Party.swift

import SwiftUI
import Combine

struct Track: Hashable, Identifiable {
    var id: Int
    
    let name: String
    
    var voteScore: Int = 0
    var currentVote: VoteDirection = .none
}

var tracks = [
    Track(id: 0, name: "Red Hot Chili Peppers"),
    Track(id: 1, name: "Sour Fruit")
]

class AppState: ObservableObject, Identifiable {
    var willChange = ObservableObjectPublisher()
    
    @Published var tracks: [Track] = []
}

struct PlayerView: View {
    let skipAction: () -> Void
    
    var body: some View {
        VStack {
            HStack {
                Button(action: self.skipAction) {
                    Image(systemName: "arrow.right.to.line")
                }
            }
        }
    }
}

struct PartyView: View {
    @ObservedObject var state: AppState
    
    init(state: AppState) {
        self.state = state
        self.state.tracks = tracks
    }
    
    var body: some View {
        VStack {
            PlayerView(
                skipAction: {
                    guard self.state.tracks.count > 0 else { return }
                    self.state.tracks.remove(at: 0)
                }
            )
            Playlist(tracks: self.$state.tracks)
        }
    }
}

struct Playlist: View {
    @Binding var tracks: [Track]
    
    var body: some View {
        List(self.tracks) { track in
            TrackRow(track: self.$tracks[track.id])
        }
    }
}

struct TrackRow: View {
    @Binding var track: Track
    
    var body: some View {
        HStack {
            Text(track.name)
            VoteButtons(vote: $track.currentVote)
        }
    }
}

enum VoteDirection {
    case up
    case down
    case none
}

struct VoteButtons: View {
    @Binding var vote: VoteDirection
    
    var body: some View {
        VStack {
            Image(systemName: vote == .up ? "arrowtriangle.up.fill" : "arrowtriangle.up")
                .onTapGesture {
            	 self.vote = .up
            }
            Image(systemName: vote == .down ? "arrowtriangle.down.fill" : "arrowtriangle.down")
                .onTapGesture {
           	     self.vote = .down
            }
        }
    }
}

struct ContentView : View {
    var body: some View {
        PartyView(state: AppState())
    }
}