components/camel-xj/src/main/java/org/apache/camel/component/xj/XmlJsonStreamWriter.java

/*
 * 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
 *
 *      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 org.apache.camel.component.xj;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

import javax.xml.namespace.NamespaceContext;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonToken;

/**
 * XML Json bridge. Explicitly using StreamWriter and not XMLEventWriter because saxon wants that.
 */
public class XmlJsonStreamWriter implements XMLStreamWriter {

    private final JsonGenerator jsonGenerator;

    /**
     * Root element of the internal tree
     */
    private TreeElement treeRoot;

    /**
     * Reference to current "level-s" element
     */
    private TreeElement currentTreeElement;

    /**
     * Creates a new XmlJsonStreamWriter instance
     * @param jsonGenerator the {@link JsonGenerator} to use to write the json document
     */
    public XmlJsonStreamWriter(JsonGenerator jsonGenerator) {
        this.jsonGenerator = jsonGenerator;
    }

    @Override
    public void writeStartElement(String localName) {
        writeStartElement(null, localName, null);
    }

    @Override
    public void writeStartElement(String namespaceURI, String localName) {
        writeStartElement(null, localName, namespaceURI);
    }

    @Override
    public void writeStartElement(String prefix, String localName, String namespaceURI) {
        final TreeElement treeElement = new TreeElement(currentTreeElement, XMLStreamConstants.START_ELEMENT, localName);

        currentTreeElement.addChild(treeElement);
        currentTreeElement = treeElement;
    }

    @Override
    public void writeEmptyElement(String namespaceURI, String localName) {
        writeStartElement(null, namespaceURI, localName);
        writeEndElement();
    }

    @Override
    public void writeEmptyElement(String prefix, String localName, String namespaceURI) {
        writeStartElement(prefix, localName, namespaceURI);
        writeEndElement();
    }

    @Override
    public void writeEmptyElement(String localName) {
        writeStartElement(null, localName, null);
        writeEndElement();
    }

    @Override
    public void writeEndElement() {
        currentTreeElement.writeEnd();
        currentTreeElement = currentTreeElement.parent;
    }

    @Override
    public void writeEndDocument() throws XMLStreamException {
        try {
            treeRoot.write(jsonGenerator);
        } catch (IOException e) {
            throw new XMLStreamException(e);
        }
    }

    @Override
    public void close() throws XMLStreamException {
        try {
            jsonGenerator.close();
        } catch (IOException e) {
            throw new XMLStreamException(e);
        }
    }

    @Override
    public void flush() throws XMLStreamException {
        try {
            jsonGenerator.flush();
        } catch (IOException e) {
            throw new XMLStreamException(e);
        }
    }

    @Override
    public void writeAttribute(String localName, String value) {
        writeAttribute(null, null, localName, value);
    }

    @Override
    public void writeAttribute(String prefix, String namespaceURI, String localName, String value) {
        if (XJConstants.NS_XJ.equals(namespaceURI)) {
            switch (localName) {
            case XJConstants.TYPE_HINT_NAME:
                currentTreeElement.setName(value);
                return;
            case XJConstants.TYPE_HINT_TYPE:
                currentTreeElement.setJsonToken(XJConstants.TYPE_JSONTYPE_MAP.get(value));
                return;
            default:
                return;
            }
        }

        final TreeElement treeElement = new TreeElement(currentTreeElement, XMLStreamConstants.ATTRIBUTE, JsonToken.VALUE_STRING, localName);
        treeElement.setValue(value);

        currentTreeElement.addChild(treeElement);
    }

    @Override
    public void writeAttribute(String namespaceURI, String localName, String value) {
        writeAttribute(null, namespaceURI, localName, value);
    }

    @Override
    public void writeNamespace(String prefix, String namespaceURI) {
        // ignore event - we don't care
    }

    @Override
    public void writeDefaultNamespace(String namespaceURI) {
        // ignore event - we don't care
    }

    @Override
    public void writeComment(String data) {
        // ignore event - we don't care
    }

    @Override
    public void writeProcessingInstruction(String target) {
        // ignore event - we don't care
    }

    @Override
    public void writeProcessingInstruction(String target, String data) {
        // ignore event - we don't care
    }

    @Override
    public void writeCData(String data) {
        writeCharacters(data);
    }

    @Override
    public void writeDTD(String dtd) {
        // ignore event - we don't care
    }

    @Override
    public void writeEntityRef(String name) {
        // ignore event - we don't care
    }

