Tusker/Tusker/Screens/Compose/EmojiPickerCollectionViewController.swift

//
//  EmojiPickerCollectionViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 10/12/20.
//  Copyright © 2020 Shadowfacts. All rights reserved.
//

import UIKit
import Pachyderm

private let reuseIdentifier = "EmojiCell"

protocol EmojiPickerCollectionViewControllerDelegate: AnyObject {
    func selectedEmoji(_ emoji: Emoji)
}

// It would be nice to replace this with a LazyVGrid when the deployment target is bumped to 14.0
class EmojiPickerCollectionViewController: UICollectionViewController {

    weak var delegate: EmojiPickerCollectionViewControllerDelegate?
    
    private weak var mastodonController: MastodonController!

    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    
    var searchQuery: String = "" {
        didSet {
            guard let emojis = mastodonController.customEmojis else { return }
            let snapshot = createFilteredSnapshot(emojis: emojis)
            DispatchQueue.main.async {
                self.dataSource.apply(snapshot)
            }
        }
    }
    
    init(mastodonController: MastodonController) {
        self.mastodonController = mastodonController
        
        let itemWidth = NSCollectionLayoutDimension.fractionalWidth(1.0 / 10)
        let itemSize = NSCollectionLayoutSize(widthDimension: itemWidth, heightDimension: itemWidth)
        let item = NSCollectionLayoutItem(layoutSize: itemSize)
        
        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: itemWidth)
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
        group.interItemSpacing = .fixed(4)
        
        let section = NSCollectionLayoutSection(group: group)
        section.interGroupSpacing = 4
        
        let layout = UICollectionViewCompositionalLayout(section: section)
        
        super.init(collectionViewLayout: layout)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        additionalSafeAreaInsets = UIEdgeInsets(top: 0, left: 8, bottom: 0, right: 8)
        // use negative indicator insets to bring the indicators back to the edge of the containing view
        // using collectionView.contentInset doesn't work the compositional layout ignores the inset when calculating fractional widths
        collectionView.scrollIndicatorInsets = UIEdgeInsets(top: 0, left: -8, bottom: 0, right: -8)
        collectionView.contentInset = UIEdgeInsets(top: 8, left: 0, bottom: 8, right: 0)
        
        collectionView.backgroundColor = .clear
        collectionView.register(EmojiCollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
        
        dataSource = UICollectionViewDiffableDataSource(collectionView: collectionView) { (collectionView, indexPath, item) -> UICollectionViewCell? in
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! EmojiCollectionViewCell
            cell.updateUI(emoji: item.emoji)
            return cell
        }
        
        mastodonController.getCustomEmojis { (emojis) in
            DispatchQueue.main.async {
                self.dataSource.apply(self.createFilteredSnapshot(emojis: emojis))
            }
        }
    }
    
    private func createFilteredSnapshot(emojis: [Emoji]) -> NSDiffableDataSourceSnapshot<Section, Item> {
        let items: [Item]
        if searchQuery.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
            items = emojis.map { Item(emoji: $0) }
        } else {
            items = emojis
                .map { ($0, FuzzyMatcher.match(pattern: searchQuery, str: $0.shortcode)) }
                .filter(\.1.matched)
                .sorted { $0.1.score > $1.1.score }
                .map { Item(emoji: $0.0) }
        }
        
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        snapshot.appendSections([.emojis])
        snapshot.appendItems(items)
        return snapshot
    }

    // MARK: UICollectionViewDelegate
    
    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath) else { return }
        delegate?.selectedEmoji(item.emoji)
    }

}

extension EmojiPickerCollectionViewController {
    enum Section {
        case emojis
    }
    
    struct Item: Hashable, Equatable {
        let emoji: Emoji
        
        func hash(into hasher: inout Hasher) {
            hasher.combine(emoji.shortcode)
        }
        
        static func ==(lhs: Item, rhs: Item) -> Bool {
            lhs.emoji.shortcode == rhs.emoji.shortcode
        }
    }
}