//
//  PieChartRenderer.swift
//  Charts
//
//  Copyright 2015 Daniel Cohen Gindi & Philipp Jahoda
//  A port of MPAndroidChart for iOS
//  Licensed under Apache License 2.0
//
//  https://github.com/danielgindi/Charts
//

import Foundation
import CoreGraphics

#if canImport(UIKit)
    import UIKit
#endif

#if canImport(Cocoa)
import Cocoa
#endif

open class PieChartRenderer: DataRenderer
{
    @objc open weak var chart: PieChartView?

    @objc public init(chart: PieChartView, animator: Animator, viewPortHandler: ViewPortHandler)
    {
        super.init(animator: animator, viewPortHandler: viewPortHandler)

        self.chart = chart
    }

    open override func drawData(context: CGContext)
    {
        guard let chart = chart else { return }

        let pieData = chart.data

        if pieData != nil
        {
            // If we redraw the data, remove and repopulate accessible elements to update label values and frames
            accessibleChartElements.removeAll()

            for set in pieData!.dataSets as! [IPieChartDataSet]
                where set.isVisible && set.entryCount > 0
            {
                drawDataSet(context: context, dataSet: set)
            }
        }
    }

    @objc open func calculateMinimumRadiusForSpacedSlice(
        center: CGPoint,
        radius: CGFloat,
        angle: CGFloat,
        arcStartPointX: CGFloat,
        arcStartPointY: CGFloat,
        startAngle: CGFloat,
        sweepAngle: CGFloat) -> CGFloat
    {
        let angleMiddle = startAngle + sweepAngle / 2.0

        // Other point of the arc
        let arcEndPointX = center.x + radius * cos((startAngle + sweepAngle).DEG2RAD)
        let arcEndPointY = center.y + radius * sin((startAngle + sweepAngle).DEG2RAD)

        // Middle point on the arc
        let arcMidPointX = center.x + radius * cos(angleMiddle.DEG2RAD)
        let arcMidPointY = center.y + radius * sin(angleMiddle.DEG2RAD)

        // This is the base of the contained triangle
        let basePointsDistance = sqrt(
            pow(arcEndPointX - arcStartPointX, 2) +
                pow(arcEndPointY - arcStartPointY, 2))

        // After reducing space from both sides of the "slice",
        //   the angle of the contained triangle should stay the same.
        // So let's find out the height of that triangle.
        let containedTriangleHeight = (basePointsDistance / 2.0 *
            tan((180.0 - angle).DEG2RAD / 2.0))

        // Now we subtract that from the radius
        var spacedRadius = radius - containedTriangleHeight

        // And now subtract the height of the arc that's between the triangle and the outer circle
        spacedRadius -= sqrt(
            pow(arcMidPointX - (arcEndPointX + arcStartPointX) / 2.0, 2) +
                pow(arcMidPointY - (arcEndPointY + arcStartPointY) / 2.0, 2))

        return spacedRadius
    }

    /// Calculates the sliceSpace to use based on visible values and their size compared to the set sliceSpace.
    @objc open func getSliceSpace(dataSet: IPieChartDataSet) -> CGFloat
    {
        guard
            dataSet.automaticallyDisableSliceSpacing,
            let data = chart?.data as? PieChartData
            else { return dataSet.sliceSpace }

        let spaceSizeRatio = dataSet.sliceSpace / min(viewPortHandler.contentWidth, viewPortHandler.contentHeight)
        let minValueRatio = dataSet.yMin / data.yValueSum * 2.0

        let sliceSpace = spaceSizeRatio > CGFloat(minValueRatio)
            ? 0.0
            : dataSet.sliceSpace

        return sliceSpace
    }

    @objc open func drawDataSet(context: CGContext, dataSet: IPieChartDataSet)
    {
        guard let chart = chart else {return }

        var angle: CGFloat = 0.0
        let rotationAngle = chart.rotationAngle

        let phaseX = animator.phaseX
        let phaseY = animator.phaseY

        let entryCount = dataSet.entryCount
        let drawAngles = chart.drawAngles
        let center = chart.centerCircleBox
        let radius = chart.radius
        let drawInnerArc = chart.drawHoleEnabled && !chart.drawSlicesUnderHoleEnabled
        let userInnerRadius = drawInnerArc ? radius * chart.holeRadiusPercent : 0.0

        var visibleAngleCount = 0
        for j in 0 ..< entryCount
        {
            guard let e = dataSet.entryForIndex(j) else { continue }
            if ((abs(e.y) > Double.ulpOfOne))
            {
                visibleAngleCount += 1
            }
        }

        let sliceSpace = visibleAngleCount <= 1 ? 0.0 : getSliceSpace(dataSet: dataSet)

        context.saveGState()

