/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    Provides a layout that allows you to put a background behind another

                layout.

*/

import CoreGraphics

/// A layout that diplays its background content behind its foreground content.

struct BackgroundLayout<Background: Layout, Foreground: Layout>: Layout where Background.Content == Foreground.Content {

    typealias Content = Background.Content

    var background: Background

    var foreground: Foreground

    mutating func layout(in rect: CGRect) {

        background.layout(in: rect)

        foreground.layout(in: rect)

    }

    var contents: [Content] {

        return background.contents + foreground.contents

    }

}

/**

    In this extension we define a methods that allow us to easily chain layouts

    together. For example, you can now take any `Layout` type and call

    `withBackground(backgroundLayout)` to get the same layout but with a background. 

    This is a convenient alternative to using initializer syntax if you're composing multiple

    layouts together.

*/

extension Layout {

    /// Returns a layout that shows `self` in front of `background`.

    func withBackground<Background: Layout>(_ background: Background) -> BackgroundLayout<Background, Self> where Background.Content == Content {

        return BackgroundLayout(background: background, foreground: self)

    }

}