    @Override
    public void writeStartDocument() {
        writeStartDocument(null);
    }

    @Override
    public void writeStartDocument(String version) {
        writeStartDocument(null, version);
    }

    @Override
    public void writeStartDocument(String encoding, String version) {
        final TreeElement treeElement = new TreeElement(null, XMLStreamConstants.START_DOCUMENT, JsonToken.NOT_AVAILABLE);
        this.treeRoot = treeElement;
        this.currentTreeElement = treeElement;
    }

    @Override
    public void writeCharacters(String text) {
        // check for non coalescing read
        final List<TreeElement> childs = currentTreeElement.childs;
        if (childs.size() > 0) {
            final TreeElement child = childs.get(childs.size() - 1);
            if (child.getXmlEvent() == XMLStreamConstants.CHARACTERS) {
                child.appendValue(text);

                return;
            }
        }

        final TreeElement treeElement = new TreeElement(currentTreeElement, XMLStreamConstants.CHARACTERS, JsonToken.VALUE_STRING);
        treeElement.setValue(text);

        currentTreeElement.addChild(treeElement);
    }

    @Override
    public void writeCharacters(char[] text, int start, int len) {
        writeCharacters(new String(text, start, len));
    }

    @Override
    public String getPrefix(String uri) {
        return null;
    }

    @Override
    public void setPrefix(String prefix, String uri) {
        // ignore - ATM we don't care
    }

    @Override
    public void setDefaultNamespace(String uri) {
        // ignore - ATM we don't care
    }

    @Override
    public NamespaceContext getNamespaceContext() {
        throw new UnsupportedOperationException(XJConstants.UNSUPPORTED_OPERATION_EXCEPTION_MESSAGE);
    }

    @Override
    public void setNamespaceContext(NamespaceContext context) {
        // ignore - ATM we don't care
    }

    @Override
    public Object getProperty(String name) throws IllegalArgumentException {
        throw new IllegalArgumentException(name + " unsupported");
    }

    /**
     * Class that represents an element of the internal tree
     */
    private static class TreeElement {

        private TreeElement parent;
        private List<TreeElement> childs = Collections.emptyList();

        private String name;
        private String value;
        private int xmlEvent;
        private JsonToken jsonToken;

        TreeElement(TreeElement parent, int xmlEvent, String name) {
            this.parent = parent;
            this.xmlEvent = xmlEvent;
            this.name = name;
        }

        TreeElement(TreeElement parent, int xmlEvent, JsonToken jsonToken) {
            this.parent = parent;
            this.xmlEvent = xmlEvent;
            this.jsonToken = jsonToken;
        }

        TreeElement(TreeElement parent, int xmlEvent, JsonToken jsonToken, String name) {
            this.parent = parent;
            this.xmlEvent = xmlEvent;
            this.jsonToken = jsonToken;
            this.name = name;
        }

        int getXmlEvent() {
            return this.xmlEvent;
        }

        void addChild(TreeElement treeElement) {
            if (this.childs == Collections.EMPTY_LIST) {
                this.childs = new ArrayList<>(1);
            }

            this.childs.add(treeElement);
        }

        void setJsonToken(JsonToken jsonToken) {
            if (this.jsonToken == null) {
                this.jsonToken = jsonToken;
            }
        }

        void setName(String name) {
            this.name = name;
        }

        void setValue(String value) {
            this.value = value;
        }

        void appendValue(String value) {
            this.value += value;
        }

        void writeEnd() {
            if (jsonToken == null) {
                // no type hints
                writeEndNoTypeHints();
            } else {
                // type hints given
                writeEndHaveTypeHints();
            }
        }

        private void writeEndNoTypeHints() {
            if (xmlEvent == XMLStreamConstants.START_ELEMENT) {
                if (childs.isEmpty()) {
                    // empty root element
                    if (this.parent.jsonToken == JsonToken.NOT_AVAILABLE) {
                        jsonToken = JsonToken.START_OBJECT;
                    } else {
                        jsonToken = JsonToken.FIELD_NAME;

                        final TreeElement treeElement = new TreeElement(this, -1, JsonToken.VALUE_STRING);
                        treeElement.setValue("");
                        this.addChild(treeElement);
                    }
                } else if (childs.size() == 1 && childs.get(0).xmlEvent == XMLStreamConstants.CHARACTERS) {
                    // just character childs.

