// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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//
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package org.eclipse.persistence.internal.libraries.asm.commons;

import java.io.ByteArrayOutputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

import org.eclipse.persistence.internal.libraries.asm.ClassVisitor;
import org.eclipse.persistence.internal.libraries.asm.FieldVisitor;
import org.eclipse.persistence.internal.libraries.asm.MethodVisitor;
import org.eclipse.persistence.internal.libraries.asm.Opcodes;

/**
 * A {@link ClassVisitor} that adds a serial version unique identifier to a class if missing. Here
 * is typical usage of this class:
 *
 * <pre>
 *   ClassWriter cw = new ClassWriter(...);
 *   ClassVisitor sv = new SerialVersionUIDAdder(cw);
 *   ClassVisitor ca = new MyClassAdapter(sv);
 *   new ClassReader(orginalClass).accept(ca, false);
 * </pre>
 *
 * The SVUID algorithm can be found <a href=
 * "http://java.sun.com/j2se/1.4.2/docs/guide/serialization/spec/class.html"
 * >http://java.sun.com/j2se/1.4.2/docs/guide/serialization/spec/class.html</a>:
 *
 * <pre>
 * The serialVersionUID is computed using the signature of a stream of bytes
 * that reflect the class definition. The National Institute of Standards and
 * Technology (NIST) Secure Hash Algorithm (SHA-1) is used to compute a
 * signature for the stream. The first two 32-bit quantities are used to form a
 * 64-bit hash. A java.lang.DataOutputStream is used to convert primitive data
 * types to a sequence of bytes. The values input to the stream are defined by
 * the Java Virtual Machine (VM) specification for classes.
 *
 * The sequence of items in the stream is as follows:
 *
 * 1. The class name written using UTF encoding.
 * 2. The class modifiers written as a 32-bit integer.
 * 3. The name of each interface sorted by name written using UTF encoding.
 * 4. For each field of the class sorted by field name (except private static
 * and private transient fields):
 * 1. The name of the field in UTF encoding.
 * 2. The modifiers of the field written as a 32-bit integer.
 * 3. The descriptor of the field in UTF encoding
 * 5. If a class initializer exists, write out the following:
 * 1. The name of the method, &lt;clinit&gt;, in UTF encoding.
 * 2. The modifier of the method, java.lang.reflect.Modifier.STATIC,
 * written as a 32-bit integer.
 * 3. The descriptor of the method, ()V, in UTF encoding.
 * 6. For each non-private constructor sorted by method name and signature:
 * 1. The name of the method, &lt;init&gt;, in UTF encoding.
 * 2. The modifiers of the method written as a 32-bit integer.
 * 3. The descriptor of the method in UTF encoding.
 * 7. For each non-private method sorted by method name and signature:
 * 1. The name of the method in UTF encoding.
 * 2. The modifiers of the method written as a 32-bit integer.
 * 3. The descriptor of the method in UTF encoding.
 * 8. The SHA-1 algorithm is executed on the stream of bytes produced by
 * DataOutputStream and produces five 32-bit values sha[0..4].
 *
 * 9. The hash value is assembled from the first and second 32-bit values of
 * the SHA-1 message digest. If the result of the message digest, the five
 * 32-bit words H0 H1 H2 H3 H4, is in an array of five int values named
 * sha, the hash value would be computed as follows:
 *
 * long hash = ((sha[0] &gt;&gt;&gt; 24) &amp; 0xFF) |
 * ((sha[0] &gt;&gt;&gt; 16) &amp; 0xFF) &lt;&lt; 8 |
 * ((sha[0] &gt;&gt;&gt; 8) &amp; 0xFF) &lt;&lt; 16 |
 * ((sha[0] &gt;&gt;&gt; 0) &amp; 0xFF) &lt;&lt; 24 |
 * ((sha[1] &gt;&gt;&gt; 24) &amp; 0xFF) &lt;&lt; 32 |
 * ((sha[1] &gt;&gt;&gt; 16) &amp; 0xFF) &lt;&lt; 40 |
 * ((sha[1] &gt;&gt;&gt; 8) &amp; 0xFF) &lt;&lt; 48 |
 * ((sha[1] &gt;&gt;&gt; 0) &amp; 0xFF) &lt;&lt; 56;
 * </pre>
 *
 * @author Rajendra Inamdar, Vishal Vishnoi
 */
public class SerialVersionUIDAdder extends ClassVisitor {

  /** Flag that indicates if we need to compute SVUID. */
  private boolean computeSVUID;

