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

namespace FruityFoundation.Base.Structures;

public static class MaybeExtensions
{
	public static Maybe<T> FirstOrEmpty<T>(this IEnumerable<T> collection)
	{
		using var enumerator = collection.GetEnumerator();
		
		return !enumerator.MoveNext() ? Maybe.Empty<T>() : enumerator.Current;
	}

	public static Maybe<T> FirstOrEmpty<T>(this IEnumerable<T> collection, Func<T, bool> pred)
	{
		foreach (var item in collection)
			if (pred(item))
				return item;
		
		return Maybe.Empty<T>();
	}

	public static Maybe<TValue> TryGetValue<TKey, TValue>(this IDictionary<TKey, TValue> dict, TKey key) =>
		dict.TryGetValue(key, out var value) ? Maybe.Just(value) : Maybe.Empty<TValue>();

	public static Maybe<TValue> TryGet<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dict, TKey key) =>
		dict.TryGetValue(key, out var value) ? Maybe.Just(value) : Maybe.Empty<TValue>();

	public static T? ToNullable<T>(this Maybe<T> item) where T : struct =>
		item.HasValue ? item.Value : null;
}