﻿/*
 * 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.Internal;

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

public sealed class StateManager<TState> : IStateManager<TState> where TState : notnull
{
    private readonly object _lock;
    private readonly StateTaskCollection<TState> _stateTasks;
    private readonly TState[] _finalStates;

    public StateManager(TState initialState, params TState[] finalStates)
    {
        _lock = new object();
        _stateTasks = new StateTaskCollection<TState>();
        _finalStates = finalStates;
        CurrentState = initialState;
    }

    public TState CurrentState { get; private set; }

    public TState SetState(TState state)
    {
        lock (_lock)
        {
            if (IsFinalState(CurrentState) || CurrentState.Equals(state))
                return CurrentState;

            var formerState = CurrentState;
            CurrentState = state;

            if (IsFinalState(CurrentState))
                _stateTasks.CompleteAllTasks(CurrentState);
            else
                _stateTasks.CompleteTasksAwaiting(CurrentState);

            return formerState;
        }
    }

    public ValueTask<TState> StateChangedTo(TState state, CancellationToken cancellationToken)
    {
        lock (_lock)
        {
            if (IsFinalState(CurrentState) || CurrentState.Equals(state))
                return new ValueTask<TState>(CurrentState);
            return new ValueTask<TState>(_stateTasks.CreateTaskFor(state, StateChanged.To, cancellationToken));
        }
    }

    public ValueTask<TState> StateChangedFrom(TState state, CancellationToken cancellationToken)
    {
        lock (_lock)
        {
            if (IsFinalState(CurrentState) || !CurrentState.Equals(state))
                return new ValueTask<TState>(CurrentState);
            return new ValueTask<TState>(_stateTasks.CreateTaskFor(state, StateChanged.From, cancellationToken));
        }
    }

    public bool IsFinalState(TState state)
    {
        for (var i = 0; i < _finalStates.Length; ++i)
        {
            if (_finalStates[i].Equals(state))
                return true;
        }

        return false;
    }

    public bool IsFinalState()
        => IsFinalState(CurrentState);
}