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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.event;

import net.sf.saxon.expr.parser.Loc;
import net.sf.saxon.om.AttributeMap;
import net.sf.saxon.om.NamespaceMap;
import net.sf.saxon.om.NodeName;
import net.sf.saxon.s9api.Location;
import net.sf.saxon.str.UnicodeString;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.str.CompressedWhitespace;
import net.sf.saxon.type.SchemaType;
import net.sf.saxon.str.UnicodeBuilder;

/**
 * The CommentStripper class is a filter that removes all comments and processing instructions.
 * It also concatenates text nodes that are split by comments and PIs. This follows the rules for
 * processing stylesheets; it is also used for removing comments and PIs from the tree seen
 * by XPath expressions used to process XSD 1.1 assertions
 *
 */


public class CommentStripper extends ProxyReceiver {

    /*@Nullable*/ private CompressedWhitespace savedWhitespace = null;
    private final UnicodeBuilder buffer = new UnicodeBuilder();

    /**
     * Default constructor for use in subclasses
     *
     * @param next the next receiver in the pipeline
     */

    public CommentStripper(Receiver next) {
        super(next);
    }

    @Override
    public void startElement(NodeName elemName, SchemaType type,
                             AttributeMap attributes, NamespaceMap namespaces,
                             Location location, int properties)
            throws XPathException {
        flush();
        nextReceiver.startElement(elemName, type, attributes, namespaces, location, properties);
    }

    /**
     * Callback interface for SAX: not for application use
     */

    @Override
    public void endElement() throws XPathException {
        flush();
        nextReceiver.endElement();
    }

    /**
     * Handle a text node. Because we're often handling stylesheets on this path, whitespace text
     * nodes will often be stripped but we can't strip them immediately because of the case
     * [element]   [!-- comment --]text[/element], where the space before the comment is considered
     * significant. But it's worth going to some effort to avoid uncompressing the whitespace in the
     * more common case, so that it can easily be detected and stripped downstream.
     */

    @Override
    public void characters(UnicodeString chars, Location locationId, int properties) throws XPathException {
        if (chars instanceof CompressedWhitespace) {
            if (buffer.isEmpty() && savedWhitespace == null) {
                savedWhitespace = (CompressedWhitespace) chars;
            } else {
                buffer.accept(((CompressedWhitespace) chars).uncompress());
            }
        } else {
            if (savedWhitespace != null) {
                buffer.accept(savedWhitespace.uncompress());
                savedWhitespace = null;
            }
            buffer.accept(chars);
        }

    }

    /**
     * Remove comments
     */

    @Override
    public void comment(UnicodeString chars, Location locationId, int properties) {
    }

    /**
     * Remove processing instructions
     */

    @Override
    public void processingInstruction(String name, UnicodeString data, Location locationId, int properties) {
    }

    /**
     * Flush the character buffer
     *
     * @throws net.sf.saxon.trans.XPathException
     *          if a failure occurs writing the output
     */

    private void flush() throws XPathException {
        if (!buffer.isEmpty()) {
            nextReceiver.characters(buffer.toUnicodeString(), Loc.NONE, ReceiverOption.NONE);
        } else if (savedWhitespace != null) {
            nextReceiver.characters(savedWhitespace, Loc.NONE, ReceiverOption.NONE);
        }
        savedWhitespace = null;
        buffer.clear();
    }

}