/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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
 *
 *      https://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 org.apache.tools.ant.filters;

import java.io.IOException;
import java.io.Reader;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.nio.charset.StandardCharsets;

import org.apache.tools.ant.BuildException;

Assembles the constants declared in a Java class in
key1=value1(line separator)key2=value2
format.
Notes:

This filter uses the BCEL external toolkit.
This assembles only those constants that are not created
using the syntax new whatever()
This assembles constants declared using the basic datatypes
and String only.
The access modifiers of the declared constants do not matter.

Example:
<classconstants/>
Or:
<filterreader
   classname="org.apache.tools.ant.filters.ClassConstants"/>
/**
 * Assembles the constants declared in a Java class in
 * <code>key1=value1(line separator)key2=value2</code>
 * format.
 *<p>Notes:</p>
 * <ol>
 * <li>This filter uses the BCEL external toolkit.
 * <li>This assembles only those constants that are not created
 * using the syntax <code>new whatever()</code>
 * <li>This assembles constants declared using the basic datatypes
 * and String only.</li>
 * <li>The access modifiers of the declared constants do not matter.</li>
 *</ol>
 * <p>Example:</p>
 * <pre>&lt;classconstants/&gt;</pre>
 * Or:
 * <pre>&lt;filterreader
 *    classname=&quot;org.apache.tools.ant.filters.ClassConstants&quot;/&gt;</pre>
 */
public final class ClassConstants
    extends BaseFilterReader
    implements ChainableReader {
    
Data that must be read from, if not null. /** Data that must be read from, if not null. */
    private String queuedData = null;

    
Helper Class to be invoked via reflection. /** Helper Class to be invoked via reflection. */
    private static final String JAVA_CLASS_HELPER =
        "org.apache.tools.ant.filters.util.JavaClassHelper";

    
Constructor for "dummy" instances.
See Also:
BaseFilterReader.BaseFilterReader()/**
     * Constructor for "dummy" instances.
     *
     * @see BaseFilterReader#BaseFilterReader()
     */
    public ClassConstants() {
        super();
    }

    
Creates a new filtered reader. The contents of the passed-in reader
are expected to be the name of the class from which to produce a
list of constants.
Params:
in – A Reader object providing the underlying stream.
          Must not be null./**
     * Creates a new filtered reader. The contents of the passed-in reader
     * are expected to be the name of the class from which to produce a
     * list of constants.
     *
     * @param in A Reader object providing the underlying stream.
     *           Must not be <code>null</code>.
     */
    public ClassConstants(final Reader in) {
        super(in);
    }

    
Reads and assembles the constants declared in a class file.
Throws:
IOException – if the underlying stream throws an IOException
during reading, or if the constants for the specified class cannot
be read (for example due to the class not being found).
Returns:
the next character in the list of constants, or -1
if the end of the resulting stream has been reached/**
     * Reads and assembles the constants declared in a class file.
     *
     * @return the next character in the list of constants, or -1
     * if the end of the resulting stream has been reached
     *
     * @exception IOException if the underlying stream throws an IOException
     * during reading, or if the constants for the specified class cannot
     * be read (for example due to the class not being found).
     */
    public int read() throws IOException {
        int ch = -1;

        if (queuedData != null && queuedData.isEmpty()) {
            queuedData = null;
        }

        if (queuedData == null) {
            final String clazz = readFully();
            if (clazz == null || clazz.isEmpty()) {
                ch = -1;
            } else {
                final byte[] bytes = clazz.getBytes(StandardCharsets.ISO_8859_1);
                try {
                    final Class<?> javaClassHelper = Class.forName(JAVA_CLASS_HELPER);
                    if (javaClassHelper != null) {
                        final Method getConstants =
                            javaClassHelper.getMethod("getConstants", byte[].class);
                        // getConstants is a static method, no need to
                        // pass in the object
                        final StringBuffer sb = (StringBuffer)
                                getConstants.invoke(null, (Object) bytes);
                        if (sb.length() > 0) {
                            queuedData = sb.toString();
                            return read();
                        }
                    }
                } catch (NoClassDefFoundError | RuntimeException ex) {
                    throw ex;
                } catch (InvocationTargetException ex) {
                    Throwable t = ex.getTargetException();
                    if (t instanceof NoClassDefFoundError) {
                        throw (NoClassDefFoundError) t;
                    }
                    if (t instanceof RuntimeException) {
                        throw (RuntimeException) t;
                    }
                    throw new BuildException(t);
                } catch (Exception ex) {
                    throw new BuildException(ex);
                }
            }
        } else {
            ch = queuedData.charAt(0);
            queuedData = queuedData.substring(1);
            if (queuedData.isEmpty()) {
                queuedData = null;
            }
        }
        return ch;
    }

    
Creates a new ClassConstants using the passed in
Reader for instantiation.
Params:
rdr – A Reader object providing the underlying stream.
           Must not be null.
Returns:
a new filter based on this configuration, but filtering
        the specified reader/**
     * Creates a new ClassConstants using the passed in
     * Reader for instantiation.
     *
     * @param rdr A Reader object providing the underlying stream.
     *            Must not be <code>null</code>.
     *
     * @return a new filter based on this configuration, but filtering
     *         the specified reader
     */
    public Reader chain(final Reader rdr) {
        return new ClassConstants(rdr);
    }
}