/// ContentLoader is a lightweight state manager for loading and displaying content and/or errors.
/// It allows you to repeatedly make requests and display new content or cached content in the event of an error.
/// Commonly known as RemoteData or LCE (Loading / Content / Error).
/// Inspired by https://tech.instacart.com/lce-modeling-data-loading-in-rxjava-b798ac98d80
///
final class ContentLoader<T> {
    init() { }

    @discardableResult func loader(_ loader: (() -> Void)?) -> ContentLoader<T> {
        self.loader = loader
        return self
    }

    @discardableResult func update(_ update: (() -> Void)?) -> ContentLoader<T> {
        self.update = update
        return self
    }

    private var loader: (() -> Void)?
    private var update: (() -> Void)?

    var loading: Bool = false
    var content: T?
    var error: Error?

    var hasContent: Bool { return content != nil }
    var hasError: Bool { return error != nil }

    func load() {
        loading = true
        loader?()
    }

    func success(content: T) {
        self.content = content
        self.loading = false
        update?()
    }

    func failure(error: Error?) {
        self.error = error
        self.loading = false
        update?()
    }
}


// usage psudocode

class ViewController {
    let contentLoader = ContentLoader<JSON>()
  
    init {
        self.contentLoader.loader({
            async {
                loadData { data, error in 
                    if let json = JSON(data) {
                        self.contentLoader.success(json)
                    } else {
                        self.contentLoader.failure(error ?? ParsingError())
                    }
                }
            }

        }).update({
            updateTheUI()
        }).load()
    }
      
    func updateTheUI() {
        // Handle the state enum to draw correct UI
    }
}