/*
 * Java Genetic Algorithm Library (jenetics-8.3.0).
 * Copyright (c) 2007-2025 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.ext.util;

import static java.util.Objects.requireNonNull;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.CharBuffer;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import io.jenetics.internal.util.Lifecycle.IOValue;

/**
 * This class contains helper classes, which are the building blocks for handling
 * CSV files.
 * <ul>
 *     <li>{@link LineReader}: This class allows you to read the lines of a
 *     CSV file. The result will be a {@link Stream} of CSV lines and are
 *     not split.</li>
 *     <li>{@link LineSplitter}: This class is responsible for splitting one
 *     CSV line into column values.</li>
 *     <li>{@link ColumnIndexes}: Allows defining the projection/embedding of
 *     the split/joined column values.</li>
 *     <li>{@link ColumnJoiner}: Joining a column array into a CSV line, which
 *     can be joined into a whole CSV string.</li>
 * </ul>
 * <p>
 * Additionally, this class contains a set of helper methods for CSV handling
 * using default configurations.
 * <p>
 * <b>Reading and splitting CSV lines</b>
 * {@snippet class="Snippets" region="readRows"}
 * <p>
 * <b>Joining columns and creating CSV string</b>
 * {@snippet class="Snippets" region="CsvSupportSnippets.collect"}
 * <p>
 * <b>Parsing CSV string</b>
 * {@snippet class="Snippets" region="parseCsv"}
 * <p>
 * <b>Parsing double values, given as CSV string</b>
 * <p>
 * Another example is to parse double values, which are given as CSV string and
 * use this data for running a regression analysis.
 * {@snippet class="Snippets" region="DoublesParsingSnippets.parseDoubles"}
 *
 * @see <a href="https://tools.ietf.org/html/rfc4180">RFC-4180</a>
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 8.2
 * @since 8.1
 */
public final class CsvSupport {

        /**
         * Holds the CSV column <em>separator</em> character.
         *
         * @param value the separator character
         *
         * @version 8.1
         * @since 8.1
         */
        public record Separator(char value) {

                /**
                 * The default separator character, '{@code ,}'.
                 */
                public static final Separator DEFAULT = new Separator(',');

                /**
                 * Creates a new Separator char object.
                 *
                 * @param value the separator character
                 * @throws IllegalArgumentException if the given separator character is
                 *         a line break character
                 */
                public Separator {
                        if (isLineBreak(value)) {
                                throw new IllegalArgumentException(
                                        "Given separator char is a line break character."
                                );
                        }
                }
        }

        /**
         * Holds the CSV column <em>quote</em> character. The following excerpt from
         * <a href="https://tools.ietf.org/html/rfc4180">RFC-4180</a> defines when
         * a quote character has to be used.
         * <pre>
         *     5.  Each field may or may not be enclosed in double quotes (however
         *         some programs, such as Microsoft Excel, do not use double quotes
         *         at all).  If fields are not enclosed with double quotes, then
         *         double quotes may not appear inside the fields.  For example:
         *
         *         "aaa","bbb","ccc" CRLF
         *         zzz,yyy,xxx
         *
         *     6.  Fields containing line breaks (CRLF), double quotes, and commas
         *         should be enclosed in double-quotes.  For example:
         *
         *         "aaa","b CRLF
         *         bb","ccc" CRLF
         *         zzz,yyy,xxx
         *
         *     7.  If double-quotes are used to enclose fields, then a double-quote
         *         appearing inside a field must be escaped by preceding it with
         *         another double quote.  For example:
         *
         *         "aaa","b""bb","ccc"
         * </pre>
         *
         * @param value the quote character
         *
         * @version 8.1
         * @since 8.1
         */
        public record Quote(char value) {

                /**
                 * The default quote character, '{@code "}'.
                 */
                public static final Quote DEFAULT = new Quote('"');

                /**
                 * The zero '\0' character.
                 */
                public static final Quote ZERO = new Quote('\0');

                /**
                 * Creates a new Quote char object.
                 *
                 * @param value the quote character
                 * @throws IllegalArgumentException if the given quote character is
                 *         a line break character
                 */
                public Quote {
                        if (isLineBreak(value)) {
                                throw new IllegalArgumentException(
                                        "Given quote char is a line break character."
                                );
                        }
                }
        }

