//
// namespace.cs: Tracks namespaces
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//   Marek Safar (marek.safar@seznam.cz)
//
// Copyright 2001 Ximian, Inc.
// Copyright 2003-2008 Novell, Inc.
// Copyright 2011 Xamarin Inc
//
using System;
using System.Collections.Generic;
using System.Linq;

namespace Mono.CSharp {

	public class RootNamespace : Namespace {

		readonly string alias_name;
		readonly Dictionary<string, Namespace> all_namespaces;

		public RootNamespace (string alias_name)
			: base (null, String.Empty)
		{
			this.alias_name = alias_name;

			all_namespaces = new Dictionary<string, Namespace> ();
			all_namespaces.Add ("", this);
		}

		public string Alias {
			get {
				return alias_name;
			}
		}

		public static void Error_GlobalNamespaceRedefined (Report report, Location loc)
		{
			report.Error (1681, loc, "The global extern alias cannot be redefined");
		}

		public void RegisterNamespace (Namespace child)
		{
			if (child != this)
				all_namespaces.Add (child.Name, child);
		}

		public bool IsNamespace (string name)
		{
			return all_namespaces.ContainsKey (name);
		}

		protected void RegisterNamespace (string dotted_name)
		{
			if (dotted_name != null && dotted_name.Length != 0 && ! IsNamespace (dotted_name))
				GetNamespace (dotted_name, true);
		}

		public override string GetSignatureForError ()
		{
			return alias_name + "::";
		}
	}

	public class GlobalRootNamespace : RootNamespace
	{
		public GlobalRootNamespace ()
			: base ("global")
		{
		}
	}

	//
	// Namespace cache for imported and compiled namespaces
	//
	// This is an Expression to allow it to be referenced in the
	// compiler parse/intermediate tree during name resolution.
	//
	public class Namespace : FullNamedExpression
	{
		Namespace parent;
		string fullname;
		protected Dictionary<string, Namespace> namespaces;
		protected Dictionary<string, IList<TypeSpec>> types;
		Dictionary<string, TypeExpr> cached_types;
		RootNamespace root;
		bool cls_checked;

		public readonly MemberName MemberName;

		/// <summary>
		///   Constructor Takes the current namespace and the
		///   name.  This is bootstrapped with parent == null
		///   and name = ""
		/// </summary>
		public Namespace (Namespace parent, string name)
		{
			// Expression members.
			this.eclass = ExprClass.Namespace;
			this.Type = InternalType.Namespace;
			this.loc = Location.Null;

			this.parent = parent;

			if (parent != null)
				this.root = parent.root;
			else
				this.root = this as RootNamespace;

			if (this.root == null)
				throw new InternalErrorException ("Root namespaces must be created using RootNamespace");
			
			string pname = parent != null ? parent.fullname : "";
				
			if (pname == "")
				fullname = name;
			else
				fullname = parent.fullname + "." + name;

			if (fullname == null)
				throw new InternalErrorException ("Namespace has a null fullname");

			if (parent != null && parent.MemberName != MemberName.Null)
				MemberName = new MemberName (parent.MemberName, name, Location.Null);
			else if (name.Length == 0)
				MemberName = MemberName.Null;
			else
				MemberName = new MemberName (name, Location.Null);

			namespaces = new Dictionary<string, Namespace> ();
			cached_types = new Dictionary<string, TypeExpr> ();

			root.RegisterNamespace (this);
		}

		#region Properties

		/// <summary>
		///   The qualified name of the current namespace
		/// </summary>
		public string Name {
			get { return fullname; }
		}

		/// <summary>
		///   The parent of this namespace, used by the parser to "Pop"
		///   the current namespace declaration
		/// </summary>
		public Namespace Parent {
			get { return parent; }
		}

		#endregion

		protected override Expression DoResolve (ResolveContext ec)
		{
			return this;
		}

		public void Error_NamespaceDoesNotExist (IMemberContext ctx, string name, int arity, Location loc)
		{
			var retval = LookupType (ctx, name, arity, LookupMode.IgnoreAccessibility, loc);
			if (retval != null) {
				ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (retval.Type);
				ErrorIsInaccesible (ctx, retval.GetSignatureForError (), loc);
				return;
			}

			retval = LookupType (ctx, name, -System.Math.Max (1, arity), LookupMode.Probing, loc);
			if (retval != null) {
				Error_TypeArgumentsCannotBeUsed (ctx, retval.Type, arity, loc);
				return;
			}