        // Make the chart header the first element in the accessible elements array
        // We can do this in drawDataSet, since we know PieChartView can have only 1 dataSet
        // Also since there's only 1 dataset, we don't use the typical createAccessibleHeader() here.
        // NOTE: - Since we want to summarize the total count of slices/portions/elements, use a default string here
        // This is unlike when we are naming individual slices, wherein it's alright to not use a prefix as descriptor.
        // i.e. We want to VO to say "3 Elements" even if the developer didn't specify an accessibility prefix
        // If prefix is unspecified it is safe to assume they did not want to use "Element 1", so that uses a default empty string
        let prefix: String = chart.data?.accessibilityEntryLabelPrefix ?? "Element"
        let description = chart.chartDescription?.text ?? dataSet.label ?? chart.centerText ??  "Pie Chart"

        let
        element = NSUIAccessibilityElement(accessibilityContainer: chart)
        element.accessibilityLabel = description + ". \(entryCount) \(prefix + (entryCount == 1 ? "" : "s"))"
        element.accessibilityFrame = chart.bounds
        element.isHeader = true
        accessibleChartElements.append(element)

        for j in 0 ..< entryCount
        {
            let sliceAngle = drawAngles[j]
            var innerRadius = userInnerRadius

            guard let e = dataSet.entryForIndex(j) else { continue }
            
            defer
            {
                // From here on, even when skipping (i.e for highlight),
                //  increase the angle
                angle += sliceAngle * CGFloat(phaseX)
            }

            // draw only if the value is greater than zero
            if abs(e.y) < Double.ulpOfOne { continue }
            
            // Skip if highlighted
            if dataSet.isHighlightEnabled && chart.needsHighlight(index: j)
            {
                continue
            }
        
            let accountForSliceSpacing = sliceSpace > 0.0 && sliceAngle <= 180.0

            context.setFillColor(dataSet.color(atIndex: j).cgColor)

            let sliceSpaceAngleOuter = visibleAngleCount == 1 ?
                0.0 :
                sliceSpace / radius.DEG2RAD
            let startAngleOuter = rotationAngle + (angle + sliceSpaceAngleOuter / 2.0) * CGFloat(phaseY)
            var sweepAngleOuter = (sliceAngle - sliceSpaceAngleOuter) * CGFloat(phaseY)
            if sweepAngleOuter < 0.0
            {
                sweepAngleOuter = 0.0
            }

            let arcStartPointX = center.x + radius * cos(startAngleOuter.DEG2RAD)
            let arcStartPointY = center.y + radius * sin(startAngleOuter.DEG2RAD)

            let path = CGMutablePath()

            path.move(to: CGPoint(x: arcStartPointX,
                                  y: arcStartPointY))

            path.addRelativeArc(center: center, radius: radius, startAngle: startAngleOuter.DEG2RAD, delta: sweepAngleOuter.DEG2RAD)

            if drawInnerArc &&
                (innerRadius > 0.0 || accountForSliceSpacing)
            {
                if accountForSliceSpacing
                {
                    var minSpacedRadius = calculateMinimumRadiusForSpacedSlice(
                        center: center,
                        radius: radius,
                        angle: sliceAngle * CGFloat(phaseY),
                        arcStartPointX: arcStartPointX,
                        arcStartPointY: arcStartPointY,
                        startAngle: startAngleOuter,
                        sweepAngle: sweepAngleOuter)
                    if minSpacedRadius < 0.0
                    {
                        minSpacedRadius = -minSpacedRadius
                    }
                    innerRadius = min(max(innerRadius, minSpacedRadius), radius)
                }

