MessageKit/Sources/Controllers/MessagesViewController.swift

/*
 MIT License

 Copyright (c) 2017 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 MessagesViewController: UIViewController {
    
    // MARK: - Properties [Public]

    /// The `MessagesCollectionView` managed by the messages view controller object.
    open var messagesCollectionView = MessagesCollectionView()

    /// The `MessageInputBar` used as the `inputAccessoryView` in the view controller.
    open var messageInputBar = MessageInputBar()
    
    /// A Boolean value that determines whether the `MessagesCollectionView` scrolls to the
    /// bottom on the view's first layout.
    ///
    /// The default value of this property is `false`.
    open var scrollsToBottomOnFirstLayout: Bool = false

    /// A Boolean value that determines whether the `MessagesCollectionView` scrolls to the
    /// bottom whenever the `InputTextView` begins editing.
    ///
    /// The default value of this property is `false`.
    open var scrollsToBottomOnKeybordBeginsEditing: Bool = false

    open override var canBecomeFirstResponder: Bool {
        return true
    }

    open override var inputAccessoryView: UIView? {
        return messageInputBar
    }

    open override var shouldAutorotate: Bool {
        return false
    }
    
    /// A Boolean value used to determine if `viewDidLayoutSubviews()` has been called.
    private var isFirstLayout: Bool = true

    // MARK: - View Life Cycle

    open override func viewDidLoad() {
        super.viewDidLoad()

        
        extendedLayoutIncludesOpaqueBars = true
        automaticallyAdjustsScrollViewInsets = false
        view.backgroundColor = .white
        messagesCollectionView.keyboardDismissMode = .interactive
        messagesCollectionView.alwaysBounceVertical = true
        
        
        setupSubviews()
        setupConstraints()
        registerReusableViews()
        setupDelegates()

    }

    open override func viewDidLayoutSubviews() {
        // Hack to prevent animation of the contentInset after viewDidAppear
        if isFirstLayout {
            defer { isFirstLayout = false }

            addKeyboardObservers()
            messagesCollectionView.contentInset.bottom = keyboardOffsetFrame.height
            messagesCollectionView.scrollIndicatorInsets.bottom = keyboardOffsetFrame.height
            
            //Scroll to bottom at first load
            if scrollsToBottomOnFirstLayout {
                messagesCollectionView.scrollToBottom(animated: false)
            }
        }
    }

    // MARK: - Initializers

    deinit {
        removeKeyboardObservers()
    }

    // MARK: - Methods [Private]

    /// Sets the delegate and dataSource of the messagesCollectionView property.
    private func setupDelegates() {
        messagesCollectionView.delegate = self
        messagesCollectionView.dataSource = self
    }

    /// Registers all cells and supplementary views of the messagesCollectionView property.
    private func registerReusableViews() {

        messagesCollectionView.register(TextMessageCell.self)
        messagesCollectionView.register(MediaMessageCell.self)
        messagesCollectionView.register(LocationMessageCell.self)

        messagesCollectionView.register(MessageFooterView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionFooter)
        messagesCollectionView.register(MessageHeaderView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader)
        messagesCollectionView.register(MessageDateHeaderView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader)

    }

    /// Adds the messagesCollectionView to the controllers root view.
    private func setupSubviews() {
        view.addSubview(messagesCollectionView)
    }

    /// Sets the constraints of the `MessagesCollectionView`.
    private func setupConstraints() {
        messagesCollectionView.translatesAutoresizingMaskIntoConstraints = false
        
        let top = messagesCollectionView.topAnchor.constraint(equalTo: view.topAnchor, constant: topLayoutGuide.length)
        let bottom = messagesCollectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        if #available(iOS 11.0, *) {
            let leading = messagesCollectionView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor)
            let trailing = messagesCollectionView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor)
            NSLayoutConstraint.activate([top, bottom, trailing, leading])
        } else {
            let leading = messagesCollectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor)
            let trailing = messagesCollectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor)
            NSLayoutConstraint.activate([top, bottom, trailing, leading])
        }
        adjustScrollViewInset()
    }
    