			Namespace ns;
			if (arity > 0 && namespaces.TryGetValue (name, out ns)) {
				ns.Error_TypeArgumentsCannotBeUsed (ctx, null, arity, loc);
				return;
			}

			if (this is GlobalRootNamespace) {
				ctx.Module.Compiler.Report.Error (400, loc,
					"The type or namespace name `{0}' could not be found in the global namespace (are you missing an assembly reference?)",
					name);
			} else {
				ctx.Module.Compiler.Report.Error (234, loc,
					"The type or namespace name `{0}' does not exist in the namespace `{1}'. Are you missing an assembly reference?",
					name, GetSignatureForError ());
			}
		}

		public override string GetSignatureForError ()
		{
			return fullname;
		}

		public Namespace AddNamespace (MemberName name)
		{
			Namespace ns_parent;
			if (name.Left != null) {
				if (parent != null)
					ns_parent = parent.AddNamespace (name.Left);
				else
					ns_parent = AddNamespace (name.Left);
			} else {
				ns_parent = this;
			}

			Namespace ns;
			if (!ns_parent.namespaces.TryGetValue (name.Basename, out ns)) {
				ns = new Namespace (ns_parent, name.Basename);
				ns_parent.namespaces.Add (name.Basename, ns);
			}

			return ns;
		}

		// TODO: Replace with CreateNamespace where MemberName is created for the method call
		public Namespace GetNamespace (string name, bool create)
		{
			int pos = name.IndexOf ('.');

			Namespace ns;
			string first;
			if (pos >= 0)
				first = name.Substring (0, pos);
			else
				first = name;

			if (!namespaces.TryGetValue (first, out ns)) {
				if (!create)
					return null;

				ns = new Namespace (this, first);
				namespaces.Add (first, ns);
			}

			if (pos >= 0)
				ns = ns.GetNamespace (name.Substring (pos + 1), create);

			return ns;
		}

		public IList<TypeSpec> GetAllTypes (string name)
		{
			IList<TypeSpec> found;
			if (types == null || !types.TryGetValue (name, out found))
				return null;

			return found;
		}

		public TypeExpr LookupType (IMemberContext ctx, string name, int arity, LookupMode mode, Location loc)
		{
			if (types == null)
				return null;

			TypeExpr te;
			if (arity == 0 && cached_types.TryGetValue (name, out te))
				return te;

			IList<TypeSpec> found;
			if (!types.TryGetValue (name, out found))
				return null;

			TypeSpec best = null;
			foreach (var ts in found) {
				if (ts.Arity == arity) {
					if (best == null) {
						if ((ts.Modifiers & Modifiers.INTERNAL) != 0 && !ts.MemberDefinition.IsInternalAsPublic (ctx.Module.DeclaringAssembly) && mode != LookupMode.IgnoreAccessibility)
							continue;

						best = ts;
						continue;
					}

					if (best.MemberDefinition.IsImported && ts.MemberDefinition.IsImported) {
						if (mode == LookupMode.Normal) {
							ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (best);
							ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ts);
							ctx.Module.Compiler.Report.Error (433, loc, "The imported type `{0}' is defined multiple times", ts.GetSignatureForError ());
						}
						break;
					}

					if (best.MemberDefinition.IsImported)
						best = ts;

					if ((best.Modifiers & Modifiers.INTERNAL) != 0 && !best.MemberDefinition.IsInternalAsPublic (ctx.Module.DeclaringAssembly))
						continue;

					if (mode != LookupMode.Normal)
						continue;

					if (ts.MemberDefinition.IsImported)
						ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ts);

					ctx.Module.Compiler.Report.Warning (436, 2, loc,
						"The type `{0}' conflicts with the imported type of same name'. Ignoring the imported type definition",
						best.GetSignatureForError ());
				}

				//
				// Lookup for the best candidate with the closest arity match
				//
				if (arity < 0) {
					if (best == null) {
						best = ts;
					} else if (System.Math.Abs (ts.Arity + arity) < System.Math.Abs (best.Arity + arity)) {
						best = ts;
					}
				}
			}

			if (best == null)
				return null;

			te = new TypeExpression (best, Location.Null);

			// TODO MemberCache: Cache more
			if (arity == 0 && mode == LookupMode.Normal)
				cached_types.Add (name, te);

			return te;
		}

		TypeSpec LookupType (string name, int arity)
		{
			if (types == null)
				return null;

			IList<TypeSpec> found;
			if (types.TryGetValue (name, out found)) {
				TypeSpec best = null;

				foreach (var ts in found) {
					if (ts.Arity == arity)
						return ts;

					//
					// Lookup for the best candidate with closest arity match
					//
					if (arity < 0) {
						if (best == null) {
							best = ts;
						} else if (System.Math.Abs (ts.Arity + arity) < System.Math.Abs (best.Arity + arity)) {
							best = ts;
						}
					}
				}
				
				return best;
			}

			return null;
		}

		public FullNamedExpression LookupTypeOrNamespace (IMemberContext ctx, string name, int arity, LookupMode mode, Location loc)
		{
			var texpr = LookupType (ctx, name, arity, mode, loc);

