Tusker/Tusker/Views/ContentTextView.swift

//
//  ContentTextView.swift
//  Tusker
//
//  Created by Shadowfacts on 1/18/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import SwiftSoup
import Pachyderm
import SafariServices

private let emojiRegex = try! NSRegularExpression(pattern: ":(\\w+):", options: [])

class ContentTextView: LinkTextView {
    
    weak var navigationDelegate: TuskerNavigationDelegate?
    weak var overrideMastodonController: MastodonController?
    var mastodonController: MastodonController? { overrideMastodonController ?? navigationDelegate?.apiController }

    var defaultFont: UIFont = .systemFont(ofSize: 17)
    var defaultColor: UIColor = .label
    
    private(set) var hasEmojis = false
    
    // The link range currently being previewed
    private var currentPreviewedLinkRange: NSRange?
    // The preview created in the previewForHighlighting method, so that we can use the same one in previewForDismissing.
    private weak var currentTargetedPreview: UITargetedPreview?
    
    override func awakeFromNib() {
        super.awakeFromNib()
        
        delegate = self
        
        // Disable layer masking, otherwise the context menu opening animation
        // may be clipped if it's at an edge of the text view
        layer.masksToBounds = false
        addInteraction(UIContextMenuInteraction(delegate: self))
        
        textDragInteraction?.isEnabled = false
        
        textContainerInset = .zero
        textContainer.lineFragmentPadding = 0
        
        // the text view's builtin link interaction code is tied to isSelectable, so we need to use our own tap recognizer
        let recognizer = UITapGestureRecognizer(target: self, action: #selector(textTapped(_:)))
        addGestureRecognizer(recognizer)
    }
    
    // MARK: - Emojis
    func setEmojis(_ emojis: [Emoji]) {
        guard !emojis.isEmpty else {
            hasEmojis = false
            return
        }
        hasEmojis = true
        
        let emojiImages = MultiThreadDictionary<String, UIImage>(name: "ContentTextView Emoji Images")
        
        let group = DispatchGroup()
        
        for emoji in emojis {
            group.enter()
            _ = ImageCache.emojis.get(emoji.url) { (_, image) in
                defer { group.leave() }
                guard let image = image,
                      let transformedImage = ImageGrayscalifier.convertIfNecessary(url: emoji.url, image: image) else {
                    return
                }
                emojiImages[emoji.shortcode] = transformedImage
            }
        }
        
        group.notify(queue: .main) {
            let mutAttrString = NSMutableAttributedString(attributedString: self.attributedText!)
            let string = mutAttrString.string
            let matches = emojiRegex.matches(in: string, options: [], range: mutAttrString.fullRange)
            // replaces the emojis started from the end of the string as to not alter the indexes of the other emojis
            for match in matches.reversed() {
                let shortcode = (string as NSString).substring(with: match.range(at: 1))
                guard let emojiImage = emojiImages[shortcode] else {
                    continue
                }
                
                let attachment = NSTextAttachment(emojiImage: emojiImage, in: self.font!, with: self.textColor ?? .label)
                let attachmentStr = NSAttributedString(attachment: attachment)
                mutAttrString.replaceCharacters(in: match.range, with: attachmentStr)
            }
            
            self.attributedText = mutAttrString
            self.setNeedsLayout()
            self.setNeedsDisplay()
        }
    }

    // MARK: - HTML Parsing
    func setTextFromHtml(_ html: String) {
        let doc = try! SwiftSoup.parse(html)
        let body = doc.body()!
        
        let attributedText = attributedTextForHTMLNode(body)
        let mutAttrString = NSMutableAttributedString(attributedString: attributedText)
        mutAttrString.trimTrailingCharactersInSet(.whitespacesAndNewlines)
        mutAttrString.collapseWhitespace()
        
        self.attributedText = mutAttrString
    }
    
    private func attributedTextForHTMLNode(_ node: Node, usePreformattedText: Bool = false) -> NSAttributedString {
        switch node {
        case let node as TextNode:
            let text: String
            if usePreformattedText {
                text = node.getWholeText()
            } else {
                text = node.text()
            }
            return NSAttributedString(string: text, attributes: [.font: defaultFont, .foregroundColor: defaultColor])
        case let node as Element:
            let attributed = NSMutableAttributedString(string: "", attributes: [.font: defaultFont, .foregroundColor: defaultColor])
            for child in node.getChildNodes() {
                attributed.append(attributedTextForHTMLNode(child, usePreformattedText: usePreformattedText || node.tagName() == "pre"))
            }
            
