/*
 * Java Genetic Algorithm Library (jenetics-8.1.0).
 * Copyright (c) 2007-2024 Franz Wilhelmstötter
 *
 * Licensed 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.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.xml.stream;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import static javax.xml.stream.XMLStreamConstants.CDATA;
import static javax.xml.stream.XMLStreamConstants.CHARACTERS;
import static javax.xml.stream.XMLStreamConstants.END_ELEMENT;
import static javax.xml.stream.XMLStreamConstants.START_ELEMENT;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;

import io.jenetics.xml.stream.Reader.Type;

/**
 * XML reader class, used for reading objects in XML format.
 * <b>XML</b>
 * <pre> {@code
 * <int-chromosome length="3">
 *     <min>-2147483648</min>
 *     <max>2147483647</max>
 *     <alleles>
 *         <allele>-1878762439</allele>
 *         <allele>-957346595</allele>
 *         <allele>-88668137</allele>
 *     </alleles>
 * </int-chromosome>
 * } </pre>
 *
 * <b>Reader definition</b>
 * {@snippet lang="java":
 * final Reader<IntegerChromosome> reader =
 *     elem(
 *         (Object[] v) -> {
 *             final int length = (int)v[0];
 *             final int min = (int)v[1];
 *             final int max = (int)v[2];
 *             final List<Integer> alleles = (List<Integer>)v[3];
 *             assert alleles.size() == length;
 *
 *             return IntegerChromosome.of(
 *                 alleles.stream()
 *                     .map(value -> IntegerGene.of(value, min, max))
 *                     .toArray(IntegerGene[]::new)
 *             );
 *         },
 *         "int-chromosome",
 *         attr("length").map(Integer::parseInt),
 *         elem("min", text().map(Integer::parseInt)),
 *         elem("max", text().map(Integer::parseInt)),
 *         elem("alleles",
 *             elems(elem("allele", text().map(Integer::parseInt)))
 *         )
 *     );
 * }
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.9
 * @since 3.9
 */
public abstract class Reader<T> {

        /**
         * Represents the XML element type.
         */
        enum Type {

                /**
                 * Denotes a element reader.
                 */
                ELEM,

                /**
                 * Denotes a element attribute reader.
                 */
                ATTR,

                /**
                 * Denotes a reader of elements of the same type.
                 */
                LIST,

                /**
                 * Denotes a reader of the text of a element.
                 */
                TEXT

        }

        private final String _name;
        private final Type _type;

        /**
         * Create a new XML reader with the given name and type.
         *
         * @param name the element name of the reader
         * @param type the element type of the reader
         * @throws NullPointerException if one of the give arguments is {@code null}
         */
        Reader(final String name, final Type type) {
                _name = requireNonNull(name);
                _type = requireNonNull(type);
        }

        /**
         * Read the given type from the underlying XML stream {@code reader}.
         *
         * {@snippet lang="java":
         * try (AutoCloseableXMLStreamReader xml = XML.reader(in)) {
         *     // Move XML stream to first the element.
         *     xml.next();
         *     return reader.read(xml);
         * }
         * }
         *
         * @param xml the underlying XML stream {@code reader}
         * @return the data read from the XML stream, maybe {@code null}
         * @throws XMLStreamException if an error occurs while reading the value
         * @throws NullPointerException if the given {@code xml} stream reader is
         *         {@code null}
         */
        public abstract T read(final XMLStreamReader xml) throws XMLStreamException;

        /**
         * Create a new reader for the new mapped type {@code B}.
         *
         * @param mapper the mapper function
         * @param <B> the target type of the new reader
         * @return a new reader
         * @throws NullPointerException if the given {@code mapper} function is
         *         {@code null}
         */
        public <B> Reader<B> map(final Function<? super T, ? extends B> mapper) {
                requireNonNull(mapper);

                return new Reader<>(_name, _type) {
                        @Override
                        public B read(final XMLStreamReader xml)
                                throws XMLStreamException {
                                try {
                                        return mapper.apply(Reader.this.read(xml));
                                } catch (RuntimeException e) {
                                        throw new XMLStreamException(e);
                                }
                        }
                };
        }

