// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
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// modification, are permitted provided that the following conditions
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//    notice, this list of conditions and the following disclaimer in the
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//    this software without specific prior written permission.
//
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package io.ebean.enhance.asm.commons;

import io.ebean.enhance.asm.AnnotationVisitor;
import io.ebean.enhance.asm.Label;
import io.ebean.enhance.asm.MethodVisitor;
import io.ebean.enhance.asm.Opcodes;
import io.ebean.enhance.asm.Type;
import io.ebean.enhance.asm.TypePath;

/**
 * A {@link MethodVisitor} that renumbers local variables in their order of appearance. This adapter
 * allows one to easily add new local variables to a method. It may be used by inheriting from this
 * class, but the preferred way of using it is via delegation: the next visitor in the chain can
 * indeed add new locals when needed by calling {@link #newLocal} on this adapter (this requires a
 * reference back to this {@link LocalVariablesSorter}).
 *
 * @author Chris Nokleberg
 * @author Eugene Kuleshov
 * @author Eric Bruneton
 */
public class LocalVariablesSorter extends MethodVisitor {

  /** The type of the java.lang.Object class. */
  private static final Type OBJECT_TYPE = Type.getObjectType("java/lang/Object");

  /**
   * The mapping from old to new local variable indices. A local variable at index i of size 1 is
   * remapped to 'mapping[2*i]', while a local variable at index i of size 2 is remapped to
   * 'mapping[2*i+1]'.
   */
  private int[] remappedVariableIndices = new int[40];

  /**
   * The local variable types after remapping. The format of this array is the same as in {@link
   * MethodVisitor#visitFrame}, except that long and double types use two slots.
   */
  private Object[] remappedLocalTypes = new Object[20];

  /** The index of the first local variable, after formal parameters. */
  protected final int firstLocal;

  /** The index of the next local variable to be created by {@link #newLocal}. */
  protected int nextLocal;

  /**
   * Constructs a new {@link LocalVariablesSorter}. <i>Subclasses must not use this constructor</i>.
   * Instead, they must use the {@link #LocalVariablesSorter(int, int, String, MethodVisitor)}
   * version.
   *
   * @param access access flags of the adapted method.
   * @param descriptor the method's descriptor (see {@link Type}).
   * @param methodVisitor the method visitor to which this adapter delegates calls.
   * @throws IllegalStateException if a subclass calls this constructor.
   */
  public LocalVariablesSorter(
      final int access, final String descriptor, final MethodVisitor methodVisitor) {
    this(/* latest api = */ Opcodes.ASM9, access, descriptor, methodVisitor);
    if (getClass() != LocalVariablesSorter.class) {
      throw new IllegalStateException();
    }
  }

  /**
   * Constructs a new {@link LocalVariablesSorter}.
   *
   * @param api the ASM API version implemented by this visitor. Must be one of the {@code
   *     ASM}<i>x</i> values in {@link Opcodes}.
   * @param access access flags of the adapted method.
   * @param descriptor the method's descriptor (see {@link Type}).
   * @param methodVisitor the method visitor to which this adapter delegates calls.
   */
  protected LocalVariablesSorter(
      final int api, final int access, final String descriptor, final MethodVisitor methodVisitor) {
    super(api, methodVisitor);
    nextLocal = (Opcodes.ACC_STATIC & access) == 0 ? 1 : 0;
    for (Type argumentType : Type.getArgumentTypes(descriptor)) {
      nextLocal += argumentType.getSize();
    }
    firstLocal = nextLocal;
  }