        /**
         * Holds the column indexes, which should be part of the split or join
         * operation. When used in the {@link LineSplitter}, it lets you filter the
         * split column and define its order. When used in the {@link ColumnJoiner},
         * it can be used to define the column index in the resulting CSV for a
         * given row array.
         *
         * @apiNote
         * The column indexes is <em>thread-safe</em> and can be shared between
         * different threads.
         *
         * @see LineSplitter
         * @see ColumnJoiner
         *
         * @param values the column indexes which are part of the split result
         *
         * @version 8.1
         * @since 8.1
         */
        public record ColumnIndexes(int... values) {

                /**
                 * Indicating that <em>all</em> columns should be part of the split
                 * result.
                 */
                public static final ColumnIndexes ALL = new ColumnIndexes();

                /**
                 * Create a new column indexes object.
                 *
                 * @param values the column indexes
                 */
                public ColumnIndexes {
                        values = values.clone();
                }

                @Override
                public int[] values() {
                        return values.clone();
                }

                @Override
                public int hashCode() {
                        return Arrays.hashCode(values);
                }

                @Override
                public boolean equals(final Object obj) {
                        return obj instanceof ColumnIndexes ci &&
                                Arrays.equals(values, ci.values);
                }

                @Override
                public String toString() {
                        return Arrays.toString(values);
                }
        }

        /**
         * The newline string used for writing the CSV file: {@code \r\n}.
         */
        public static final String EOL = "\r\n";


        private CsvSupport() {
        }

        private static boolean isLineBreak(final char c) {
                return switch (c) {
                        case '\n', '\r' -> true;
                        default -> false;
                };
        }

        /**
         * Splits the CSV file, given by the {@code reader}, into a  {@link Stream}
         * of CSV lines. The CSV is split at line breaks, as long as they are not
         * part of a quoted column. For reading the CSV lines, the default quote
         * character, {@link Quote#DEFAULT}, is used.
         *
         * @apiNote
         * The returned stream must be closed by the caller, which also closes the
         * CSV {@code reader}.
         *
         * @see #readAllLines(Readable)
         *
         * @param reader the CSV source reader. The reader is automatically closed
         *        when the returned line stream is closed.
         * @return the stream of CSV lines
         * @throws NullPointerException if the given {@code reader} is {@code null}
         */
        public static Stream<String> lines(final Readable reader) {
                return LineReader.DEFAULT.read(reader);
        }

        /**
         * Splits the CSV file, given by the {@code reader}, into a  {@code Stream}
         * of CSV rows. The CSV is split at line breaks, as long as they are not
         * part of a quoted column. For reading the CSV lines, the default quote
         * character, {@link Quote#DEFAULT}, is used. Then each line is split into
         * its columns using the default separator character.
         *
         * @apiNote
         * The returned stream must be closed by the caller, which also closes the
         * CSV {@code reader}.
         *
         * @see #readAllRows(Readable)
         *
         * @param reader the CSV source reader. The reader is automatically closed
         *        when the returned line stream is closed.
         * @return the stream of CSV rows
         * @throws NullPointerException if the given {@code reader} is {@code null}
         */
        public static Stream<String[]> rows(final Readable reader) {
                final var splitter = new LineSplitter();
                return lines(reader).map(splitter::split);
        }

        /**
         * Splits the CSV file, given by the {@code reader}, into a  {@code List}
         * of CSV lines. The CSV is split at line breaks, as long as they are not
         * part of a quoted column. For reading the CSV lines, the default quote
         * character, {@link Quote#DEFAULT}, is used.
         *
         * @see #lines(Readable)
         *
         * @param reader the reader stream to split into CSV lines
         * @return the list of CSV lines
         * @throws NullPointerException if the given {@code reader} is {@code null}
         * @throws IOException if reading the CSV lines fails
         */
        public static List<String> readAllLines(final Readable reader)
                throws IOException
        {
                try (var lines = lines(reader)) {
                        return lines.toList();
                } catch (UncheckedIOException e) {
                        throw e.getCause();
                }
        }