                let sliceSpaceAngleInner = visibleAngleCount == 1 || innerRadius == 0.0 ?
                    0.0 :
                    sliceSpace / innerRadius.DEG2RAD
                let startAngleInner = rotationAngle + (angle + sliceSpaceAngleInner / 2.0) * CGFloat(phaseY)
                var sweepAngleInner = (sliceAngle - sliceSpaceAngleInner) * CGFloat(phaseY)
                if sweepAngleInner < 0.0
                {
                    sweepAngleInner = 0.0
                }
                let endAngleInner = startAngleInner + sweepAngleInner

                path.addLine(
                    to: CGPoint(
                        x: center.x + innerRadius * cos(endAngleInner.DEG2RAD),
                        y: center.y + innerRadius * sin(endAngleInner.DEG2RAD)))

                path.addRelativeArc(center: center, radius: innerRadius, startAngle: endAngleInner.DEG2RAD, delta: -sweepAngleInner.DEG2RAD)
            }
            else
            {
                if accountForSliceSpacing
                {
                    let angleMiddle = startAngleOuter + sweepAngleOuter / 2.0

                    let sliceSpaceOffset =
                        calculateMinimumRadiusForSpacedSlice(
                            center: center,
                            radius: radius,
                            angle: sliceAngle * CGFloat(phaseY),
                            arcStartPointX: arcStartPointX,
                            arcStartPointY: arcStartPointY,
                            startAngle: startAngleOuter,
                            sweepAngle: sweepAngleOuter)

                    let arcEndPointX = center.x + sliceSpaceOffset * cos(angleMiddle.DEG2RAD)
                    let arcEndPointY = center.y + sliceSpaceOffset * sin(angleMiddle.DEG2RAD)

                    path.addLine(
                        to: CGPoint(
                            x: arcEndPointX,
                            y: arcEndPointY))
                }
                else
                {
                    path.addLine(to: center)
                }
            }

            path.closeSubpath()

            context.beginPath()
            context.addPath(path)
            context.fillPath(using: .evenOdd)

            let axElement = createAccessibleElement(withIndex: j,
                                                    container: chart,
                                                    dataSet: dataSet)
            { (element) in
                element.accessibilityFrame = path.boundingBoxOfPath
            }

            accessibleChartElements.append(axElement)
        }

        // Post this notification to let VoiceOver account for the redrawn frames
        accessibilityPostLayoutChangedNotification()

        context.restoreGState()
    }

    open override func drawValues(context: CGContext)
    {
        guard
            let chart = chart,
            let data = chart.data
            else { return }

        let center = chart.centerCircleBox

        // get whole the radius
        let radius = chart.radius
        let rotationAngle = chart.rotationAngle
        let drawAngles = chart.drawAngles
        let absoluteAngles = chart.absoluteAngles

        let phaseX = animator.phaseX
        let phaseY = animator.phaseY

        var labelRadiusOffset = radius / 10.0 * 3.0

        if chart.drawHoleEnabled
        {
            labelRadiusOffset = (radius - (radius * chart.holeRadiusPercent)) / 2.0
        }

        let labelRadius = radius - labelRadiusOffset

        let dataSets = data.dataSets

        let yValueSum = (data as! PieChartData).yValueSum

        let drawEntryLabels = chart.isDrawEntryLabelsEnabled
        let usePercentValuesEnabled = chart.usePercentValuesEnabled

        var angle: CGFloat = 0.0
        var xIndex = 0

        context.saveGState()
        defer { context.restoreGState() }

        for i in 0 ..< dataSets.count
        {
            guard let dataSet = dataSets[i] as? IPieChartDataSet else { continue }

            let drawValues = dataSet.isDrawValuesEnabled

            if !drawValues && !drawEntryLabels && !dataSet.isDrawIconsEnabled
            {
                continue
            }

            let iconsOffset = dataSet.iconsOffset

            let xValuePosition = dataSet.xValuePosition
            let yValuePosition = dataSet.yValuePosition

            let valueFont = dataSet.valueFont
            let entryLabelFont = dataSet.entryLabelFont ?? chart.entryLabelFont
            let lineHeight = valueFont.lineHeight

            guard let formatter = dataSet.valueFormatter else { continue }

            for j in 0 ..< dataSet.entryCount
            {
                guard let e = dataSet.entryForIndex(j) else { continue }
                let pe = e as? PieChartDataEntry

                if xIndex == 0
                {
                    angle = 0.0
                }
                else
                {
                    angle = absoluteAngles[xIndex - 1] * CGFloat(phaseX)
                }

                let sliceAngle = drawAngles[xIndex]
                let sliceSpace = getSliceSpace(dataSet: dataSet)
                let sliceSpaceMiddleAngle = sliceSpace / labelRadius.DEG2RAD