			Namespace ns;
			if (arity == 0 && namespaces.TryGetValue (name, out ns)) {
				if (texpr == null)
					return ns;

				if (mode != LookupMode.Probing) {
					ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (texpr.Type);
					// ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (ns.loc, "");
					ctx.Module.Compiler.Report.Warning (437, 2, loc,
						"The type `{0}' conflicts with the imported namespace `{1}'. Using the definition found in the source file",
						texpr.GetSignatureForError (), ns.GetSignatureForError ());
				}

				if (texpr.Type.MemberDefinition.IsImported)
					return ns;
			}

			return texpr;
		}

		//
		// Completes types with the given `prefix'
		//
		public IEnumerable<string> CompletionGetTypesStartingWith (string prefix)
		{
			if (types == null)
				return Enumerable.Empty<string> ();

			var res = from item in types
					  where item.Key.StartsWith (prefix) && item.Value.Any (l => (l.Modifiers & Modifiers.PUBLIC) != 0)
					  select item.Key;

			if (namespaces != null)
				res = res.Concat (from item in namespaces where item.Key.StartsWith (prefix) select item.Key);

			return res;
		}

		// 
		// Looks for extension method in this namespace
		//
		public List<MethodSpec> LookupExtensionMethod (IMemberContext invocationContext, TypeSpec extensionType, string name, int arity)
		{
			if (types == null)
				return null;

			List<MethodSpec> found = null;

			// TODO: Add per namespace flag when at least 1 type has extension

			foreach (var tgroup in types.Values) {
				foreach (var ts in tgroup) {
					if ((ts.Modifiers & Modifiers.METHOD_EXTENSION) == 0)
						continue;

					var res = ts.MemberCache.FindExtensionMethods (invocationContext, extensionType, name, arity);
					if (res == null)
						continue;

					if (found == null) {
						found = res;
					} else {
						found.AddRange (res);
					}
				}
			}

			return found;
		}

		public void AddType (ModuleContainer module, TypeSpec ts)
		{
			if (types == null) {
				types = new Dictionary<string, IList<TypeSpec>> (64);
			}

			var name = ts.Name;
			IList<TypeSpec> existing;
			if (types.TryGetValue (name, out existing)) {
				TypeSpec better_type;
				TypeSpec found;
				if (existing.Count == 1) {
					found = existing[0];
					if (ts.Arity == found.Arity) {
						better_type = IsImportedTypeOverride (module, ts, found);
						if (better_type == found)
							return;

						if (better_type != null) {
							existing [0] = better_type;
							return;
						}
					}

					existing = new List<TypeSpec> ();
					existing.Add (found);
					types[name] = existing;
				} else {
					for (int i = 0; i < existing.Count; ++i) {
						found = existing[i];
						if (ts.Arity != found.Arity)
							continue;

						better_type = IsImportedTypeOverride (module, ts, found);
						if (better_type == found)
							return;

						if (better_type != null) {
							existing.RemoveAt (i);
							--i;
							continue;
						}
					}
				}

				existing.Add (ts);
			} else {
				types.Add (name, new TypeSpec[] { ts });
			}
		}

		//
		// We import any types but in the situation there are same types
		// but one has better visibility (either public or internal with friend)
		// the less visible type is removed from the namespace cache
		//
		public static TypeSpec IsImportedTypeOverride (ModuleContainer module, TypeSpec ts, TypeSpec found)
		{
			var ts_accessible = (ts.Modifiers & Modifiers.PUBLIC) != 0 || ts.MemberDefinition.IsInternalAsPublic (module.DeclaringAssembly);
			var found_accessible = (found.Modifiers & Modifiers.PUBLIC) != 0 || found.MemberDefinition.IsInternalAsPublic (module.DeclaringAssembly);

			if (ts_accessible && !found_accessible)
				return ts;

			// found is better always better for accessible or inaccessible ts
			if (!ts_accessible)
				return found;

			return null;
		}

		public void RemoveContainer (TypeContainer tc)
		{
			types.Remove (tc.Basename);
			cached_types.Remove (tc.Basename);
		}

		public override FullNamedExpression ResolveAsTypeOrNamespace (IMemberContext mc)
		{
			return this;
		}

		public void SetBuiltinType (BuiltinTypeSpec pts)
		{
			var found = types[pts.Name];
			cached_types.Remove (pts.Name);
			if (found.Count == 1) {
				types[pts.Name][0] = pts;
			} else {
				throw new NotImplementedException ();
			}
		}

		public void VerifyClsCompliance ()
		{
			if (types == null || cls_checked)
				return;

			cls_checked = true;

