import SwiftUI
import Combine

extension UIScreen{
  static let screenWidth = UIScreen.main.bounds.size.width
  static let screenHeight = UIScreen.main.bounds.size.height
  static let screenSize = UIScreen.main.bounds.size
}

let lightUpProtocol = PassthroughSubject<(Int,Int),Never>()

struct ContentView: View {
  let timer = Timer.publish(every: 0.4, on: .main, in: .common).autoconnect()
  
  @State var lightUp = 0
  @State var column = 0
  var body: some View {
    ZStack {
      Color.black
        .onReceive(timer) { value in
          let rnd = Int.random(in: 0..<32)
          doIt(column: rnd)
        }
      HStack(alignment: .top, content: {
        ForEach(0..<24) { foo in
          LetterView(column: foo)
        }
      })
    }
  }
  func doIt(column: Int) {
    var lightUp = 0
    var row = 0
    Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true) { timer in
      row += 1
      lightUpProtocol.send((lightUp,column))
      if lightUp < 32 {
        lightUp += 1
      } else {
        lightUp = 0
      }
      if row == 32 {
        timer.invalidate()
      }
    }
  }
}

struct LetterView: View {
  @State var column:Int
  @State var letters:[String] = []
  @State var alpha:[Double] = []
  @State var color:[Color] = []
  @State var ready = false
  
  var body: some View {
    VStack(alignment: .center, spacing: 0, content: {
      if !ready {
        Color.clear
          .frame(width: 0, height: 0)
          .onAppear {
            for _ in 0...32 {
              let rnd = UInt8.random(in: 65...91)
              letters.append(String(UnicodeScalar(rnd)))
              alpha.append(0)
              color.append(Color.white)
            }
            ready = true
          }
      } else {
        ForEach ((0..<letters.count), id: \.self) { dix in
          Text(letters[dix])
            .bold()
            .foregroundColor(color[dix])
            .opacity(alpha[dix])
            .onReceive(lightUpProtocol) { value in
              let (foo,bar) = value
              if bar == column {
                if foo == dix {
                  alpha[dix] = 1.0
                  color[dix] = Color.white
                } else {
                  color[dix] = Color.green
                  alpha[dix] -= 0.1
                }
              }
            }
        }
      }
    })
  }
}