// Copyright (c) 2019, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

package com.android.tools.r8.ir.optimize;

import com.android.tools.r8.contexts.CompilationContext.MethodProcessingContext;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexClass;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexItemFactory;
import com.android.tools.r8.graph.DexMethod;
import com.android.tools.r8.graph.DexProto;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.MethodAccessFlags;
import com.android.tools.r8.graph.ProgramMethod;
import com.android.tools.r8.ir.code.ConstClass;
import com.android.tools.r8.ir.code.IRCode;
import com.android.tools.r8.ir.code.Instruction;
import com.android.tools.r8.ir.code.InstructionListIterator;
import com.android.tools.r8.ir.code.InvokeStatic;
import com.android.tools.r8.ir.code.InvokeVirtual;
import com.android.tools.r8.ir.code.Value;
import com.android.tools.r8.ir.desugar.ServiceLoaderSourceCode;
import com.android.tools.r8.shaking.AppInfoWithLiveness;
import com.android.tools.r8.synthesis.SyntheticNaming.SyntheticKind;
import com.google.common.collect.ImmutableList;
import java.util.ArrayList;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;

/**
 * ServiceLoaderRewriter will attempt to rewrite calls on the form of: ServiceLoader.load(X.class,
 * X.class.getClassLoader()).iterator() ... to Arrays.asList(new X[] { new Y(), ..., new Z()
 * }).iterator() for classes Y..Z specified in the META-INF/services/X.
 *
 * <p>The reason for this optimization is to not have the ServiceLoader.load on the distributed R8
 * in AGP, since this can potentially conflict with debug versions added to a build.gradle file as:
 * classpath 'com.android.tools:r8:a.b.c' Additionally, it might also result in improved performance
 * because ServiceLoader.load is really slow on Android because it has to do a reflective lookup.
 *
 * <p>A call to ServiceLoader.load(X.class) is implicitly the same as ServiceLoader.load(X.class,
 * Thread.getContextClassLoader()) which can have different behavior in Android if a process host
 * multiple applications:
 *
 * <pre>
 * See <a href="https://stackoverflow.com/questions/13407006/android-class-loader-may-fail-for-
 * processes-that-host-multiple-applications">https://stackoverflow.com/questions/13407006/
 * android-class-loader-may-fail-for-processes-that-host-multiple-applications</a>
 * </pre>
 *
 * We therefore only conservatively rewrite if the invoke is on is on the form
 * ServiceLoader.load(X.class, X.class.getClassLoader()) or ServiceLoader.load(X.class, null).
 *
 * Android Nougat do not use ClassLoader.getSystemClassLoader() when passing null and will
 * almost certainly fail when trying to find the service. It seems unlikely that programs rely on
 * this behaviour.
 */
public class ServiceLoaderRewriter {

  private final AppView<AppInfoWithLiveness> appView;
  private final List<ProgramMethod> serviceLoadMethods = new ArrayList<>();

  public ServiceLoaderRewriter(AppView<AppInfoWithLiveness> appView) {
    this.appView = appView;
  }

  public List<ProgramMethod> getServiceLoadMethods() {
    return serviceLoadMethods;
  }

  public void rewrite(IRCode code, MethodProcessingContext methodProcessingContext) {
    DexItemFactory factory = appView.dexItemFactory();
    InstructionListIterator instructionIterator = code.instructionListIterator();
    // Create a map from service type to loader methods local to this context since two
    // service loader calls to the same type in different methods and in the same wave can race.
    Map<DexType, DexEncodedMethod> synthesizedServiceLoaders = new IdentityHashMap<>();
    while (instructionIterator.hasNext()) {
      Instruction instruction = instructionIterator.next();

      // Check if instruction is an invoke static on the desired form of ServiceLoader.load.
      if (!instruction.isInvokeStatic()
          || instruction.asInvokeStatic().getInvokedMethod()
              != factory.serviceLoaderMethods.loadWithClassLoader) {
        continue;
      }

      InvokeStatic serviceLoaderLoad = instruction.asInvokeStatic();
      Value serviceLoaderLoadOut = serviceLoaderLoad.outValue();
      if (serviceLoaderLoadOut.numberOfAllUsers() != 1 || serviceLoaderLoadOut.hasPhiUsers()) {
        continue;
      }

      // Check that the only user is a call to iterator().
      if (!serviceLoaderLoadOut.singleUniqueUser().isInvokeVirtual()
          || serviceLoaderLoadOut.singleUniqueUser().asInvokeVirtual().getInvokedMethod()
              != factory.serviceLoaderMethods.iterator) {
        continue;
      }

      // Check that the first argument is a const class.
      Value argument = serviceLoaderLoad.inValues().get(0).getAliasedValue();
      if (argument.isPhi() || !argument.definition.isConstClass()) {
        continue;
      }

      ConstClass constClass = argument.getConstInstruction().asConstClass();

      // Check that the service is not kept.
      if (appView.appInfo().isPinned(constClass.getValue())) {
        continue;
      }

      // Check that the service is configured in the META-INF/services.
      if (!appView.appServices().allServiceTypes().contains(constClass.getValue())) {
        // Error already reported in the Enqueuer.
        continue;
      }

      // Check that we are not service loading anything from a feature into base.
      if (appView
          .appServices()
          .hasServiceImplementationsInFeature(appView, constClass.getValue())) {
        continue;
      }