                // offset needed to center the drawn text in the slice
                let angleOffset = (sliceAngle - sliceSpaceMiddleAngle / 2.0) / 2.0

                angle = angle + angleOffset

                let transformedAngle = rotationAngle + angle * CGFloat(phaseY)

                let value = usePercentValuesEnabled ? e.y / yValueSum * 100.0 : e.y
                let valueText = formatter.stringForValue(
                    value,
                    entry: e,
                    dataSetIndex: i,
                    viewPortHandler: viewPortHandler)

                let sliceXBase = cos(transformedAngle.DEG2RAD)
                let sliceYBase = sin(transformedAngle.DEG2RAD)

                let drawXOutside = drawEntryLabels && xValuePosition == .outsideSlice
                let drawYOutside = drawValues && yValuePosition == .outsideSlice
                let drawXInside = drawEntryLabels && xValuePosition == .insideSlice
                let drawYInside = drawValues && yValuePosition == .insideSlice

                let valueTextColor = dataSet.valueTextColorAt(j)
                let entryLabelColor = dataSet.entryLabelColor ?? chart.entryLabelColor

                if drawXOutside || drawYOutside
                {
                    let valueLineLength1 = dataSet.valueLinePart1Length
                    let valueLineLength2 = dataSet.valueLinePart2Length
                    let valueLinePart1OffsetPercentage = dataSet.valueLinePart1OffsetPercentage

                    var pt2: CGPoint
                    var labelPoint: CGPoint
                    var align: NSTextAlignment

                    var line1Radius: CGFloat

                    if chart.drawHoleEnabled
                    {
                        line1Radius = (radius - (radius * chart.holeRadiusPercent)) * valueLinePart1OffsetPercentage + (radius * chart.holeRadiusPercent)
                    }
                    else
                    {
                        line1Radius = radius * valueLinePart1OffsetPercentage
                    }

                    let polyline2Length = dataSet.valueLineVariableLength
                        ? labelRadius * valueLineLength2 * abs(sin(transformedAngle.DEG2RAD))
                        : labelRadius * valueLineLength2

                    let pt0 = CGPoint(
                        x: line1Radius * sliceXBase + center.x,
                        y: line1Radius * sliceYBase + center.y)

                    let pt1 = CGPoint(
                        x: labelRadius * (1 + valueLineLength1) * sliceXBase + center.x,
                        y: labelRadius * (1 + valueLineLength1) * sliceYBase + center.y)

                    if transformedAngle.truncatingRemainder(dividingBy: 360.0) >= 90.0 && transformedAngle.truncatingRemainder(dividingBy: 360.0) <= 270.0
                    {
                        pt2 = CGPoint(x: pt1.x - polyline2Length, y: pt1.y)
                        align = .right
                        labelPoint = CGPoint(x: pt2.x - 5, y: pt2.y - lineHeight)
                    }
                    else
                    {
                        pt2 = CGPoint(x: pt1.x + polyline2Length, y: pt1.y)
                        align = .left
                        labelPoint = CGPoint(x: pt2.x + 5, y: pt2.y - lineHeight)
                    }

                    DrawLine: do
                    {
                        if dataSet.useValueColorForLine
                        {
                            context.setStrokeColor(dataSet.color(atIndex: j).cgColor)
                        }
                        else if let valueLineColor = dataSet.valueLineColor
                        {
                            context.setStrokeColor(valueLineColor.cgColor)
                        }
                        else
                        {
                            return
                        }
                        context.setLineWidth(dataSet.valueLineWidth)

                        context.move(to: CGPoint(x: pt0.x, y: pt0.y))
                        context.addLine(to: CGPoint(x: pt1.x, y: pt1.y))
                        context.addLine(to: CGPoint(x: pt2.x, y: pt2.y))

