Tusker/Tusker/Views/Attachment Cells/ComposeAttachmentTableViewCell.swift

//
//  ComposeAttachmentTableViewCell.swift
//  Tusker
//
//  Created by Shadowfacts on 3/13/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Photos
import AVFoundation
import Vision

protocol ComposeAttachmentTableViewCellDelegate: class {
    func composeAttachment(_ cell: ComposeAttachmentTableViewCell, present viewController: UIViewController, animated: Bool)
    func removeAttachment(_ cell: ComposeAttachmentTableViewCell)
    func attachmentDescriptionChanged(_ cell: ComposeAttachmentTableViewCell)
    func composeAttachmentDescriptionHeightChanged(_ cell: ComposeAttachmentTableViewCell)
}

class ComposeAttachmentTableViewCell: UITableViewCell {
    
    weak var delegate: ComposeAttachmentTableViewCellDelegate?

    @IBOutlet weak var assetImageView: UIImageView!
    @IBOutlet weak var descriptionTextView: UITextView!
    @IBOutlet weak var descriptionTextViewHeightConstraint: NSLayoutConstraint!
    @IBOutlet weak var descriptionPlaceholderLabel: UILabel!
    @IBOutlet weak var removeButton: UIButton!
    @IBOutlet weak var activityIndicator: UIActivityIndicatorView!
    
    var attachment: CompositionAttachment!
    
    var state: State = .allowEntry {
        didSet {
            switch state {
            case .allowEntry:
                descriptionTextView.isEditable = true
                updateDescriptionPlaceholderLabel()
                activityIndicator.stopAnimating()
            case .recognizingText:
                descriptionTextView.isEditable = false
                descriptionPlaceholderLabel.isHidden = true
                activityIndicator.startAnimating()
            }
        }
    }
    
    private var textRecognitionRequest: VNRecognizeTextRequest?

    override func awakeFromNib() {
        super.awakeFromNib()
        
        assetImageView.layer.masksToBounds = true
        assetImageView.layer.cornerRadius = 8
        
        descriptionTextView.delegate = self
    }
    
    func updateUI(for attachment: CompositionAttachment) {
        self.attachment = attachment
        
        descriptionTextView.text = attachment.attachmentDescription
        updateDescriptionPlaceholderLabel()

        assetImageView.contentMode = .scaleAspectFill
        assetImageView.backgroundColor = .secondarySystemBackground
        switch attachment.data {
        case let .image(image):
            assetImageView.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
                guard self.attachment == attachment else { return }
                self.assetImageView.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) {
                assetImageView.image = UIImage(cgImage: cgImage)
            }
        case let .drawing(drawing):
            assetImageView.image = drawing.imageInLightMode(from: drawing.bounds)
            assetImageView.contentMode = .scaleAspectFit
            assetImageView.backgroundColor = .white
        }
    }
    
    func updateDescriptionPlaceholderLabel() {
        descriptionPlaceholderLabel.isHidden = !descriptionTextView.text.isEmpty
    }
    
    func setEnabled(_ enabled: Bool) {
        descriptionTextView.isEditable = enabled
        removeButton.isEnabled = enabled
    }
    
    func recognizeTextFromImage() {
        precondition(attachment.data.type == .image)
        state = .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 {
                        self.state = .allowEntry
    
                        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.descriptionTextView.text = text
                            self.textViewDidChange(self.descriptionTextView)
                        }
                    }
                }
                request.recognitionLevel = .accurate
                request.usesLanguageCorrection = true
                self.textRecognitionRequest = request
                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.state = .allowEntry
                            let title = NSLocalizedString("Text Recognition Failed", comment: "text recognition error alert title")
                            let message = error.localizedDescription
                            let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
                            self.delegate?.composeAttachment(self, present: alert, animated: true)
                        }
                    }
                }
            }
        }
    }
    
    override func prepareForReuse() {
        super.prepareForReuse()
        assetImageView.image = nil
        descriptionTextViewHeightConstraint.constant = 80
    }

    @IBAction func removeButtonPressed(_ sender: Any) {
        textRecognitionRequest?.cancel()
        delegate?.removeAttachment(self)
    }
    
}

extension ComposeAttachmentTableViewCell {
    enum State {
        case allowEntry, recognizingText
    }
}

extension ComposeAttachmentTableViewCell: UITextViewDelegate {
    func textViewDidChange(_ textView: UITextView) {
        attachment.attachmentDescription = textView.text
        updateDescriptionPlaceholderLabel()
        delegate?.attachmentDescriptionChanged(self)
        let smallestSize = textView.sizeThatFits(CGSize(width: textView.bounds.width, height: .greatestFiniteMagnitude))
        let old = descriptionTextViewHeightConstraint.constant
        descriptionTextViewHeightConstraint.constant = max(80, smallestSize.height)
        if old != descriptionTextViewHeightConstraint.constant {
            delegate?.composeAttachmentDescriptionHeightChanged(self)
        }

    }
}