			// TODO: This is quite ugly way to check for CLS compliance at namespace level

			var locase_types = new Dictionary<string, List<TypeSpec>> (StringComparer.OrdinalIgnoreCase);
			foreach (var tgroup in types.Values) {
				foreach (var tm in tgroup) {
					if ((tm.Modifiers & Modifiers.PUBLIC) == 0 || !tm.IsCLSCompliant ())
						continue;

					List<TypeSpec> found;
					if (!locase_types.TryGetValue (tm.Name, out found)) {
						found = new List<TypeSpec> ();
						locase_types.Add (tm.Name, found);
					}

					found.Add (tm);
				}
			}

			foreach (var locase in locase_types.Values) {
				if (locase.Count < 2)
					continue;

				bool all_same = true;
				foreach (var notcompliant in locase) {
					all_same = notcompliant.Name == locase[0].Name;
					if (!all_same)
						break;
				}

				if (all_same)
					continue;

				TypeContainer compiled = null;
				foreach (var notcompliant in locase) {
					if (!notcompliant.MemberDefinition.IsImported) {
						if (compiled != null)
							compiled.Compiler.Report.SymbolRelatedToPreviousError (compiled);

						compiled = notcompliant.MemberDefinition as TypeContainer;
					} else {
						compiled.Compiler.Report.SymbolRelatedToPreviousError (notcompliant);
					}
				}

				compiled.Compiler.Report.Warning (3005, 1, compiled.Location,
					"Identifier `{0}' differing only in case is not CLS-compliant", compiled.GetSignatureForError ());
			}
		}
	}

	//
	// Namespace block as created by the parser
	//
	public class NamespaceContainer : TypeContainer, IMemberContext
	{
		static readonly Namespace[] empty_namespaces = new Namespace[0];
		static readonly string[] empty_using_list = new string[0];

		Namespace ns;

		readonly ModuleContainer module;
		readonly CompilationSourceFile file;

		public new readonly NamespaceContainer Parent;

		int symfile_id;

		List<UsingNamespace> clauses;

		// Used by parsed to check for parser errors
		public bool DeclarationFound;

		Namespace[] namespace_using_table;
		Dictionary<string, UsingAliasNamespace> aliases;

		public NamespaceContainer (MemberName name, ModuleContainer module, NamespaceContainer parent, CompilationSourceFile sourceFile)
			: base ((TypeContainer) parent ?? module, name, null, MemberKind.Namespace)
		{
			this.module = module;
			this.Parent = parent;
			this.file = sourceFile;

			if (parent != null)
				ns = parent.NS.AddNamespace (name);
			else if (name != null)
				ns = module.GlobalRootNamespace.AddNamespace (name);
			else
				ns = module.GlobalRootNamespace;

			containers = new List<TypeContainer> ();
		}

		#region Properties

		public override AttributeTargets AttributeTargets {
			get {
				throw new NotSupportedException ();
			}
		}

		public override string DocCommentHeader {
			get {
				throw new NotSupportedException ();
			}
		}

		public Namespace NS {
			get {
				return ns;
			}
		}

		public override ModuleContainer Module {
			get {
				return module;
			}
		}

		public CompilationSourceFile SourceFile {
			get {
				return file;
			}
		}

		public List<UsingNamespace> Usings {
			get {
				return clauses;
			}
		}

		public override string[] ValidAttributeTargets {
			get {
				throw new NotSupportedException ();
			}
		}

		#endregion

		public void AddUsing (UsingNamespace un)
		{
			if (DeclarationFound){
				Compiler.Report.Error (1529, un.Location, "A using clause must precede all other namespace elements except extern alias declarations");
			}

			if (clauses == null)
				clauses = new List<UsingNamespace> ();

			clauses.Add (un);
		}

		public void AddUsing (UsingAliasNamespace un)
		{
			if (DeclarationFound){
				Compiler.Report.Error (1529, un.Location, "A using clause must precede all other namespace elements except extern alias declarations");
			}