                        context.drawPath(using: CGPathDrawingMode.stroke)
                    }
                    
                    if drawXOutside && drawYOutside
                    {
                        ChartUtils.drawText(
                            context: context,
                            text: valueText,
                            point: labelPoint,
                            align: align,
                            attributes: [NSAttributedString.Key.font: valueFont, NSAttributedString.Key.foregroundColor: valueTextColor]
                        )

                        if j < data.entryCount && pe?.label != nil
                        {
                            ChartUtils.drawText(
                                context: context,
                                text: pe!.label!,
                                point: CGPoint(x: labelPoint.x, y: labelPoint.y + lineHeight),
                                align: align,
                                attributes: [
                                    NSAttributedString.Key.font: entryLabelFont ?? valueFont,
                                    NSAttributedString.Key.foregroundColor: entryLabelColor ?? valueTextColor]
                            )
                        }
                    }
                    else if drawXOutside
                    {
                        if j < data.entryCount && pe?.label != nil
                        {
                            ChartUtils.drawText(
                                context: context,
                                text: pe!.label!,
                                point: CGPoint(x: labelPoint.x, y: labelPoint.y + lineHeight / 2.0),
                                align: align,
                                attributes: [
                                    NSAttributedString.Key.font: entryLabelFont ?? valueFont,
                                    NSAttributedString.Key.foregroundColor: entryLabelColor ?? valueTextColor]
                            )
                        }
                    }
                    else if drawYOutside
                    {
                        ChartUtils.drawText(
                            context: context,
                            text: valueText,
                            point: CGPoint(x: labelPoint.x, y: labelPoint.y + lineHeight / 2.0),
                            align: align,
                            attributes: [NSAttributedString.Key.font: valueFont, NSAttributedString.Key.foregroundColor: valueTextColor]
                        )
                    }
                }

                if drawXInside || drawYInside
                {
                    // calculate the text position
                    let x = labelRadius * sliceXBase + center.x
                    let y = labelRadius * sliceYBase + center.y - lineHeight

                    if drawXInside && drawYInside
                    {
                        ChartUtils.drawText(
                            context: context,
                            text: valueText,
                            point: CGPoint(x: x, y: y),
                            align: .center,
                            attributes: [NSAttributedString.Key.font: valueFont, NSAttributedString.Key.foregroundColor: valueTextColor]
                        )

                        if j < data.entryCount && pe?.label != nil
                        {
                            ChartUtils.drawText(
                                context: context,
                                text: pe!.label!,
                                point: CGPoint(x: x, y: y + lineHeight),
                                align: .center,
                                attributes: [
                                    NSAttributedString.Key.font: entryLabelFont ?? valueFont,
                                    NSAttributedString.Key.foregroundColor: entryLabelColor ?? valueTextColor]
                            )
                        }
                    }
                    else if drawXInside
                    {
                        if j < data.entryCount && pe?.label != nil
                        {
                            ChartUtils.drawText(
                                context: context,
                                text: pe!.label!,
                                point: CGPoint(x: x, y: y + lineHeight / 2.0),
                                align: .center,
                                attributes: [
                                    NSAttributedString.Key.font: entryLabelFont ?? valueFont,
                                    NSAttributedString.Key.foregroundColor: entryLabelColor ?? valueTextColor]
                            )
                        }
                    }
                    else if drawYInside
                    {
                        ChartUtils.drawText(
                            context: context,
                            text: valueText,
                            point: CGPoint(x: x, y: y + lineHeight / 2.0),
                            align: .center,
                            attributes: [NSAttributedString.Key.font: valueFont, NSAttributedString.Key.foregroundColor: valueTextColor]
                        )
                    }
                }

                if let icon = e.icon, dataSet.isDrawIconsEnabled
                {
                    // calculate the icon's position

                    let x = (labelRadius + iconsOffset.y) * sliceXBase + center.x
                    var y = (labelRadius + iconsOffset.y) * sliceYBase + center.y
                    y += iconsOffset.x

                    ChartUtils.drawImage(context: context,
                                         image: icon,
                                         x: x,
                                         y: y,
                                         size: icon.size)
                }

                xIndex += 1
            }
        }
    }

    open override func drawExtras(context: CGContext)
    {
        drawHole(context: context)
        drawCenterText(context: context)
    }

