Swift_Charts

import SwiftUI
import Charts

struct Temperature: Identifiable {
    var id: String { day }
    let day: String
    let degree: Double
}

struct City: Identifiable {
    var id: String { name }
    let name: String
    let temperatures: [Temperature]
    var average: Double {
        let result = temperatures.reduce(0) { partialResult, temperature in
            return partialResult + temperature.degree
        }
        
        return result / Double(temperatures.count)
    }
}

class ViewModel: ObservableObject {
    @Published var cities: [City] = [
        City(name: "Karlsruhe", temperatures: [
            .init(day: "Monday", degree: 31),
            .init(day: "Tuesday", degree: 35),
            .init(day: "Wednesday", degree: 39),
            .init(day: "Thursday", degree: 23),
            .init(day: "Friday", degree: 25),
            .init(day: "Saturday", degree: 19.5),
            .init(day: "Sunday", degree: 32.8)
        ]),
        City(name: "Frankfurt", temperatures: [
            .init(day: "Monday", degree: 28),
            .init(day: "Tuesday", degree: 23),
            .init(day: "Wednesday", degree: 34),
            .init(day: "Thursday", degree: 18),
            .init(day: "Friday", degree: 19.6),
            .init(day: "Saturday", degree: 21.5),
            .init(day: "Sunday", degree: 26.8)
        ])
    ]
}

struct ChartView: View {
    @ObservedObject private var model: ViewModel = ViewModel()
    
    var body: some View {
        Chart(model.cities) { city in
                RuleMark(y: .value("Average", city.average))
                    .foregroundStyle(by: .value("City", city.name))
                
                ForEach(city.temperatures) { temperature in
                    LineMark(x: .value("Day", temperature.day),
                            y: .value("Temperature", temperature.degree))
                }
                .position(by: .value("City", city.name))
                .symbol(by: .value("City", city.name))
                .foregroundStyle(by: .value("City", city.name))
            
            
        }
        .chartYScale(domain: 15 ... 40)
        .frame(height: 300)
        .padding()
    }
}

struct ChartView_Previews: PreviewProvider {
    static var previews: some View {
        ChartView()
    }
}