// 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 System.Runtime.Serialization;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis
{
    /// <summary>
    /// Provides information about the way a particular symbol is being used at a symbol reference node.
    /// For namespaces and types, this corresponds to values from <see cref="TypeOrNamespaceUsageInfo"/>.
    /// For methods, fields, properties, events, locals and parameters, this corresponds to values from <see cref="ValueUsageInfo"/>.
    /// </summary>
    [DataContract]
    internal readonly struct SymbolUsageInfo : IEquatable<SymbolUsageInfo>
    {
        public static readonly SymbolUsageInfo None = Create(ValueUsageInfo.None);
 
        [DataMember(Order = 0)]
        public ValueUsageInfo? ValueUsageInfoOpt { get; }
 
        [DataMember(Order = 1)]
        public TypeOrNamespaceUsageInfo? TypeOrNamespaceUsageInfoOpt { get; }
 
        // Must be public since it's used for deserialization.
        public SymbolUsageInfo(ValueUsageInfo? valueUsageInfoOpt, TypeOrNamespaceUsageInfo? typeOrNamespaceUsageInfoOpt)
        {
            Debug.Assert(valueUsageInfoOpt.HasValue ^ typeOrNamespaceUsageInfoOpt.HasValue);
 
            ValueUsageInfoOpt = valueUsageInfoOpt;
            TypeOrNamespaceUsageInfoOpt = typeOrNamespaceUsageInfoOpt;
        }
 
        public static SymbolUsageInfo Create(ValueUsageInfo valueUsageInfo)
            => new(valueUsageInfo, typeOrNamespaceUsageInfoOpt: null);
 
        public static SymbolUsageInfo Create(TypeOrNamespaceUsageInfo typeOrNamespaceUsageInfo)
            => new(valueUsageInfoOpt: null, typeOrNamespaceUsageInfo);
 
        public bool IsReadFrom()
            => ValueUsageInfoOpt.HasValue && ValueUsageInfoOpt.Value.IsReadFrom();
 
        public bool IsWrittenTo()
            => ValueUsageInfoOpt.HasValue && ValueUsageInfoOpt.Value.IsWrittenTo();
 
        public bool IsNameOnly()
            => ValueUsageInfoOpt.HasValue && ValueUsageInfoOpt.Value.IsNameOnly();
 
        public override bool Equals(object? obj)
            => obj is SymbolUsageInfo && Equals((SymbolUsageInfo)obj);
 
        public bool Equals(SymbolUsageInfo other)
        {
            if (ValueUsageInfoOpt.HasValue)
            {
                return other.ValueUsageInfoOpt.HasValue &&
                    ValueUsageInfoOpt.Value == other.ValueUsageInfoOpt.Value;
            }
            else
            {
                RoslynDebug.Assert(TypeOrNamespaceUsageInfoOpt.HasValue);
                return other.TypeOrNamespaceUsageInfoOpt.HasValue &&
                    TypeOrNamespaceUsageInfoOpt.Value == other.TypeOrNamespaceUsageInfoOpt.Value;
            }
        }
 
        public override int GetHashCode()
            => Hash.Combine(((int?)ValueUsageInfoOpt)?.GetHashCode() ?? 0, ((int?)TypeOrNamespaceUsageInfoOpt)?.GetHashCode() ?? 0);
    }
}