mastodon-ios/Mastodon/Scene/Share/ViewModel/ListBatchFetchViewModel.swift

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//
// ListBatchFetchViewModel.swift
// Mastodon
//
// Created by Cirno MainasuK on 2021-11-10.
//
import UIKit
import Combine
// ref: Texture.ASBatchFetchingDelegate
final class ListBatchFetchViewModel {
var disposeBag = Set<AnyCancellable>()
// timer running on `common` mode
let timerPublisher = Timer.publish(every: 1.0, on: .main, in: .common)
.autoconnect()
.share()
.eraseToAnyPublisher()
// input
private(set) weak var scrollView: UIScrollView?
let hasMore = CurrentValueSubject<Bool, Never>(true)
// output
let shouldFetch = PassthroughSubject<Void, Never>()
init() {
Publishers.CombineLatest(
hasMore,
timerPublisher
)
.sink { [weak self] hasMore, _ in
guard let self = self else { return }
guard hasMore else { return }
guard let scrollView = self.scrollView else { return }
// skip trigger if user interacting
if scrollView.isDragging || scrollView.isTracking { return }
// send fetch request
if scrollView.contentSize.height < scrollView.frame.height {
self.shouldFetch.send()
} else {
let frame = scrollView.frame
let contentOffset = scrollView.contentOffset
let contentSize = scrollView.contentSize
let visibleBottomY = contentOffset.y + frame.height
let offset = 2 * frame.height
let fetchThrottleOffsetY = contentSize.height - offset
if visibleBottomY > fetchThrottleOffsetY {
self.shouldFetch.send()
}
}
}
.store(in: &disposeBag)
}
}
extension ListBatchFetchViewModel {
func setup(scrollView: UIScrollView) {
self.scrollView = scrollView
}
}