            switch node.tagName() {
            case "br":
                attributed.append(NSAttributedString(string: "\n"))
            case "a":
                if let link = try? node.attr("href"),
                    let url = URL(string: link) {
                    attributed.addAttribute(.link, value: url, range: attributed.fullRange)
                }
            case "p":
                attributed.append(NSAttributedString(string: "\n\n"))
            case "em", "i":
                let currentFont: UIFont = attributed.attribute(.font, at: 0, effectiveRange: nil) as? UIFont ?? self.font!
                attributed.addAttribute(.font, value: currentFont.withTraits(.traitItalic)!, range: attributed.fullRange)
            case "strong", "b":
                let currentFont: UIFont = attributed.attribute(.font, at: 0, effectiveRange: nil) as? UIFont ?? self.font!
                attributed.addAttribute(.font, value: currentFont.withTraits(.traitBold)!, range: attributed.fullRange)
            case "del":
                attributed.addAttribute(.strikethroughStyle, value: NSUnderlineStyle.single.rawValue, range: attributed.fullRange)
            case "code":
                attributed.addAttribute(.font, value: UIFont.monospacedSystemFont(ofSize: self.font!.pointSize, weight: .regular), range: attributed.fullRange)
            case "pre":
                attributed.addAttribute(.font, value: UIFont.monospacedSystemFont(ofSize: self.font!.pointSize, weight: .regular), range: attributed.fullRange)
                attributed.append(NSAttributedString(string: "\n\n"))
            case "ol", "ul":
                attributed.trimLeadingCharactersInSet(.whitespacesAndNewlines)
                attributed.append(NSAttributedString(string: "\n\n"))
            case "li":
                let parentEl = node.parent()!
                let parentTag = parentEl.tagName()
                let bullet: NSAttributedString
                if parentTag == "ol" {
                    let index = (try? node.elementSiblingIndex()) ?? 0
                    // we use the monospace digit font so that the periods of all the list items line up
                    bullet = NSAttributedString(string: "\(index + 1).\t", attributes: [.font: UIFont.monospacedDigitSystemFont(ofSize: self.font!.pointSize, weight: .regular)])
                } else if parentTag == "ul" {
                    bullet = NSAttributedString(string: "\u{2022}\t")
                } else {
                    bullet = NSAttributedString()
                }
                attributed.insert(bullet, at: 0)
                attributed.append(NSAttributedString(string: "\n"))
            default:
                break
            }
            
            return attributed
        default:
            fatalError("Unexpected node type \(type(of: node))")
        }
    }
    
    // MARK: - Interaction
    
    // only accept touches that are over a link
    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        if getLinkAtPoint(point) != nil || isSelectable {
            return super.hitTest(point, with: event)
        } else {
            return nil
        }
    }
    
    @objc func textTapped(_ recognizer: UITapGestureRecognizer) {
        // if there currently is a selection, deselct it on single-tap
        if selectedRange.length > 0 {
            // location doesn't matter since we are non-editable and the cursor isn't visible
            selectedRange = NSRange(location: 0, length: 0)
        }
        
        let location = recognizer.location(in: self)
        if let (link, range) = getLinkAtPoint(location) {
            let text = (self.text as NSString).substring(with: range)
            handleLinkTapped(url: link, text: text)
        }
    }

    func getLinkAtPoint(_ point: CGPoint) -> (URL, NSRange)? {
        let locationInTextContainer = CGPoint(x: point.x - textContainerInset.left, y: point.y - textContainerInset.top)
        var partialFraction: CGFloat = 0
        let characterIndex = layoutManager.characterIndex(for: locationInTextContainer, in: textContainer, fractionOfDistanceBetweenInsertionPoints: &partialFraction)
        if characterIndex < textStorage.length && partialFraction < 1 {
            var range = NSRange()
            if let link = textStorage.attribute(.link, at: characterIndex, longestEffectiveRange: &range, in: textStorage.fullRange) as? URL {
                return (link, range)
            }
        }
        return nil
    }
    
    func handleLinkTapped(url: URL, text: String) {
        if let mention = getMention(for: url, text: text) {
            navigationDelegate?.selected(mention: mention)
        } else if let tag = getHashtag(for: url, text: text) {
            navigationDelegate?.selected(tag: tag)
        } else {
            navigationDelegate?.selected(url: url)
        }
    }
    
    // MARK: - Navigation
    
    func getViewController(forLink url: URL, inRange range: NSRange) -> UIViewController {
        let text = (self.text as NSString).substring(with: range)
        
        if let mention = getMention(for: url, text: text) {
            return ProfileViewController(accountID: mention.id, mastodonController: mastodonController!)
        } else if let tag = getHashtag(for: url, text: text) {
            return HashtagTimelineViewController(for: tag, mastodonController: mastodonController!)
        } else {
            return SFSafariViewController(url: url)
        }
    }
    
    open func getMention(for url: URL, text: String) -> Mention? {
        return nil
    }
    
    open func getHashtag(for url: URL, text: String) -> Hashtag? {
        if text.starts(with: "#") {
            let tag = String(text.dropFirst())
            return Hashtag(name: tag, url: url)
        } else {
            return nil
        }
    }

