error with code 1 if the request is cancelled, which we don't want to show an alert for.
                        guard (error as NSError).code != 1 else { return }
                        DispatchQueue.main.async {
                            self.mode = .allowEntry
                            self.isShowingTextRecognitionFailedAlert = true
                            self.textRecognitionErrorMessage = error.localizedDescription
                        }
                    }
                }
            }
        }
    }
}

extension ComposeAttachmentRow {
    enum Mode {
        case allowEntry, recognizingText
    }
}

//struct ComposeAttachmentRow_Previews: PreviewProvider {
//    static var previews: some View {
//        ComposeAttachmentRow()
//    }
//}