// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under MIT X11 license (for details please see \doc\license.txt)

using System;
using System.Linq;
using ICSharpCode.NRefactory.CSharp;
using ICSharpCode.NRefactory.CSharp.PatternMatching;

namespace ICSharpCode.Decompiler.Ast.Transforms
{
	/// <summary>
	/// Combines query expressions and removes transparent identifiers.
	/// </summary>
	public class CombineQueryExpressions : IAstTransform
	{
		readonly DecompilerContext context;
		
		public CombineQueryExpressions(DecompilerContext context)
		{
			this.context = context;
		}
		
		public void Run(AstNode compilationUnit)
		{
			if (!context.Settings.QueryExpressions)
				return;
			CombineQueries(compilationUnit);
		}
		
		void CombineQueries(AstNode node)
		{
			for (AstNode child = node.FirstChild; child != null; child = child.NextSibling) {
				CombineQueries(child);
			}
			QueryExpression query = node as QueryExpression;
			if (query != null) {
				QueryFromClause fromClause = (QueryFromClause)query.Clauses.First();
				QueryExpression innerQuery = fromClause.Expression as QueryExpression;
				if (innerQuery != null) {
					if (TryRemoveTransparentIdentifier(query, fromClause, innerQuery)) {
						RemoveTransparentIdentifierReferences(query);
					}
				}
			}
		}
		
		static readonly QuerySelectClause selectTransparentIdentifierPattern = new QuerySelectClause {
			Expression = new ObjectCreateExpression {
				Initializer = new ArrayInitializerExpression {
					Elements = {
						new NamedNode("nae1", new NamedArgumentExpression { Expression = new IdentifierExpression() }),
						new NamedNode("nae2", new NamedArgumentExpression { Expression = new AnyNode() })
					}
				}
			}};
		
		bool IsTransparentIdentifier(string identifier)
		{
			return identifier.StartsWith("<>", StringComparison.Ordinal) && identifier.Contains("TransparentIdentifier");
		}
		
		bool TryRemoveTransparentIdentifier(QueryExpression query, QueryFromClause fromClause, QueryExpression innerQuery)
		{
			if (!IsTransparentIdentifier(fromClause.Identifier))
				return false;
			Match match = selectTransparentIdentifierPattern.Match(innerQuery.Clauses.Last());
			if (match == null)
				return false;
			QuerySelectClause selectClause = (QuerySelectClause)innerQuery.Clauses.Last();
			NamedArgumentExpression nae1 = match.Get<NamedArgumentExpression>("nae1").Single();
			NamedArgumentExpression nae2 = match.Get<NamedArgumentExpression>("nae2").Single();
			if (nae1.Identifier != ((IdentifierExpression)nae1.Expression).Identifier)
				return false;
			IdentifierExpression nae2IdentExpr = nae2.Expression as IdentifierExpression;
			if (nae2IdentExpr != null && nae2.Identifier == nae2IdentExpr.Identifier) {
				// from * in (from x in ... select new { x = x, y = y }) ...
				// =>
				// from x in ... ...
				fromClause.Remove();
				selectClause.Remove();
				// Move clauses from innerQuery to query
				QueryClause insertionPos = null;
				foreach (var clause in innerQuery.Clauses) {
					query.Clauses.InsertAfter(insertionPos, insertionPos = clause.Detach());
				}
			} else {
				// from * in (from x in ... select new { x = x, y = expr }) ...
				// =>
				// from x in ... let y = expr ...
				fromClause.Remove();
				selectClause.Remove();
				// Move clauses from innerQuery to query
				QueryClause insertionPos = null;
				foreach (var clause in innerQuery.Clauses) {
					query.Clauses.InsertAfter(insertionPos, insertionPos = clause.Detach());
				}
				query.Clauses.InsertAfter(insertionPos, new QueryLetClause { Identifier = nae2.Identifier, Expression = nae2.Expression.Detach() });
			}
			return true;
		}
		
		/// <summary>
		/// Removes all occurrences of transparent identifiers
		/// </summary>
		void RemoveTransparentIdentifierReferences(AstNode node)
		{
			foreach (AstNode child in node.Children) {
				RemoveTransparentIdentifierReferences(child);
			}
			MemberReferenceExpression mre = node as MemberReferenceExpression;
			if (mre != null) {
				IdentifierExpression ident = mre.Target as IdentifierExpression;
				if (ident != null && IsTransparentIdentifier(ident.Identifier)) {
					IdentifierExpression newIdent = new IdentifierExpression(mre.MemberName);
					mre.TypeArguments.MoveTo(newIdent.TypeArguments);
					newIdent.CopyAnnotationsFrom(mre);
					newIdent.RemoveAnnotations<PropertyDeclaration>(); // remove the reference to the property of the anonymous type
					mre.ReplaceWith(newIdent);
					return;
				}
			}
		}
	}
}