/*

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

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 An extension to `CGContext` to draw the horizontal lines in a `GraphView`.

 */

import UIKit

extension CGContext {

    func drawGraphLines(in size: CGSize) {

        // Configure context settings.

        self.saveGState()

        setShouldAntialias(false)

        translateBy(x: 0, y: size.height / 2.0)

        // Add lines to the context.

        let gridLineSpacing = size.height / 8.0

        for index in -3...3 {

            // Skip the center line.

            guard index != 0 else { continue }

            let position = floor(gridLineSpacing * CGFloat(index))

            move(to: CGPoint(x: 0, y: position))

            addLine(to: CGPoint(x: size.width, y: position))

        }

        // Stroke the lines.

        setStrokeColor(UIColor.darkGray.cgColor)

        strokePath()

        // Add and stroke the center line.

        move(to: CGPoint(x: 0, y: 0))

        addLine(to: CGPoint(x: size.width, y: 0))

        setStrokeColor(UIColor.lightGray.cgColor)

        strokePath()

        // Restore the context state.

        self.restoreGState()

    }

}