using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace SJK.Functional;

public struct Option<T> : IEquatable<Option<T>>
{
    private readonly T? _value;
    [MemberNotNullWhen(true, nameof(_value))]
    public bool HasValue { get; }
    public static Option<T> None => new(default, false);
    public static Option<T> Some(T value) => new(value, true);
    private Option(T? value, bool hasValue)
    {
        Debug.Assert(!(value is null && hasValue), "Can not create an option with a null value had say it has one");

        _value = value;
        HasValue = hasValue;
    }
    public T? Value => HasValue ? _value : throw new InvalidOperationException("Can not retrive value when there is no value.");

    // [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public TResult Match<TResult>(Func<T, TResult> some, Func<TResult> none) => HasValue ? some(_value) : none();
    // [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public Option<TResult> Map<TResult>(Func<T, TResult> f) => HasValue ? Option<TResult>.Some(f(_value)) : Option<TResult>.None;
    // [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public Option<TResult> Bind<TResult>(Func<T, Option<TResult>> f) => HasValue ? f(_value) : Option<TResult>.None;
    // [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public T OrDefault(T value) => HasValue ? _value : value;
    // [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public T Or(Func<T> factory) => HasValue ? _value : factory();

    public override bool Equals([NotNullWhen(true)] object? obj) => obj is Option<T> other && Equals(other);

    public bool Equals(Option<T> other) => (HasValue == other.HasValue) && (!HasValue || EqualityComparer<T>.Default.Equals(_value, other._value));

    public override int GetHashCode() => HasValue ? EqualityComparer<T>.Default.GetHashCode(_value) : 0;
    public override string ToString() => HasValue ? $"Some({_value})" : $"None<{typeof(T).Name}>()";
}