using System;
using System.Collections.Generic;
using System.Linq;
using EE = System.Collections.Generic.IEnumerable<Gallium.Entity>;

namespace Gallium
{
    public static class EnumerableEntityExtensions1
    {
        public static EE ForEachEntity<T1>(
            this EE entities,
            Func<Entity, T1, Entity> lambda)
        {
            return entities
                .Select(x => x.Has<T1>() ? lambda(x, x.Get<T1>()) : x);
        }

        /// <summary>
        /// Runs an inner set of operation for entities that have a specific
        /// component.
        /// </summary>
        /// <param name="entities">The input to scan.</param>
        /// <param name="lambda">
        /// The list operation for the ones that have those
        /// components.
        /// </param>
        /// <typeparam name="T1">The type of the first component.</typeparam>
        /// <returns>
        /// A combined list of components, with entities without the component
        /// coming first and the ones with the component coming last after being
        /// processed by the lambda.
        /// </returns>
        public static EE ForEntities<T1>(
            this EE entities,
            Func<EE, EE> lambda)
        {
            List<Entity> list = entities.ToList();
            EE has = lambda(list.HasComponents<T1>());
            EE hasNot = list.NotComponents<T1>();

            return hasNot.Union(has);
        }

        public static EE HasComponents<T1>(this EE entities)
        {
            return entities
                .Where(x => x.Has<T1>());
        }

        public static EE NotComponents<T1>(this EE entities)
        {
            return entities
                .Where(x => !x.Has<T1>());
        }

        public static EE WhereEntities<T1>(
            this EE entities,
            Func<Entity, T1, bool> lambda,
            bool includeWithoutComponent = true)
        {
            return entities
                .Where(
                    x => x.Has<T1>()
                        ? lambda(x, x.Get<T1>())
                        : includeWithoutComponent);
        }
    }
}