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

namespace StardewModdingAPI.Utilities
{
    /// <summary>Manages a separate value for each player in split-screen mode. This can safely be used in non-split-screen mode too, it'll just have a single state in that case.</summary>
    /// <typeparam name="T">The state class.</typeparam>
    public class PerScreen<T>
    {
        /*********
        ** Fields
        *********/
        /// <summary>Create the initial value for a player.</summary>
        private readonly Func<T> CreateNewState;

        /// <summary>The tracked values for each player.</summary>
        private readonly IDictionary<int, T> States = new Dictionary<int, T>();

        /// <summary>The last <see cref="Context.LastRemovedScreenId"/> value for which this instance was updated.</summary>
        private int LastRemovedScreenId;


        /*********
        ** Accessors
        *********/
        /// <summary>The value for the current player.</summary>
        /// <remarks>The value is initialized the first time it's requested for that player, unless it's set manually first.</remarks>
        public T Value
        {
            get
            {
                this.RemoveDeadPlayers();
                return this.States.TryGetValue(Context.ScreenId, out T state)
                    ? state
                    : this.States[Context.ScreenId] = this.CreateNewState();
            }
            set
            {
                this.RemoveDeadPlayers();
                this.States[Context.ScreenId] = value;
            }
        }


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        public PerScreen()
            : this(null) { }

        /// <summary>Construct an instance.</summary>
        /// <param name="createNewState">Create the initial state for a player screen.</param>
        public PerScreen(Func<T> createNewState)
        {
            this.CreateNewState = createNewState ?? (() => default);
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Remove players who are no longer have a split-screen index.</summary>
        /// <returns>Returns whether any players were removed.</returns>
        private void RemoveDeadPlayers()
        {
            if (this.LastRemovedScreenId == Context.LastRemovedScreenId)
                return;

            this.LastRemovedScreenId = Context.LastRemovedScreenId;
            foreach (int id in this.States.Keys.ToArray())
            {
                if (!Context.HasScreenId(id))
                    this.States.Remove(id);
            }
        }
    }
}