/*
 * Copyright 2014 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.dev.jjs.impl;

import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JDeclaredType;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JMethodCall;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.thirdparty.guava.common.collect.ImmutableList;

/**
 * Java8 default methods are implemented by creating a forwarding (with static dispatch) the
 * implementing method on implementing classes to an the default method in an interface (which is
 * modeled as an instance method). JavaScript lacks the notion of interfaces and GWT consequently
 * does not generate prototypes nor instance method for interfaces. Due to that fact this pass
 * devirtualizes the default methods into static interface methods.
 * <p>
 * This devirtualization could also be handled by Devirtualizer.
 */
public class DevirtualizeDefaultMethodForwarding {

  public static void exec(final JProgram program) {
    final MakeCallsStatic.CreateStaticImplsVisitor staticImplCreator =
        new MakeCallsStatic.CreateStaticImplsVisitor(program);
    // 1. create the static implementations. Also process reference only types so that the mapping
    // between a method and its devirtualized version is consistent during incremental compilation.
    // NOTE: the process needs to be done in two steps because the creation of static implementation
    // might introduce call sites in types that were already processed and hence would not be
    // rewritten (bug #9453).
    for (JDeclaredType type : program.getDeclaredTypes()) {
      // Iterate over the methods using a copy to avoid ConcurrentModificationException as the
      // the devirualized method is added to the type following the current method.
      for (JMethod method : ImmutableList.copyOf(type.getMethods())) {
        if (method.isDefaultMethod()) {
          staticImplCreator.getOrCreateStaticImpl(program, method);
        }
      }
    }

    // 2. Devirtualize (static dispatch) calls to the default method.
    new JModVisitor() {
      @Override
      public void endVisit(JMethodCall x, Context ctx) {
        JMethod targetMethod = x.getTarget();
        if (targetMethod.isDefaultMethod() && x.isStaticDispatchOnly()) {
          assert x.getInstance() != null;

          JMethod staticMethod = program.getStaticImpl(targetMethod);
          assert staticMethod != null;
          // Need to devirtualize because instance methods are not  emitted for interfaces.
          JMethodCall callStaticMethod = new JMethodCall(x.getSourceInfo(), null, staticMethod);
          // Add the qualifier as a first parameter (usually 'this', unless the enclosing method was
          // devirtualized first).
          callStaticMethod.addArg(x.getInstance());
          callStaticMethod.addArgs(x.getArgs());
          ctx.replaceMe(callStaticMethod);
        }
      }
    }.accept(program);
  }
}