LoopingIterator.swift

//
//  LoopingIterator.swift
//
//  Created by Chris Nevin on 01/11/2016.
//  Copyright © 2016 CJNevin. All rights reserved.
//

import Foundation

public struct LoopingIterator<Base: Collection> : IteratorProtocol {
    private let collection: Base
    public var index: Base.Index
    public var endIndex: Base.Index

    public var current: Base.Iterator.Element? {
        if (collection.startIndex...collection.endIndex).contains(index) {
            return collection[index]
        } else {
            return nil
        }
    }

    public init(collection: Base) {
        self.collection = collection
        self.index = collection.startIndex
        self.endIndex = collection.endIndex
    }

    @discardableResult public mutating func next() -> Base.Iterator.Element? {
        guard !collection.isEmpty else {
            return nil
        }

        let result = collection[index]
        collection.formIndex(after: &index)
        if index == collection.endIndex {
            index = collection.startIndex
        }
        return result
    }
}

public extension Array {
    public func makeLoopingIterator() -> LoopingIterator<Array> {
        return LoopingIterator(collection: self)
    }
}