// 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.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis
{
    /// <summary>
    /// Compares descriptors by the values that we write to a SARIF log and nothing else.
    ///
    /// We cannot just use <see cref="DiagnosticDescriptor"/>'s built-in implementation
    /// of <see cref="IEquatable{DiagnosticDescriptor}"/> for two reasons:
    ///
    /// 1. <see cref="DiagnosticDescriptor.MessageFormat"/> is part of that built-in 
    ///    equatability, but we do not write it out, and so descriptors differing only
    ///    by MessageFormat (common) would lead to duplicate rule metadata entries in
    ///    the log.
    ///
    /// 2. <see cref="DiagnosticDescriptor.CustomTags"/> is *not* part of that built-in
    ///    equatability, but we do write them out, and so descriptors differing only
    ///    by CustomTags (rare) would cause only one set of tags to be reported in the
    ///    log.
    /// </summary>
    internal sealed class SarifDiagnosticComparer : IEqualityComparer<DiagnosticDescriptor>
    {
        public static readonly SarifDiagnosticComparer Instance = new SarifDiagnosticComparer();
 
        private SarifDiagnosticComparer()
        {
        }
 
        public bool Equals(DiagnosticDescriptor? x, DiagnosticDescriptor? y)
        {
            if (ReferenceEquals(x, y))
            {
                return true;
            }
 
            if (x is null || y is null)
            {
                return false;
            }
 
            return x.Category == y.Category
                && x.DefaultSeverity == y.DefaultSeverity
                && x.Description.Equals(y.Description)
                && x.HelpLinkUri == y.HelpLinkUri
                && x.Id == y.Id
                && x.IsEnabledByDefault == y.IsEnabledByDefault
                && x.Title.Equals(y.Title)
                && x.ImmutableCustomTags.SequenceEqual(y.ImmutableCustomTags);
        }
 
        public int GetHashCode(DiagnosticDescriptor obj)
        {
            if (obj is null)
            {
                return 0;
            }
 
            return Hash.Combine(obj.Category.GetHashCode(),
                Hash.Combine(((int)obj.DefaultSeverity).GetHashCode(),
                Hash.Combine(obj.Description.GetHashCode(),
                Hash.Combine(obj.HelpLinkUri.GetHashCode(),
                Hash.Combine(obj.Id.GetHashCode(),
                Hash.Combine(obj.IsEnabledByDefault.GetHashCode(),
                Hash.Combine(obj.Title.GetHashCode(),
                Hash.CombineValues(obj.ImmutableCustomTags))))))));
        }
    }
}