﻿/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace DotPulsar.Abstractions;

using System.Threading;
using System.Threading.Tasks;

/// <summary>
/// A state change monitoring abstraction.
/// </summary>
public interface IState<TState> where TState : notnull
{
    /// <summary>
    /// Ask whether the current state is final, meaning that it will never change.
    /// </summary>
    /// <returns>
    /// True if it's final and False if it's not.
    /// </returns>
    bool IsFinalState();

    /// <summary>
    /// Ask whether the provided state is final, meaning that it will never change.
    /// </summary>
    /// <returns>
    /// True if it's final and False if it's not.
    /// </returns>
    bool IsFinalState(TState state);

    /// <summary>
    /// Wait for the state to change to a specific state.
    /// </summary>
    /// <returns>
    /// The current state.
    /// </returns>
    /// <remarks>
    /// If the state change to a final state, then all awaiting tasks will complete.
    /// </remarks>
    ValueTask<TState> OnStateChangeTo(TState state, CancellationToken cancellationToken = default);

    /// <summary>
    /// Wait for the state to change from a specific state.
    /// </summary>
    /// <returns>
    /// The current state.
    /// </returns>
    /// <remarks>
    /// If the state change to a final state, then all awaiting tasks will complete.
    /// </remarks>
    ValueTask<TState> OnStateChangeFrom(TState state, CancellationToken cancellationToken = default);
}