                    // empty root element
                    if (this.parent.jsonToken == JsonToken.NOT_AVAILABLE) {
                        jsonToken = JsonToken.START_OBJECT;

                        final TreeElement child = childs.get(0);
                        if (isWhitespace(child.value)) {
                            childs.remove(0);
                        } else {
                            // create new intermediary element
                            final TreeElement treeElement = new TreeElement(this, -1, JsonToken.FIELD_NAME, XJConstants.JSON_WRITER_MIXED_CONTENT_TEXT_KEY);
                            treeElement.addChild(child);
                            childs.set(childs.indexOf(child), treeElement);
                            child.parent = treeElement;
                        }
                    } else {
                        jsonToken = JsonToken.FIELD_NAME;
                    }
                } else {
                    // mixed content fixup.
                    final Iterator<TreeElement> iterator = childs.iterator();
                    while (iterator.hasNext()) {
                        TreeElement element = iterator.next();
                        if (element.jsonToken == JsonToken.VALUE_STRING) {
                            if (isWhitespace(element.value)) {
                                // remove element if is (ignorable-) whitespace
                                iterator.remove();
                            } else {
                                // create new intermediary element
                                final TreeElement treeElement = new TreeElement(this, -1, JsonToken.FIELD_NAME,
                                        element.name != null ? element.name : XJConstants.JSON_WRITER_MIXED_CONTENT_TEXT_KEY);
                                treeElement.addChild(element);
                                childs.set(childs.indexOf(element), treeElement);
                                element.parent = treeElement;
                                element.jsonToken = JsonToken.VALUE_STRING;
                            }
                        }
                    }

                    jsonToken = JsonToken.START_OBJECT;

                    wrapChildsInArrayIfNecessary();
                }
            } else {
                throw new IllegalStateException("XMLEvent: " + xmlEvent + "; Json Token: " + jsonToken);
            }
        }

        private void writeEndHaveTypeHints() {
            switch (jsonToken) {
            case VALUE_NULL:
            case VALUE_STRING:
            case VALUE_NUMBER_INT:
            case VALUE_NUMBER_FLOAT:
            case VALUE_TRUE:
            case VALUE_FALSE:
                if (childs.isEmpty()) {
                    final TreeElement treeElement = new TreeElement(this, -1, jsonToken);
                    treeElement.setValue("");
                    this.addChild(treeElement);

                    jsonToken = JsonToken.FIELD_NAME;
                } else if (childs.size() == 1) {
                    childs.get(0).jsonToken = jsonToken;
                    jsonToken = JsonToken.FIELD_NAME;
                } else {
                    // create FIELD childs if element contains text and attributes.
                    final Iterator<TreeElement> iterator = childs.iterator();
                    while (iterator.hasNext()) {
                        TreeElement element = iterator.next();
                        if (isValueToken(element.jsonToken)) {
                            if (isWhitespace(element.value)) {
                                // remove element if is (ignorable-) whitespace
                                iterator.remove();
                            } else {
                                // create new intermediary element
                                final TreeElement treeElement = new TreeElement(this, -1, JsonToken.FIELD_NAME,
                                        element.name != null ? element.name : XJConstants.JSON_WRITER_MIXED_CONTENT_TEXT_KEY);
                                treeElement.addChild(element);
                                childs.set(childs.indexOf(element), treeElement);
                                element.parent = treeElement;
                                if (element.xmlEvent == XMLStreamConstants.CHARACTERS) {
                                    element.jsonToken = jsonToken;
                                }
                            }
                        }
                    }

                    jsonToken = JsonToken.START_OBJECT;

                    wrapChildsInArrayIfNecessary();
                }
                break;
            case START_OBJECT:
            case START_ARRAY:
                // mixed content fixup.
                final Iterator<TreeElement> iterator = childs.iterator();
                while (iterator.hasNext()) {
                    TreeElement element = iterator.next();
                    if (isValueToken(element.jsonToken)) {
                        if (isWhitespace(element.value)) {
                            // remove element if is (ignorable-) whitespace
                            iterator.remove();
                        } else {
                            // create new intermediary element
                            final TreeElement treeElement = new TreeElement(this, -1, JsonToken.FIELD_NAME, XJConstants.JSON_WRITER_MIXED_CONTENT_TEXT_KEY);
                            treeElement.addChild(element);
                            childs.set(childs.indexOf(element), treeElement);
                            element.parent = treeElement;
                        }
                    }
                }

                if (jsonToken != JsonToken.START_ARRAY) {
                    wrapChildsInArrayIfNecessary();
                }

                break;
            default:
                throw new IllegalStateException("XMLEvent: " + xmlEvent + "; Json Token: " + jsonToken);
            }
        }

        private void wrapChildsInArrayIfNecessary() {
            final Map<String, Set<TreeElement>> childElementsMap = childs.stream()
                    .collect(Collectors.groupingBy(o -> o.name, HashMap::new, Collectors.toCollection(LinkedHashSet::new)));

