protocol EmojiPickerCollectionViewDelegate: AnyObject {
    func emojiPicker(_ emojiPicker: EmojiPickerCollectionView, didSelectEmoji emoji: EmojiWithSkinTones)
    func emojiPickerWillBeginDragging(_ emojiPicker: EmojiPickerCollectionView)
}

class EmojiPickerCollectionView: UICollectionView {
    let layout: UICollectionViewFlowLayout

    weak var pickerDelegate: EmojiPickerCollectionViewDelegate?

    private var recentEmoji: [EmojiWithSkinTones] = []
    var hasRecentEmoji: Bool { !recentEmoji.isEmpty }

    private var allSendableEmojiByCategory: [Emoji.Category: [EmojiWithSkinTones]] = [:]
    private lazy var allSendableEmoji: [EmojiWithSkinTones] = {
        return Array(allSendableEmojiByCategory.values).flatMap({$0})
    }()

    static let emojiWidth: CGFloat = 38
    static let margins: CGFloat = 16
    static let minimumSpacing: CGFloat = 10

    public var searchText: String? {
        didSet {
            searchWithText(searchText)
        }
    }

    private var emojiSearchResults: [EmojiWithSkinTones] = []

    public var isSearching: Bool {
        if let searchText = searchText, searchText.count != 0 {
            return true
        }

        return false
    }

    lazy var tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(dismissSkinTonePicker))

    init() {
        layout = UICollectionViewFlowLayout()
        layout.itemSize = CGSize(width: Self.emojiWidth, height: Self.emojiWidth)
        layout.minimumInteritemSpacing = EmojiPickerCollectionView.minimumSpacing
        layout.sectionInset = UIEdgeInsets(top: 0, leading: EmojiPickerCollectionView.margins, bottom: 0, trailing: EmojiPickerCollectionView.margins)

        super.init(frame: .zero, collectionViewLayout: layout)

        delegate = self
        dataSource = self

        register(EmojiCell.self, forCellWithReuseIdentifier: EmojiCell.reuseIdentifier)
        register(
            EmojiSectionHeader.self,
            forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
            withReuseIdentifier: EmojiSectionHeader.reuseIdentifier
        )

        backgroundColor = .clear

        let longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(handleLongPress))
        panGestureRecognizer.require(toFail: longPressGesture)
        addGestureRecognizer(longPressGesture)

        addGestureRecognizer(tapGestureRecognizer)
        tapGestureRecognizer.delegate = self
        
        Storage.read { transaction in
            self.recentEmoji = Storage.shared.getRecentEmoji(transaction: transaction)

            // Some emoji have two different code points but identical appearances. Let's remove them!
            // If we normalize to a different emoji than the one currently in our array, we want to drop
            // the non-normalized variant if the normalized variant already exists. Otherwise, map to the
            // normalized variant.
            for (idx, emoji) in self.recentEmoji.enumerated().reversed() {
                if !emoji.isNormalized {
                    if self.recentEmoji.contains(emoji.normalized) {
                        self.recentEmoji.remove(at: idx)
                    } else {
                        self.recentEmoji[idx] = emoji.normalized
                    }
                }
            }

            self.allSendableEmojiByCategory = Emoji.allSendableEmojiByCategoryWithPreferredSkinTones(transaction: transaction)
        }
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // This is not an exact calculation, but is simple and works for our purposes.
    var numberOfColumns: Int { Int((self.width()) / (EmojiPickerCollectionView.emojiWidth + EmojiPickerCollectionView.minimumSpacing)) }

    // At max, we show 3 rows of recent emoji
    private var maxRecentEmoji: Int { numberOfColumns * 3 }
    private var categoryIndexOffset: Int { hasRecentEmoji ? 1 : 0}

    func emojiForSection(_ section: Int) -> [EmojiWithSkinTones] {
        guard section > 0 || !hasRecentEmoji else { return Array(recentEmoji[0..<min(maxRecentEmoji, recentEmoji.count)]) }

        guard let category = Emoji.Category.allCases[safe: section - categoryIndexOffset] else {
            owsFailDebug("Unexpectedly missing category for section \(section)")
            return []
        }

        guard let categoryEmoji = allSendableEmojiByCategory[category] else {
            owsFailDebug("Unexpectedly missing emoji for category \(category)")
            return []
        }

        return categoryEmoji
    }

    func emojiForIndexPath(_ indexPath: IndexPath) -> EmojiWithSkinTones? {
        return isSearching ? emojiSearchResults[safe: indexPath.row] : emojiForSection(indexPath.section)[safe: indexPath.row]
    }

    func nameForSection(_ section: Int) -> String? {
        guard section > 0 || !hasRecentEmoji else {
            return NSLocalizedString("EMOJI_CATEGORY_RECENTS_NAME",
                                     comment: "The name for the emoji category 'Recents'")
        }

        guard let category = Emoji.Category.allCases[safe: section - categoryIndexOffset] else {
            owsFailDebug("Unexpectedly missing category for section \(section)")
            return nil
        }

        return category.localizedName
    }

    // MARK: - Search

    func searchWithText(_ searchText: String?) {
        if let searchText = searchText {
            emojiSearchResults = allSendableEmoji.filter { emoji in
                return emoji.baseEmoji.name.range(of: searchText, options: [.caseInsensitive, .anchored]) != nil
            }
        } else {
            emojiSearchResults = []
        }

        reloadData()
    }

    var scrollingToSection: Int?
    func scrollToSectionHeader(_ section: Int, animated: Bool) {
        guard let attributes = layoutAttributesForSupplementaryElement(
            ofKind: UICollectionView.elementKindSectionHeader,
            at: IndexPath(item: 0, section: section)
        ) else { return }
        scrollingToSection = section
        setContentOffset(CGPoint(x: 0, y: (attributes.frame.minY - contentInset.top)), animated: animated)
    }

    private weak var currentSkinTonePicker: EmojiSkinTonePicker?