  /** Set to true if the class already has SVUID. */
  private boolean hasSVUID;

  /** Classes access flags. */
  private int access;

  /** Internal name of the class */
  private String name;

  /** Interfaces implemented by the class. */
  private String[] interfaces;

  /** Collection of fields. (except private static and private transient fields) */
  private Collection<Item> svuidFields;

  /** Set to true if the class has static initializer. */
  private boolean hasStaticInitializer;

  /** Collection of non-private constructors. */
  private Collection<Item> svuidConstructors;

  /** Collection of non-private methods. */
  private Collection<Item> svuidMethods;

  /**
   * Constructs a new {@link SerialVersionUIDAdder}. <i>Subclasses must not use this constructor</i>.
   * Instead, they must use the {@link #SerialVersionUIDAdder(int, ClassVisitor)} version.
   *
   * @param cv a {@link ClassVisitor} to which this visitor will delegate calls.
   * @throws IllegalStateException If a subclass calls this constructor.
   */
  public SerialVersionUIDAdder(final ClassVisitor cv) {
    this(Opcodes.ASM6, cv);
    if (getClass() != SerialVersionUIDAdder.class) {
      throw new IllegalStateException();
    }
  }

  /**
   * Constructs a new {@link SerialVersionUIDAdder}.
   *
   * @param api the ASM API version implemented by this visitor. Must be one of {@link
   *     Opcodes#ASM4}, {@link Opcodes#ASM5} or {@link Opcodes#ASM6}.
   * @param cv a {@link ClassVisitor} to which this visitor will delegate calls.
   */
  protected SerialVersionUIDAdder(final int api, final ClassVisitor cv) {
    super(api, cv);
    svuidFields = new ArrayList<Item>();
    svuidConstructors = new ArrayList<Item>();
    svuidMethods = new ArrayList<Item>();
  }

  // ------------------------------------------------------------------------
  // Overridden methods
  // ------------------------------------------------------------------------

  /*
   * Visit class header and get class name, access , and interfaces
   * information (step 1,2, and 3) for SVUID computation.
   */
  @Override
  public void visit(
      final int version,
      final int access,
      final String name,
      final String signature,
      final String superName,
      final String[] interfaces) {
    computeSVUID = (access & Opcodes.ACC_ENUM) == 0;

    if (computeSVUID) {
      this.name = name;
      this.access = access;
      this.interfaces = new String[interfaces.length];
      System.arraycopy(interfaces, 0, this.interfaces, 0, interfaces.length);
    }

    super.visit(version, access, name, signature, superName, interfaces);
  }

  /*
   * Visit the methods and get constructor and method information (step 5 and
   * 7). Also determine if there is a class initializer (step 6).
   */
  @Override
  public MethodVisitor visitMethod(
      final int access,
      final String name,
      final String desc,
      final String signature,
      final String[] exceptions) {
    if (computeSVUID) {
      if ("<clinit>".equals(name)) {
        hasStaticInitializer = true;
      }
      /*
       * Remembers non private constructors and methods for SVUID
       * computation For constructor and method modifiers, only the
       * ACC_PUBLIC, ACC_PRIVATE, ACC_PROTECTED, ACC_STATIC, ACC_FINAL,
       * ACC_SYNCHRONIZED, ACC_NATIVE, ACC_ABSTRACT and ACC_STRICT flags
       * are used.
       */
      int mods =
          access
              & (Opcodes.ACC_PUBLIC
                  | Opcodes.ACC_PRIVATE
                  | Opcodes.ACC_PROTECTED
                  | Opcodes.ACC_STATIC
                  | Opcodes.ACC_FINAL
                  | Opcodes.ACC_SYNCHRONIZED
                  | Opcodes.ACC_NATIVE
                  | Opcodes.ACC_ABSTRACT
                  | Opcodes.ACC_STRICT);

