/*
 * Copyright 2008 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.SourceInfo;
import com.google.gwt.dev.jjs.SourceOrigin;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JClassType;
import com.google.gwt.dev.jjs.ast.JConditional;
import com.google.gwt.dev.jjs.ast.JDeclaredType;
import com.google.gwt.dev.jjs.ast.JLocal;
import com.google.gwt.dev.jjs.ast.JLocalRef;
import com.google.gwt.dev.jjs.ast.JMethod;
import com.google.gwt.dev.jjs.ast.JMethodBody;
import com.google.gwt.dev.jjs.ast.JMethodCall;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JParameter;
import com.google.gwt.dev.jjs.ast.JParameterRef;
import com.google.gwt.dev.jjs.ast.JProgram;
import com.google.gwt.dev.jjs.ast.JReturnStatement;
import com.google.gwt.dev.jjs.ast.JType;
import com.google.gwt.dev.jjs.ast.JTypeOracle;
import com.google.gwt.dev.jjs.ast.js.JMultiExpression;
import com.google.gwt.dev.jjs.impl.MakeCallsStatic.CreateStaticImplsVisitor;

import java.util.HashMap;
import java.util.Map;

/**
 * All call sites that might result in virtual dispatch to a JSO must be
 * rewritten to force static dispatch. This transform may NOT be run multiple
 * times; it will create ever-expanding replacement expressions.
 */
public class JsoDevirtualizer {

  /**
   * Rewrite any virtual dispatches to Object or JavaScriptObject such that
   * dispatch occurs statically for JSOs.
   */
  private class RewriteVirtualDispatches extends JModVisitor {

    /**
     * A method call at this point can be one of 5 things:
     * <ol>
     * <li>a dual dispatch interface</li>
     * <li>a single dispatch trough single-jso interface</li>
     * <li>a java.lang.Object override from JavaScriptObject</li>
     * <li>a regular dispatch (no JSOs involved or static JSO call)</li>
     * <li>in draftMode, a 'static' virtual JSO call that hasn't been made
     * static yet.</li>
     * </ol>
     */
    @Override
    public void endVisit(JMethodCall x, Context ctx) {
      JMethod method = x.getTarget();
      JMethod newMethod;
      JDeclaredType targetType = method.getEnclosingType();

      if (targetType == null) {
        return;
      }
      if (!method.needsVtable()) {
        return;
      }

      JType instanceType = x.getInstance().getType();
      // if the instance can't possibly be a JSO, don't devirtualize
      if (instanceType != program.getTypeJavaLangObject()
          && !program.typeOracle.canBeJavaScriptObject(instanceType)) {
        return;
      }

      if (polyMethodToJsoMethod.containsKey(method)) {
        // already did this one before
        newMethod = polyMethodToJsoMethod.get(method);
      } else if (program.typeOracle.isDualJsoInterface(targetType)) {
        JMethod overridingMethod =
            findOverridingMethod(method, program.typeOracle.getSingleJsoImpl(targetType));
        assert overridingMethod != null;

        JMethod jsoStaticImpl = getStaticImpl(overridingMethod);
        newMethod = getOrCreateDevirtualMethod(x, jsoStaticImpl);
        polyMethodToJsoMethod.put(method, newMethod);
      } else if (program.isJavaScriptObject(targetType)) {
        // It's a virtual JSO dispatch, usually occurs in draftCompile
        newMethod = getStaticImpl(method);
        polyMethodToJsoMethod.put(method, newMethod);
      } else if (program.typeOracle.isSingleJsoImpl(targetType)) {
        // interface dispatch with single implementing JSO concrete type
        JMethod overridingMethod =
            findOverridingMethod(method, program.typeOracle.getSingleJsoImpl(targetType));
        assert overridingMethod != null;
        newMethod = getStaticImpl(overridingMethod);
        polyMethodToJsoMethod.put(method, newMethod);
      } else if (targetType == program.getTypeJavaLangObject()) {
        // it's a java.lang.Object overriden method in JSO
        JMethod overridingMethod = findOverridingMethod(method, program.getJavaScriptObject());
        if (overridingMethod != null) {
          JMethod jsoStaticImpl = getStaticImpl(overridingMethod);
          newMethod = getOrCreateDevirtualMethod(x, jsoStaticImpl);
          polyMethodToJsoMethod.put(method, newMethod);
        } else {
          // else this method isn't overriden by JavaScriptObject
          assert false : "Object method not overriden by JavaScriptObject";
          return;
        }
      } else {
        return;
      }
      assert (newMethod != null);
      ctx.replaceMe(MakeCallsStatic.makeStaticCall(x, newMethod));
    }

    @Override
    public boolean visit(JMethod x, Context ctx) {
      // Don't rewrite the polymorphic call inside of the devirtualizing method!
      if (polyMethodToDevirtualMethods.containsValue(x)) {
        return false;
      }
      return true;
    }
  }

  public static void exec(JProgram program) {
    new JsoDevirtualizer(program).execImpl();
  }

  /**
   * Maps each Object instance methods (ie, {@link Object#equals(Object)}) onto
   * its corresponding devirtualizing method.
   */
  protected Map<JMethod, JMethod> polyMethodToJsoMethod = new HashMap<JMethod, JMethod>();

  /**
   * Contains the Cast.isJavaObject method.
   */
  private final JMethod isJavaObjectMethod;