    /// draws the hole in the center of the chart and the transparent circle / hole
    private func drawHole(context: CGContext)
    {
        guard let chart = chart else { return }

        if chart.drawHoleEnabled
        {
            context.saveGState()

            let radius = chart.radius
            let holeRadius = radius * chart.holeRadiusPercent
            let center = chart.centerCircleBox

            if let holeColor = chart.holeColor
            {
                if holeColor != NSUIColor.clear
                {
                    // draw the hole-circle
                    context.setFillColor(chart.holeColor!.cgColor)
                    context.fillEllipse(in: CGRect(x: center.x - holeRadius, y: center.y - holeRadius, width: holeRadius * 2.0, height: holeRadius * 2.0))
                }
            }

            // only draw the circle if it can be seen (not covered by the hole)
            if let transparentCircleColor = chart.transparentCircleColor
            {
                if transparentCircleColor != NSUIColor.clear &&
                    chart.transparentCircleRadiusPercent > chart.holeRadiusPercent
                {
                    let alpha = animator.phaseX * animator.phaseY
                    let secondHoleRadius = radius * chart.transparentCircleRadiusPercent

                    // make transparent
                    context.setAlpha(CGFloat(alpha))
                    context.setFillColor(transparentCircleColor.cgColor)

                    // draw the transparent-circle
                    context.beginPath()
                    context.addEllipse(in: CGRect(
                        x: center.x - secondHoleRadius,
                        y: center.y - secondHoleRadius,
                        width: secondHoleRadius * 2.0,
                        height: secondHoleRadius * 2.0))
                    context.addEllipse(in: CGRect(
                        x: center.x - holeRadius,
                        y: center.y - holeRadius,
                        width: holeRadius * 2.0,
                        height: holeRadius * 2.0))
                    context.fillPath(using: .evenOdd)
                }
            }

            context.restoreGState()
        }
    }

    /// draws the description text in the center of the pie chart makes most sense when center-hole is enabled
    private func drawCenterText(context: CGContext)
    {
        guard
            let chart = chart,
            let centerAttributedText = chart.centerAttributedText
            else { return }

        if chart.drawCenterTextEnabled && centerAttributedText.length > 0
        {
            let center = chart.centerCircleBox
            let offset = chart.centerTextOffset
            let innerRadius = chart.drawHoleEnabled && !chart.drawSlicesUnderHoleEnabled ? chart.radius * chart.holeRadiusPercent : chart.radius

            let x = center.x + offset.x
            let y = center.y + offset.y

            let holeRect = CGRect(
                x: x - innerRadius,
                y: y - innerRadius,
                width: innerRadius * 2.0,
                height: innerRadius * 2.0)
            var boundingRect = holeRect

            if chart.centerTextRadiusPercent > 0.0
            {
                boundingRect = boundingRect.insetBy(dx: (boundingRect.width - boundingRect.width * chart.centerTextRadiusPercent) / 2.0, dy: (boundingRect.height - boundingRect.height * chart.centerTextRadiusPercent) / 2.0)
            }

            let textBounds = centerAttributedText.boundingRect(with: boundingRect.size, options: [.usesLineFragmentOrigin, .usesFontLeading, .truncatesLastVisibleLine], context: nil)

            var drawingRect = boundingRect
            drawingRect.origin.x += (boundingRect.size.width - textBounds.size.width) / 2.0
            drawingRect.origin.y += (boundingRect.size.height - textBounds.size.height) / 2.0
            drawingRect.size = textBounds.size

            context.saveGState()

            let clippingPath = CGPath(ellipseIn: holeRect, transform: nil)
            context.beginPath()
            context.addPath(clippingPath)
            context.clip()

            centerAttributedText.draw(with: drawingRect, options: [.usesLineFragmentOrigin, .usesFontLeading, .truncatesLastVisibleLine], context: nil)

            context.restoreGState()
        }
    }

    open override func drawHighlighted(context: CGContext, indices: [Highlight])
    {
        guard
            let chart = chart,
            let data = chart.data
            else { return }

        context.saveGState()

        let phaseX = animator.phaseX
        let phaseY = animator.phaseY

        var angle: CGFloat = 0.0
        let rotationAngle = chart.rotationAngle

        let drawAngles = chart.drawAngles
        let absoluteAngles = chart.absoluteAngles
        let center = chart.centerCircleBox
        let radius = chart.radius
        let drawInnerArc = chart.drawHoleEnabled && !chart.drawSlicesUnderHoleEnabled
        let userInnerRadius = drawInnerArc ? radius * chart.holeRadiusPercent : 0.0

