MessageKit/Sources/Views/MessagesCollectionView.swift

/*
 MIT License
 
 Copyright (c) 2017-2019 MessageKit
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */

import UIKit

open class MessagesCollectionView: UICollectionView {

    // MARK: - Properties

    open weak var messagesDataSource: MessagesDataSource?

    open weak var messagesDisplayDelegate: MessagesDisplayDelegate?

    open weak var messagesLayoutDelegate: MessagesLayoutDelegate?

    open weak var messageCellDelegate: MessageCellDelegate?

    open var isTypingIndicatorHidden: Bool {
        return messagesCollectionViewFlowLayout.isTypingIndicatorViewHidden
    }

    private var indexPathForLastItem: IndexPath? {
        let lastSection = numberOfSections - 1
        guard lastSection >= 0, numberOfItems(inSection: lastSection) > 0 else { return nil }
        return IndexPath(item: numberOfItems(inSection: lastSection) - 1, section: lastSection)
    }

    open var messagesCollectionViewFlowLayout: MessagesCollectionViewFlowLayout {
        guard let layout = collectionViewLayout as? MessagesCollectionViewFlowLayout else {
            fatalError(MessageKitError.layoutUsedOnForeignType)
        }
        return layout
    }

    // MARK: - Initializers

    public override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        backgroundColor = .backgroundColor
        registerReusableViews()
        setupGestureRecognizers()
    }
    
    required public init?(coder aDecoder: NSCoder) {
        super.init(frame: .zero, collectionViewLayout: MessagesCollectionViewFlowLayout())
    }

    public convenience init() {
        self.init(frame: .zero, collectionViewLayout: MessagesCollectionViewFlowLayout())
    }

    // MARK: - Methods
    
    private func registerReusableViews() {
        register(TextMessageCell.self)
        register(MediaMessageCell.self)
        register(LocationMessageCell.self)
        register(AudioMessageCell.self)
        register(ContactMessageCell.self)
        register(TypingIndicatorCell.self)
        register(MessageReusableView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader)
        register(MessageReusableView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionFooter)
    }
    
    private func setupGestureRecognizers() {
        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleTapGesture(_:)))
        tapGesture.delaysTouchesBegan = true
        addGestureRecognizer(tapGesture)
    }
    
    @objc
    open func handleTapGesture(_ gesture: UIGestureRecognizer) {
        guard gesture.state == .ended else { return }
        
        let touchLocation = gesture.location(in: self)
        guard let indexPath = indexPathForItem(at: touchLocation) else { return }
        
        let cell = cellForItem(at: indexPath) as? MessageCollectionViewCell
        cell?.handleTapGesture(gesture)
    }

    // NOTE: It's possible for small content size this wouldn't work - https://github.com/MessageKit/MessageKit/issues/725
    public func scrollToLastItem(at pos: UICollectionView.ScrollPosition = .bottom, animated: Bool = true) {
        guard numberOfSections > 0 else { return }
        
        let lastSection = numberOfSections - 1
        let lastItem = numberOfItems(inSection: lastSection) - 1
        
        guard lastItem >= 0 else { return }
        
        let indexPath = IndexPath(row: lastItem, section: lastSection)
        scrollToItem(at: indexPath, at: pos, animated: animated)
    }
    
    // NOTE: This method seems to cause crash in certain cases - https://github.com/MessageKit/MessageKit/issues/725
    // Could try using `scrollToLastItem` above
    public func scrollToBottom(animated: Bool = false) {
        performBatchUpdates(nil) { [weak self] _ in
            guard let self = self else { return }
            let collectionViewContentHeight = self.collectionViewLayout.collectionViewContentSize.height
            self.scrollRectToVisible(CGRect(0.0, collectionViewContentHeight - 1.0, 1.0, 1.0), animated: animated)
        }
    }
    
    public func reloadDataAndKeepOffset() {
        // stop scrolling
        setContentOffset(contentOffset, animated: false)
        