    @objc
    private func adjustScrollViewInset() {
        if #available(iOS 11.0, *) {
            // No need to add to the top contentInset
        } else {
            let navigationBarInset = navigationController?.navigationBar.frame.height ?? 0
            let statusBarInset: CGFloat = UIApplication.shared.isStatusBarHidden ? 0 : 20
            let topInset = navigationBarInset + statusBarInset
            messagesCollectionView.contentInset.top = topInset
            messagesCollectionView.scrollIndicatorInsets.top = topInset
        }
    }
}

// MARK: - UICollectionViewDelegate & UICollectionViewDelegateFlowLayout Conformance

extension MessagesViewController: UICollectionViewDelegateFlowLayout {

    open func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        guard let messagesFlowLayout = collectionViewLayout as? MessagesCollectionViewFlowLayout else { return .zero }
        return messagesFlowLayout.sizeForItem(at: indexPath)
    }
    
    open func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
        guard let messagesCollectionView = collectionView as? MessagesCollectionView else { return .zero }
        guard let messagesDataSource = messagesCollectionView.messagesDataSource else { return .zero }
        guard let messagesLayoutDelegate = messagesCollectionView.messagesLayoutDelegate else { return .zero }
        // Could pose a problem if subclass behaviors allows more than one item per section
        let indexPath = IndexPath(item: 0, section: section)
        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)
        return messagesLayoutDelegate.headerViewSize(for: message, at: indexPath, in: messagesCollectionView)
    }
    
    open func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForFooterInSection section: Int) -> CGSize {
        guard let messagesCollectionView = collectionView as? MessagesCollectionView else { return .zero }
        guard let messagesDataSource = messagesCollectionView.messagesDataSource else { return .zero }
        guard let messagesLayoutDelegate = messagesCollectionView.messagesLayoutDelegate else { return .zero }
        // Could pose a problem if subclass behaviors allows more than one item per section
        let indexPath = IndexPath(item: 0, section: section)
        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)
        return messagesLayoutDelegate.footerViewSize(for: message, at: indexPath, in: messagesCollectionView)
    }

}

// MARK: - UICollectionViewDataSource Conformance

extension MessagesViewController: UICollectionViewDataSource {

    open func numberOfSections(in collectionView: UICollectionView) -> Int {
        guard let collectionView = collectionView as? MessagesCollectionView else { return 0 }

        // Each message is its own section
        return collectionView.messagesDataSource?.numberOfMessages(in: collectionView) ?? 0
    }

    open func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        guard let collectionView = collectionView as? MessagesCollectionView else { return 0 }

        let messageCount = collectionView.messagesDataSource?.numberOfMessages(in: collectionView) ?? 0
        // There will only ever be 1 message per section
        return messageCount > 0 ? 1 : 0

    }

    open func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        guard let messagesCollectionView = collectionView as? MessagesCollectionView else {
            fatalError("Managed collectionView: \(collectionView.debugDescription) is not a MessagesCollectionView.")
        }

        guard let messagesDataSource = messagesCollectionView.messagesDataSource else {
            fatalError("MessagesDataSource has not been set.")
        }

        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)

        switch message.data {
        case .text, .attributedText, .emoji:
            let cell = messagesCollectionView.dequeueReusableCell(TextMessageCell.self, for: indexPath)
            cell.configure(with: message, at: indexPath, and: messagesCollectionView)
            return cell
        case .photo, .video:
    	    let cell = messagesCollectionView.dequeueReusableCell(MediaMessageCell.self, for: indexPath)
            cell.configure(with: message, at: indexPath, and: messagesCollectionView)
            return cell
        case .location:
    	    let cell = messagesCollectionView.dequeueReusableCell(LocationMessageCell.self, for: indexPath)
            cell.configure(with: message, at: indexPath, and: messagesCollectionView)
            return cell
        }