        // Append highlighted accessibility slices into this array, so we can prioritize them over unselected slices
        var highlightedAccessibleElements: [NSUIAccessibilityElement] = []

        for i in 0 ..< indices.count
        {
            // get the index to highlight
            let index = Int(indices[i].x)
            if index >= drawAngles.count
            {
                continue
            }

            guard let set = data.getDataSetByIndex(indices[i].dataSetIndex) as? IPieChartDataSet else { continue }
            
            if !set.isHighlightEnabled { continue }

            let entryCount = set.entryCount
            var visibleAngleCount = 0
            for j in 0 ..< entryCount
            {
                guard let e = set.entryForIndex(j) else { continue }
                if ((abs(e.y) > Double.ulpOfOne))
                {
                    visibleAngleCount += 1
                }
            }

            if index == 0
            {
                angle = 0.0
            }
            else
            {
                angle = absoluteAngles[index - 1] * CGFloat(phaseX)
            }

            let sliceSpace = visibleAngleCount <= 1 ? 0.0 : set.sliceSpace

            let sliceAngle = drawAngles[index]
            var innerRadius = userInnerRadius

            let shift = set.selectionShift
            let highlightedRadius = radius + shift

            let accountForSliceSpacing = sliceSpace > 0.0 && sliceAngle <= 180.0

            context.setFillColor(set.highlightColor?.cgColor ?? set.color(atIndex: index).cgColor)

            let sliceSpaceAngleOuter = visibleAngleCount == 1 ?
                0.0 :
                sliceSpace / radius.DEG2RAD

            let sliceSpaceAngleShifted = visibleAngleCount == 1 ?
                0.0 :
                sliceSpace / highlightedRadius.DEG2RAD

            let startAngleOuter = rotationAngle + (angle + sliceSpaceAngleOuter / 2.0) * CGFloat(phaseY)
            var sweepAngleOuter = (sliceAngle - sliceSpaceAngleOuter) * CGFloat(phaseY)
            if sweepAngleOuter < 0.0
            {
                sweepAngleOuter = 0.0
            }

            let startAngleShifted = rotationAngle + (angle + sliceSpaceAngleShifted / 2.0) * CGFloat(phaseY)
            var sweepAngleShifted = (sliceAngle - sliceSpaceAngleShifted) * CGFloat(phaseY)
            if sweepAngleShifted < 0.0
            {
                sweepAngleShifted = 0.0
            }

            let path = CGMutablePath()

            path.move(to: CGPoint(x: center.x + highlightedRadius * cos(startAngleShifted.DEG2RAD),
                                  y: center.y + highlightedRadius * sin(startAngleShifted.DEG2RAD)))

            path.addRelativeArc(center: center, radius: highlightedRadius, startAngle: startAngleShifted.DEG2RAD,
                                delta: sweepAngleShifted.DEG2RAD)

            var sliceSpaceRadius: CGFloat = 0.0
            if accountForSliceSpacing
            {
                sliceSpaceRadius = calculateMinimumRadiusForSpacedSlice(
                    center: center,
                    radius: radius,
                    angle: sliceAngle * CGFloat(phaseY),
                    arcStartPointX: center.x + radius * cos(startAngleOuter.DEG2RAD),
                    arcStartPointY: center.y + radius * sin(startAngleOuter.DEG2RAD),
                    startAngle: startAngleOuter,
                    sweepAngle: sweepAngleOuter)
            }

            if drawInnerArc &&
                (innerRadius > 0.0 || accountForSliceSpacing)
            {
                if accountForSliceSpacing
                {
                    var minSpacedRadius = sliceSpaceRadius
                    if minSpacedRadius < 0.0
                    {
                        minSpacedRadius = -minSpacedRadius
                    }
                    innerRadius = min(max(innerRadius, minSpacedRadius), radius)
                }

