todoService.ts

import { Observable } from "./observable";

export interface Todo {
    readonly text: string;
    readonly completed: boolean;
}

export enum VisibilityFilter {
    SHOW_ALL,
    SHOW_COMPLETED,
    SHOW_ACTIVE,
}

export class TodoService {
    readonly todos = new Observable<Todo[]>([]);
    readonly visibilityFilter = new Observable(VisibilityFilter.SHOW_ALL);

    addTodo(text: string) {
        this.todos.set([...this.todos.get(), { text, completed: false }]);
    }

    toggleTodo(index: number) {
        this.todos.set(this.todos.get().map(
            (todo, i) => (i === index ? { text: todo.text, completed: !todo.completed } : todo)
        ));
    }

    setVisibilityFilter(filter: VisibilityFilter) {
        this.visibilityFilter.set(filter);
    }
}