        /**
         * Splits the CSV file, given by the {@code reader}, into a  {@code List}
         * of CSV lines. The CSV is split at line breaks, as long as they are not
         * part of a quoted column. For reading the CSV lines, the default quote
         * character, {@link Quote#DEFAULT}, is used. Then each line is split into
         * its columns using the default separator character.
         *
         * @see #rows(Readable)
         *
         * @param reader the reader stream to split into CSV lines
         * @return the list of CSV rows
         * @throws NullPointerException if the given {@code reader} is {@code null}
         * @throws IOException if reading the CSV lines fails
         */
        public static List<String[]> readAllRows(final Readable reader)
                throws IOException
        {
                try (var rows = rows(reader)) {
                        return rows.toList();
                } catch (UncheckedIOException e) {
                        throw e.getCause();
                }
        }

        /**
         * Parses the given CSV string into a list of <em>records</em>. The records
         * are created from a <em>row</em> ({@code String[]} array) by applying the
         * given {@code mapper}.
         *
         * @param csv the CSV string to parse
         * @param mapper the record mapper
         * @return the parsed record list
         * @param <T> the record type
         */
        public static <T> List<T> parse(
                final CharSequence csv,
                final Function<? super String[], ? extends T> mapper
        ) {
                requireNonNull(csv);
                requireNonNull(mapper);

                try (var rows = rows(CharBuffer.wrap(csv))) {
                        return rows
                                .map(mapper)
                                .collect(Collectors.toUnmodifiableList());
                }
        }

        /**
         * Parses the given CSV string into a list of rows.
         *
         * @param csv the CSV string to parse
         * @return the parsed CSV rows
         */
        public static List<String[]> parse(final CharSequence csv) {
                return parse(csv, Function.identity());
        }

        /**
         * Parses the given CSV string into a list of {@code double[]} array rows.
         *
         * @param csv the CSV string to parse
         * @return the parsed double data
         */
        public static List<double[]> parseDoubles(final CharSequence csv) {
                return parse(csv, CsvSupport::toDoubles);
        }

        private static double[] toDoubles(final String[] values) {
                final var result = new double[values.length];
                for (int i = 0; i < result.length; ++i) {
                        result[i] = Double.parseDouble(values[i].trim());
                }
                return result;
        }

        /**
         * Splits a given CSV {@code line} into columns. The default values for the
         * separator and quote character are used ({@link Separator#DEFAULT},
         * {@link Quote#DEFAULT}) for splitting the line.
         *
         * @param line the CSV line to split
         * @return the split CSV lines
         * @throws NullPointerException if the given {@code line} is {@code null}
         */
        public static String[] split(final CharSequence line) {
                return new LineSplitter().split(line);
        }

        /**
         * Joins the given CSV {@code columns} to one CSV line. The default values
         * for the separator and quote character are used ({@link Separator#DEFAULT},
         * {@link Quote#DEFAULT}) for joining the columns.
         *
         * @see #join(Object[])
         *
         * @param columns the CSV columns to join
         * @return the CSV line, joined from the given {@code columns}
         * @throws NullPointerException if the given {@code columns} is {@code null}
         */
        public static String join(final Iterable<?> columns) {
                return ColumnJoiner.DEFAULT.join(columns);
        }

        /**
         * Joins the given CSV {@code columns} to one CSV line. The default values
         * for the separator and quote character are used ({@link Separator#DEFAULT},
         * {@link Quote#DEFAULT}) for joining the columns.
         *
         * @see #join(Iterable)
         *
         * @param columns the CSV columns to join
         * @return the CSV line, joined from the given {@code columns}
         * @throws NullPointerException if the given {@code columns} is {@code null}
         */
        public static String join(final Object[] columns) {
                return ColumnJoiner.DEFAULT.join(columns);
        }

        /**
         * Joins the given CSV {@code columns} to one CSV line. The default values
         * for the separator and quote character are used ({@link Separator#DEFAULT},
         * {@link Quote#DEFAULT}) for joining the columns.
         *
         * @see #join(Iterable)
         * @see #join(Object[])
         *
         * @param columns the CSV columns to join
         * @return the CSV line, joined from the given {@code columns}
         * @throws NullPointerException if the given {@code columns} is {@code null}
         */
        public static String join(final String... columns) {
                return ColumnJoiner.DEFAULT.join(columns);
        }

        /**
         * Converts the given {@code record} into its components.
         *
         * @param record the record to convert
         * @return the record components
         */
        public static Object[] toComponents(final Record record) {
                try {
                        final var components = record.getClass().getRecordComponents();
                        final var elements = new Object[components.length];
                        for (int i = 0; i < elements.length; ++i) {
                                elements[i] = components[i].getAccessor().invoke(record);
                        }