        /**
         * Return the name of the element processed by this reader.
         *
         * @return the element name the reader is processing
         */
        String name() {
                return _name;
        }

        /**
         * Return the element type of the reader.
         *
         * @return the element type of the reader
         */
        Type type() {
                return _type;
        }

        @Override
        public String toString() {
                return format("Reader[%s, %s]", name(), type());
        }


        /* *************************************************************************
         * Static reader factory methods.
         * ************************************************************************/

        /**
         * Return a {@code Reader} for reading an attribute of an element.
         * <p>
         * <b>XML</b>
         * <pre> {@code <element length="3"/>}
         *
         * <b>Reader definition</b>
         * {@snippet lang="java":
         * final Reader<Integer> reader =
         *     elem(
         *         v -> (Integer)v[0],
         *         "element",
         *         attr("length").map(Integer::parseInt)
         *     );
         * } </pre>
         *
         * @param name the attribute name
         * @return an attribute reader
         * @throws NullPointerException if the given {@code name} is {@code null}
         */
        public static Reader<String> attr(final String name) {
                return new AttrReader(name);
        }

        /**
         * Return a {@code Reader} for reading the text of an element.
         * <p>
         * <b>XML</b>
         * <pre> {@code <element>1234<element>}
         *
         * <b>Reader definition</b>
         * {@snippet lang="java":
         * final Reader<Integer> reader =
         *     elem(
         *         v -> (Integer)v[0],
         *         "element",
         *         text().map(Integer::parseInt)
         *     );
         * } </pre>
         *
         * @return an element text reader
         */
        public static Reader<String> text() {
                return new TextReader();
        }

        /**
         * Return a {@code Reader} for reading an object of type {@code T} from the
         * XML element with the given {@code name}.
         *
         * <p>
         * <b>XML</b>
         * <pre> {@code <property name="size">1234<property>}
         *
         * <b>Reader definition</b>
         * {@snippet lang="java":
         * final Reader<Property> reader =
         *     elem(
         *         v -> {
         *             final String name = (String)v[0];
         *             final Integer value = (Integer)v[1];
         *             return Property.of(name, value);
         *         },
         *         "property",
         *         attr("name"),
         *         text().map(Integer::parseInt)
         *     );
         * } </pre>
         *
         * @param generator the generator function, which build the result object
         *        from the given parameter array
         * @param name the name of the root (subtree) element
         * @param children the child element reader, which creates the values
         *        forwarded to the {@code generator} function
         * @param <T> the reader result type
         * @return a node reader
         * @throws NullPointerException if one of the given arguments is {@code null}
         * @throws IllegalArgumentException if the given child readers contains more
         *         than one <em>text</em> reader
         */
        public static <T> Reader<T> elem(
                final Function<Object[], T> generator,
                final String name,
                final Reader<?>... children
        ) {
                requireNonNull(name);
                requireNonNull(generator);
                Stream.of(requireNonNull(children)).forEach(Objects::requireNonNull);

                return new ElemReader<>(name, generator, List.of(children), Type.ELEM);
        }

        /**
         * Return a {@code Reader} which reads the value from the child elements of
         * the given parent element {@code name}.
         * <p>
         * <b>XML</b>
         * <pre> {@code
         * <min><property name="size">1234<property></min>}
         * </pre>
         *
         * <b>Reader definition</b>
         * {@snippet lang="java":
         * final Reader<Property> reader =
         *     elem("min",
         *         elem(
         *             v -> {
         *                 final String name = (String)v[0];
         *                 final Integer value = (Integer)v[1];
         *                 return Property.of(name, value);
         *             },
         *             "property",
         *             attr("name"),
         *             text().map(Integer::parseInt)
         *         )
         *     );
         * }
         *
         * @param name the parent element name
         * @param reader the child elements reader
         * @param <T> the result type
         * @return a node reader
         * @throws NullPointerException if one of the given arguments is {@code null}
         */
        public static <T> Reader<T> elem(
                final String name,
                final Reader<? extends T> reader
        ) {
                requireNonNull(name);
                requireNonNull(reader);

                return elem(
                        v -> {
                                @SuppressWarnings("unchecked")
                                T value = v.length > 0 ? (T)v[0] : null;
                                return value;
                        },
                        name,
                        reader
                );
        }