      // Check that ClassLoader used is the ClassLoader defined for the service configuration
      // that we are instantiating or NULL.
      if (serviceLoaderLoad.inValues().get(1).isPhi()) {
        continue;
      }
      InvokeVirtual classLoaderInvoke =
          serviceLoaderLoad.inValues().get(1).definition.asInvokeVirtual();
      boolean isGetClassLoaderOnConstClassOrNull =
          serviceLoaderLoad.inValues().get(1).getType().isNullType()
              || (classLoaderInvoke != null
                  && classLoaderInvoke.inValues().size() == 1
                  && classLoaderInvoke.getReceiver().getAliasedValue().isConstClass()
                  && classLoaderInvoke
                          .getReceiver()
                          .getAliasedValue()
                          .getConstInstruction()
                          .asConstClass()
                          .getValue()
                      == constClass.getValue());
      if (!isGetClassLoaderOnConstClassOrNull) {
        continue;
      }

      List<DexType> dexTypes =
          appView.appServices().serviceImplementationsFor(constClass.getValue());
      List<DexClass> classes = new ArrayList<>(dexTypes.size());
      boolean seenNull = false;
      for (DexType serviceImpl : dexTypes) {
        DexClass serviceImplClazz = appView.definitionFor(serviceImpl);
        if (serviceImplClazz == null) {
          seenNull = true;
        }
        classes.add(serviceImplClazz);
      }

      if (seenNull) {
        continue;
      }

      // We can perform the rewrite of the ServiceLoader.load call.
      DexEncodedMethod synthesizedMethod =
          synthesizedServiceLoaders.computeIfAbsent(
              constClass.getValue(),
              service -> {
                DexEncodedMethod addedMethod =
                    createSynthesizedMethod(service, classes, methodProcessingContext);
                if (appView.options().isGeneratingClassFiles()) {
                  addedMethod.upgradeClassFileVersion(code.method().getClassFileVersion());
                }
                return addedMethod;
              });

      new Rewriter(code, instructionIterator, serviceLoaderLoad)
          .perform(classLoaderInvoke, synthesizedMethod.method);
    }
  }

  private DexEncodedMethod createSynthesizedMethod(
      DexType serviceType,
      List<DexClass> classes,
      MethodProcessingContext methodProcessingContext) {
    DexProto proto = appView.dexItemFactory().createProto(appView.dexItemFactory().iteratorType);
    ProgramMethod method =
        appView
            .getSyntheticItems()
            .createMethod(
                SyntheticKind.SERVICE_LOADER,
                methodProcessingContext.createUniqueContext(),
                appView.dexItemFactory(),
                builder ->
                    builder
                        .setAccessFlags(MethodAccessFlags.createPublicStaticSynthetic())
                        .setProto(proto)
                        .setCode(
                            m ->
                                ServiceLoaderSourceCode.generate(
                                    serviceType, classes, appView.dexItemFactory())));
    synchronized (serviceLoadMethods) {
      serviceLoadMethods.add(method);
    }
    return method.getDefinition();
  }

  /**
   * Rewriter assumes that the code is of the form:
   *
   * <pre>
   * ConstClass         v1 <- X
   * ConstClass         v2 <- X or NULL
   * Invoke-Virtual     v3 <- v2; method: java.lang.ClassLoader java.lang.Class.getClassLoader()
   * Invoke-Static      v4 <- v1, v3; method: java.util.ServiceLoader java.util.ServiceLoader
   *     .load(java.lang.Class, java.lang.ClassLoader)
   * Invoke-Virtual     v5 <- v4; method: java.util.Iterator java.util.ServiceLoader.iterator()
   * </pre>
   *
   * and rewrites it to:
   *
   * <pre>
   * Invoke-Static      v5 <- ; method: java.util.Iterator syn(X)()
   * </pre>
   *
   * where syn(X) is the synthesized method generated for the service class.
   *
   * <p>We rely on the DeadCodeRemover to remove the ConstClasses and any aliased values no longer
   * used.
   */
  private static class Rewriter {

    private final IRCode code;
    private final InvokeStatic serviceLoaderLoad;

    private InstructionListIterator iterator;

    Rewriter(IRCode code, InstructionListIterator iterator, InvokeStatic serviceLoaderLoad) {
      this.iterator = iterator;
      this.code = code;
      this.serviceLoaderLoad = serviceLoaderLoad;
    }

    public void perform(InvokeVirtual classLoaderInvoke, DexMethod method) {
      // Remove the ClassLoader call since this can throw and will not be removed otherwise.
      if (classLoaderInvoke != null) {
        clearGetClassLoader(classLoaderInvoke);
        iterator.nextUntil(i -> i == serviceLoaderLoad);
      }

      // Remove the ServiceLoader.load call.
      InvokeVirtual serviceLoaderIterator =
          serviceLoaderLoad.outValue().singleUniqueUser().asInvokeVirtual();
      iterator.replaceCurrentInstruction(code.createConstNull());

      // Find the iterator instruction and replace it.
      iterator.nextUntil(x -> x == serviceLoaderIterator);
      InvokeStatic synthesizedInvoke =
          new InvokeStatic(method, serviceLoaderIterator.outValue(), ImmutableList.of());
      iterator.replaceCurrentInstruction(synthesizedInvoke);
    }

    private void clearGetClassLoader(InvokeVirtual classLoaderInvoke) {
      while (iterator.hasPrevious()) {
        Instruction instruction = iterator.previous();
        if (instruction == classLoaderInvoke) {
          iterator.replaceCurrentInstruction(code.createConstNull());
          break;
        }
      }
    }
  }
}