namespace Arch.Relationships;

using global::System.Collections.Generic;
using global::System.Runtime.CompilerServices;
using Arch.Core;

/// <summary>
///     The <see cref="IRelationship"/> interface
///     is an interface that provides all methods required to act as a relationship.
/// </summary>
internal interface IRelationship
{
  /// <summary>
  ///     The amount of relationships currently in the buffer.
  /// </summary>
  int Count
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get;
  }

  /// <summary>
  ///     Removes the buffer as a component from the given world and entity.
  /// </summary>
  /// <param name="world"></param>
  /// <param name="source"></param>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal void Destroy(World world, Entity source);

  /// <summary>
  ///     Removes the relationship targeting <paramref name="target"/> from this buffer.
  /// </summary>
  /// <param name="target">The <see cref="Entity"/> in the relationship to remove.</param>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  void Remove(Entity target);
}

/// <summary>
///     A buffer storing relationships of <see cref="Entity"/> and <typeparamref name="T"/>.
/// </summary>
/// <typeparam name="T">The type of the second relationship element.</typeparam>
public class Relationship<T> : IRelationship
{

  /// <summary>
  ///     Its relations.
  /// </summary>
  internal readonly SortedList<Entity, T> _elements;

  /// <summary>
  ///     Initializes a new instance of an <see cref="Relationship{T}"/>.
  /// </summary>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal Relationship()
  {
    _elements = [];
  }

  /// <summary>
  ///     Initializes a new instance of an <see cref="Relationship{T}"/>.
  /// <remarks>Mostly for binary serialization.</remarks>
  /// </summary>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal Relationship(SortedList<Entity, T> elements)
  {
    _elements = elements;
  }

  /// <inheritdoc/>
  int IRelationship.Count
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => _elements.Count;
  }

  /// <inheritdoc cref="IRelationship.Count"/>
  internal int Count
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => ((IRelationship)this).Count;
  }

  /// <summary>
  ///     Adds a relationship to this buffer.
  /// </summary>
  /// <param name="relationship">The instance of the relationship.</param>
  /// <param name="target">The target of the relationship.</param>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal void Add(in T relationship, Entity target) => _elements.Add(target, relationship);

  /// <summary>
  ///     Sets the stored <typeparamref name="T"/> for the given <see cref="Entity"/>.
  /// </summary>
  /// <param name="entity">The <see cref="Entity"/>.</param>
  /// <param name="data">The data to store.</param>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public void Set(Entity entity, T data = default!) => _elements[entity] = data;

  /// <summary>
  ///     Determines whether the given <see cref="Relationship{T}"/> contains the passed <see cref="Entity"/> or not.
  /// </summary>
  /// <param name="entity">The <see cref="Entity"/>.</param>
  /// <returns>True or false.</returns>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public bool Contains(Entity entity) => _elements.ContainsKey(entity);

  /// <summary>
  ///     Returns the stored <typeparamref name="T"/> for the given <see cref="Entity"/>.
  /// </summary>
  /// <param name="entity">The <see cref="Entity"/>.</param>
  /// <returns>The stored <typeparamref name="T"/>.</returns>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public T Get(Entity entity) => _elements[entity];

  /// <summary>
  ///     Returns the stored <typeparamref name="T"/> for the given <see cref="Entity"/>.
  /// </summary>
  /// <param name="entity">The <see cref="Entity"/>.</param>
  /// <param name="value">The stored <typeparamref name="T"/>.</param>
  /// <returns>The stored <typeparamref name="T"/>.</returns>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public bool TryGetValue(Entity entity, out T value) => _elements.TryGetValue(entity, out value!);

  /// <inheritdoc/>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  void IRelationship.Remove(Entity target) => _elements.Remove(target);

  /// <inheritdoc cref="IRelationship.Remove(Entity)"/>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal void Remove(Entity target) => ((IRelationship)this).Remove(target);

  /// <inheritdoc/>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  void IRelationship.Destroy(World world, Entity source) => world.Remove<Relationship<T>>(source);

  /// <inheritdoc cref="IRelationship.Destroy(World, Entity)"/>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  internal void Destroy(World world, Entity source) => ((IRelationship)this).Destroy(world, source);

  /// <summary>
  ///     Creates a new <see cref="SortedListEnumerator{TValue}"/>.
  /// </summary>
  /// <returns>The new <see cref="SortedListEnumerator{TValue}"/>.</returns>
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public SortedListEnumerator<T> GetEnumerator() => new(_elements);
};