sirh3e/Rust

namespace Sirh3e.Rust.Result;

public readonly partial struct Result<TOk, TErr> : ICloneable, IEnumerable<TOk>, IEquatable<Result<TOk, TErr>>
{
    private readonly TOk _ok;
    private readonly TErr _err;

    private Result(TOk ok)
    {
        _ok = ok ?? throw new ArgumentNullException(nameof(ok));
        IsOk = true;

        _err = default;
    }

    private Result(TErr err)
    {
        _err = err ?? throw new ArgumentNullException(nameof(err));
        IsOk = false;

        _ok = default;
    }

    public static Result<TOk, TErr> Ok(TOk ok)
        => new(ok);
    public static Result<TOk, TErr> Err(TErr err)
        => new(err);

    public bool Equals(Result<TOk, TErr> other) => EqualityComparer<TOk>.Default.Equals(_ok, other._ok) 
                                                   && EqualityComparer<TErr>.Default.Equals(_err, other._err) 
                                                   && IsOk == other.IsOk;

    public IEnumerator<TOk> GetEnumerator()
#if NETCOREAPP1_0_OR_GREATER || NET46_OR_GREATER || NETSTANDARD1_3_OR_GREATER 
        => new ResultEnumerator<TOk>(IsOk ? new[] { _ok } : Array.Empty<TOk>());
#else
        => new ResultEnumerator<TOk>(IsOk ? new[] { _ok } : new TOk[0]);
#endif

    public override bool Equals(object obj)
        => obj is Result<TOk, TErr> other && Equals(other);

    public override int GetHashCode()
    {
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
        return HashCode.Combine(_ok, _err, IsOk);
#else
        //Thx to https://rehansaeed.com/gethashcode-made-easy/
        var hashCode = 17;

        hashCode = hashCode * 23 + (_ok == null ? 0 : _ok.GetHashCode());
        hashCode = hashCode * 23 + (_err == null ? 0 : _err.GetHashCode());
        hashCode = hashCode * 23 + IsErr.GetHashCode();

        return hashCode;
#endif
    }

    IEnumerator IEnumerable.GetEnumerator()
        => GetEnumerator();

    public Result<TOk, TErr> Clone()
        => IsOk ? Ok(_ok) : Err(_err);

    object ICloneable.Clone()
        => Clone();

    public static implicit operator Result<TOk, TErr>(Err<TErr> err)
        => Err(err.Value);

    public static implicit operator Result<TOk, TErr>(Ok<TOk> ok)
        => Ok(ok.Value);

    public static bool operator ==(Result<TOk, TErr> left, Result<TOk, TErr> right)
        => left.Equals(right);

    public static bool operator !=(Result<TOk, TErr> left, Result<TOk, TErr> right)
        => !(left == right);
}