using System;
using System.Collections;
using System.Collections.Generic;

namespace StardewModdingAPI.Framework.Utilities
{
    /// <summary>A <see cref="HashSet{T}"/> wrapper meant for tracking recursive contexts.</summary>
    /// <typeparam name="T">The key type.</typeparam>
    internal class ContextHash<T> : HashSet<T>
    {
        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        public ContextHash() { }

        /// <summary>Construct an instance.</summary>
        /// <param name="comparer">The <see cref="IEqualityComparer{T}"/> implementation to use when comparing values in the set, or <c>null</c> to use the default comparer for the set type.</param>
        public ContextHash(IEqualityComparer<T> comparer)
            : base(comparer) { }

        /// <summary>Add a key while an action is in progress, and remove it when it completes.</summary>
        /// <param name="key">The key to add.</param>
        /// <param name="action">The action to perform.</param>
        /// <exception cref="InvalidOperationException">The specified key is already added.</exception>
        public void Track(T key, Action action)
        {
            if(this.Contains(key))
                throw new InvalidOperationException($"Can't track context for key {key} because it's already added.");

            this.Add(key);
            try
            {
                action();
            }
            finally
            {
                this.Remove(key);
            }
        }

        /// <summary>Add a key while an action is in progress, and remove it when it completes.</summary>
        /// <typeparam name="TResult">The value type returned by the method.</typeparam>
        /// <param name="key">The key to add.</param>
        /// <param name="action">The action to perform.</param>
        public TResult Track<TResult>(T key, Func<TResult> action)
        {
            if (this.Contains(key))
                throw new InvalidOperationException($"Can't track context for key {key} because it's already added.");

            this.Add(key);
            try
            {
                return action();
            }
            finally
            {
                this.Remove(key);
            }
        }
    }
}