NetNewsWire/Shared/IconImageCache.swift

//
//  IconImageCache.swift
//  NetNewsWire-iOS
//
//  Created by Brent Simmons on 5/2/21.
//  Copyright © 2021 Ranchero Software. All rights reserved.
//

import Foundation
import Account
import Articles

class IconImageCache {

	static var shared = IconImageCache()

	private var smartFeedIconImageCache = [ItemIdentifier: IconImage]()
	private var feedIconImageCache = [ItemIdentifier: IconImage]()
	private var faviconImageCache = [ItemIdentifier: IconImage]()
	private var smallIconImageCache = [ItemIdentifier: IconImage]()
	private var authorIconImageCache = [Author: IconImage]()

	@MainActor func imageFor(_ itemID: ItemIdentifier) -> IconImage? {
		if let smartFeed = SmartFeedsController.shared.find(by: itemID) {
			return imageForFeed(smartFeed)
		}
		if let feed = AccountManager.shared.existingFeed(with: itemID) {
			return imageForFeed(feed)
		}
		return nil
	}

	@MainActor func imageForFeed(_ feedProtocol: FeedProtocol) -> IconImage? {
		guard let itemID = feedProtocol.itemID else {
			return nil
		}
		
		if let smartFeed = feedProtocol as? PseudoFeed {
			return imageForSmartFeed(smartFeed, itemID)
		}
		if let feed = feedProtocol as? Feed, let iconImage = imageForFeed(feed, itemID) {
			return iconImage
		}
		if let smallIconProvider = feedProtocol as? SmallIconProvider {
			return imageForSmallIconProvider(smallIconProvider, itemID)
		}

		return nil
	}

	@MainActor func imageForArticle(_ article: Article) -> IconImage? {
		if let iconImage = imageForAuthors(article.authors) {
			return iconImage
		}
		guard let feed = article.feed else {
			return nil
		}
		return imageForFeed(feed)
	}

	func emptyCache() {
		smartFeedIconImageCache = [ItemIdentifier: IconImage]()
		feedIconImageCache = [ItemIdentifier: IconImage]()
		faviconImageCache = [ItemIdentifier: IconImage]()
		smallIconImageCache = [ItemIdentifier: IconImage]()
		authorIconImageCache = [Author: IconImage]()
	}
}

private extension IconImageCache {
	
	func imageForSmartFeed(_ smartFeed: PseudoFeed, _ itemID: ItemIdentifier) -> IconImage? {
		if let iconImage = smartFeedIconImageCache[itemID] {
			return iconImage
		}
		if let iconImage = smartFeed.smallIcon {
			smartFeedIconImageCache[itemID] = iconImage
			return iconImage
		}
		return nil
	}

	@MainActor func imageForFeed(_ feed: Feed, _ itemID: ItemIdentifier) -> IconImage? {
		if let iconImage = feedIconImageCache[itemID] {
			return iconImage
		}
		if let iconImage = appDelegate.feedIconDownloader.icon(for: feed) {
			feedIconImageCache[itemID] = iconImage
			return iconImage
		}
		if let faviconImage = faviconImageCache[itemID] {
			return faviconImage
		}
		if let faviconImage = appDelegate.faviconDownloader.faviconAsIcon(for: feed) {
			faviconImageCache[itemID] = faviconImage
			return faviconImage
		}
		return nil
	}

	func imageForSmallIconProvider(_ provider: SmallIconProvider, _ itemID: ItemIdentifier) -> IconImage? {
		if let iconImage = smallIconImageCache[itemID] {
			return iconImage
		}
		if let iconImage = provider.smallIcon {
			smallIconImageCache[itemID] = iconImage
			return iconImage
		}
		return nil
	}

	@MainActor func imageForAuthors(_ authors: Set<Author>?) -> IconImage? {
		guard let authors = authors, authors.count == 1, let author = authors.first else {
			return nil
		}
		return imageForAuthor(author)
	}

	@MainActor func imageForAuthor(_ author: Author) -> IconImage? {
		if let iconImage = authorIconImageCache[author] {
			return iconImage
		}
		if let iconImage = appDelegate.authorAvatarDownloader.image(for: author) {
			authorIconImageCache[author] = iconImage
			return iconImage
		}
		return nil
	}
}