			AddAlias (un);
		}

		void AddAlias (UsingAliasNamespace un)
		{
			if (clauses == null) {
				clauses = new List<UsingNamespace> ();
			} else {
				foreach (var entry in clauses) {
					var a = entry as UsingAliasNamespace;
					if (a != null && a.Alias.Value == un.Alias.Value) {
						Compiler.Report.SymbolRelatedToPreviousError (a.Location, "");
						Compiler.Report.Error (1537, un.Location,
							"The using alias `{0}' appeared previously in this namespace", un.Alias.Value);
					}
				}
			}

			clauses.Add (un);
		}

		public override void AddPartial (TypeDefinition next_part)
		{
			var existing = ns.LookupType (this, next_part.MemberName.Name, next_part.MemberName.Arity, LookupMode.Probing, Location.Null);
			var td = existing != null ? existing.Type.MemberDefinition as TypeDefinition : null;
			AddPartial (next_part, td);
		}

		public override void AddTypeContainer (TypeContainer tc)
		{
			string name = tc.Basename;

			var mn = tc.MemberName;
			while (mn.Left != null) {
				mn = mn.Left;
				name = mn.Name;
			}

			MemberCore mc;
			if (defined_names.TryGetValue (name, out mc)) {
				if (tc is NamespaceContainer && mc is NamespaceContainer) {
					containers.Add (tc);
					return;
				}

				Report.SymbolRelatedToPreviousError (mc);
				if ((mc.ModFlags & Modifiers.PARTIAL) != 0 && (tc is ClassOrStruct || tc is Interface)) {
					Error_MissingPartialModifier (tc);
				} else {
					Report.Error (101, tc.Location, "The namespace `{0}' already contains a definition for `{1}'",
						GetSignatureForError (), mn.GetSignatureForError ());
				}
			} else {
				defined_names.Add (name, tc);
			}

			base.AddTypeContainer (tc);

			var tdef = tc.PartialContainer;
			if (tdef != null)
				ns.AddType (module, tdef.Definition);
		}

		public override void ApplyAttributeBuilder (Attribute a, MethodSpec ctor, byte[] cdata, PredefinedAttributes pa)
		{
			throw new NotSupportedException ();
		}

		public override void EmitContainer ()
		{
			VerifyClsCompliance ();

			base.EmitContainer ();
		}

		//
		// Does extension methods look up to find a method which matches name and extensionType.
		// Search starts from this namespace and continues hierarchically up to top level.
		//
		protected override ExtensionMethodCandidates LookupExtensionMethod (IMemberContext invocationContext, TypeSpec extensionType, string name, int arity)
		{
			return LookupExtensionMethod (invocationContext, extensionType, name, arity, this, 0);
		}

		public ExtensionMethodCandidates LookupExtensionMethod (IMemberContext invocationContext, TypeSpec extensionType, string name, int arity, NamespaceContainer container, int position)
		{
			//
			// Here we try to resume the search for extension method at the point
			// where the last bunch of candidates was found. It's more tricky than
			// it seems as we have to check both namespace containers and namespace
			// in correct order.
			//
			// Consider:
			// 
			// namespace A {
			//	using N1;
			//  namespace B.C.D {
			//		<our first search found candidates in A.B.C.D
			//  }
			// }
			//
			// In the example above namespace A.B.C.D, A.B.C and A.B have to be
			// checked before we hit A.N1 using
			//
			ExtensionMethodCandidates candidates;
			for (; container != null; container = container.Parent) {
				candidates = container.LookupExtensionMethodCandidates (invocationContext, extensionType, name, arity, ref position);
				if (candidates != null || container.MemberName == null)
					return candidates;

				var container_ns = container.ns.Parent;
				var mn = container.MemberName.Left;
				int already_checked = position - 2;
				while (already_checked-- > 0) {
					mn = mn.Left;
					container_ns = container_ns.Parent;
				}

				while (mn != null) {
					++position;

					var methods = container_ns.LookupExtensionMethod (invocationContext, extensionType, name, arity);
					if (methods != null) {
						return new ExtensionMethodCandidates (invocationContext, methods, container, position);
					}

					mn = mn.Left;
					container_ns = container_ns.Parent;
				}

				position = 0;
			}

			return null;
		}

		ExtensionMethodCandidates LookupExtensionMethodCandidates (IMemberContext invocationContext, TypeSpec extensionType, string name, int arity, ref int position)
		{
			List<MethodSpec> candidates = null;

			if (position == 0) {
				++position;

				candidates = ns.LookupExtensionMethod (invocationContext, extensionType, name, arity);
				if (candidates != null) {
					return new ExtensionMethodCandidates (invocationContext, candidates, this, position);
				}
			}

			if (position == 1) {
				++position;

				foreach (Namespace n in namespace_using_table) {
					var a = n.LookupExtensionMethod (invocationContext, extensionType, name, arity);
					if (a == null)
						continue;

					if (candidates == null)
						candidates = a;
					else
						candidates.AddRange (a);
				}

				if (candidates != null)
					return new ExtensionMethodCandidates (invocationContext, candidates, this, position);
			}