                        return elements;
                } catch (ReflectiveOperationException e) {
                        throw new IllegalArgumentException(e);
                }
        }

        /**
         * Return a collector for joining a list of CSV rows into one CSV string.
         *
         * @return a collector for joining a list of CSV rows into one CSV string
         */
        public static Collector<CharSequence, ?, String> toCsv() {
                return toCsv(EOL);
        }

        /**
         * Return a collector for joining a list of CSV rows into one CSV string.
         * For the line breaks, the given {@code eol} sequence is used.
         *
         * @param eol the end of line sequence used for line breaks
         * @return a collector for joining a list of CSV rows into one CSV string
         */
        public static Collector<CharSequence, ?, String> toCsv(String eol) {
                if (eol.isEmpty()) {
                        throw new IllegalArgumentException("EOL must not be empty.");
                }
                for (int i = 0; i < eol.length(); ++i) {
                        if (!isLineBreak(eol.charAt(i))) {
                                throw new IllegalArgumentException(
                                        "EOl contains non-linebreak char: '%s'.".formatted(eol)
                                );
                        }
                }

                return Collectors.joining(eol, "", eol);
        }


        /* *************************************************************************
         * Base CSV classes.
         * ************************************************************************/

        /**
         * This class reads CSV files and splits it into lines. It takes a quote
         * character as a parameter, which is necessary for not splitting on quoted
         * line feeds.
         * {@snippet lang="java":
         * final var csv = """
         *     0.0,0.0000
         *     0.1,0.0740
         *     0.2,0.1120
         *     0.3,0.1380
         *     0.4,0.1760
         *     0.5,0.2500
         *     0.6,0.3840
         *     0.7,0.6020
         *     0.8,0.9280
         *     0.9,1.3860
         *     1.0,2.0000
         *     """;
         *
         * final var reader = new LineReader(new Quote('"'));
         * try (Stream<String> lines = reader.read(CharBuffer.wrap(csv))) {
         *     lines.forEach(System.out::println);
         * }
         * }
         *
         * @apiNote
         * This reader obeys <em>escaped</em> line breaks according
         * <a href="https://tools.ietf.org/html/rfc4180">RFC-4180</a>. It is
         * thread-safe and can be shared between different reading threads.
         *
         * @version 8.1
         * @since 8.1
         */
        public static final class LineReader {

                private static final LineReader DEFAULT = new LineReader(Quote.DEFAULT);

                private final Quote quote;

                /**
                 * Create a new line-reader with the given {@code quote} character,
                 * which is used in the CSV file which is read.
                 *
                 * @param quote the quoting character
                 * @throws NullPointerException if the {@code quote} character is
                 *         {@code null}
                 */
                public LineReader(final Quote quote) {
                        this.quote = requireNonNull(quote);
                }

                /**
                 * Create a new line reader with default quote character {@code '"'}
                 * ({@link Quote#DEFAULT}).
                 */
                public LineReader() {
                        this(Quote.DEFAULT);
                }

                /**
                 * Reads all CSV lines from the given {@code reader}.
                 *
                 * @apiNote
                 * This method must be used within a try-with-resources statement or
                 * similar control structure to ensure that the stream's open file is
                 * closed promptly after the stream's operations have completed.
                 *
                 * @param readable the readable from which to read the CSV content
                 * @return the CSV lines from the file as a {@code Stream}
                 */
                public Stream<String> read(final Readable readable) {
                        requireNonNull(readable);

                        final IOValue<Stream<String>> result = new IOValue<>(resources -> {
                                final Readable rdr = resources.use(
                                        readable,
                                        resource -> {
                                                if (resource instanceof AutoCloseable closeable) {
                                                        try {
                                                                closeable.close();
                                                        } catch (IOException | RuntimeException | Error e) {
                                                                throw e;
                                                        } catch (Exception e) {
                                                                throw new IOException(e);
                                                        }
                                                }
                                        }
                                );

                                final var source = CharCursor.of(rdr);
                                final var line = new CharAppender();

                                final Supplier<String> nextLine = () -> {
                                        line.reset();
                                        try {
                                                return nextLine(source, line) ? line.toString() : null;
                                        } catch (IOException e) {
                                                throw new UncheckedIOException(e);
                                        }
                                };

                                return Stream.generate(nextLine)
                                        .takeWhile(Objects::nonNull);
                        });

