using MessagePack;

namespace OECS;

/// <summary>
/// A convenience base struct for relationship components.
///
/// The type parameters <typeparamref name="TSelf"/> and <typeparamref name="TTarget"/>
/// are phantom types that differentiate relationship kinds at the type level,
/// enabling type-safe queries and reverse lookups.
///
/// <example>
/// <code>
/// // Define a "ChildOf" relationship between a child and a parent entity.
/// world.AddComponent(child, new Relationship&lt;ChildOf, Parent&gt;
/// {
///     Target = parent
/// });
///
/// // Later, find all children of a parent.
/// var children = world.GetSources&lt;Relationship&lt;ChildOf, Parent&gt;&gt;(parent);
/// </code>
/// </example>
/// </summary>
[MessagePackObject]
public struct Relationship<TSelf, TTarget> : IRelationship
    where TSelf : struct where TTarget : struct
{
    /// <summary>
    /// The entity that this relationship points to.
    /// </summary>
    [Key(0)]
    public Entity Target { get; set; }
}