			return null;
		}

		public override FullNamedExpression LookupNamespaceOrType (string name, int arity, LookupMode mode, Location loc)
		{
			//
			// Only simple names (no dots) will be looked up with this function
			//
			FullNamedExpression resolved;
			for (NamespaceContainer container = this; container != null; container = container.Parent) {
				resolved = container.Lookup (name, arity, mode, loc);
				if (resolved != null || container.MemberName == null)
					return resolved;

				var container_ns = container.ns.Parent;
				var mn = container.MemberName.Left;
				while (mn != null) {
					resolved = container_ns.LookupTypeOrNamespace (this, name, arity, mode, loc);
					if (resolved != null)
						return resolved;

					mn = mn.Left;
					container_ns = container_ns.Parent;
				}
			}

			return null;
		}

		public override void GetCompletionStartingWith (string prefix, List<string> results)
		{
			foreach (var un in Usings) {
				if (un.Alias != null)
					continue;

				var name = un.NamespaceExpression.Name;
				if (name.StartsWith (prefix))
					results.Add (name);
			}


			IEnumerable<string> all = Enumerable.Empty<string> ();

			foreach (Namespace using_ns in namespace_using_table) {
				if (prefix.StartsWith (using_ns.Name)) {
					int ld = prefix.LastIndexOf ('.');
					if (ld != -1) {
						string rest = prefix.Substring (ld + 1);

						all = all.Concat (using_ns.CompletionGetTypesStartingWith (rest));
					}
				}
				all = all.Concat (using_ns.CompletionGetTypesStartingWith (prefix));
			}

			results.AddRange (all);

			base.GetCompletionStartingWith (prefix, results);
		}

		
		//
		// Looks-up a alias named @name in this and surrounding namespace declarations
		//
		public FullNamedExpression LookupExternAlias (string name)
		{
			if (aliases == null)
				return null;

			UsingAliasNamespace uan;
			if (aliases.TryGetValue (name, out uan) && uan is UsingExternAlias)
				return uan.ResolvedExpression;

			return null;
		}
		
		//
		// Looks-up a alias named @name in this and surrounding namespace declarations
		//
		public override FullNamedExpression LookupNamespaceAlias (string name)
		{
			for (NamespaceContainer n = this; n != null; n = n.Parent) {
				if (n.aliases == null)
					continue;

				UsingAliasNamespace uan;
				if (n.aliases.TryGetValue (name, out uan))
					return uan.ResolvedExpression;
			}

			return null;
		}

		FullNamedExpression Lookup (string name, int arity, LookupMode mode, Location loc)
		{
			//
			// Check whether it's in the namespace.
			//
			FullNamedExpression fne = ns.LookupTypeOrNamespace (this, name, arity, mode, loc);

			//
			// Check aliases. 
			//
			if (aliases != null && arity == 0) {
				UsingAliasNamespace uan;
				if (aliases.TryGetValue (name, out uan)) {
					if (fne != null) {
						// TODO: Namespace has broken location
						//Report.SymbolRelatedToPreviousError (fne.Location, null);
						Compiler.Report.SymbolRelatedToPreviousError (uan.Location, null);
						Compiler.Report.Error (576, loc,
							"Namespace `{0}' contains a definition with same name as alias `{1}'",
							GetSignatureForError (), name);
					}

					return uan.ResolvedExpression;
				}
			}

			if (fne != null)
				return fne;

			//
			// Lookup can be called before the namespace is defined from different namespace using alias clause
			//
			if (namespace_using_table == null) {
				DoDefineNamespace ();
			}

			//
			// Check using entries.
			//
			FullNamedExpression match = null;
			foreach (Namespace using_ns in namespace_using_table) {
				//
				// A using directive imports only types contained in the namespace, it
				// does not import any nested namespaces
				//
				fne = using_ns.LookupType (this, name, arity, mode, loc);
				if (fne == null)
					continue;

				if (match == null) {
					match = fne;
					continue;
				}

				// Prefer types over namespaces
				var texpr_fne = fne as TypeExpr;
				var texpr_match = match as TypeExpr;
				if (texpr_fne != null && texpr_match == null) {
					match = fne;
					continue;
				} else if (texpr_fne == null) {
					continue;
				}

