Signal-iOS/Signal/ConversationView/Loading/CVRenderState.swift

//
// Copyright 2020 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
//

import SignalServiceKit
import SignalUI

// This captures all of the state loaded by the CVLoadCoordinator.
//
// It is intended to be an immutable, comprehensive snapshot of all
// loaded state needed to render CVC at a given state of time.
class CVRenderState {

    static let renderStateId_unknown: UInt = 0

    private static let idCounter = AtomicUInt(1, lock: .sharedGlobal)

    let renderStateId: UInt

    let threadViewModel: ThreadViewModel
    let prevThreadViewModel: ThreadViewModel?
    var isEmptyInitialState: Bool {
        prevThreadViewModel == nil
    }

    let conversationViewModel: ConversationViewModel

    var isFirstLoad: Bool {
        if
            let loadType = self.loadType,
            case CVLoadType.loadInitialMapping = loadType
        {
            return true
        }
        return false
    }

    // All of CVRenderState's state should be immutable.
    let items: [CVRenderItem]
    let canLoadOlderItems: Bool
    let canLoadNewerItems: Bool

    // The "view state" values that were used when loading this render state.
    let viewStateSnapshot: CVViewStateSnapshot
    let loadType: CVLoadType?

    let loadDate = Date()

    // These values reflect the style and view state at the time
    // was load began. They may be obsolete.
    var conversationStyle: ConversationStyle {
        viewStateSnapshot.conversationStyle
    }

    // TODO: We might want to precompute: interactionIndexMap, focusItemIndex, unreadIndicatorIndex

    var disappearingMessagesConfiguration: DisappearingMessagesConfigurationRecord {
        threadViewModel.disappearingMessagesConfiguration
    }

    let indexPathOfUnreadIndicator: IndexPath?

    private let interactionIdToIndexPathMap: [String: IndexPath]
    /// Maps each collapsed interaction's uniqueId to the uniqueId of its parent CollapseSetInteraction.
    private let collapsedInteractionToParentUniqueIdMap: [String: String]

    let allIndexPaths: [IndexPath]

    init(
        threadViewModel: ThreadViewModel,
        prevThreadViewModel: ThreadViewModel?,
        conversationViewModel: ConversationViewModel,
        items: [CVRenderItem],
        canLoadOlderItems: Bool,
        canLoadNewerItems: Bool,
        viewStateSnapshot: CVViewStateSnapshot,
        loadType: CVLoadType?,
    ) {
        self.threadViewModel = threadViewModel
        self.prevThreadViewModel = prevThreadViewModel
        self.conversationViewModel = conversationViewModel
        self.items = items
        self.canLoadOlderItems = canLoadOlderItems
        self.canLoadNewerItems = canLoadNewerItems
        self.viewStateSnapshot = viewStateSnapshot
        self.loadType = loadType

        self.renderStateId = Self.idCounter.increment()

        let messageSection = CVLoadCoordinator.messageSection
        var indexPathOfUnreadIndicator: IndexPath?
        var interactionIdToIndexPathMap = [String: IndexPath]()
        var collapsedInteractionToParentUniqueIdMap = [String: String]()
        var allIndexPaths = [IndexPath]()
        for (index, item) in items.enumerated() {
            let indexPath = IndexPath(row: index, section: messageSection)
            interactionIdToIndexPathMap[item.interaction.uniqueId] = indexPath
            allIndexPaths.append(indexPath)

            if item.interactionType == .unreadIndicator {
                indexPathOfUnreadIndicator = indexPath
            }
            if
                item.interactionType == .collapseSet,
                let collapseSet = item.interaction as? CollapseSetInteraction
            {
                for collapsed in collapseSet.collapsedInteractions {
                    collapsedInteractionToParentUniqueIdMap[collapsed.uniqueId] = collapseSet.uniqueId
                }
            }
        }
        self.indexPathOfUnreadIndicator = indexPathOfUnreadIndicator
        self.interactionIdToIndexPathMap = interactionIdToIndexPathMap
        self.collapsedInteractionToParentUniqueIdMap = collapsedInteractionToParentUniqueIdMap
        self.allIndexPaths = allIndexPaths
    }

    static func defaultRenderState(
        threadViewModel: ThreadViewModel,
        conversationViewModel: ConversationViewModel,
        viewStateSnapshot: CVViewStateSnapshot,
    ) -> CVRenderState {
        CVRenderState(
            threadViewModel: threadViewModel,
            prevThreadViewModel: nil,
            conversationViewModel: conversationViewModel,
            items: [],
            canLoadOlderItems: false,
            canLoadNewerItems: false,
            viewStateSnapshot: viewStateSnapshot,
            loadType: nil,
        )
    }

    func indexPath(forInteractionUniqueId interactionUniqueId: String) -> IndexPath? {
        interactionIdToIndexPathMap[interactionUniqueId]
    }

    /// Returns the uniqueId of the CollapseSetInteraction that contains
    /// the given interaction if it is inside a collapse set.
    func collapseSetUniqueId(forCollapsedInteractionId interactionId: String) -> String? {
        collapsedInteractionToParentUniqueIdMap[interactionId]
    }

    var debugDescription: String {
        isEmptyInitialState ? "empty" : "[items: \(items.count)]"
    }
}