                let sliceSpaceAngleInner = visibleAngleCount == 1 || innerRadius == 0.0 ?
                    0.0 :
                    sliceSpace / innerRadius.DEG2RAD
                let startAngleInner = rotationAngle + (angle + sliceSpaceAngleInner / 2.0) * CGFloat(phaseY)
                var sweepAngleInner = (sliceAngle - sliceSpaceAngleInner) * CGFloat(phaseY)
                if sweepAngleInner < 0.0
                {
                    sweepAngleInner = 0.0
                }
                let endAngleInner = startAngleInner + sweepAngleInner

                path.addLine(
                    to: CGPoint(
                        x: center.x + innerRadius * cos(endAngleInner.DEG2RAD),
                        y: center.y + innerRadius * sin(endAngleInner.DEG2RAD)))

                path.addRelativeArc(center: center, radius: innerRadius,
                                    startAngle: endAngleInner.DEG2RAD,
                                    delta: -sweepAngleInner.DEG2RAD)
            }
            else
            {
                if accountForSliceSpacing
                {
                    let angleMiddle = startAngleOuter + sweepAngleOuter / 2.0

                    let arcEndPointX = center.x + sliceSpaceRadius * cos(angleMiddle.DEG2RAD)
                    let arcEndPointY = center.y + sliceSpaceRadius * sin(angleMiddle.DEG2RAD)

                    path.addLine(
                        to: CGPoint(
                            x: arcEndPointX,
                            y: arcEndPointY))
                }
                else
                {
                    path.addLine(to: center)
                }
            }

            path.closeSubpath()

            context.beginPath()
            context.addPath(path)
            context.fillPath(using: .evenOdd)

            let axElement = createAccessibleElement(withIndex: index,
                                                    container: chart,
                                                    dataSet: set)
            { (element) in
                element.accessibilityFrame = path.boundingBoxOfPath
                element.isSelected = true
            }

            highlightedAccessibleElements.append(axElement)
        }

        // Prepend selected slices before the already rendered unselected ones.
        // NOTE: - This relies on drawDataSet() being called before drawHighlighted in PieChartView.
        if !accessibleChartElements.isEmpty {
            accessibleChartElements.insert(contentsOf: highlightedAccessibleElements, at: 1)
        }

        context.restoreGState()
    }

    /// Creates an NSUIAccessibilityElement representing a slice of the PieChart.
    /// The element only has it's container and label set based on the chart and dataSet. Use the modifier to alter traits and frame.
    private func createAccessibleElement(withIndex idx: Int,
                                         container: PieChartView,
                                         dataSet: IPieChartDataSet,
                                         modifier: (NSUIAccessibilityElement) -> ()) -> NSUIAccessibilityElement {

        let element = NSUIAccessibilityElement(accessibilityContainer: container)

        guard let e = dataSet.entryForIndex(idx) else { return element }
        guard let formatter = dataSet.valueFormatter else { return element }
        guard let data = container.data as? PieChartData else { return element }

        var elementValueText = formatter.stringForValue(
            e.y,
            entry: e,
            dataSetIndex: idx,
            viewPortHandler: viewPortHandler)

        if container.usePercentValuesEnabled {
            let value = e.y / data.yValueSum * 100.0
            let valueText = formatter.stringForValue(
                value,
                entry: e,
                dataSetIndex: idx,
                viewPortHandler: viewPortHandler)

            elementValueText = valueText
        }

        let pieChartDataEntry = (dataSet.entryForIndex(idx) as? PieChartDataEntry)
        let isCount = data.accessibilityEntryLabelSuffixIsCount
        let prefix = data.accessibilityEntryLabelPrefix?.appending("\(idx + 1)") ?? pieChartDataEntry?.label ?? ""
        let suffix = data.accessibilityEntryLabelSuffix ?? ""
        element.accessibilityLabel = "\(prefix) : \(elementValueText) \(suffix  + (isCount ? (e.y == 1.0 ? "" : "s") : "") )"

        // The modifier allows changing of traits and frame depending on highlight, rotation, etc
        modifier(element)

        return element
    }
}
