MessageKit/Sources/Layout/MessagesCollectionViewFlowLayout.swift

/*
 MIT License

 Copyright (c) 2017-2018 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
import AVFoundation

/// The layout object used by `MessagesCollectionView` to determine the size of all
/// framework provided `MessageCollectionViewCell` subclasses.
open class MessagesCollectionViewFlowLayout: UICollectionViewFlowLayout {

    open override class var layoutAttributesClass: AnyClass {
        return MessagesCollectionViewLayoutAttributes.self
    }

    internal var itemWidth: CGFloat {
        guard let collectionView = collectionView else { return 0 }
        return collectionView.frame.width - sectionInset.left - sectionInset.right
    }

    // MARK: - Initializers

    public override init() {
        super.init()

        textMessageSizeCalculator.layout = self
        attributedTextMessageSizeCalculator.layout = self
        emojiMessageSizeCalculator.layout = self
        photoMessageSizeCalculator.layout = self
        videoMessageSizeCalculator.layout = self
        locationMessageSizeCalculator.layout = self

        sectionInset = UIEdgeInsets(top: 4, left: 8, bottom: 4, right: 8)

        NotificationCenter.default.addObserver(self, selector: #selector(MessagesCollectionViewFlowLayout.handleOrientationChange(_:)), name: .UIDeviceOrientationDidChange, object: nil)
    }

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

    deinit {
        NotificationCenter.default.removeObserver(self)
    }

    // MARK: - Attributes

    open override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        guard let attributesArray = super.layoutAttributesForElements(in: rect) as? [MessagesCollectionViewLayoutAttributes] else {
            return nil
        }
        for attributes in attributesArray where attributes.representedElementCategory == .cell {
            let cellSizeCalculator = cellSizeCalculatorForItem(at: attributes.indexPath)
            cellSizeCalculator.configure(attributes: attributes)
        }
        return attributesArray
    }

    open override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        guard let attributes = super.layoutAttributesForItem(at: indexPath) as? MessagesCollectionViewLayoutAttributes else {
            return nil
        }
        if attributes.representedElementCategory == .cell {
            let cellSizeCalculator = cellSizeCalculatorForItem(at: attributes.indexPath)
            cellSizeCalculator.configure(attributes: attributes)
        }
        return attributes
    }

    // MARK: - Layout Invalidation

    open override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return collectionView?.bounds.width != newBounds.width
    }

    open override func invalidationContext(forBoundsChange newBounds: CGRect) -> UICollectionViewLayoutInvalidationContext {
        let context = super.invalidationContext(forBoundsChange: newBounds)
        guard let flowLayoutContext = context as? UICollectionViewFlowLayoutInvalidationContext else { return context }
        flowLayoutContext.invalidateFlowLayoutDelegateMetrics = shouldInvalidateLayout(forBoundsChange: newBounds)
        return flowLayoutContext
    }

    @objc
    private func handleOrientationChange(_ notification: Notification) {
        invalidateLayout()
    }

    // MARK: - Cell Sizing

    var textMessageSizeCalculator = TextMessageSizeCalculator()
    var attributedTextMessageSizeCalculator = TextMessageSizeCalculator()
    var emojiMessageSizeCalculator = TextMessageSizeCalculator()
    var photoMessageSizeCalculator = MediaMessageSizeCalculator()
    var videoMessageSizeCalculator = MediaMessageSizeCalculator()
    var locationMessageSizeCalculator = LocationMessageSizeCalculator()

    open func cellSizeCalculatorForItem(at indexPath: IndexPath) -> MessageSizeCalculator {
        let message = messagesDataSource.messageForItem(at: indexPath, in: messagesCollectionView)
        switch message.data {
        case .text:
            return textMessageSizeCalculator
        case .attributedText:
            return attributedTextMessageSizeCalculator
        case .emoji:
            return emojiMessageSizeCalculator
        case .photo:
            return photoMessageSizeCalculator
        case .video:
            return videoMessageSizeCalculator
        case .location:
            return locationMessageSizeCalculator
        case .custom:
            fatalError("Must return a CellSizeCalculator for MessageData.custom(Any?)")
        }
    }

    open func sizeForItem(at indexPath: IndexPath) -> CGSize {
        let calculator = cellSizeCalculatorForItem(at: indexPath)
        return calculator.sizeForItem(at: indexPath)
    }
}

// MARK: - Helpers

extension MessagesCollectionViewFlowLayout {

    internal var messagesCollectionView: MessagesCollectionView {
        guard let messagesCollectionView = collectionView as? MessagesCollectionView else {
            fatalError(MessageKitError.layoutUsedOnForeignType)
        }
        return messagesCollectionView
    }

    internal var messagesDataSource: MessagesDataSource {
        guard let messagesDataSource = messagesCollectionView.messagesDataSource else {
            fatalError(MessageKitError.nilMessagesDataSource)
        }
        return messagesDataSource
    }

    internal var messagesLayoutDelegate: MessagesLayoutDelegate {
        guard let messagesLayoutDelegate = messagesCollectionView.messagesLayoutDelegate else {
            fatalError(MessageKitError.nilMessagesLayoutDelegate)
        }
        return messagesLayoutDelegate
    }
}