package com.ibm.wala.cast.tree.rewrite;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import com.ibm.wala.cast.tree.CAstControlFlowMap;
import com.ibm.wala.cast.tree.CAstEntity;
import com.ibm.wala.cast.tree.CAstNode;
import com.ibm.wala.cast.tree.CAstNodeTypeMap;
import com.ibm.wala.cast.tree.CAstSourcePositionMap;
import com.ibm.wala.cast.tree.impl.CAstImpl;
import com.ibm.wala.cast.tree.impl.DelegatingEntity;
import com.ibm.wala.cast.tree.rewrite.CAstBasicRewriter.NonCopyingContext;
import com.ibm.wala.cast.tree.rewrite.CAstRewriter.Rewrite;
import com.ibm.wala.cast.util.AstConstantCollector;
import com.ibm.wala.util.collections.EmptyIterator;
import com.ibm.wala.util.collections.HashSetFactory;
import com.ibm.wala.util.collections.Pair;

public class AstConstantFolder {
  static class AssignSkipContext extends NonCopyingContext {
    private Set<CAstNode> skip = HashSetFactory.make();
  }
  
  public static CAstEntity fold(CAstEntity ce) {
    Map<String,Object> constants = AstConstantCollector.collectConstants(ce);
    if (constants.isEmpty()) {
      return ce;
    } else {
      Rewrite nce = new CAstCloner(new CAstImpl(), new AssignSkipContext(), true) {

        @Override
        protected CAstNode copyNodes(CAstNode root, CAstControlFlowMap cfg, NonCopyingContext c,
            Map<Pair<CAstNode, NoKey>, CAstNode> nodeMap) {
          
          if (root.getKind() == CAstNode.ASSIGN) {
            ((AssignSkipContext)c).skip.add(root.getChild(0));
          }
          
          if (root.getKind() == CAstNode.VAR && constants.containsKey(root.getChild(0).getValue()) && ! ((AssignSkipContext)c).skip.contains(root)) {
            return Ast.makeConstant(constants.get(root.getChild(0).getValue()));
          } else {
            return super.copyNodes(root, cfg, c, nodeMap);
          }
        } 
        
      }.rewrite(ce.getAST(), ce.getControlFlow(), ce.getSourceMap(), ce.getNodeTypeMap(), ce.getAllScopedEntities());
      return new DelegatingEntity(ce) {

        @Override
        public CAstNode getAST() {
           return nce.newRoot();
        }

        @Override
        public CAstControlFlowMap getControlFlow() {
           return nce.newCfg();
        }

        @Override
        public CAstSourcePositionMap getSourceMap() {
          return nce.newPos();
        }

        @Override
        public CAstNodeTypeMap getNodeTypeMap() {
          return nce.newTypes();
        }

        @Override
        public Map<CAstNode, Collection<CAstEntity>> getAllScopedEntities() {
          return nce.newChildren();
        }

        @Override
        public Iterator<CAstEntity> getScopedEntities(CAstNode construct) {
          Collection<CAstEntity> children = nce.newChildren().get(construct);
          return children==null? EmptyIterator.instance(): children.iterator();
        }
      };
    }
  }
}
