ProgressBar.swift

import UIKit

@IBDesignable final class ProgressBarView: UIView {

    @IBInspectable var barColor: UIColor = UIColor.ex.red
    @IBInspectable var trackColor: UIColor = UIColor.ex.gray
    @IBInspectable var barThickness: CGFloat = 8.0
    @IBInspectable var barPadding: CGFloat = 0.0
    @IBInspectable var trackPadding: CGFloat = 0.0
    @IBInspectable var progressValue: Int = 0 {
        didSet {
            progressValue = max(min(progressValue, 100), 0)
            setNeedsDisplay()
        }
    }


    // MARK: - Draw

    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else { return }

        context.saveGState()
        drawTrack(with: context)
        drawProgressBar(with: context)
        context.restoreGState()
    }

    private var percentage: CGFloat {
        let calibratedWidth = frame.size.width - (barPadding * 2) - (trackOffset * 2)
        let progress = (CGFloat(progressValue) / 100) * calibratedWidth
        return progress < 0 ? barPadding : progress
    }

    private var trackHeight: CGFloat {
        return barThickness + trackPadding
    }

    private var trackOffset: CGFloat {
        return trackHeight / 2.0
    }

    private func drawTrack(with context: CGContext) {
        context.setStrokeColor(trackColor.cgColor)
        context.beginPath()
        context.setLineWidth(trackHeight)
        context.move(to: CGPoint(x: barPadding + trackOffset, y: frame.size.height / 2))
        context.addLine(to: CGPoint(x: frame.size.width - barPadding - trackOffset, y: frame.size.height / 2))
        context.setLineCap(CGLineCap.round)
        context.strokePath()
    }

    private func drawProgressBar(with context: CGContext) {
        context.setStrokeColor(barColor.cgColor)
        context.setLineWidth(barThickness)
        context.beginPath()
        context.move(to: CGPoint(x: barPadding + trackOffset, y: frame.size.height / 2))
        context.addLine(to: CGPoint(x: barPadding + trackOffset + percentage, y: frame.size.height / 2))
        context.setLineCap(CGLineCap.round)
        context.strokePath()
    }
}