                        return result.get().onClose(() ->
                                result.release(UncheckedIOException::new)
                        );
                }

                private boolean nextLine(final CharCursor chars, final CharAppender line)
                        throws IOException
                {
                        boolean quoted = false;
                        boolean escaped = false;
                        boolean eol = false;

                        int next = -2;
                        int i = 0;

                        while (next >= 0 || (i = chars.next()) != -1) {
                                final char current = next != -2 ? (char)next : (char)i;
                                next = -2;

                                if (isLineBreak(current)) {
                                        if (quoted) {
                                                line.append(current);
                                        } else {
                                                eol = true;
                                        }
                                } else if (current == quote.value) {
                                        if (quoted) {
                                                if (!escaped && (next = chars.next()) == quote.value) {
                                                        escaped = true;
                                                } else {
                                                        if (escaped) {
                                                                escaped = false;
                                                        } else {
                                                                quoted = false;
                                                        }
                                                }
                                        } else {
                                                quoted = true;
                                        }
                                        line.append(current);
                                } else {
                                        line.append(current);
                                }

                                if (eol) {
                                        eol = false;
                                        if (line.nonEmpty()) {
                                                return true;
                                        }
                                }
                        }

                        if (quoted) {
                                throw new IllegalArgumentException(
                                        "Unbalanced quote character: '%s'."
                                                .formatted(toString(line))
                                );
                        }
                        return line.nonEmpty();
                }

                private static String toString(final Object value) {
                        final var line = value.toString();
                        return line.length() > 15 ? line.substring(0, 15) + "..." : line;
                }
        }

        /**
         * Splitting a CSV line into columns (records).
         * <h2>Examples</h2>
         * <b>Simple usage</b>
         * {@snippet class="Snippets" region="LineSplitterSnippets.simpleSplit"}
         *
         * <b>Projecting and re-ordering columns</b>
         * {@snippet class="Snippets" region="LineSplitterSnippets.projectingSplit"}
         *
         * @implNote
         * The split {@code String[]} array will never contain {@code null} values.
         * Empty columns will be returned as empty strings.
         *
         * @apiNote
         * A line splitter ist <b>not</b> thread-safe and can't be shared between
         * different threads.
         *
         * @version 8.1
         * @since 8.1
         */
        public static final class LineSplitter {
                private final Separator separator;
                private final Quote quote;

                private final ColumnList columns;
                private final CharAppender column = new CharAppender();

                /**
                 * Create a new line splitter with the given parameters.
                 *
                 * @param separator the separator character used by the CSV line to split
                 * @param quote the quote character used by the CSV line to split
                 * @param projection the column indexes which should be part of the split
                 *        result
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public LineSplitter(
                        final Separator separator,
                        final Quote quote,
                        final ColumnIndexes projection
                ) {
                        if (separator.value == quote.value) {
                                throw new IllegalArgumentException(
                                        "Separator and quote char must be different: %s == %s."
                                                .formatted(separator.value, quote.value)
                                );
                        }

                        this.separator = separator;
                        this.quote = quote;
                        this.columns = new ColumnList(projection);
                }

                /**
                 * Create a new line splitter with the given parameters.
                 *
                 * @param separator the separator character used by the CSV line to split
                 * @param quote the quote character used by the CSV line to split
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public LineSplitter(final Separator separator, final Quote quote) {
                        this(separator, quote, ColumnIndexes.ALL);
                }

                /**
                 * Create a new line splitter with the given parameters. The default
                 * quote character, {@link Quote#DEFAULT}, will be used by the created
                 * splitter.
                 *
                 * @param separator the separator character used by the CSV line to split
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public LineSplitter(final Separator separator) {
                        this(separator, Quote.DEFAULT, ColumnIndexes.ALL);
                }

                /**
                 * Create a new line splitter with the given parameters. The default
                 * separator character, {@link Separator#DEFAULT}, will be used by the
                 * created splitter.
                 *
                 * @param quote the quote character used by the CSV line to split
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public LineSplitter(final Quote quote) {
                        this(Separator.DEFAULT, quote, ColumnIndexes.ALL);
                }

