PieChartCellModels.swift

struct ChartCellModel: Identifiable {
    let id = UUID()
    let color: Color
    let value: CGFloat
    let name: String
}

final class ChartDataModel: ObservableObject {
    var chartCellModel: [ChartCellModel]
    var startingAngle = Angle(degrees: 0)
    private var lastBarEndAngle = Angle(degrees: 0)
    
        
    init(dataModel: [ChartCellModel]) {
        chartCellModel = dataModel
    }
    
    var totalValue: CGFloat {
        chartCellModel.reduce(CGFloat(0)) { (result, data) -> CGFloat in
            result + data.value
        }
    }
    
    func angle(for value: CGFloat) -> Angle {
        if startingAngle != lastBarEndAngle {
            startingAngle = lastBarEndAngle
        }
        lastBarEndAngle += Angle(degrees: Double(value / totalValue) * 360 )
        print(lastBarEndAngle.degrees)
        return lastBarEndAngle
    }
}

let sample = [ ChartCellModel(color: Color.red, value: 123, name: "Math"),
               ChartCellModel(color: Color.yellow, value: 233, name: "Physics"),
               ChartCellModel(color: Color.pink, value: 73, name: "Chemistry"),
               ChartCellModel(color: Color.blue, value: 731, name: "Litrature"),
               ChartCellModel(color: Color.green, value: 51, name: "Art")]