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

namespace MfGames.Gallium;

/// <summary>
/// Extension methods for IEnumerable&lt;Entity&gt; that split the entity into two
/// sequences, one that contains the
/// various components and the other list which does not.
/// </summary>
public static class SplitEntityExtensions
{
    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given generic components
    /// and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <typeparam name="T1">
    /// A component to require to be in included in the first
    /// list.
    /// </typeparam>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity
        <T1>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, bool>? test = null)
    {
        test ??= (
            e,
            v1) => true;

        return entities.SplitEntity(
            typeof(T1),
            (
                e,
                v1) => test(e, (T1)v1));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given generic components
    /// and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <typeparam name="T1">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T2">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity
        <T1, T2>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, bool>? test = null)
    {
        test ??= (
            e,
            v1,
            v2) => true;

        return entities.SplitEntity(
            typeof(T1),
            typeof(T2),
            (
                e,
                v1,
                v2) => test(e, (T1)v1, (T2)v2));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given generic components
    /// and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <typeparam name="T1">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T2">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T3">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity
        <T1, T2, T3>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, T3, bool>? test = null)
    {
        test ??= (
            e,
            v1,
            v2,
            v3) => true;

        return entities.SplitEntity(
            typeof(T1),
            typeof(T2),
            typeof(T3),
            (
                e,
                v1,
                v2,
                v3) => test(e, (T1)v1, (T2)v2, (T3)v3));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given generic components
    /// and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <typeparam name="T1">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T2">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T3">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <typeparam name="T4">
    /// A component to require to be in included in the first list.
    /// </typeparam>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity
        <T1, T2, T3, T4>(
            this IEnumerable<Entity> entities,
            Func<Entity, T1, T2, T3, T4, bool>? test = null)
    {
        test ??= (
            e,
            v1,
            v2,
            v3,
            v4) => true;

        return entities.SplitEntity(
            typeof(T1),
            typeof(T2),
            typeof(T3),
            typeof(T4),
            (
                e,
                v1,
                v2,
                v3,
                v4) => test(e, (T1)v1, (T2)v2, (T3)v3, (T4)v4));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given component types and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="t1">The type of a required component.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity(
        this IEnumerable<Entity> entities,
        Type t1,
        Func<Entity, object, bool> test)
    {
        return SplitEntity(entities, a => a.Has(t1) && test(a, a.Get<object>(t1)));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given component types and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="t1">The type of a required component.</param>
    /// <param name="t2">The type of a required component.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity(
        this IEnumerable<Entity> entities,
        Type t1,
        Type t2,
        Func<Entity, object, object, bool> test)
    {
        return SplitEntity(entities, a => a.HasAll(t1, t2));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given component types and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="t1">The type of a required component.</param>
    /// <param name="t2">The type of a required component.</param>
    /// <param name="t3">The type of a required component.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity(
        this IEnumerable<Entity> entities,
        Type t1,
        Type t2,
        Type t3,
        Func<Entity, object, object, object, bool> test)
    {
        return SplitEntity(entities, a => a.HasAll(t1, t2, t3));
    }

    /// <summary>
    /// Splits the enumeration of entities into two separate enumerations, ones that
    /// have the given component types and those which do not.
    /// </summary>
    /// <param name="entities">The entities to split into two lists.</param>
    /// <param name="t1">The type of a required component.</param>
    /// <param name="t2">The type of a required component.</param>
    /// <param name="t3">The type of a required component.</param>
    /// <param name="t4">The type of a required component.</param>
    /// <param name="test">
    /// An additional test function to determine if the entity is
    /// included in the has list. If null, then entities with all the components will
    /// be included.
    /// </param>
    /// <returns>A pair of enumerations, ones with the components and ones without.</returns>
    public static SplitEntityEnumerations SplitEntity(
        this IEnumerable<Entity> entities,
        Type t1,
        Type t2,
        Type t3,
        Type t4,
        Func<Entity, object, object, object, object, bool> test)
    {
        return SplitEntity(
            entities,
            a => a.HasAll(t1, t2, t3, t4)
                && test(
                    a,
                    a.Get<object>(t1),
                    a.Get<object>(t2),
                    a.Get<object>(t3),
                    a.Get<object>(t4)));
    }

    private static SplitEntityEnumerations SplitEntity(
        IEnumerable<Entity> entities,
        Func<Entity, bool> keySelector)
    {
        if (entities == null)
        {
            throw new ArgumentNullException(nameof(entities));
        }

        IEnumerable<IGrouping<bool, Entity>> group = entities
            .GroupBy(keySelector, a => a)
            .ToList();

        IEnumerable<Entity>? has = group
            .Where(a => a.Key)
            .SelectMany(a => a);

        IEnumerable<Entity>? hasNot = group
            .Where(a => !a.Key)
            .SelectMany(a => a);

        return new SplitEntityEnumerations(has, hasNot);
    }
}