using System;
using System.Collections.Generic;

namespace ExtendedCollections;

public static class EnumerableExtensions
{
    public static IEnumerable<TResult> Combine<TResult, T1, T2>(this IEnumerable<T1> @this, IEnumerable<T2> other, Func<T1, T2, TResult> combiner)
    {
        foreach(var value1 in @this)
        {
            foreach(var value2 in other)
            {
                yield return combiner.Invoke(value1, value2);
            }
        }
    }

    public static int IndexOf<T>(this IEnumerable<T> enumerable, T item)
    {
        if(enumerable is IList<T> list)
            return list.IndexOf(item);
        if(enumerable is string str && item is char ch)
            return str.IndexOf(ch);

        int i = 0;
        foreach(var value in enumerable)
        {
            if(Equals(value, item))
                return i;
            ++i;
        }

        return -1;
    }
}