        /**
         * Return a {@code Reader} which collects the elements, read by the given
         * child {@code reader}, and returns it as a list of these elements.
         * <p>
         * <b>XML</b>
         * <pre> {@code
         * <properties length="3">
         *     <property>-1878762439</property>
         *     <property>-957346595</property>
         *     <property>-88668137</property>
         * </properties>
         * } </pre>
         *
         * <b>Reader definition</b>
         * {@snippet lang="java":
         * Reader<List<Integer>> reader =
         *     elem(
         *         v -> (List<Integer>)v[0],
         *         "properties",
         *         elems(elem("property", text().map(Integer::parseInt)))
         *     );
         * }
         *
         * @param reader the child element reader
         * @param <T> the element type
         * @return a list reader
         */
        public static <T> Reader<List<T>> elems(final Reader<? extends T> reader) {
                return new ListReader<>(reader);
        }
}


/* *****************************************************************************
 * XML reader implementations.
 * ****************************************************************************/

/**
 * Reader implementation for reading the attribute of the current node.
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.9
 * @since 3.9
 */
final class AttrReader extends Reader<String> {

        AttrReader(final String name) {
                super(name, Type.ATTR);
        }

        @Override
        public String read(final XMLStreamReader xml) throws XMLStreamException {
                xml.require(START_ELEMENT, null, null);
                return xml.getAttributeValue(null, name());
        }

}

/**
 * Reader implementation for reading the text of the current node.
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.9
 * @since 3.9
 */
final class TextReader extends Reader<String> {

        TextReader() {
                super("", Type.TEXT);
        }

        @Override
        public String read(final XMLStreamReader xml) throws XMLStreamException {
                final StringBuilder out = new StringBuilder();

                int type = xml.getEventType();
                do {
                        out.append(xml.getText());
                } while (xml.hasNext() && (type = xml.next()) == CHARACTERS || type == CDATA);


                return out.toString();
        }
}

/**
 * Reader implementation for reading list of elements.
 *
 * @param <T> the element type
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.9
 * @since 3.9
 */
final class ListReader<T> extends Reader<List<T>> {

        private final Reader<? extends T> _adoptee;

        ListReader(final Reader<? extends T> adoptee) {
                super(adoptee.name(), Type.LIST);
                _adoptee = adoptee;
        }

        @Override
        public List<T> read(final XMLStreamReader xml) throws XMLStreamException {
                xml.require(START_ELEMENT, null, name());
                return Collections.singletonList(_adoptee.read(xml));
        }
}

/**
 * The main XML element reader implementation.
 *
 * @param <T> the reader data type
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.9
 * @since 3.9
 */
final class ElemReader<T> extends Reader<T> {

        // Given parameters.
        private final Function<Object[], T> _creator;
        private final List<Reader<?>> _children;

        // Derived parameters.
        private final Map<String, Integer> _readerIndexMapping = new HashMap<>();
        private final int[] _attrReaderIndexes;
        private final int[] _textReaderIndex;

        ElemReader(
                final String name,
                final Function<Object[], T> creator,
                final List<Reader<?>> children,
                final Type type
        ) {
                super(name, type);