				// It can be top level accessibility only
				var better = Namespace.IsImportedTypeOverride (module, texpr_match.Type, texpr_fne.Type);
				if (better == null) {
					if (mode == LookupMode.Normal) {
						Compiler.Report.SymbolRelatedToPreviousError (texpr_match.Type);
						Compiler.Report.SymbolRelatedToPreviousError (texpr_fne.Type);
						Compiler.Report.Error (104, loc, "`{0}' is an ambiguous reference between `{1}' and `{2}'",
							name, texpr_match.GetSignatureForError (), texpr_fne.GetSignatureForError ());
					}

					return match;
				}

				if (better == texpr_fne.Type)
					match = texpr_fne;
			}

			return match;
		}

		public int SymbolFileID {
			get {
				if (symfile_id == 0 && file.SourceFileEntry != null) {
					int parent_id = Parent == null ? 0 : Parent.SymbolFileID;

					string [] using_list = empty_using_list;
					if (clauses != null) {
						// TODO: Why is it needed, what to do with aliases
						var ul = new List<string> ();
						foreach (var c in clauses) {
							ul.Add (c.ResolvedExpression.GetSignatureForError ());
						}
						
						using_list = ul.ToArray ();
					}

					symfile_id = SymbolWriter.DefineNamespace (ns.Name, file.CompileUnitEntry, using_list, parent_id);
				}
				return symfile_id;
			}
		}

		static void MsgtryRef (string s)
		{
			Console.WriteLine ("    Try using -r:" + s);
		}

		static void MsgtryPkg (string s)
		{
			Console.WriteLine ("    Try using -pkg:" + s);
		}

		public static void Error_NamespaceNotFound (Location loc, string name, Report Report)
		{
			Report.Error (246, loc, "The type or namespace name `{0}' could not be found. Are you missing a using directive or an assembly reference?",
				name);

			switch (name) {
			case "Gtk": case "GtkSharp":
				MsgtryPkg ("gtk-sharp-2.0");
				break;

			case "Gdk": case "GdkSharp":
				MsgtryPkg ("gdk-sharp-2.0");
				break;

			case "Glade": case "GladeSharp":
				MsgtryPkg ("glade-sharp-2.0");
				break;

			case "System.Drawing":
			case "System.Web.Services":
			case "System.Web":
			case "System.Data":
			case "System.Windows.Forms":
				MsgtryRef (name);
				break;
			}
		}

		protected override void DefineNamespace ()
		{
			if (namespace_using_table == null)
				DoDefineNamespace ();

			base.DefineNamespace ();
		}

		void DoDefineNamespace ()
		{
			namespace_using_table = empty_namespaces;

			if (clauses != null) {
				var list = new List<Namespace> (clauses.Count);
				bool post_process_using_aliases = false;

				for (int i = 0; i < clauses.Count; ++i) {
					var entry = clauses[i];

					if (entry.Alias != null) {
						if (aliases == null)
							aliases = new Dictionary<string, UsingAliasNamespace> ();

						//
						// Aliases are not available when resolving using section
						// except extern aliases
						//
						if (entry is UsingExternAlias) {
							entry.Define (this);
							if (entry.ResolvedExpression != null)
								aliases.Add (entry.Alias.Value, (UsingExternAlias) entry);

							clauses.RemoveAt (i--);
						} else {
							post_process_using_aliases = true;
						}

						continue;
					}

					entry.Define (this);

					Namespace using_ns = entry.ResolvedExpression as Namespace;
					if (using_ns == null)
						continue;

					if (list.Contains (using_ns)) {
						Compiler.Report.Warning (105, 3, entry.Location,
							"The using directive for `{0}' appeared previously in this namespace", using_ns.GetSignatureForError ());
					} else {
						list.Add (using_ns);
					}
				}

				namespace_using_table = list.ToArray ();

				if (post_process_using_aliases) {
					for (int i = 0; i < clauses.Count; ++i) {
						var entry = clauses[i];
						if (entry.Alias != null) {
							entry.Define (this);
							if (entry.ResolvedExpression != null) {
								aliases.Add (entry.Alias.Value, (UsingAliasNamespace) entry);
							}

							clauses.RemoveAt (i--);
						}
					}
				}
			}
		}

		public void EnableUsingClausesRedefinition ()
		{
			namespace_using_table = null;
		}

		internal override void GenerateDocComment (DocumentationBuilder builder)
		{
			if (containers != null) {
				foreach (var tc in containers)
					tc.GenerateDocComment (builder);
			}
		}

		public override string GetSignatureForError ()
		{
			return MemberName == null ? "global::" : base.GetSignatureForError ();
		}

		public override void RemoveContainer (TypeContainer next_part)
		{
			base.RemoveContainer (next_part);
			NS.RemoveContainer (next_part);
		}

		protected override bool VerifyClsCompliance ()
		{
			if (Module.IsClsComplianceRequired ()) {
				if (MemberName != null && MemberName.Name[0] == '_') {
					Warning_IdentifierNotCompliant ();
				}

				ns.VerifyClsCompliance ();
				return true;
			}

			return false;
		}
	}

	public class UsingNamespace
	{
		readonly ATypeNameExpression expr;
		readonly Location loc;
		protected FullNamedExpression resolved;

		public UsingNamespace (ATypeNameExpression expr, Location loc)
		{
			this.expr = expr;
			this.loc = loc;
		}

