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

using MfGames.Gallium;

namespace MfGames.Nitride.Contents;

/// <summary>
/// Various extension methods for working with content.
/// </summary>
public static class EntityContentExtensions
{
    /// <summary>
    /// Retrieves the single registered content entity inside the component.
    /// If there is more than one, this will throw an exception.
    /// </summary>
    /// <param name="entity">The entity to query.</param>
    /// <returns>The one and only content component.</returns>
    public static IContent GetContent(this Entity entity)
    {
        Type type = entity.GetComponentTypes()
            .Single(x => typeof(IContent).IsAssignableFrom(x));

        return entity.Get<IContent>(type);
    }

    /// <summary>
    /// Determines if the entity has at least one content component.
    /// </summary>
    /// <param name="entity">The entity to inspect.</param>
    /// <returns>True if there is a component extending `IContent`.</returns>
    public static bool HasContent(this Entity entity)
    {
        return entity.GetComponentTypes()
            .Any(x => typeof(IContent).IsAssignableFrom(x));
    }

    /// <summary>
    /// Remove all existing content components from the entity and then adds
    /// the new component into the entity before returning it.
    /// </summary>
    /// <param name="entity">The entity to query and modify.</param>
    /// <param name="content">The content to add to the entity.</param>
    /// <typeparam name="TType">The base type of the content.</typeparam>
    /// <returns>The entity or a copy with the new component.</returns>
    public static Entity SetContent<TType>(
        this Entity entity,
        TType content)
        where TType : IContent
    {
        IEnumerable<Type>? existing = entity.GetComponentTypes()
            .Where(x => typeof(IContent).IsAssignableFrom(x));

        foreach (Type? component in existing)
        {
            entity = entity.Remove(component);
        }

        return entity.Add(content);
    }
}