Sources/NeedleFoundation/Bootstrap.swift

//
//  Copyright (c) 2018. Uber Technologies
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
//

import Foundation

/// An empty protocol that can be used for any components that require no
/// dependencies. This can be used as the dependency protocol of the root
/// component of a dependency graph.
public protocol EmptyDependency: AnyObject {}

/// The dependency provider that conforms to `EmptyDependency`. This is
/// used to bootstrap the root component of a dependency graph.
public class EmptyDependencyProvider: EmptyDependency {

    /// Initializer.
    ///
    /// - parameter component: The component instance.
    public init(component: Scope) {}
}

/// The base implementation of a component thet represents the root of
/// a dependency graph. A subclass defining the root scope should
/// inherit from this class instead of the generic `Component` class.
///
/// - SeeAlso: `Component`.
open class BootstrapComponent: Component<EmptyDependency> {

    /// Initializer.
    public init() {
        super.init(parent: BigBang())
    }

    // MARK: - Private

    private class BigBang: Scope {
        fileprivate let path: [String] = ["^"]
        /// This component does not have a parent. Do not access this property.
        fileprivate var parent: Scope {
            // With properly generated Needle code, this property should never
            // be accessed.
            fatalError("BootstrapComponent does not have a parent, do not use this property.")
        }

        #if NEEDLE_DYNAMIC
        func find<T>(property: String, skipThisLevel: Bool) -> T {
            fatalError("Unable to find \(property) anywhere along the path to the root")
        }
        #endif
        
        fileprivate init() {}
    }
}