// Copyright Epic Games, Inc. All Rights Reserved.

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using EpicGames.Core;

namespace UnrealBuildTool
{
	/// <summary>
	/// Contains the name of an identifier. Individual objects are unique.
	/// </summary>
	class Identifier : IComparable<Identifier>
	{
		/// <summary>
		/// The name of this identifier
		/// </summary>
		string Name;

		/// <summary>
		/// Global map of name to identifier instance
		/// </summary>
		static ConcurrentDictionary<string, Identifier> NameToIdentifier = new ConcurrentDictionary<string, Identifier>(StringComparer.Ordinal);

		/// <summary>
		/// Constructor
		/// </summary>
		/// <param name="Name">Name of this identifier</param>
		private Identifier(string Name)
		{
			this.Name = Name;
		}

		/// <summary>
		/// Finds or adds an identifer with the given name
		/// </summary>
		/// <param name="Name">Name of the identifier</param>
		/// <returns>New Identifier instance</returns>
		public static Identifier FindOrAdd(string Name)
		{
			Identifier? Result;
			if(!NameToIdentifier.TryGetValue(Name, out Result))
			{
				Identifier NewIdentifier = new Identifier(Name);
				if(NameToIdentifier.TryAdd(Name, NewIdentifier))
				{
					Result = NewIdentifier;
				}
				else
				{
					Result = NameToIdentifier[Name];
				}
			}
			return Result;
		}

		/// <summary>
		/// Compares this identifier to another identifier
		/// </summary>
		/// <param name="Other">Identifier to compare to</param>
		/// <returns>Value indicating which identifier should sort first</returns>
		public int CompareTo(Identifier? Other)
		{
			return ReferenceEquals(Other, null)? 1 : Name.CompareTo(Other.Name);
		}

		/// <summary>
		/// Formats this identifer as a string for debugging
		/// </summary>
		/// <returns>Name of this identifier</returns>
		public override string ToString()
		{
			return Name;
		}
	}

	/// <summary>
	/// Well known predefined identifiers
	/// </summary>
	class Identifiers
	{
		public static readonly Identifier Include = Identifier.FindOrAdd("include");
		public static readonly Identifier Define = Identifier.FindOrAdd("define");
		public static readonly Identifier Undef = Identifier.FindOrAdd("undef");
		public static readonly Identifier If = Identifier.FindOrAdd("if");
		public static readonly Identifier Ifdef = Identifier.FindOrAdd("ifdef");
		public static readonly Identifier Ifndef = Identifier.FindOrAdd("ifndef");
		public static readonly Identifier Elif = Identifier.FindOrAdd("elif");
		public static readonly Identifier Else = Identifier.FindOrAdd("else");
		public static readonly Identifier Endif = Identifier.FindOrAdd("endif");
		public static readonly Identifier Defined = Identifier.FindOrAdd("defined");
		public static readonly Identifier Pragma = Identifier.FindOrAdd("pragma");
		public static readonly Identifier Once = Identifier.FindOrAdd("once");
		public static readonly Identifier Error = Identifier.FindOrAdd("error");
		public static readonly Identifier Warning = Identifier.FindOrAdd("warning");
		public static readonly Identifier __VA_ARGS__ = Identifier.FindOrAdd("__VA_ARGS__");
		public static readonly Identifier __FILE__ = Identifier.FindOrAdd("__FILE__");
		public static readonly Identifier __LINE__ = Identifier.FindOrAdd("__LINE__");
		public static readonly Identifier __COUNTER__ = Identifier.FindOrAdd("__COUNTER__");
		public static readonly Identifier Sizeof = Identifier.FindOrAdd("sizeof");
		public static readonly Identifier Alignof = Identifier.FindOrAdd("alignof");
		public static readonly Identifier __has_builtin = Identifier.FindOrAdd("__has_builtin");
		public static readonly Identifier __has_feature = Identifier.FindOrAdd("__has_feature");
		public static readonly Identifier __building_module = Identifier.FindOrAdd("__building_module");
		public static readonly Identifier __pragma = Identifier.FindOrAdd("__pragma");
	}

	/// <summary>
	/// Helper functions for serialization
	/// </summary>
	static class IdentifierExtensionMethods
	{
		/// <summary>
		/// Read an identifier from a binary archive
		/// </summary>
		/// <param name="Reader">Reader to serialize data from</param>
		/// <returns>Instance of the serialized identifier</returns>
		public static Identifier ReadIdentifier(this BinaryArchiveReader Reader)
		{
			return Reader.ReadObjectReference<Identifier>(() => Identifier.FindOrAdd(Reader.ReadString()!))!;
		}

		/// <summary>
		/// Write an identifier to a binary archive
		/// </summary>
		/// <param name="Writer">Writer to serialize data to</param>
		/// <param name="Identifier">Identifier to write</param>
		public static void WriteIdentifier(this BinaryArchiveWriter Writer, Identifier? Identifier)
		{
			Writer.WriteObjectReference<Identifier?>(Identifier, () => Writer.WriteString(Identifier!.ToString()));
		}
	}
}