  @Override
  public void visitVarInsn(final int opcode, final int varIndex) {
    Type varType;
    switch (opcode) {
      case Opcodes.LLOAD:
      case Opcodes.LSTORE:
        varType = Type.LONG_TYPE;
        break;
      case Opcodes.DLOAD:
      case Opcodes.DSTORE:
        varType = Type.DOUBLE_TYPE;
        break;
      case Opcodes.FLOAD:
      case Opcodes.FSTORE:
        varType = Type.FLOAT_TYPE;
        break;
      case Opcodes.ILOAD:
      case Opcodes.ISTORE:
        varType = Type.INT_TYPE;
        break;
      case Opcodes.ALOAD:
      case Opcodes.ASTORE:
      case Opcodes.RET:
        varType = OBJECT_TYPE;
        break;
      default:
        throw new IllegalArgumentException("Invalid opcode " + opcode);
    }
    super.visitVarInsn(opcode, remap(varIndex, varType));
  }

  @Override
  public void visitIincInsn(final int varIndex, final int increment) {
    super.visitIincInsn(remap(varIndex, Type.INT_TYPE), increment);
  }

  @Override
  public void visitMaxs(final int maxStack, final int maxLocals) {
    super.visitMaxs(maxStack, nextLocal);
  }

  @Override
  public void visitLocalVariable(
      final String name,
      final String descriptor,
      final String signature,
      final Label start,
      final Label end,
      final int index) {
    int remappedIndex = remap(index, Type.getType(descriptor));
    super.visitLocalVariable(name, descriptor, signature, start, end, remappedIndex);
  }

  @Override
  public AnnotationVisitor visitLocalVariableAnnotation(
      final int typeRef,
      final TypePath typePath,
      final Label[] start,
      final Label[] end,
      final int[] index,
      final String descriptor,
      final boolean visible) {
    Type type = Type.getType(descriptor);
    int[] remappedIndex = new int[index.length];
    for (int i = 0; i < remappedIndex.length; ++i) {
      remappedIndex[i] = remap(index[i], type);
    }
    return super.visitLocalVariableAnnotation(
        typeRef, typePath, start, end, remappedIndex, descriptor, visible);
  }

  @Override
  public void visitFrame(
      final int type,
      final int numLocal,
      final Object[] local,
      final int numStack,
      final Object[] stack) {
    if (type != Opcodes.F_NEW) { // Uncompressed frame.
      throw new IllegalArgumentException(
          "LocalVariablesSorter only accepts expanded frames (see ClassReader.EXPAND_FRAMES)");
    }

    // Create a copy of remappedLocals.
    Object[] oldRemappedLocals = new Object[remappedLocalTypes.length];
    System.arraycopy(remappedLocalTypes, 0, oldRemappedLocals, 0, oldRemappedLocals.length);

    updateNewLocals(remappedLocalTypes);

    // Copy the types from 'local' to 'remappedLocals'. 'remappedLocals' already contains the
    // variables added with 'newLocal'.
    int oldVar = 0; // Old local variable index.
    for (int i = 0; i < numLocal; ++i) {
      Object localType = local[i];
      if (localType != Opcodes.TOP) {
        Type varType = OBJECT_TYPE;
        if (localType == Opcodes.INTEGER) {
          varType = Type.INT_TYPE;
        } else if (localType == Opcodes.FLOAT) {
          varType = Type.FLOAT_TYPE;
        } else if (localType == Opcodes.LONG) {
          varType = Type.LONG_TYPE;
        } else if (localType == Opcodes.DOUBLE) {
          varType = Type.DOUBLE_TYPE;
        } else if (localType instanceof String) {
          varType = Type.getObjectType((String) localType);
        }
        setFrameLocal(remap(oldVar, varType), localType);
      }
      oldVar += localType == Opcodes.LONG || localType == Opcodes.DOUBLE ? 2 : 1;
    }

    // Remove TOP after long and double types as well as trailing TOPs.
    oldVar = 0;
    int newVar = 0;
    int remappedNumLocal = 0;
    while (oldVar < remappedLocalTypes.length) {
      Object localType = remappedLocalTypes[oldVar];
      oldVar += localType == Opcodes.LONG || localType == Opcodes.DOUBLE ? 2 : 1;
      if (localType != null && localType != Opcodes.TOP) {
        remappedLocalTypes[newVar++] = localType;
        remappedNumLocal = newVar;
      } else {
        remappedLocalTypes[newVar++] = Opcodes.TOP;
      }
    }