                /**
                 * Create a new line splitter with the given parameters. Only the defined
                 * columns will be part of the split result and the default separator
                 * character, {@link Separator#DEFAULT}, and default quote character,
                 * {@link Quote#DEFAULT}, is used by the created splitter.
                 *
                 * @param projection the column indexes which should be part of the split
                 *        result
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public LineSplitter(final ColumnIndexes projection) {
                        this(Separator.DEFAULT, Quote.DEFAULT, projection);
                }

                /**
                 * Create a new line splitter with default values.
                 */
                public LineSplitter() {
                        this(Separator.DEFAULT, Quote.DEFAULT, ColumnIndexes.ALL);
                }

                /**
                 * Splitting the given CSV {@code line} into its columns.
                 *
                 * @implNote
                 * The split {@code String[]} array will never contain {@code null} values.
                 * Empty columns will be returned as empty strings.
                 *
                 * @param line the CSV line to split
                 * @return the split CSV columns
                 * @throws NullPointerException if the CSV {@code line} is {@code null}
                 */
                public String[] split(final CharSequence line) {
                        columns.clear();
                        column.reset();

                        boolean quoted = false;
                        boolean escaped = false;
                        boolean full = false;

                        int quoteIndex = 0;

                        for (int i = 0, n = line.length(); i < n && !full; ++i) {
                                final int previous = i > 0 ? line.charAt(i - 1) : -1;
                                final char current = line.charAt(i);
                                final int next = i + 1 < line.length() ? line.charAt(i + 1) : -1;

                                if (current == quote.value) {
                                        if (quoted) {
                                                if (!escaped && quote.value == next) {
                                                        escaped = true;
                                                } else {
                                                        if (escaped) {
                                                                column.append(quote.value);
                                                                escaped = false;
                                                        } else {
                                                                if (next != -1 && separator.value != next) {
                                                                        throw new IllegalArgumentException("""
                                                                                Only separator character, '%s', allowed \
                                                                                after quote, but found '%c':
                                                                                %s
                                                                                """.formatted(
                                                                                        separator.value,
                                                                                next,
                                                                                        toErrorDesc(line, i + 1)
                                                                                )
                                                                        );
                                                                }

                                                                add(column);
                                                                full = columns.isFull();
                                                                quoted = false;
                                                        }
                                                }
                                        } else {
                                                if (previous != -1 && separator.value != previous) {
                                                        throw new IllegalArgumentException("""
                                                                Only separator character, '%s', allowed before \
                                                                quote, but found '%c':
                                                                %s
                                                                """.formatted(
                                                                        separator.value,
                                                                previous,
                                                                        toErrorDesc(line, Math.max(i - 1, 0))
                                                                )
                                                        );
                                                }

                                                quoted = true;
                                                quoteIndex = i;
                                        }
                                } else if (current == separator.value) {
                                        if (quoted) {
                                                column.append(current);
                                        } else if (separator.value == previous || previous == -1) {
                                                add(column);
                                                full = columns.isFull();
                                        }
                                } else {
                                        // Read till the next token separator.
                                        int j = i;
                                        char c;
                                        while (j < line.length() && !isTokenSeparator(c = line.charAt(j))) {
                                                column.append(c);
                                                ++j;
                                        }
                                        if (j != i - 1) {
                                                i = j - 1;
                                        }

                                        if (!quoted) {
                                                add(column);
                                                full = columns.isFull();
                                        }
                                }
                        }

                        if (quoted) {
                                throw new IllegalArgumentException("""
                                        Unbalanced quote character.
                                        %s
                                        """.formatted(toErrorDesc(line, quoteIndex))
                                );
                        }
                        if (line.isEmpty() ||
                                separator.value == line.charAt(line.length() - 1))
                        {
                                add(column);
                        }

                        return columns.toArray();
                }

                private void add(final CharAppender column) {
                        columns.add(column.toString());
                        column.reset();
                }

                private boolean isTokenSeparator(final char c) {
                        return c == separator.value || c == quote.value;
                }

                private static String toErrorDesc(final CharSequence line, final int pos) {
                        return """
                                %s
                                %s
                                """.formatted(
                                        line.toString().stripTrailing(),
                                        " ".repeat(pos) + "^"
                                );
                }
        }


        /**
         * Column collection, which is backed up by a string list.
         */
        static final class ColumnList {
                private final StringList columns = new StringList();
                private final ColumnIndexes projection;

                private int index = 0;
                private int count = 0;

                ColumnList(final ColumnIndexes projection) {
                        this.projection = requireNonNull(projection);
                }

