FruityFoundation/Base/Structures/Maybe.cs

namespace FruityFoundation.Base.Structures;

using System;

public static class Maybe
{
	public static Maybe<T> Create<T>(T value) => new(value);

	public static Maybe<T> Create<T>(T value, Func<bool> evalIsEmpty) =>
		evalIsEmpty()
			? Empty<T>()
			: new Maybe<T>(value);

	public static Maybe<T> Empty<T>() => new();
}

public readonly record struct Maybe<T>
{
	private readonly T _value;
	public bool HasValue { get; }

	internal Maybe(T val) : this()
	{
		_value = val;
		HasValue = true;
	}

	public T Value
	{
		get
		{
			if (!HasValue)
				throw new InvalidOperationException($"{nameof(Maybe<T>)} value is empty");

			return _value;
		}
	}

	public T OrValue(T orVal)
	{
		if (!HasValue)
			return orVal;

		return Value;
	}

	public T OrEval(Func<T> valueFactory)
	{
		if (!HasValue)
			return valueFactory();

		return Value;
	}

	public bool Try(out T val)
	{
		val = HasValue ? Value : default!;

		return HasValue;
	}

	public T OrThrow(string msg)
	{
		if (!HasValue)
			throw new ApplicationException(msg);

		return Value;
	}

	public T OrThrow(Func<string> messageFactory)
	{
		if (!HasValue)
			throw new ApplicationException(messageFactory());

		return Value;
	}

	public T OrThrow(Func<Exception> exFactory)
	{
		if (!HasValue)
			throw exFactory();

		return Value;
	}

	public Maybe<TOutput> Map<TOutput>(Func<T, TOutput> transformer)
	{
		if (!HasValue)
			return Maybe.Empty<TOutput>();

		var newValue = transformer(Value);
		return new Maybe<TOutput>(newValue);
	}

	public Maybe<TOutput> Bind<TOutput>(Func<T, Maybe<TOutput>> binder) =>
		HasValue ? binder(Value) : Maybe.Empty<TOutput>();

	public Maybe<T> EmptyBind(Func<Maybe<T>> maybeFactory) =>
		HasValue ? this : maybeFactory();

	public Maybe<T> EmptyBind(Maybe<T> maybe) =>
		HasValue ? this : maybe;

	public Maybe<TOutput> Cast<TOutput>()
	{
		if (!HasValue)
			return Maybe.Empty<TOutput>();

		try
		{
			var t = typeof(TOutput);
			t = Nullable.GetUnderlyingType(t) ?? t;

			var output = Value == null
				? default
				: (TOutput)Convert.ChangeType(Value, t);

			if (output == null)
				return Maybe.Empty<TOutput>();

			return Maybe.Create(output);
		}
		catch (InvalidCastException)
		{
			return Maybe.Empty<TOutput>();
		}
	}

	public static implicit operator Maybe<T>(T val) => Maybe.Create(val);

	public override string ToString()
	{
		if (!HasValue)
			return "<empty>";

		return _value?.ToString() ?? "<null>";
	}
}