GridApp.swift

GridApp.swift

import SwiftUI
import Charts

// Required entitlement:
// <key>com.apple.security.network.client</key><true/>

enum Signal: Int { case red, yellow, green }

struct Value {
  let date       : Date
  let percentage : Float
  let signal     : Signal?
}

struct ChartView: View {
  
  let values        : [ Value ]
  let currentSignal : Signal?

  var body: some View {
    Chart {
      LinePlot(
        values,
        x: .value("Date", \.date),
        y: .value("Percentage", \.percentage)
      )
    }
    .chartYScale(domain: 0.0...100.0)
  }
}

struct ContentView: View {
  
  @State var values       = [ Value ]()
  @State var currentValue : Value?

  func fetchIt() async {
    do {
      let url =
        URL(string: "https://api.energy-charts.info/signal?country=de")!
      let (data,_) = try await URLSession.shared.data(from: url)
      
      struct Result: Decodable {
        var unix_seconds : [ Int   ] // in 15min steps, starting at day
        var share        : [ Float ] // Anteil EE an Last
        var signal       : [ Int   ]
      }
      let result = try JSONDecoder().decode(Result.self, from: data)
      
      values = result.unix_seconds.enumerated().map { idx, ts in
        Value(date: Date(timeIntervalSince1970: TimeInterval(ts)),
              percentage: idx < result.share.count ? result.share[idx] : 0,
              signal: idx < result.signal.count
                      ? Signal(rawValue: result.signal[idx]) : nil)
      }
      let now = Date()
      currentValue = values.firstIndex(where: { $0.date > now })
        .flatMap { $0 - 1 }
        .flatMap { $0 >= 0 ? values[$0] : nil }
    }
    catch { currentValue = nil }
  }
  
  var body: some View {
    VStack {
      if let currentValue {
        ChartView(values: values, currentSignal: currentValue.signal)
      }
      else {
        Button("Retry") { Task { await fetchIt()} }
          .foregroundStyle(.red)
      }
    }
    .padding()
    .task {
      await fetchIt()
    }
  }
}

@main
struct GridApp: App {
  
  var body: some Scene {
    MenuBarExtra {
      ContentView()
    }
    label: {
      Label("Grid", systemImage: "chandelier")
    }
    .menuBarExtraStyle(.window)
  }
}