metatext/View Models/StatusListViewModel.swift

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// Copyright © 2020 Metabolist. All rights reserved.
import Foundation
import Combine
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class StatusListViewModel: ObservableObject {
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@Published private(set) var statusIDs = [[String]]()
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@Published var alertItem: AlertItem?
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@Published private(set) var loading = false
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private(set) var maintainScrollPositionOfStatusID: String?
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private var statuses = [String: Status]()
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private let statusListService: StatusListService
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private var statusViewModelCache = [Status: (StatusViewModel, AnyCancellable)]()
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private var cancellables = Set<AnyCancellable>()
init(statusListService: StatusListService) {
self.statusListService = statusListService
statusListService.statusSections
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.handleEvents(receiveOutput: { [weak self] in
self?.determineIfScrollPositionShouldBeMaintained(newStatusSections: $0)
self?.cleanViewModelCache(newStatusSections: $0)
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self?.statuses = Dictionary(uniqueKeysWithValues: $0.reduce([], +).map { ($0.id, $0) })
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})
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.assignErrorsToAlertItem(to: \.alertItem, on: self)
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.map { $0.map { section in section.map(\.id) } }
.assign(to: &$statusIDs)
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}
}
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extension StatusListViewModel {
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var contextParentID: String? { statusListService.contextParentID }
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func request(maxID: String? = nil, minID: String? = nil) {
statusListService.request(maxID: maxID, minID: minID)
.assignErrorsToAlertItem(to: \.alertItem, on: self)
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.handleEvents(
receiveSubscription: { [weak self] _ in self?.loading = true },
receiveCompletion: { [weak self] _ in self?.loading = false })
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.sink { _ in }
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.store(in: &cancellables)
}
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func statusViewModel(id: String) -> StatusViewModel? {
guard let status = statuses[id] else { return nil }
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var statusViewModel: StatusViewModel
if let cachedViewModel = statusViewModelCache[status]?.0 {
statusViewModel = cachedViewModel
} else {
statusViewModel = StatusViewModel(statusService: statusListService.statusService(status: status))
statusViewModelCache[status] = (statusViewModel, statusViewModel.events
.flatMap { $0 }
.assignErrorsToAlertItem(to: \.alertItem, on: self)
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.sink { _ in })
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}
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statusViewModel.isContextParent = status.id == contextParentID
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statusViewModel.isPinned = statusListService.isPinned(status: status)
statusViewModel.isReplyInContext = statusListService.isReplyInContext(status: status)
statusViewModel.hasReplyFollowing = statusListService.hasReplyFollowing(status: status)
return statusViewModel
}
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func contextViewModel(id: String) -> StatusListViewModel? {
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guard let status = statuses[id] else { return nil }
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return StatusListViewModel(statusListService: statusListService.contextService(status: status))
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}
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}
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private extension StatusListViewModel {
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func determineIfScrollPositionShouldBeMaintained(newStatusSections: [[Status]]) {
maintainScrollPositionOfStatusID = nil // clear old value
// Maintain scroll position of parent after initial load of context
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if let contextParentID = contextParentID, statusIDs.reduce([], +) == [contextParentID] {
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maintainScrollPositionOfStatusID = contextParentID
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}
}
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func cleanViewModelCache(newStatusSections: [[Status]]) {
let newStatuses = Set(newStatusSections.reduce([], +))
statusViewModelCache = statusViewModelCache.filter { newStatuses.contains($0.key) }
}
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}