                /**
                 * Appends a {@code column} to the column collection.
                 *
                 * @param column the column to add
                 */
                void add(String column) {
                        if (!isFull()) {
                                count += set(column, index++);
                        }
                }

                private int set(String element, int column) {
                        int updated = 0;

                        if (projection.values.length == 0) {
                                columns.add(element);
                                ++updated;
                        } else {
                                int pos = -1;
                                while ((pos = indexOf(projection.values, pos + 1, column)) != -1) {
                                        for (int i = columns.size(); i <= pos; ++i) {
                                                columns.add(null);
                                        }
                                        columns.set(pos, element);
                                        ++updated;
                                }
                        }

                        return updated;
                }

                private static int indexOf(int[] array, int start, int value) {
                        for (int i = start; i < array.length; ++i) {
                                if (array[i] == value) {
                                        return i;
                                }
                        }

                        return -1;
                }

                /**
                 * Checks whether another column can be added.
                 *
                 * @return {@code true} if another column can be added to this
                 *         collection, {@code false} otherwise
                 */
                boolean isFull() {
                        return
                                projection.values.length > 0 &&
                                projection.values.length <= count;
                }

                /**
                 * Removes all columns.
                 */
                public void clear() {
                        columns.clear();
                        index = 0;
                        count = 0;
                }

                String[] toArray() {
                        for (int i = columns.size(); i < projection.values.length; ++i) {
                                columns.add(null);
                        }
                        return columns.toArray();
                }

        }

        /**
         * This class joins an array of columns into one CSV line.
         *
         * <h2>Examples</h2>
         * <b>Simple usage</b>
         * {@snippet class="Snippets" region="ColumnJoinerSnippets.simpleJoin"}
         *
         * <b>Embedding and re-ordering data</b>
         * {@snippet class="Snippets" region="ColumnJoinerSnippets.embedToCsv"}
         *
         * @apiNote
         * The column joiner is <em>thread-safe</em> and can be shared between
         * different threads.
         *
         * @version 8.1
         * @since 8.1
         */
        public static final class ColumnJoiner {

                /**
                 * Default column joiner, which is using default separator character,
                 * {@link Separator#DEFAULT}, and default quote character,
                 * {@link Quote#DEFAULT}.
                 */
                public static final ColumnJoiner DEFAULT = new ColumnJoiner(
                        Separator.DEFAULT,
                        Quote.DEFAULT,
                        ColumnIndexes.ALL
                );

                /**
                 * The CSV line splitter parameter.
                 *
                 * @param separator the column separator char
                 * @param quote the qute char
                 * @param embedding the column indices to read. If empty, all split
                 *        columns are used.
                 */
                private record Param(char separator, char quote, int... embedding) {

                        private String escape(Object value) {
                                final var quoteStr = String.valueOf(quote);

                                if (value == null) {
                                        return "";
                                } else {
                                        var stringValue = value.toString();
                                        var string = stringValue.replace(quoteStr, quoteStr + quoteStr);

                                        if (stringValue.length() != string.length() || mustEscape(string)) {
                                                return quoteStr + string + quoteStr;
                                        } else {
                                                return stringValue;
                                        }
                                }
                        }

                        private boolean mustEscape(CharSequence value) {
                                for (int i = 0; i < value.length(); ++i) {
                                        final char c = value.charAt(i);
                                        if (c == separator || isLineBreak(c)) {
                                                return true;
                                        }
                                }
                                return false;
                        }
                }

                private final Param param;
                private final int columnCount;

                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param separator the CSV separator character used by the joiner
                 * @param quote the CSV quote character used by the joiner
                 * @param embedding the column indexes to join
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(
                        final Separator separator,
                        final Quote quote,
                        final ColumnIndexes embedding
                ) {
                        if (separator.value == quote.value) {
                                throw new IllegalArgumentException(
                                        "Separator and quote char must be different: %s == %s."
                                                .formatted(separator.value, quote.value)
                                );
                        }

                        param = new Param(separator.value, quote.value, embedding.values);
                        columnCount = Math.max(max(param.embedding) + 1, 0);
                }

                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param separator the CSV separator character used by the joiner
                 * @param quote the CSV quote character used by the joiner
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(final Separator separator, final Quote quote) {
                        this(separator, quote, ColumnIndexes.ALL);
                }

