extension FeatureItem {
    var isInCollection: Bool { return true }
    var isCollection: Bool { return false }
    var icon: String? { return nil }
}

protocol FeatureCollectionItem: FeatureItem {
    var prefersInlineDisplay: Bool { get }

    var count: Int { get }
    subscript(index: Int) -> FeatureItem { get }
}

extension FeatureCollectionItem {
    var isCollection: Bool { return true }
    var prefersInlineDisplay: Bool { return false }
}

struct FeatureItemList<ItemDataSource: DataSource>: FeatureCollectionItem where ItemDataSource.Item == FeatureItem {
    let key: FeatureItemKey
    let title: String
    let icon: String?
    private let items: ItemDataSource

    init(title: String, key: FeatureItemKey, icon: String? = nil, items: ItemDataSource) {
        self.title = title
        self.key = key
        self.icon = icon
        self.items = items
    }

    var count: Int {
        return self.items.numberOfItems
    }

    subscript(index: Int) -> FeatureItem {
        return self.items.item(at: index)
    }
}

extension FeatureItemList: Collection {
    var startIndex: Int {
        return 0
    }

    var endIndex: Int {
        return self.numberOfItems
    }

    func index(after i: Int) -> Int {
        return i + 1
    }
}