    }

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

        guard let messagesCollectionView = collectionView as? MessagesCollectionView else {
            fatalError("Managed collectionView: \(collectionView.debugDescription) is not a MessagesCollectionView.")
        }

        guard let dataSource = messagesCollectionView.messagesDataSource else {
            fatalError("MessagesDataSource has not been set.")
        }

        guard let displayDelegate = messagesCollectionView.messagesDisplayDelegate else {
            fatalError("MessagesDisplayDelegate has not been set.")
        }

        let message = dataSource.messageForItem(at: indexPath, in: messagesCollectionView)

        switch kind {
        case UICollectionElementKindSectionHeader:
            return displayDelegate.messageHeaderView(for: message, at: indexPath, in: messagesCollectionView)
        case UICollectionElementKindSectionFooter:
            return displayDelegate.messageFooterView(for: message, at: indexPath, in: messagesCollectionView)
        default:
            fatalError("Unrecognized element of kind: \(kind)")
        }

    }
    
}

// MARK: - Keyboard Handling

fileprivate extension MessagesViewController {

    func addKeyboardObservers() {
        NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboardDidChangeState), name: .UIKeyboardWillChangeFrame, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(handleTextViewDidBeginEditing), name: .UITextViewTextDidBeginEditing, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(adjustScrollViewInset), name: .UIDeviceOrientationDidChange, object: nil)
    }

    func removeKeyboardObservers() {
        NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillChangeFrame, object: nil)
        NotificationCenter.default.removeObserver(self, name: .UITextViewTextDidBeginEditing, object: nil)
        NotificationCenter.default.removeObserver(self, name: .UIDeviceOrientationDidChange, object: nil)
    }

    @objc
    func handleTextViewDidBeginEditing(_ notification: Notification) {
        
        if scrollsToBottomOnKeybordBeginsEditing {
            guard let inputTextView = notification.object as? InputTextView, inputTextView === messageInputBar.inputTextView else { return }
            messagesCollectionView.scrollToBottom(animated: true)
        }
    }

    @objc
    func handleKeyboardDidChangeState(_ notification: Notification) {

        guard let keyboardEndFrame = notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? CGRect else { return }

        if (keyboardEndFrame.origin.y + keyboardEndFrame.size.height) > UIScreen.main.bounds.height {
            // Hardware keyboard is found
            let bottomInset = view.frame.size.height - keyboardEndFrame.origin.y - iPhoneXBottomInset
            messagesCollectionView.contentInset.bottom = bottomInset
            messagesCollectionView.scrollIndicatorInsets.bottom = bottomInset

        } else {
            //Software keyboard is found
            let bottomInset = keyboardEndFrame.height > keyboardOffsetFrame.height ? (keyboardEndFrame.height - iPhoneXBottomInset) : keyboardOffsetFrame.height
            messagesCollectionView.contentInset.bottom = bottomInset
            messagesCollectionView.scrollIndicatorInsets.bottom = bottomInset
        }
        
    }
    
    fileprivate var keyboardOffsetFrame: CGRect {
        guard let inputFrame = inputAccessoryView?.frame else { return .zero }
        return CGRect(origin: inputFrame.origin, size: CGSize(width: inputFrame.width, height: inputFrame.height - iPhoneXBottomInset))
    }
    
    /// On the iPhone X the inputAccessoryView is anchored to the layoutMarginesGuide.bottom anchor so the frame of the inputAccessoryView
    /// is larger than the required offset for the MessagesCollectionView
    ///
    /// - Returns: The safeAreaInsets.bottom if its an iPhoneX, else 0
    fileprivate var iPhoneXBottomInset: CGFloat {
        if #available(iOS 11.0, *) {
            guard UIScreen.main.nativeBounds.height == 2436 else { return 0 }
            return view.safeAreaInsets.bottom
        }
        return 0
    }
}