/*
 * Copyright 2017 Google Inc. All Rights Reserved.
 *
 * 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.turbine.deps;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableList.Builder;
import com.google.common.collect.ImmutableMap;
import com.google.turbine.binder.Binder.BindingResult;
import com.google.turbine.binder.ClassPath;
import com.google.turbine.binder.bound.TypeBoundClass;
import com.google.turbine.binder.bytecode.BytecodeBoundClass;
import com.google.turbine.binder.env.CompoundEnv;
import com.google.turbine.binder.env.Env;
import com.google.turbine.binder.env.SimpleEnv;
import com.google.turbine.binder.sym.ClassSymbol;
import com.google.turbine.bytecode.ClassFile;
import com.google.turbine.bytecode.ClassFile.FieldInfo;
import com.google.turbine.bytecode.ClassFile.InnerClass;
import com.google.turbine.bytecode.ClassWriter;
import com.google.turbine.model.TurbineFlag;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * Collects the minimal compile-time API for symbols in the supertype closure of compiled classes.
 * This allows header compilations to be performed against a classpath containing only direct
 * dependencies and no transitive dependencies.
 */
public class Transitive {

  public static ImmutableMap<String, byte[]> collectDeps(
      ClassPath bootClassPath, BindingResult bound) {
    ImmutableMap.Builder<String, byte[]> transitive = ImmutableMap.builder();
    for (ClassSymbol sym : superClosure(bound)) {
      BytecodeBoundClass info = bound.classPathEnv().get(sym);
      if (info == null) {
        // the symbol wasn't loaded from the classpath
        continue;
      }
      if (bootClassPath.env().get(sym) != null) {
        // don't export symbols loaded from the bootclasspath
        continue;
      }
      transitive.put(sym.binaryName(), ClassWriter.writeClass(trimClass(info.classFile())));
    }
    return transitive.build();
  }

  /**
   * Removes information from repackaged classes that will not be needed by upstream compilations.
   */
  public static ClassFile trimClass(ClassFile cf) {
    // drop non-constant fields
    Builder<FieldInfo> fields = ImmutableList.builder();
    for (FieldInfo f : cf.fields()) {
      if (f.value() != null) {
        fields.add(f);
      }
    }
    // Remove InnerClass attributes that are unnecessary after pruning the types they refer to.
    // To do this for javac, we would have to scan all remaining signatures and preserve attributes
    // for reachable inner classes, but turbine only needs the attributes for the immediate
    // children or parent of the current class.
    Builder<InnerClass> innerClasses = ImmutableList.builder();
    for (InnerClass i : cf.innerClasses()) {
      if (i.innerClass().equals(cf.name()) || i.outerClass().equals(cf.name())) {
        innerClasses.add(i);
      }
    }
    return new ClassFile(
        cf.access(),
        cf.name(),
        cf.signature(),
        cf.superName(),
        cf.interfaces(),
        // drop methods, except for annotations where we need to resolve key/value information
        (cf.access() & TurbineFlag.ACC_ANNOTATION) == TurbineFlag.ACC_ANNOTATION
            ? cf.methods()
            : ImmutableList.of(),
        fields.build(),
        // unnecessary annotations are dropped during class reading, the only remaining ones are
        // well-known @interface meta-annotations (e.g. @Retention, etc.)
        cf.annotations(),
        innerClasses.build(),
        cf.typeAnnotations(),
        /* module= */ null);
  }

  private static Set<ClassSymbol> superClosure(BindingResult bound) {
    Env<ClassSymbol, TypeBoundClass> env =
        CompoundEnv.<ClassSymbol, TypeBoundClass>of(new SimpleEnv<>(bound.units()))
            .append(bound.classPathEnv());
    Set<ClassSymbol> closure = new LinkedHashSet<>();
    for (ClassSymbol sym : bound.units().keySet()) {
      addSuperTypes(closure, env, sym);
    }
    Set<ClassSymbol> directChildren = new LinkedHashSet<>();
    for (ClassSymbol sym : closure) {
      TypeBoundClass info = env.get(sym);
      if (info != null) {
        directChildren.addAll(info.children().values());
      }
    }
    closure.addAll(directChildren);
    return closure;
  }

  private static void addSuperTypes(
      Set<ClassSymbol> closure, Env<ClassSymbol, TypeBoundClass> env, ClassSymbol sym) {
    if (!closure.add(sym)) {
      return;
    }
    TypeBoundClass info = env.get(sym);
    if (info == null) {
      return;
    }
    if (info.superclass() != null) {
      addSuperTypes(closure, env, info.superclass());
    }
    for (ClassSymbol i : info.interfaces()) {
      addSuperTypes(closure, env, i);
    }
  }
}