		#region Properties

		public virtual SimpleMemberName Alias {
			get {
				return null;
			}
		}

		public Location Location {
			get {
				return loc;
			}
		}

		public ATypeNameExpression NamespaceExpression	{
			get {
				return expr;
			}
		}

		public FullNamedExpression ResolvedExpression {
			get {
				return resolved;
			}
		}

		#endregion

		public string GetSignatureForError ()
		{
			return expr.GetSignatureForError ();
		}

		public virtual void Define (NamespaceContainer ctx)
		{
			resolved = expr.ResolveAsTypeOrNamespace (ctx);
			var ns = resolved as Namespace;
			if (ns == null) {
				if (resolved != null) {
					ctx.Module.Compiler.Report.SymbolRelatedToPreviousError (resolved.Type);
					ctx.Module.Compiler.Report.Error (138, Location,
						"`{0}' is a type not a namespace. A using namespace directive can only be applied to namespaces",
						GetSignatureForError ());
				}
			}
		}
	}

	public class UsingExternAlias : UsingAliasNamespace
	{
		public UsingExternAlias (SimpleMemberName alias, Location loc)
			: base (alias, null, loc)
		{
		}

		public override void Define (NamespaceContainer ctx)
		{
			resolved = ctx.Module.GetRootNamespace (Alias.Value);
			if (resolved == null) {
				ctx.Module.Compiler.Report.Error (430, Location,
					"The extern alias `{0}' was not specified in -reference option",
					Alias.Value);
			}
		}
	}

	public class UsingAliasNamespace : UsingNamespace
	{
		readonly SimpleMemberName alias;

		public struct AliasContext : IMemberContext
		{
			readonly NamespaceContainer ns;

			public AliasContext (NamespaceContainer ns)
			{
				this.ns = ns;
			}

			public TypeSpec CurrentType {
				get {
					return null;
				}
			}

			public TypeParameters CurrentTypeParameters {
				get {
					return null;
				}
			}

			public MemberCore CurrentMemberDefinition {
				get {
					return null;
				}
			}

			public bool IsObsolete {
				get {
					return false;
				}
			}

			public bool IsUnsafe {
				get {
					throw new NotImplementedException ();
				}
			}

			public bool IsStatic {
				get {
					throw new NotImplementedException ();
				}
			}

			public ModuleContainer Module {
				get {
					return ns.Module;
				}
			}

			public string GetSignatureForError ()
			{
				throw new NotImplementedException ();
			}

			public ExtensionMethodCandidates LookupExtensionMethod (TypeSpec extensionType, string name, int arity)
			{
				return null;
			}

			public FullNamedExpression LookupNamespaceOrType (string name, int arity, LookupMode mode, Location loc)
			{
				var fne = ns.NS.LookupTypeOrNamespace (ns, name, arity, mode, loc);
				if (fne != null)
					return fne;

				//
				// Only extern aliases are allowed in this context
				//
				fne = ns.LookupExternAlias (name);
				if (fne != null || ns.MemberName == null)
					return fne;

				var container_ns = ns.NS.Parent;
				var mn = ns.MemberName.Left;
				while (mn != null) {
					fne = container_ns.LookupTypeOrNamespace (this, name, arity, mode, loc);
					if (fne != null)
						return fne;

					mn = mn.Left;
					container_ns = container_ns.Parent;
				}

				if (ns.Parent != null)
					return ns.Parent.LookupNamespaceOrType (name, arity, mode, loc);

				return null;
			}

			public FullNamedExpression LookupNamespaceAlias (string name)
			{
				return ns.LookupNamespaceAlias (name);
			}
		}

		public UsingAliasNamespace (SimpleMemberName alias, ATypeNameExpression expr, Location loc)
			: base (expr, loc)
		{
			this.alias = alias;
		}

		public override SimpleMemberName Alias {
			get {
				return alias;
			}
		}

		public override void Define (NamespaceContainer ctx)
		{
			//
			// The namespace-or-type-name of a using-alias-directive is resolved as if
			// the immediately containing compilation unit or namespace body had no
			// using-directives. A using-alias-directive may however be affected
			// by extern-alias-directives in the immediately containing compilation
			// unit or namespace body
			//
			// We achieve that by introducing alias-context which redirect any local
			// namespace or type resolve calls to parent namespace
			//
			resolved = NamespaceExpression.ResolveAsTypeOrNamespace (new AliasContext (ctx));
		}
	}
}