            // create arrays if element with the same name occurs more than once.
            for (Map.Entry<String, Set<TreeElement>> mapEntry : childElementsMap.entrySet()) {
                if (mapEntry.getValue().size() > 1) {
                    if (childElementsMap.size() == 1) {
                        jsonToken = JsonToken.START_ARRAY;
                    } else {
                        final TreeElement treeElement = new TreeElement(this, -1, JsonToken.START_ARRAY, mapEntry.getKey());
                        treeElement.childs = new ArrayList<>(mapEntry.getValue());
                        for (TreeElement child : treeElement.childs) {
                            child.parent = treeElement;
                        }

                        final List<TreeElement> newChildList = new ArrayList<>(this.childs.size() - mapEntry.getValue().size() + 1);
                        for (TreeElement e : this.childs) {
                            if (!mapEntry.getValue().contains(e)) {
                                newChildList.add(e);
                            }
                        }
                        childs = newChildList;
                        childs.add(treeElement);
                    }
                }
            }
        }

        private boolean isWhitespace(String text) {
            int len = text.length();
            int st = 0;

            while ((st < len) && (text.charAt(st) <= ' ')) {
                st++;
            }

            return st == len;
        }

        private boolean isValueToken(JsonToken jsonToken) {
            return jsonToken == JsonToken.VALUE_STRING
                    || jsonToken == JsonToken.VALUE_NUMBER_FLOAT
                    || jsonToken == JsonToken.VALUE_NUMBER_INT
                    || jsonToken == JsonToken.VALUE_TRUE
                    || jsonToken == JsonToken.VALUE_FALSE
                    || jsonToken == JsonToken.VALUE_NULL;
        }

        void write(JsonGenerator jsonGenerator) throws IOException {
            switch (jsonToken) {
            case NOT_AVAILABLE:
                break;
            case START_OBJECT:
                if (parent.jsonToken == JsonToken.START_OBJECT) {
                    jsonGenerator.writeObjectFieldStart(name);
                } else {
                    jsonGenerator.writeStartObject();
                }

                break;
            case START_ARRAY:
                if (parent.jsonToken == JsonToken.START_OBJECT) {
                    jsonGenerator.writeArrayFieldStart(name);
                } else {
                    jsonGenerator.writeStartArray();
                }

                break;
            case FIELD_NAME:
                if (parent.jsonToken != JsonToken.START_ARRAY) {
                    jsonGenerator.writeFieldName(name);
                }

                break;
            case VALUE_STRING:
                jsonGenerator.writeString(value);

                break;
            case VALUE_NUMBER_INT:
            case VALUE_NUMBER_FLOAT:
            case VALUE_TRUE:
            case VALUE_FALSE:
                if (value == null || value.isEmpty()) {
                    jsonGenerator.writeNull();
                } else {
                    jsonGenerator.writeRawValue(value);
                }

                break;
            case VALUE_NULL:
                jsonGenerator.writeNull();

                break;
            default:
                throw new IllegalStateException("XMLEvent: " + xmlEvent + "; Json Token: " + jsonToken);
            }

            for (TreeElement treeElement : childs) {
                treeElement.write(jsonGenerator);
            }

            switch (jsonToken) {
            case START_OBJECT:
                jsonGenerator.writeEndObject();
                break;
            case START_ARRAY:
                jsonGenerator.writeEndArray();
                break;
            case VALUE_NULL:
            case NOT_AVAILABLE:
            case FIELD_NAME:
            case VALUE_STRING:
            case VALUE_NUMBER_INT:
            case VALUE_NUMBER_FLOAT:
            case VALUE_TRUE:
            case VALUE_FALSE:
                // nop;
                break;
            default:
                throw new IllegalStateException("XMLEvent: " + xmlEvent + "; Json Token: " + jsonToken);
            }
        }

        @Override
        public String toString() {
            return "TreeElement{"
                    + "name='" + name + '\''
                    + ", value='" + value + '\''
                    + ", xmlEvent=" + xmlEvent
                    + ", jsonToken=" + jsonToken
                    + '}';
        }
    }
}