Message collection

import SendbirdChatSDK

class CustomViewController: UIViewController {
    // The following properties should be initialized before using them.
    var collection: MessageCollection?
    var channel: GroupChannel?
    var startingPoint: Int64!

    func createMessageCollection() {
        // You can use a MessageListParams instance for MessageCollection.
        let params = MessageListParams()
        params.reverse = false
        params.isInclusive = false
        params.messageTypeFilter = .all
        params.includeMetaArray = false
        params.includeReactions = false
        // You can add other params setters.
        // ...
        
        guard let channel = self.channel else {
            return
        }

        self.collection = SendbirdChat.createMessageCollection(channel: channel, startingPoint: self.startingPoint, params: params)
        self.collection?.delegate = self
    }

    // Initialize messages from startingPoint.
    func initialize() {
        guard let collection = self.collection else {
            return
        }
        
        collection.startCollection(initPolicy: .cacheAndReplaceByApi, cacheResultHandler: { messages, error in
            // Messages are retrieved from the local cache.
            // They might be too outdated compared to startingPoint.
        }, apiResultHandler: { messages, error in
            // Messages are retrieved from the Sendbird server through the API.
            // According to MessageCollectionInitPolicy.cacheAndReplaceByApi,
            // the existing data source needs to be cleared
            // before adding retrieved messages to the local cache.
        })
    }

    // ...
}

class CustomViewController: UIViewController {
    // ...

    // Load the previous messages when the scroll reaches
    // the first message in the chat view.
    func loadPrevious() {
        guard let collection = self.collection else {
            return
        }
        
        if collection.hasPrevious {
            collection.loadPrevious { messages, error in
                guard error == nil else {
                    // Handle error.
                    return 
                }
            }
        }
    }

    // Load the next set of messages when the scroll reaches
    // the last message in the chat view.
    func loadNext() {
        guard let collection = self.collection else {
            return
        }
        
        if collection.hasNext {
            collection.loadNext { messages, error in
                guard error == nil else {
                    // Handle error.
                    return 
                }
            }
        }
    }


    // ...
}

extension CustomViewController: MessageCollectionDelegate {
    func messageCollection(_ collection: MessageCollection, context: MessageContext, channel: GroupChannel, addedMessages: [BaseMessage]) {
        switch context.sendingStatus {
        case .succeeded:
            // Add messages to your data source.
        case .pending:
            // Add pending messages to your data source.
        default:
        }
    }

    func messageCollection(_ collection: MessageCollection, context: MessageContext, channel: GroupChannel, updatedMessages: [BaseMessage]) {
        switch context.sendingStatus {
        case .succeeded:
            // Update the send status of sent messages.
        case .pending:  (failed -> pending)
            // Update the send status from failed to pending in your data source.
            // Remove the failed message from the data source.
        case .failed:   (pending -> failed)
            // Update the send status from pending to failed in your data source.
            // Remove the pending message from the data source.
        case .canceled: (pending -> canceled)
            // Remove the pending message from the data source.
            // Implement codes to process canceled messages on your end.
            // The Chat SDK doesn't store canceled messages.
        default:
        }
    }

    func messageCollection(_ collection: MessageCollection, context: MessageContext, channel: GroupChannel, deletedMessages: [BaseMessage]) {
        switch context.sendingStatus {
        case .succeeded:
            // Remove the sent message from your data source.
        case .failed:
            // Remove the failed message from your data source.
        default:
        }
    }

    func messageCollection(_ collection: MessageCollection, context: MessageContext, updatedChannel channel: GroupChannel) {
        // Change the chat view with the updated channel information.
    }

    func messageCollection(_ collection: MessageCollection, context: MessageContext, deletedChannel channelURL: String) {
        // This is called when a channel was deleted.
        // So the current chat view should be cleared.
    }

    func didDetectHugeGap(_ collection: MessageCollection) {
        // The Chat SDK detects that more than 300 messages are missing.

        // Dispose of the current collection.
        collection.dispose()

        // Create a new message collection object.
        self.createMessageCollection()

        // An additional implementation is required for initialization.
    }
}

class ChatViewController: UIViewController {
    // ...

    func dispose() {
        self.collection?.dispose()
    }

    // ...
}