// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Diagnostics;
using Microsoft.CodeAnalysis.Symbols;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.CodeGen
{
    /// <summary>
    /// Unique identification of an emitted entity (method, lambda, closure) used for debugging purposes (EnC).
    /// </summary>
    /// <remarks>
    /// When used for a synthesized method the ordinal and generation numbers are included its name.
    /// For user defined methods the ordinal is included in Custom Debug Information record attached to the method.
    /// </remarks>
    internal readonly record struct DebugId : IComparable<DebugId>
    {
        public const int UndefinedOrdinal = -1;

        /// <summary>
        /// The index of the method in member list of the containing type, or <see cref="UndefinedOrdinal"/> if undefined.
        /// </summary>
        public readonly int Ordinal;

        /// <summary>
        /// The EnC generation the method was defined in (0 is the baseline build).
        /// </summary>
        public readonly int Generation;

        public DebugId(int ordinal, int generation)
        {
            Debug.Assert(ordinal >= 0 || ordinal == UndefinedOrdinal);
            Debug.Assert(generation >= 0);

            this.Ordinal = ordinal;
            this.Generation = generation;
        }

        public int CompareTo(DebugId other)
            => Ordinal.CompareTo(other.Ordinal) is int result and not 0 ? result : Generation.CompareTo(other.Generation);

        public override string ToString()
            => (Generation > 0) ? $"{Ordinal}{WellKnownGeneratedNames.GenerationSeparator}{Generation}" : Ordinal.ToString(System.Globalization.CultureInfo.InvariantCulture);
    }
}