      // all non private methods
      if ((access & Opcodes.ACC_PRIVATE) == 0) {
        if ("<init>".equals(name)) {
          svuidConstructors.add(new Item(name, mods, desc));
        } else if (!"<clinit>".equals(name)) {
          svuidMethods.add(new Item(name, mods, desc));
        }
      }
    }

    return super.visitMethod(access, name, desc, signature, exceptions);
  }

  /*
   * Gets class field information for step 4 of the algorithm. Also determines
   * if the class already has a SVUID.
   */
  @Override
  public FieldVisitor visitField(
      final int access,
      final String name,
      final String desc,
      final String signature,
      final Object value) {
    if (computeSVUID) {
      if ("serialVersionUID".equals(name)) {
        // since the class already has SVUID, we won't be computing it.
        computeSVUID = false;
        hasSVUID = true;
      }
      /*
       * Remember field for SVUID computation For field modifiers, only
       * the ACC_PUBLIC, ACC_PRIVATE, ACC_PROTECTED, ACC_STATIC,
       * ACC_FINAL, ACC_VOLATILE, and ACC_TRANSIENT flags are used when
       * computing serialVersionUID values.
       */
      if ((access & Opcodes.ACC_PRIVATE) == 0
          || (access & (Opcodes.ACC_STATIC | Opcodes.ACC_TRANSIENT)) == 0) {
        int mods =
            access
                & (Opcodes.ACC_PUBLIC
                    | Opcodes.ACC_PRIVATE
                    | Opcodes.ACC_PROTECTED
                    | Opcodes.ACC_STATIC
                    | Opcodes.ACC_FINAL
                    | Opcodes.ACC_VOLATILE
                    | Opcodes.ACC_TRANSIENT);
        svuidFields.add(new Item(name, mods, desc));
      }
    }

    return super.visitField(access, name, desc, signature, value);
  }

  /**
   * Handle a bizarre special case. Nested classes (static classes declared inside another class)
   * that are protected have their access bit set to public in their class files to deal with some
   * odd reflection situation. Our SVUID computation must do as the JVM does and ignore access bits
   * in the class file in favor of the access bits InnerClass attribute.
   */
  @Override
  public void visitInnerClass(
      final String aname, final String outerName, final String innerName, final int attr_access) {
    if ((name != null) && name.equals(aname)) {
      this.access = attr_access;
    }
    super.visitInnerClass(aname, outerName, innerName, attr_access);
  }

  /*
   * Add the SVUID if class doesn't have one
   */
  @Override
  public void visitEnd() {
    // compute SVUID and add it to the class
    if (computeSVUID && !hasSVUID) {
      try {
        addSVUID(computeSVUID());
      } catch (Throwable e) {
        throw new RuntimeException("Error while computing SVUID for " + name, e);
      }
    }

    super.visitEnd();
  }

  // ------------------------------------------------------------------------
  // Utility methods
  // ------------------------------------------------------------------------

  /**
   * Returns true if the class already has a SVUID field. The result of this method is only valid
   * when visitEnd is or has been called.
   *
   * @return true if the class already has a SVUID field.
   */
  public boolean hasSVUID() {
    return hasSVUID;
  }

  protected void addSVUID(long svuid) {
    FieldVisitor fv =
        super.visitField(
            Opcodes.ACC_FINAL + Opcodes.ACC_STATIC, "serialVersionUID", "J", null, svuid);
    if (fv != null) {
      fv.visitEnd();
    }
  }

  /**
   * Computes and returns the value of SVUID.
   *
   * @return Returns the serial version UID
   * @throws IOException if an I/O error occurs
   */
  protected long computeSVUID() throws IOException {
    ByteArrayOutputStream bos;
    DataOutputStream dos = null;
    long svuid = 0;

    try {
      bos = new ByteArrayOutputStream();
      dos = new DataOutputStream(bos);

      /*
       * 1. The class name written using UTF encoding.
       */
      dos.writeUTF(name.replace('/', '.'));

      /*
       * 2. The class modifiers written as a 32-bit integer.
       */
      int access = this.access;
      if ((access & Opcodes.ACC_INTERFACE) != 0) {
        access =
            (svuidMethods.size() > 0)
                ? (access | Opcodes.ACC_ABSTRACT)
                : (access & ~Opcodes.ACC_ABSTRACT);
      }
      dos.writeInt(
          access
              & (Opcodes.ACC_PUBLIC
                  | Opcodes.ACC_FINAL
                  | Opcodes.ACC_INTERFACE
                  | Opcodes.ACC_ABSTRACT));

      /*
       * 3. The name of each interface sorted by name written using UTF
       * encoding.
       */
      Arrays.sort(interfaces);
      for (int i = 0; i < interfaces.length; i++) {
        dos.writeUTF(interfaces[i].replace('/', '.'));
      }

      /*
       * 4. For each field of the class sorted by field name (except
       * private static and private transient fields):
       *
       * 1. The name of the field in UTF encoding. 2. The modifiers of the
       * field written as a 32-bit integer. 3. The descriptor of the field
       * in UTF encoding
       *
       * Note that field signatures are not dot separated. Method and
       * constructor signatures are dot separated. Go figure...
       */
      writeItems(svuidFields, dos, false);

      /*
       * 5. If a class initializer exists, write out the following: 1. The
       * name of the method, <clinit>, in UTF encoding. 2. The modifier of
       * the method, java.lang.reflect.Modifier.STATIC, written as a
       * 32-bit integer. 3. The descriptor of the method, ()V, in UTF
       * encoding.
       */
      if (hasStaticInitializer) {
        dos.writeUTF("<clinit>");
        dos.writeInt(Opcodes.ACC_STATIC);
        dos.writeUTF("()V");
      } // if..

