using System.Diagnostics.CodeAnalysis;

namespace SJK.Functional;
public interface IOption<T> : IEquatable<IOption<T>>
{
    /// <summary>
    /// Applies a function to the contained value if it exists (is not None), otherwise applies a default function.
    /// </summary>
    /// <param name="onSome">Function to apply if the option contains a value.</param>
    /// <param name="onNone">Function to apply if the option does not contain a value.</param>
    /// <returns>The result of applying either the onSome or onNone function.</returns>
    TResult Match<TResult>(Func<T, TResult> onSome, Func<TResult> onNone);
    void Match(Action<T> onSome,Action onNone);

    /// <summary>
    /// Chains operations on the contained value using a function that returns an option.
    /// </summary>
    /// <param name="f">A function that takes the contained value and returns an option.</param>
    /// <returns>An option resulting from applying the function f to the contained value.</returns>
    IOption<TResult> Bind<TResult>(Func<T, IOption<TResult>> f);

    /// <summary>
    /// Maps a function over the contained value if it exists (is not None).
    /// </summary>
    /// <param name="f">The function to apply to the contained value.</param>
    /// <returns>An option containing the result of applying f to the contained value.</returns>
    IOption<TResult> Map<TResult>(Func<T, TResult> f);

    /// <summary>
    /// Returns the contained value if it exists (is not None), otherwise returns the provided default value.
    /// </summary>
    /// <param name="aDefault">The default value to return if the option does not contain a value.</param>
    /// <returns>The contained value or the default value.</returns>
    T Or(T aDefault);

    /// <summary>
    /// Returns the contained value if it exists (is not None), otherwise calls the provided default function.
    /// </summary>
    /// <param name="aDefault">The default value to return if the option does not contain a value.</param>
    /// <returns>The contained value or the default value.</returns>
    T Or(Func<T> aDefault);

    /// <summary>
    /// Checks if the option contains a value (is not None) and outputs it if true.
    /// </summary>
    /// <param name="value">An out parameter that will be assigned the contained value if it exists.</param>
    /// <returns>true if the option contains a value; false otherwise.</returns>
    bool HasValue([NotNullWhen(true)]out T? value);
    // [Obsolete]
    bool HasValue();
}