}

extension ContentTextView: UITextViewDelegate {
    func textView(_ textView: UITextView, shouldInteractWith URL: URL, in characterRange: NSRange, interaction: UITextItemInteraction) -> Bool {
        // disable the text view's link interactions, we handle tapping links ourself with a gesture recognizer
        return false
    }
}

extension ContentTextView: MenuPreviewProvider {
    func getPreviewProviders(for location: CGPoint, sourceViewController: UIViewController) -> PreviewProviders? {
        fatalError("unimplemented")
    }
}

extension ContentTextView: UIContextMenuInteractionDelegate {
    func contextMenuInteraction(_ interaction: UIContextMenuInteraction, configurationForMenuAtLocation location: CGPoint) -> UIContextMenuConfiguration? {
        if let (link, range) = getLinkAtPoint(location) {
            // Store the previewed link range for use in the previewForHighlighting method
            currentPreviewedLinkRange = range
            
            let preview: UIContextMenuContentPreviewProvider = {
                self.getViewController(forLink: link, inRange: range)
            }
            let actions: UIContextMenuActionProvider = { (_) in
                let text = (self.text as NSString).substring(with: range)
                let actions: [UIMenuElement]
                if let mention = self.getMention(for: link, text: text) {
                    actions = self.actionsForProfile(accountID: mention.id, sourceView: self)
                } else if let tag = self.getHashtag(for: link, text: text) {
                    actions = self.actionsForHashtag(tag, sourceView: self)
                } else {
                    actions = self.actionsForURL(link, sourceView: self)
                }
                return UIMenu(title: "", image: nil, identifier: nil, options: [], children: actions)
            }
            
            return UIContextMenuConfiguration(identifier: nil, previewProvider: preview, actionProvider: actions)
        } else {
            currentPreviewedLinkRange = nil
            return nil
        }
    }
    
    func contextMenuInteraction(_ interaction: UIContextMenuInteraction, previewForHighlightingMenuWithConfiguration configuration: UIContextMenuConfiguration) -> UITargetedPreview? {
        // If there isn't a link range, use the default system-generated preview.
        guard let range = currentPreviewedLinkRange else {
            return nil
        }
        currentPreviewedLinkRange = nil
        
        // Determine the line rects that the link takes up in the coordinate space of this view.
        var rects = [CGRect]()
        layoutManager.enumerateEnclosingRects(forGlyphRange: range, withinSelectedGlyphRange: NSRange(location: NSNotFound, length: 0), in: textContainer) { (rect, stop) in
            rects.append(rect)
        }
        
        // Try to create a snapshot view of this view to disply as the preview.
        // If a snapshot view cannot be created, we bail and use the system-provided preview.
        guard let snapshot = self.snapshotView(afterScreenUpdates: false) else {
            return nil
        }
        
        // Mask the snapshot layer to only show the text of the link, and nothing else.
        // By default, the system-applied mask is too wide and other content may seep in.
        let path = UIBezierPath(wrappingAround: rects)
        let maskLayer = CAShapeLayer()
        maskLayer.path = path.cgPath
        snapshot.layer.mask = maskLayer
        
        // The preview parameters describe how the preview view is shown inside the preview.
        let parameters = UIPreviewParameters(textLineRects: rects as [NSValue])
        
        // Calculate the smallest rect enclosing all of the text line rects, in the coordinate space of this view.
        var minX: CGFloat = .greatestFiniteMagnitude, maxX: CGFloat = -.greatestFiniteMagnitude, minY: CGFloat = .greatestFiniteMagnitude, maxY: CGFloat = -.greatestFiniteMagnitude
        for rect in rects {
            minX = min(rect.minX, minX)
            maxX = max(rect.maxX, maxX)
            minY = min(rect.minY, minY)
            maxY = max(rect.maxY, maxY)
        }
        // The center point of the the minimum enclosing rect in our coordinate space is the point where the
        // center of the preview should be, since that's also in this view's coordinate space.
        let rectsCenter = CGPoint(x: (minX + maxX) / 2, y: (minY + maxY) / 2)
        
        // The preview target describes how the preview is positioned.
        let target = UIPreviewTarget(container: self, center: rectsCenter)
        
        // Create a dummy containerview for the snapshot view, since using a view with a CALayer mask and UIPreviewParameters(textLineRects:)
        // causes the mask to be ignored. See FB7832297
        let snapshotContainer = UIView(frame: snapshot.bounds)
        snapshotContainer.backgroundColor = .systemBackground
        snapshotContainer.addSubview(snapshot)
        
        let preview = UITargetedPreview(view: snapshotContainer, parameters: parameters, target: target)
        currentTargetedPreview = preview
        return preview
    }
    
    func contextMenuInteraction(_ interaction: UIContextMenuInteraction, previewForDismissingMenuWithConfiguration configuration: UIContextMenuConfiguration) -> UITargetedPreview? {
        // Use the same preview for dismissing as was used for highlighting, so that the link animates back to the original position.
        return currentTargetedPreview
    }
    
    func contextMenuInteraction(_ interaction: UIContextMenuInteraction, willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration, animator: UIContextMenuInteractionCommitAnimating) {
        if let viewController = animator.previewViewController {
            animator.preferredCommitStyle = .pop
            animator.addCompletion {
                self.navigationDelegate?.show(viewController)
            }
        }
    }
}