      /*
       * 6. For each non-private constructor sorted by method name and
       * signature: 1. The name of the method, <init>, in UTF encoding. 2.
       * The modifiers of the method written as a 32-bit integer. 3. The
       * descriptor of the method in UTF encoding.
       */
      writeItems(svuidConstructors, dos, true);

      /*
       * 7. For each non-private method sorted by method name and
       * signature: 1. The name of the method in UTF encoding. 2. The
       * modifiers of the method written as a 32-bit integer. 3. The
       * descriptor of the method in UTF encoding.
       */
      writeItems(svuidMethods, dos, true);

      dos.flush();

      /*
       * 8. The SHA-1 algorithm is executed on the stream of bytes
       * produced by DataOutputStream and produces five 32-bit values
       * sha[0..4].
       */
      byte[] hashBytes = computeSHAdigest(bos.toByteArray());

      /*
       * 9. The hash value is assembled from the first and second 32-bit
       * values of the SHA-1 message digest. If the result of the message
       * digest, the five 32-bit words H0 H1 H2 H3 H4, is in an array of
       * five int values named sha, the hash value would be computed as
       * follows:
       *
       * long hash = ((sha[0] >>> 24) & 0xFF) | ((sha[0] >>> 16) & 0xFF)
       * << 8 | ((sha[0] >>> 8) & 0xFF) << 16 | ((sha[0] >>> 0) & 0xFF) <<
       * 24 | ((sha[1] >>> 24) & 0xFF) << 32 | ((sha[1] >>> 16) & 0xFF) <<
       * 40 | ((sha[1] >>> 8) & 0xFF) << 48 | ((sha[1] >>> 0) & 0xFF) <<
       * 56;
       */
      for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
        svuid = (svuid << 8) | (hashBytes[i] & 0xFF);
      }
    } finally {
      // close the stream (if open)
      if (dos != null) {
        dos.close();
      }
    }

    return svuid;
  }

  /**
   * Returns the SHA-1 message digest of the given value.
   *
   * @param value the value whose SHA message digest must be computed.
   * @return the SHA-1 message digest of the given value.
   */
  protected byte[] computeSHAdigest(final byte[] value) {
    try {
      return MessageDigest.getInstance("SHA").digest(value);
    } catch (Exception e) {
      throw new UnsupportedOperationException(e.toString());
    }
  }

  /**
   * Sorts the items in the collection and writes it to the data output stream
   *
   * @param itemCollection collection of items
   * @param dos a <code>DataOutputStream</code> value
   * @param dotted a <code>boolean</code> value
   * @exception IOException if an error occurs
   */
  private static void writeItems(
      final Collection<Item> itemCollection, final DataOutput dos, final boolean dotted)
      throws IOException {
    int size = itemCollection.size();
    Item[] items = itemCollection.toArray(new Item[size]);
    Arrays.sort(items);
    for (int i = 0; i < size; i++) {
      dos.writeUTF(items[i].name);
      dos.writeInt(items[i].access);
      dos.writeUTF(dotted ? items[i].desc.replace('/', '.') : items[i].desc);
    }
  }

  // ------------------------------------------------------------------------
  // Inner classes
  // ------------------------------------------------------------------------

  private static class Item implements Comparable<Item> {

    final String name;

    final int access;

    final String desc;

    Item(final String name, final int access, final String desc) {
      this.name = name;
      this.access = access;
      this.desc = desc;
    }

    public int compareTo(final Item other) {
      int retVal = name.compareTo(other.name);
      if (retVal == 0) {
        retVal = desc.compareTo(other.desc);
      }
      return retVal;
    }

    @Override
    public boolean equals(final Object o) {
      if (o instanceof Item) {
        return compareTo((Item) o) == 0;
      }
      return false;
    }

    @Override
    public int hashCode() {
      return (name + desc).hashCode();
    }
  }
}