    // Visit the remapped frame.
    super.visitFrame(type, remappedNumLocal, remappedLocalTypes, numStack, stack);

    // Restore the original value of 'remappedLocals'.
    remappedLocalTypes = oldRemappedLocals;
  }

  // -----------------------------------------------------------------------------------------------

  /**
   * Constructs a new local variable of the given type.
   *
   * @param type the type of the local variable to be created.
   * @return the identifier of the newly created local variable.
   */
  public int newLocal(final Type type) {
    Object localType;
    switch (type.getSort()) {
      case Type.BOOLEAN:
      case Type.CHAR:
      case Type.BYTE:
      case Type.SHORT:
      case Type.INT:
        localType = Opcodes.INTEGER;
        break;
      case Type.FLOAT:
        localType = Opcodes.FLOAT;
        break;
      case Type.LONG:
        localType = Opcodes.LONG;
        break;
      case Type.DOUBLE:
        localType = Opcodes.DOUBLE;
        break;
      case Type.ARRAY:
        localType = type.getDescriptor();
        break;
      case Type.OBJECT:
        localType = type.getInternalName();
        break;
      default:
        throw new AssertionError();
    }
    int local = newLocalMapping(type);
    setLocalType(local, type);
    setFrameLocal(local, localType);
    return local;
  }

  /**
   * Notifies subclasses that a new stack map frame is being visited. The array argument contains
   * the stack map frame types corresponding to the local variables added with {@link #newLocal}.
   * This method can update these types in place for the stack map frame being visited. The default
   * implementation of this method does nothing, i.e. a local variable added with {@link #newLocal}
   * will have the same type in all stack map frames. But this behavior is not always the desired
   * one, for instance if a local variable is added in the middle of a try/catch block: the frame
   * for the exception handler should have a TOP type for this new local.
   *
   * @param newLocals the stack map frame types corresponding to the local variables added with
   *     {@link #newLocal} (and null for the others). The format of this array is the same as in
   *     {@link MethodVisitor#visitFrame}, except that long and double types use two slots. The
   *     types for the current stack map frame must be updated in place in this array.
   */
  protected void updateNewLocals(final Object[] newLocals) {
    // The default implementation does nothing.
  }

  /**
   * Notifies subclasses that a local variable has been added or remapped. The default
   * implementation of this method does nothing.
   *
   * @param local a local variable identifier, as returned by {@link #newLocal}.
   * @param type the type of the value being stored in the local variable.
   */
  protected void setLocalType(final int local, final Type type) {
    // The default implementation does nothing.
  }

  private void setFrameLocal(final int local, final Object type) {
    int numLocals = remappedLocalTypes.length;
    if (local >= numLocals) {
      Object[] newRemappedLocalTypes = new Object[Math.max(2 * numLocals, local + 1)];
      System.arraycopy(remappedLocalTypes, 0, newRemappedLocalTypes, 0, numLocals);
      remappedLocalTypes = newRemappedLocalTypes;
    }
    remappedLocalTypes[local] = type;
  }

  private int remap(final int varIndex, final Type type) {
    if (varIndex + type.getSize() <= firstLocal) {
      return varIndex;
    }
    int key = 2 * varIndex + type.getSize() - 1;
    int size = remappedVariableIndices.length;
    if (key >= size) {
      int[] newRemappedVariableIndices = new int[Math.max(2 * size, key + 1)];
      System.arraycopy(remappedVariableIndices, 0, newRemappedVariableIndices, 0, size);
      remappedVariableIndices = newRemappedVariableIndices;
    }
    int value = remappedVariableIndices[key];
    if (value == 0) {
      value = newLocalMapping(type);
      setLocalType(value, type);
      remappedVariableIndices[key] = value + 1;
    } else {
      value--;
    }
    return value;
  }

  protected int newLocalMapping(final Type type) {
    int local = nextLocal;
    nextLocal += type.getSize();
    return local;
  }
}