MessageKit/Sources/MessagesCollectionViewFlowLayout.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 MessagesCollectionViewFlowLayout: UICollectionViewFlowLayout {

    // MARK: - Properties

    open var messageLabelFont: UIFont
    open var messageLabelInsets: UIEdgeInsets
    open var messageToViewEdgePadding: CGFloat

    open var cellTopLabelFont: UIFont
    open var cellTopLabelInsets: UIEdgeInsets
    open var topLabelBeginsAfterAvatar: Bool

    open var cellBottomLabelFont: UIFont
    open var cellBottomLabelInsets: UIEdgeInsets
    open var bottomLabelBeginsAfterAvatar: Bool

    open var incomingAvatarSize: CGSize
    open var outgoingAvatarSize: CGSize

    fileprivate var avatarBottomPadding: CGFloat = 2
    fileprivate var avatarMessagePadding: CGFloat = 4

    fileprivate var messagesCollectionView: MessagesCollectionView? {
        return collectionView as? MessagesCollectionView
    }

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

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

    // MARK: - Initializers

    override public init() {

        messageLabelFont = UIFont.preferredFont(forTextStyle: .body)
        messageLabelInsets = UIEdgeInsets(top: 7, left: 14, bottom: 7, right: 14)
        messageToViewEdgePadding = 30.0

        cellTopLabelFont = UIFont.preferredFont(forTextStyle: .caption2)
        cellTopLabelInsets = .zero
        topLabelBeginsAfterAvatar = false

        cellBottomLabelFont = UIFont.preferredFont(forTextStyle: .caption1)
        cellBottomLabelInsets = .zero
        bottomLabelBeginsAfterAvatar = false

        incomingAvatarSize = CGSize(width: 30, height: 30)
        outgoingAvatarSize = CGSize(width: 30, height: 30)

        super.init()

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

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

    // MARK: - Methods

    override open func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {

        guard let attributesArray = super.layoutAttributesForElements(in: rect) as? [MessagesCollectionViewLayoutAttributes] else { return nil }

        attributesArray.forEach { attributes in
            if attributes.representedElementCategory == UICollectionElementCategory.cell {
                configure(attributes: attributes)
            }
        }

        return attributesArray
    }

    override open func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {

        guard let attributes = super.layoutAttributesForItem(at: indexPath) as? MessagesCollectionViewLayoutAttributes else { return nil }

        if attributes.representedElementCategory == UICollectionElementCategory.cell {
            configure(attributes: attributes)
        }

        return attributes

    }

    private func configure(attributes: MessagesCollectionViewLayoutAttributes) {

        guard let messagesCollectionView = messagesCollectionView else { return }
        guard let dataSource = messagesCollectionView.messagesDataSource else { return }

        let indexPath = attributes.indexPath

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

        attributes.messageContainerSize = messageContainerSize(for: message, at: indexPath)
        attributes.messageLabelFont = messageLabelFont
        attributes.messageLabelInsets = messageLabelInsets
        attributes.messageToViewEdgePadding = messageToViewEdgePadding

        attributes.cellTopLabelSize = cellTopLabelSize(for: message, at: indexPath)
        attributes.cellTopLabelFont = cellTopLabelFont
        attributes.cellTopLabelInsets = cellTopLabelInsets
        attributes.topLabelBeginsAfterAvatar = topLabelBeginsAfterAvatar

        attributes.cellBottomLabelSize = cellBottomLabelSize(for: message, at: indexPath)
        attributes.cellBottomLabelFont = cellBottomLabelFont
        attributes.cellBottomLabelInsets = cellBottomLabelInsets
        attributes.bottomLabelBeginsAfterAvatar = bottomLabelBeginsAfterAvatar

        attributes.avatarSize = avatarSize(for: message)
        attributes.avatarBottomPadding = avatarBottomPadding
        attributes.avatarMessagePadding = avatarMessagePadding

        attributes.direction = dataSource.isFromCurrentSender(message: message) ? .outgoing : .incoming

    }

    override open func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {

        return collectionView?.bounds.width != newBounds.width || collectionView?.bounds.height != newBounds.height

    }

    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
    }

}

extension MessagesCollectionViewFlowLayout {

    // MARK: - Size Calculations

    func avatarSize(for message: MessageType) -> CGSize {

        guard let messagesCollectionView = messagesCollectionView else { return .zero }
        guard let messagesDataSource = messagesCollectionView.messagesDataSource else { return .zero }

        let isOutgoingMessage = messagesDataSource.isFromCurrentSender(message: message)

        return isOutgoingMessage ? outgoingAvatarSize : incomingAvatarSize
    }

    func messageContainerSize(for message: MessageType, at indexPath: IndexPath) -> CGSize {

        let messageWidth = messageContainerWidth(for: message, at: indexPath)
        let messageHeight = messageContainerHeight(for: message, at: indexPath)

        return CGSize(width: messageWidth, height: messageHeight)
    }

    func cellTopLabelSize(for message: MessageType, at indexPath: IndexPath) -> CGSize {

        let topLabelWidth = cellTopLabelWidth(for: message)
        let topLabelHeight = cellTopLabelHeight(for: message, at: indexPath)

        return CGSize(width: topLabelWidth, height: topLabelHeight)