  /**
   * Contains the set of devirtualizing methods that replace polymorphic calls
   * to Object methods.
   */
  private final Map<JMethod, JMethod> polyMethodToDevirtualMethods =
      new HashMap<JMethod, JMethod>();

  private final JProgram program;

  private final CreateStaticImplsVisitor staticImplCreator;

  private JsoDevirtualizer(JProgram program) {
    this.program = program;
    this.isJavaObjectMethod = program.getIndexedMethod("Cast.isJavaObject");
    staticImplCreator = new CreateStaticImplsVisitor(program);
  }

  private void execImpl() {
    JClassType jsoType = program.getJavaScriptObject();
    if (jsoType == null) {
      return;
    }

    RewriteVirtualDispatches rewriter = new RewriteVirtualDispatches();
    rewriter.accept(program);
    assert (rewriter.didChange());
  }

  /**
   * Finds the method that overrides this method, starting with the target
   * class.
   */
  private JMethod findOverridingMethod(JMethod method, JClassType target) {
    if (target == null) {
      return null;
    }
    for (JMethod overridingMethod : target.getMethods()) {
      if (JTypeOracle.methodsDoMatch(method, overridingMethod)) {
        return overridingMethod;
      }
    }
    return findOverridingMethod(method, target.getSuperClass());
  }

  /**
   * Create a conditional method to discriminate between static and virtual
   * dispatch.
   * 
   * <pre>
    * static boolean equals__devirtual$(Object this, Object other) {
    *   return Cast.isJavaObject(this) ? this.equals(other) : JavaScriptObject.equals$(this, other);
    * }
    * </pre>
   */
  private JMethod getOrCreateDevirtualMethod(JMethodCall polyMethodCall, JMethod jsoImpl) {
    JMethod polyMethod = polyMethodCall.getTarget();
    /**
     * TODO(cromwellian) generate a inlined expression instead of Method Because
     * devirtualization happens after optimization, the devirtual methods don't
     * optimize well in the JS pass. Consider "inlining" a hand optimized
     * devirtual method at callsites instead of a JMethodCall. As a bonus, the
     * inlined code can be specialized for each callsite, for example, if there
     * are no side effects, then there's no need for a temporary. Or, if the
     * instance can't possibly be java.lang.String, then the JSO check becomes a
     * cheaper check for typeMarker.
     */
    if (polyMethodToDevirtualMethods.containsKey(polyMethod)) {
      return polyMethodToDevirtualMethods.get(polyMethod);
    }

    JClassType jsoType = program.getJavaScriptObject();
    SourceInfo sourceInfo = jsoType.getSourceInfo().makeChild(SourceOrigin.UNKNOWN);

    // Create the new method.
    String name = polyMethod.getName() + "__devirtual$";
    JMethod newMethod =
        program.createMethod(sourceInfo, name, jsoType, polyMethod.getType(), false, true, true,
            false, false);
    newMethod.setSynthetic();

    // Setup parameters.
    JParameter thisParam =
        JProgram.createParameter(sourceInfo, "this$static", program.getTypeJavaLangObject(), true,
            true, newMethod);
    for (JParameter oldParam : polyMethod.getParams()) {
      JProgram.createParameter(sourceInfo, oldParam.getName(), oldParam.getType(), true, false,
          newMethod);
    }
    newMethod.freezeParamTypes();
    newMethod.addThrownExceptions(polyMethod.getThrownExceptions());
    sourceInfo.addCorrelation(sourceInfo.getCorrelator().by(newMethod));

    // maybeJsoInvocation = this$static
    JLocal temp =
        JProgram.createLocal(sourceInfo, "maybeJsoInvocation", thisParam.getType(), true,
            (JMethodBody) newMethod.getBody());
    JMultiExpression multi = new JMultiExpression(sourceInfo);

    // (maybeJsoInvocation = this$static, )
    multi.exprs.add(JProgram.createAssignmentStmt(sourceInfo, new JLocalRef(sourceInfo, temp),
        new JParameterRef(sourceInfo, thisParam)).getExpr());

    // Build from bottom up.
    // isJavaObject(temp)
    JMethodCall condition = new JMethodCall(sourceInfo, null, isJavaObjectMethod);
    condition.addArg(new JLocalRef(sourceInfo, temp));

    // temp.method(args)
    JMethodCall thenValue =
        new JMethodCall(sourceInfo, new JLocalRef(sourceInfo, temp), polyMethod);
    for (JParameter param : newMethod.getParams()) {
      if (param != thisParam) {
        thenValue.addArg(new JParameterRef(sourceInfo, param));
      }
    }

    // jso$method(temp, args)
    JMethodCall elseValue = new JMethodCall(sourceInfo, null, jsoImpl);
    elseValue.addArg(new JLocalRef(sourceInfo, temp));
    for (JParameter param : newMethod.getParams()) {
      if (param != thisParam) {
        elseValue.addArg(new JParameterRef(sourceInfo, param));
      }
    }

    // isJavaObject(temp) ? temp.method(args) : jso$method(temp, args)
    JConditional conditional =
        new JConditional(sourceInfo, polyMethod.getType(), condition, thenValue, elseValue);

    multi.exprs.add(conditional);

    JReturnStatement returnStatement = new JReturnStatement(sourceInfo, multi);
    ((JMethodBody) newMethod.getBody()).getBlock().addStmt(returnStatement);
    polyMethodToDevirtualMethods.put(polyMethod, newMethod);

    return newMethod;
  }

  private JMethod getStaticImpl(JMethod method) {
    assert !method.isStatic();
    JMethod staticImpl = program.getStaticImpl(method);
    if (staticImpl == null) {
      staticImplCreator.accept(method);
      staticImpl = program.getStaticImpl(method);
    }
    return staticImpl;
  }
}