elmy.swift

//
//  ContentView.swift
//  Store
//
//  Created by Chris Eidhof on 05.02.20.
//  Copyright © 2020 Chris Eidhof. All rights reserved.
//

import SwiftUI

final class Store<A>: ObservableObject {
    @Published var value: A
    init(_ value: A) {
        self.value = value
    }
}

enum Action {
    case addTodo(String)
    case toggle(UUID)
    case delete(UUID)
}

protocol Elmy {
    associatedtype Message
    associatedtype V: View
    typealias Send = (Message) -> ()
    func run(_ send: @escaping Send) -> V
}

extension Store where A == [Todo] {
    func interpret(action: Action) {
        switch action {
        case .addTodo(let title):
            value.append(Todo(title: title))
        case .toggle(let id):
            guard let i = value.firstIndex(where: { $0.id == id }) else { return }
            value[i].done.toggle()
        case .delete(let id):
            value.removeAll(where: { $0.id == id })
        }
    }
}

struct Todo: Identifiable {
    var id = UUID()
    var title: String
    var done = false
}

let todos: [Todo] = []

struct AllTodos: Elmy {
    var todos: [Todo]
    func run(_ send: @escaping (Action) -> ()) -> some View {
        List {
            ForEach(todos) { todo in
                Button(action: {
                    send(.toggle(todo.id))
                }) {
                    HStack {
                        Text(todo.title)
                        Spacer()
                        if todo.done {
                            Text("✓")
                        }
                    }
                }
            }.onDelete(perform: { ix in
                for id in ix.map({ self.todos[$0].id }) {
                    send(.delete(id))
                }
            })
        }.navigationBarItems(trailing: Button("+", action: {
            send(.addTodo("New Todo"))
        }))
    }
}

struct ContentView: View {
    @ObservedObject var store = Store(todos)
    var body: some View {
        NavigationView {
            AllTodos(todos: store.value).run(self.store.interpret)
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}