Tusker/Tusker/Views/EmojiLabel.swift

//
//  EmojiLabel.swift
//  Tusker
//
//  Created by Shadowfacts on 3/1/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm

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

class EmojiLabel: UILabel {
    
    private var emojiIdentifier: String?
    private var emojiRequests: [ImageCache.Request] = []
    
    func setEmojis(_ emojis: [Emoji], identifier: String) {
        guard emojis.count > 0, let attributedText = attributedText else { return }
        
        self.emojiIdentifier = identifier
        emojiRequests.forEach { $0.cancel() }
        emojiRequests = []
        
        let matches = emojiRegex.matches(in: attributedText.string, options: [], range: attributedText.fullRange)
        let emojiImages = CachedDictionary<UIImage>(name: "EmojiLabel Emoji Images")
        
        let group = DispatchGroup()
        
        for emoji in emojis {
            // only make requests for emojis that are present in the text to avoid making unnecessary network requests
            guard matches.contains(where: { (match) in
                let matchShortcode = (attributedText.string as NSString).substring(with: match.range(at: 1))
                return emoji.shortcode == matchShortcode
            }) else {
                continue
            }
            
            group.enter()
            let request = ImageCache.emojis.get(emoji.url) { (data) in
                defer { group.leave() }
                guard let data = data, let image = UIImage(data: data) else {
                    return
                }
                emojiImages[emoji.shortcode] = image
            }
            if let request = request {
                emojiRequests.append(request)
            }
        }
        
        group.notify(queue: .main) { [weak self] in
            // if e.g. the account changes before all emojis are loaded, don't bother trying to set them
            guard let self = self, self.emojiIdentifier == identifier else { return }
            
            let mutAttrString = NSMutableAttributedString(attributedString: attributedText)
            // replaces the emojis starting from the end of the string as to not alter the indicies of preceeding emojis
            for match in matches.reversed() {
                let shortcode = (mutAttrString.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)
                let attachmentStr = NSAttributedString(attachment: attachment)
                mutAttrString.replaceCharacters(in: match.range, with: attachmentStr)
            }
            
            self.attributedText = mutAttrString
            self.setNeedsLayout()
            self.setNeedsDisplay()
        }
    }
    
    func removeEmojis() {
        emojiIdentifier = nil
        emojiRequests.forEach { $0.cancel() }
        emojiRequests = []
    }
    
}

extension EmojiLabel {
    func updateForAccountDisplayName(account: Account) {
        if Preferences.shared.hideCustomEmojiInUsernames {
            self.text = account.displayNameWithoutCustomEmoji
            self.removeEmojis()
        } else {
            self.text = account.displayOrUserName
            self.setEmojis(account.emojis, identifier: account.id)
        }
    }
}