using System;
using System.Collections.Generic;

namespace Gallium
{
    public static class ForEntityExtensions
    {
        /// <summary>
        /// Selects an entity from the given list, filtering on entities with
        /// the given components. If the entity doesn't match, it is passed as it.
        /// </summary>
        /// <param name="entities">The entities to parse.</param>
        /// <param name="selectWithComponents">
        /// The transformation function for the entity
        /// and selected components. If this returns null, then the entity will be filtered
        /// out.
        /// </param>
        /// <typeparam name="T1">The type of the first component.</typeparam>
        /// <returns>An enumeration of transformed entities.</returns>
        public static IEnumerable<Entity> ForEntity<T1>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, Entity?> selectWithComponents)
        {
            return entities.SelectEntity(selectWithComponents, a => a);
        }

        /// <summary>
        /// Selects an entity from the given list, filtering on entities with
        /// the given components. If the entity doesn't match, it is passed as it.
        /// </summary>
        /// <param name="entities">The entities to parse.</param>
        /// <param name="selectWithComponents">
        /// The transformation function for the entity
        /// and selected components. If this returns null, then the entity will be filtered
        /// out.
        /// </param>
        /// <typeparam name="T1">The type of the first component.</typeparam>
        /// <typeparam name="T2">The type of the second component.</typeparam>
        /// <returns>An enumeration of transformed entities.</returns>
        public static IEnumerable<Entity> ForEntity<T1, T2>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, Entity?> selectWithComponents)
        {
            return entities.SelectEntity(selectWithComponents, a => a);
        }

        /// <summary>
        /// Selects an entity from the given list, filtering on entities with
        /// the given components. If the entity doesn't match, it is passed as it.
        /// </summary>
        /// <param name="entities">The entities to parse.</param>
        /// <param name="selectWithComponents">
        /// The transformation function for the entity
        /// and selected components. If this returns null, then the entity will be filtered
        /// out.
        /// </param>
        /// <typeparam name="T1">The type of the first component.</typeparam>
        /// <typeparam name="T2">The type of the second component.</typeparam>
        /// <typeparam name="T3">The type of the third component.</typeparam>
        /// <returns>An enumeration of transformed entities.</returns>
        public static IEnumerable<Entity> ForEntity<T1, T2, T3>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, T3, Entity?> selectWithComponents)
        {
            return entities.SelectEntity(selectWithComponents, a => a);
        }

        /// <summary>
        /// Selects an entity from the given list, filtering on entities with
        /// the given components. If the entity doesn't match, it is passed as it.
        /// </summary>
        /// <param name="entities">The entities to parse.</param>
        /// <param name="selectWithComponents">
        /// The transformation function for the entity
        /// and selected components. If this returns null, then the entity will be filtered
        /// out.
        /// </param>
        /// <typeparam name="T1">The type of the first component.</typeparam>
        /// <typeparam name="T2">The type of the second component.</typeparam>
        /// <typeparam name="T3">The type of the third component.</typeparam>
        /// <typeparam name="T4">The type of the third component.</typeparam>
        /// <returns>An enumeration of transformed entities.</returns>
        public static IEnumerable<Entity> ForEntity<T1, T2, T3, T4>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, T3, T4, Entity?> selectWithComponents)
        {
            return entities.SelectEntity<T1, T2, T3, T4>(
                selectWithComponents,
                a => a);
        }
    }
}