using System;
using System.Threading.Tasks;
using System.Collections.Generic;

namespace Cobilas.Threading.Tasks {
#pragma warning disable CS1591 // O comentário XML ausente não foi encontrado para o tipo ou membro visível publicamente
    public static class TaskPool {
#pragma warning restore CS1591 // O comentário XML ausente não foi encontrado para o tipo ou membro visível publicamente
        private readonly static List<Task> tasksList = new List<Task>();

        /// <summary>Returns the number of allocated tasks.</summary>
        public static int Count => tasksList.Count;
        /// <summary>The number of tasks that are already vacant.</summary>
        public static int VacantTaskCount {
            get {
                int res = byte.MaxValue;
                for (int I = 0; I < Count; I++)
                    if (tasksList[I].IsFaulted || tasksList[I].IsCompleted || tasksList[I].IsCanceled)
                        res++;
                return res;
            }
        }
        /// <summary>The number of tasks that are not vacant.</summary>
        public static int NonVacantTaskCount => Count - VacantTaskCount;

        /// <summary>The number of tasks that are not vacant.</summary>
        public static void InitTask(Action action, out Task task) {
            int taskIndex = GetVacantTask();
            if (taskIndex >= 0) {
                task = tasksList[taskIndex] = 
                    tasksList[taskIndex].ContinueWith(ct => { ct.Dispose(); action(); });
            } else tasksList.Add(task = Task.Run(action));
        }

        /// <summary>The number of tasks that are not vacant.</summary>
        public static void InitTask(Action action)
            => InitTask(action, out _);

        /// <summary>The number of tasks that are not vacant.</summary>
        public static void InitTask<TRes>(Func<TRes> func, out Task<TRes> res) {
            int taskIndex = GetVacantTask();
            if (taskIndex >= 0) {
                tasksList[taskIndex] = 
                    tasksList[taskIndex].ContinueWith<TRes>(ct => {
                        ct.Dispose(); 
                        return func();
                    });
                res = (Task<TRes>)tasksList[taskIndex];
            } else tasksList.Add(res = Task.Run<TRes>(func));
        }

        /// <summary>The number of tasks that are not vacant.</summary>
        public static void InitTask<TRes>(Func<TRes> func)
            => InitTask<TRes>(func, out _);

        private static int GetVacantTask() {
            for (int I = 0; I < Count; I++)
                if (tasksList[I].IsFaulted || tasksList[I].IsCompleted || tasksList[I].IsCanceled)
                    return I;
            return -1;
        }
    }
}