using System;
using System.Diagnostics.CodeAnalysis;

namespace Npgsql.Internal.Postgres;

/// <summary>
/// A discriminated union of <see cref="Oid" /> and <see cref="DataTypeName" />.
/// </summary>
[Experimental(NpgsqlDiagnostics.ConvertersExperimental)]
public readonly struct PgTypeId: IEquatable<PgTypeId>
{
    readonly DataTypeName _dataTypeName;
    readonly Oid _oid;

    public PgTypeId(DataTypeName name) => _dataTypeName = name;
    public PgTypeId(Oid oid) => _oid = oid;

    [MemberNotNullWhen(true, nameof(_dataTypeName))]
    public bool IsDataTypeName => _dataTypeName != default;
    public bool IsOid => _dataTypeName == default;

    public DataTypeName DataTypeName
        => IsDataTypeName ? _dataTypeName : throw new InvalidOperationException("This value does not describe a DataTypeName.");

    public Oid Oid
        => IsOid ? _oid : throw new InvalidOperationException("This value does not describe an Oid.");

    public static implicit operator PgTypeId(DataTypeName name) => new(name);
    public static implicit operator PgTypeId(Oid id) => new(id);

    public override string ToString() => IsOid ? "OID " + _oid : "DataTypeName " + _dataTypeName.Value;

    public bool Equals(PgTypeId other)
    {
        if (IsOid && other.IsOid)
            return _oid == other._oid;
        if (IsDataTypeName && other.IsDataTypeName)
            return _dataTypeName.Equals(other._dataTypeName);
        return false;
    }

    public override bool Equals(object? obj) => obj is PgTypeId other && Equals(other);
    public override int GetHashCode() => IsOid ? _oid.GetHashCode() : _dataTypeName.GetHashCode();
    public static bool operator ==(PgTypeId left, PgTypeId right) => left.Equals(right);
    public static bool operator !=(PgTypeId left, PgTypeId right) => !left.Equals(right);

    internal bool IsUnspecified => IsOid && _oid == Oid.Unspecified || _dataTypeName == DataTypeName.Unspecified;
}