        // calculate the offset and reloadData
        let beforeContentSize = contentSize
        reloadData()
        layoutIfNeeded()
        let afterContentSize = contentSize
        
        // reset the contentOffset after data is updated
        let newOffset = CGPoint(
            x: contentOffset.x + (afterContentSize.width - beforeContentSize.width),
            y: contentOffset.y + (afterContentSize.height - beforeContentSize.height))
        setContentOffset(newOffset, animated: false)
    }

    // MARK: - Typing Indicator API

    /// Notifies the layout that the typing indicator will change state
    ///
    /// - Parameters:
    ///   - isHidden: A Boolean value that is to be the new state of the typing indicator
    internal func setTypingIndicatorViewHidden(_ isHidden: Bool) {
        messagesCollectionViewFlowLayout.setTypingIndicatorViewHidden(isHidden)
    }
    
    /// A method that by default checks if the section is the last in the
    /// `messagesCollectionView` and that `isTypingIndicatorViewHidden`
    /// is FALSE
    ///
    /// - Parameter section
    /// - Returns: A Boolean indicating if the TypingIndicator should be presented at the given section
    public func isSectionReservedForTypingIndicator(_ section: Int) -> Bool {
        return messagesCollectionViewFlowLayout.isSectionReservedForTypingIndicator(section)
    }

    // MARK: View Register/Dequeue

    /// Registers a particular cell using its reuse-identifier
    public func register<T: UICollectionViewCell>(_ cellClass: T.Type) {
        register(cellClass, forCellWithReuseIdentifier: String(describing: T.self))
    }

    /// Registers a reusable view for a specific SectionKind
    public func register<T: UICollectionReusableView>(_ reusableViewClass: T.Type, forSupplementaryViewOfKind kind: String) {
        register(reusableViewClass,
                 forSupplementaryViewOfKind: kind,
                 withReuseIdentifier: String(describing: T.self))
    }
    
    /// Registers a nib with reusable view for a specific SectionKind
    public func register<T: UICollectionReusableView>(_ nib: UINib? = UINib(nibName: String(describing: T.self), bundle: nil), headerFooterClassOfNib headerFooterClass: T.Type, forSupplementaryViewOfKind kind: String) {
        register(nib,
                 forSupplementaryViewOfKind: kind,
                 withReuseIdentifier: String(describing: T.self))        
    }

    /// Generically dequeues a cell of the correct type allowing you to avoid scattering your code with guard-let-else-fatal
    public func dequeueReusableCell<T: UICollectionViewCell>(_ cellClass: T.Type, for indexPath: IndexPath) -> T {
        guard let cell = dequeueReusableCell(withReuseIdentifier: String(describing: T.self), for: indexPath) as? T else {
            fatalError("Unable to dequeue \(String(describing: cellClass)) with reuseId of \(String(describing: T.self))")
        }
        return cell
    }

    /// Generically dequeues a header of the correct type allowing you to avoid scattering your code with guard-let-else-fatal
    public func dequeueReusableHeaderView<T: UICollectionReusableView>(_ viewClass: T.Type, for indexPath: IndexPath) -> T {
        let view = dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: String(describing: T.self), for: indexPath)
        guard let viewType = view as? T else {
            fatalError("Unable to dequeue \(String(describing: viewClass)) with reuseId of \(String(describing: T.self))")
        }
        return viewType
    }

    /// Generically dequeues a footer of the correct type allowing you to avoid scattering your code with guard-let-else-fatal
    public func dequeueReusableFooterView<T: UICollectionReusableView>(_ viewClass: T.Type, for indexPath: IndexPath) -> T {
        let view = dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionFooter, withReuseIdentifier: String(describing: T.self), for: indexPath)
        guard let viewType = view as? T else {
            fatalError("Unable to dequeue \(String(describing: viewClass)) with reuseId of \(String(describing: T.self))")
        }
        return viewType
    }

}