Swiftgram/TelegramCore/WebpagePreview.swift

import Foundation
#if os(macOS)
    import PostboxMac
    import SwiftSignalKitMac
    import MtProtoKitMac
#else
    import Postbox
    import SwiftSignalKit
    import MtProtoKitDynamic
#endif

public func webpagePreview(account: Account, url: String) -> Signal<TelegramMediaWebpage?, NoError> {
    return account.network.request(Api.functions.messages.getWebPagePreview(message: url))
        |> `catch` { _ -> Signal<Api.MessageMedia, NoError> in
            return .single(.messageMediaEmpty)
        }
        |> mapToSignal { result -> Signal<TelegramMediaWebpage?, NoError> in
            switch result {
                case let .messageMediaWebPage(webpage):
                    if let media = telegramMediaWebpageFromApiWebpage(webpage) {
                        if case .Loaded = media.content {
                            return .single(media)
                        } else {
                            return .single(media) |> then(account.stateManager.updatedWebpage(media.webpageId) |> map { Optional($0) })
                        }
                    } else {
                        return .single(nil)
                    }
                default:
                    return .single(nil)
            }
        }
}