    @objc
    func handleLongPress(sender: UILongPressGestureRecognizer) {

        switch sender.state {
        case .began:
            let point = sender.location(in: self)
            guard let indexPath = indexPathForItem(at: point) else { return }
            guard let emoji = emojiForIndexPath(indexPath) else { return }
            guard let cell = cellForItem(at: indexPath) else { return }

            currentSkinTonePicker?.dismiss()
            currentSkinTonePicker = EmojiSkinTonePicker.present(referenceView: cell, emoji: emoji) { [weak self] emoji in
                guard let self = self else { return }

                if let emoji = emoji {
                    Storage.write { transaction in
                        Storage.shared.recordRecentEmoji(emoji, transaction: transaction)
                        emoji.baseEmoji.setPreferredSkinTones(emoji.skinTones, transaction: transaction)
                    }

                    self.pickerDelegate?.emojiPicker(self, didSelectEmoji: emoji)
                }

                self.currentSkinTonePicker?.dismiss()
                self.currentSkinTonePicker = nil
            }
        case .changed:
            currentSkinTonePicker?.didChangeLongPress(sender)
        case .ended:
            currentSkinTonePicker?.didEndLongPress(sender)
        default:
            break
        }
    }

    @objc
    func dismissSkinTonePicker() {
        currentSkinTonePicker?.dismiss()
        currentSkinTonePicker = nil
    }
}

extension EmojiPickerCollectionView: UIGestureRecognizerDelegate {
    override func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        if gestureRecognizer == tapGestureRecognizer {
            return currentSkinTonePicker != nil
        }

        return true
    }
}

extension EmojiPickerCollectionView: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let emoji = emojiForIndexPath(indexPath) else {
            return owsFailDebug("Missing emoji for indexPath \(indexPath)")
        }

        Storage.write { transaction in
            Storage.shared.recordRecentEmoji(emoji, transaction: transaction)
        }

        pickerDelegate?.emojiPicker(self, didSelectEmoji: emoji)
    }
}

extension EmojiPickerCollectionView: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return isSearching ? emojiSearchResults.count : emojiForSection(section).count
    }

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return isSearching ? 1 : Emoji.Category.allCases.count + categoryIndexOffset
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = dequeueReusableCell(withReuseIdentifier: EmojiCell.reuseIdentifier, for: indexPath)

        guard let emojiCell = cell as? EmojiCell else {
            owsFailDebug("unexpected cell type")
            return cell
        }

        guard let emoji = emojiForIndexPath(indexPath) else {
            owsFailDebug("unexpected indexPath")
            return cell
        }

        emojiCell.configure(emoji: emoji)

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {

        let supplementaryView = dequeueReusableSupplementaryView(
            ofKind: kind,
            withReuseIdentifier: EmojiSectionHeader.reuseIdentifier,
            for: indexPath
        )

        guard let sectionHeader = supplementaryView as? EmojiSectionHeader else {
            owsFailDebug("unexpected supplementary view type")
            return supplementaryView
        }

        sectionHeader.label.text = nameForSection(indexPath.section)

        return sectionHeader
    }
}

extension EmojiPickerCollectionView: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView,
                          layout collectionViewLayout: UICollectionViewLayout,
                          referenceSizeForHeaderInSection section: Int) -> CGSize {
        guard !isSearching else {
            return CGSize.zero
        }

        let measureCell = EmojiSectionHeader()
        measureCell.label.text = nameForSection(section)
        return measureCell.sizeThatFits(CGSize(width: self.width(), height: .greatestFiniteMagnitude))
    }
}

private class EmojiCell: UICollectionViewCell {
    static let reuseIdentifier = "EmojiCell"

    let emojiLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)

        backgroundColor = .clear

        emojiLabel.font = .boldSystemFont(ofSize: 32)
        contentView.addSubview(emojiLabel)
        emojiLabel.autoPinEdgesToSuperviewEdges()

        // For whatever reason, some emoji glyphs occasionally have different typographic widths on certain devices
        // e.g. 👩‍🦰: 36x38.19, 👱‍♀️: 40x38. (See: commit message for more info)
        // To workaround this, we can clip the label instead of truncating. It appears to only clip the additional
        // typographic space. In either case, it's better than truncating and seeing an ellipsis.
        emojiLabel.lineBreakMode = .byClipping
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func configure(emoji: EmojiWithSkinTones) {
        emojiLabel.text = emoji.rawValue
    }
}

private class EmojiSectionHeader: UICollectionReusableView {
    static let reuseIdentifier = "EmojiSectionHeader"

    let label = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)

        layoutMargins = UIEdgeInsets(
            top: 16,
            leading: EmojiPickerCollectionView.margins,
            bottom: 6,
            trailing: EmojiPickerCollectionView.margins
        )

        label.font = .systemFont(ofSize: Values.smallFontSize)
        label.textColor = Colors.text
        addSubview(label)
        label.autoPinEdgesToSuperviewMargins()
        label.setCompressionResistanceHigh()
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func sizeThatFits(_ size: CGSize) -> CGSize {
        var labelSize = label.sizeThatFits(size)
        labelSize.width += layoutMargins.left + layoutMargins.right
        labelSize.height += layoutMargins.top + layoutMargins.bottom
        return labelSize
    }
}