                _creator = requireNonNull(creator);
                _children = requireNonNull(children);

                for (int i = 0; i < _children.size(); ++i) {
                        _readerIndexMapping.put(_children.get(i).name(), i);
                }
                _attrReaderIndexes = IntStream.range(0, _children.size())
                        .filter(i -> _children.get(i).type() == Type.ATTR)
                        .toArray();
                _textReaderIndex = IntStream.range(0, _children.size())
                        .filter(i -> _children.get(i).type() == Type.TEXT)
                        .toArray();

                if (_textReaderIndex.length > 1) {
                        throw new IllegalArgumentException(
                                "Found more than one TEXT reader."
                        );
                }
        }

        @Override
        public T read(final XMLStreamReader xml)
                throws XMLStreamException
        {
                xml.require(START_ELEMENT, null, name());

                final List<ReaderResult> results = _children.stream()
                        .map(ReaderResult::of)
                        .toList();

                final ReaderResult text = _textReaderIndex.length == 1
                        ? results.get(_textReaderIndex[0])
                        : null;

                for (int i : _attrReaderIndexes) {
                        final ReaderResult result = results.get(i);
                        result.put(result.reader().read(xml));
                }

                if (xml.hasNext()) {
                        xml.next();

                        boolean hasNext = false;
                        do {
                switch (xml.getEventType()) {
                    case START_ELEMENT -> {
                        final ReaderResult result = results.get(
                                                        _readerIndexMapping.get(xml.getLocalName())
                        );
                        if (result != null) {
                            result.put(result.reader().read(xml));
                            if (xml.hasNext()) {
                                hasNext = true;
                                xml.next();
                            } else {
                                hasNext = false;
                            }
                        }
                    }
                    case CHARACTERS, CDATA -> {
                        if (text != null) {
                            text.put(text.reader().read(xml));
                        } else {
                            xml.next();
                        }
                        hasNext = true;
                    }
                    case END_ELEMENT -> {
                        if (name().equals(xml.getLocalName())) {
                            try {
                                return _creator.apply(results.stream()
                                        .map(ReaderResult::value)
                                        .toArray());
                            } catch (RuntimeException e) {
                                throw new XMLStreamException(e);
                            }
                        }
                    }
                }

                        } while (hasNext);
                }

                throw new XMLStreamException(format(
                        "Premature end of file while reading '%s'.", name()
                ));
        }

}

/**
 * Helper interface for storing the XML reader (intermediate) results.
 */
interface ReaderResult {

        /**
         * Return the underlying XML reader, which reads the result.
         *
         * @return return the underlying XML reader
         */
        Reader<?> reader();

        /**
         * Put the given {@code value} to the reader result.
         *
         * @param value the reader result
         */
        void put(final Object value);

        /**
         * Return the current reader result value.
         *
         * @return the current reader result value
         */
        Object value();

        /**
         * Create a reader result for the given XML reader
         *
         * @param reader the XML reader
         * @return a reader result for the given reader
         */
        static ReaderResult of(final Reader<?> reader) {
                return reader.type() == Type.LIST
                        ? new ListResult(reader)
                        : new ValueResult(reader);
        }

}

/**
 * Result object for values read from XML elements.
 */
final class ValueResult implements ReaderResult {

        private final Reader<?> _reader;
        private Object _value;

        ValueResult(final Reader<?> reader) {
                _reader = reader;
        }

        @Override
        public void put(final Object value) {
                _value = value;
        }

        @Override
        public Reader<?> reader() {
                return _reader;
        }


        @Override
        public Object value() {
                return _value;
        }

}

/**
 * Result object for list values read from XML elements.
 */
final class ListResult implements ReaderResult {

        private final Reader<?> _reader;
        private final List<Object> _value = new ArrayList<>();

        ListResult(final Reader<?> reader) {
                _reader = reader;
        }

        @Override
        public void put(final Object value) {
                if (value instanceof List) {
                        _value.addAll((List<?>)value);
                } else {
                        _value.add(value);
                }
        }

        @Override
        public Reader<?> reader() {
                return _reader;
        }

        @Override
        public List<Object> value() {
                return _value;
        }

}