    }

    func cellBottomLabelSize(for message: MessageType, at indexPath: IndexPath) -> CGSize {

        let bottomLabelWidth = cellBottomLabelWidth(for: message)
        let bottomLabelHeight = cellBottomLabelHeight(for: message, at: indexPath)

        return CGSize(width: bottomLabelWidth, height: bottomLabelHeight)

    }

    // MARK: - Width Calculations


    func cellTopLabelWidth(for message: MessageType) -> CGFloat {
        if topLabelBeginsAfterAvatar {
            return itemWidth - avatarSize(for: message).width
        } else {
            return itemWidth
        }
    }

    func cellBottomLabelWidth(for message: MessageType) -> CGFloat {
        if bottomLabelBeginsAfterAvatar {
            return itemWidth - avatarSize(for: message).width
        } else {
            return itemWidth
        }
    }

    func availableWidthForMessageContainer(considering message: MessageType) -> CGFloat {
        let avatarWidth = avatarSize(for: message).width
        let avatarWidthPlusPadding = avatarWidth == 0 ? 0 : avatarWidth + avatarMessagePadding
        let horizontalMessageInsets = messageLabelInsets.left + messageLabelInsets.right
        let availableWidth = itemWidth - avatarWidthPlusPadding - horizontalMessageInsets - messageToViewEdgePadding
        return availableWidth
    }

    // MARK: - View Height Calculations

    func cellTopLabelHeight(for message: MessageType, at indexPath: IndexPath) -> CGFloat {

        guard let messagesCollectionView = messagesCollectionView else { return 0 }
        guard let displayDataSource = messagesCollectionView.messagesDataSource as? MessagesDisplayDataSource else { return 0 }
        guard let topLabelText = displayDataSource.cellTopLabelTextForMessage(message, at: indexPath) else { return 0 }

        let availableWidth = cellTopLabelWidth(for: message)

        let estimatedHeight = topLabelText.height(considering: availableWidth, and: cellTopLabelFont)

        return estimatedHeight.rounded(.up)

    }

    func cellBottomLabelHeight(for message: MessageType, at indexPath: IndexPath) -> CGFloat {

        guard let messagesCollectionView = messagesCollectionView else { return 0 }
        guard let displayDataSource = messagesCollectionView.messagesDataSource as? MessagesDisplayDataSource else { return 0 }
        guard let bottomLabelText = displayDataSource.cellBottomLabelTextForMessage(message, at: indexPath) else { return 0 }

        let availableWidth = cellBottomLabelWidth(for: message)

        let estimatedHeight = bottomLabelText.height(considering: availableWidth, and: cellBottomLabelFont)

        return estimatedHeight.rounded(.up)
    }

    func minimumCellHeight(for message: MessageType, at indexPath: IndexPath) -> CGFloat {

        let size = avatarSize(for: message)
        let avatarHeightPlusBottomPadding = size.height == 0 ? 0 : size.height + avatarBottomPadding
        let bottomLabelHeight = cellBottomLabelHeight(for: message, at: indexPath)
        let topLabelHeight = cellTopLabelHeight(for: message, at: indexPath)

        let minimumHeight = topLabelHeight + avatarHeightPlusBottomPadding + bottomLabelHeight

        return minimumHeight

    }

    func messageContainerHeight(for message: MessageType, at indexPath: IndexPath) -> CGFloat{

        // This is a switch because we will support other message types in the future
        switch message.data {
        case .text(let text):
            let availableWidth = availableWidthForMessageContainer(considering: message)
            let estimatedHeight = text.height(considering: availableWidth, and: messageLabelFont)
            let verticalMessageInsets = messageLabelInsets.top + messageLabelInsets.bottom
            let finalHeight = estimatedHeight.rounded(.up) + verticalMessageInsets
            return finalHeight
        }

    }

    // MARK: - View Width Calculations

    func messageContainerWidth(for message: MessageType, at indexPath: IndexPath) -> CGFloat {

        // This is a switch because we will support other message types in the future
        switch message.data {
        case .text(let text):
            let containerHeight = messageContainerHeight(for: message, at: indexPath)
            let estimatedWidth = text.width(considering: containerHeight, and: messageLabelFont)
            let availableWidth = availableWidthForMessageContainer(considering: message)
            let horizontalMessageInsets = messageLabelInsets.left + messageLabelInsets.right
            let widthToUse = estimatedWidth.rounded(.up) > availableWidth ? availableWidth : estimatedWidth
            let finalWidth = widthToUse + horizontalMessageInsets
            return finalWidth
        }

    }

    // MARK: - Cell Size Calculations

    func estimatedCellHeight(for message: MessageType, at indexPath: IndexPath) -> CGFloat {

        let containerHeight = messageContainerHeight(for: message, at: indexPath)
        let topLabelHeight = cellTopLabelHeight(for: message, at: indexPath)
        let bottomLabelheight = cellBottomLabelHeight(for: message, at: indexPath)

        return topLabelHeight + containerHeight + bottomLabelheight

    }

    func sizeForItem(at indexPath: IndexPath) -> CGSize {

        guard let messagesCollectionView = messagesCollectionView else { return .zero }
        guard let dataSource = messagesCollectionView.messagesDataSource else { return .zero }

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

        let minimumHeight = minimumCellHeight(for: message, at: indexPath)
        let estimatedHeight = estimatedCellHeight(for: message, at: indexPath)
        let finalHeight = estimatedHeight < minimumHeight ? minimumHeight : estimatedHeight

        return CGSize(width: itemWidth, height: finalHeight)


    }

}