                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param separator the CSV separator character used by the joiner
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(final Separator separator) {
                        this(separator, Quote.DEFAULT, ColumnIndexes.ALL);
                }

                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param separator the CSV separator character used by the joiner
                 * @param embedding the column indexes to join
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(final Separator separator, final ColumnIndexes embedding) {
                        this(separator, Quote.DEFAULT, embedding);
                }


                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param quote the CSV quote character used by the joiner
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(final Quote quote) {
                        this(Separator.DEFAULT, quote, ColumnIndexes.ALL);
                }

                /**
                 * Create a new column joiner with the given <em>embedding</em> column
                 * indexes.
                 *
                 * @param embedding the embedding column indexes
                 */
                public ColumnJoiner(final ColumnIndexes embedding) {
                        this(Separator.DEFAULT, Quote.DEFAULT, embedding);
                }

                /**
                 * Create a new column joiner with the given parameters.
                 *
                 * @param quote the CSV quote character used by the joiner
                 * @param embedding the column indexes to join
                 * @throws NullPointerException if one of the parameters is {@code null}
                 */
                public ColumnJoiner(final Quote quote, final ColumnIndexes embedding) {
                        this(Separator.DEFAULT, quote, embedding);
                }

                private static int max(int[] array) {
                        int max = Integer.MIN_VALUE;
                        for (int value : array) {
                                if (value > max) {
                                        max = value;
                                }
                        }
                        return max;
                }

                /**
                 * Joins the given CSV {@code columns}, using the given separator and
                 * quote character.
                 *
                 * @param columns the CSV columns to join
                 * @return the joined CSV columns
                 */
                public String join(final Iterable<?> columns) {
                        if (param.embedding.length == 0) {
                                return join0(columns);
                        } else {
                                final var values = new Object[columnCount];
                                final var it = columns.iterator();
                                int i = 0;
                                while (it.hasNext() && i < param.embedding.length) {
                                        final var col = it.next();
                                        final var index = param.embedding[i++];
                                        if (index >= 0) {
                                                values[index] = col;
                                        }
                                }

                                return join0(Arrays.asList(values));
                        }
                }

                private String join0(final Iterable<?> cols) {
                        final var row = new StringBuilder();
                        final var it = cols.iterator();
                        while (it.hasNext()) {
                                final var column = it.next();
                                row.append(param.escape(column));
                                if (it.hasNext()) {
                                        row.append(param.separator);
                                }
                        }

                        return row.toString();
                }

                /**
                 * Joins the given CSV {@code columns}, using the given separator and
                 * quote character.
                 *
                 * @param columns the CSV columns to join
                 * @return the joined CSV columns
                 */
                public String join(final Object[] columns) {
                        return join(Arrays.asList(columns));
                }
        }

        /**
         * Character source interface.
         *
         * @since 8.2
         * @version 8.2
         */
        sealed interface CharCursor {
                /**
                 * Return the next character or -1 if there is no one.
                 *
                 * @return the next character or -1 if there is no one
                 * @throws IOException if reading the next character failed
                 */
                int next() throws IOException;

                /**
                 * Return the correct kind of {@code CharCursor}, depending on the
                 * given {@code readable} type
                 *
                 * @param readable the character source
                 * @return a new character cursor
                 */
                static CharCursor of(final Readable readable) {
                        return readable instanceof CharBuffer cb
                                ? new CharBufferCharCursor(cb)
                                : new ReadableCharCursor(readable);
                }
        }

        /**
         * Cursor <em>view</em> on a readable object.
         *
         * @since 8.2
         * @version 8.2
         */
        static final class ReadableCharCursor implements CharCursor {
                private static final int SIZE = 1024;
                private final Readable readable;
                private final CharBuffer buffer;

                ReadableCharCursor(final Readable readable) {
                        this.readable = requireNonNull(readable);
                        this.buffer = CharBuffer.allocate(SIZE).flip();
                }

                @Override
                public int next() throws IOException {
                        if (!buffer.hasRemaining()) {
                                if (!fill()) {
                                        return -1;
                                }
                        }

                        return buffer.get();
                }

                private boolean fill() throws IOException {
                        int n;
                        int i = 0;
                        buffer.clear();
                        do {
                                n = readable.read(buffer);
                        } while (n == 0 && i++ < 1000); // Make sure re-read will terminate.
                        buffer.flip();

                        return n > 0;
                }
        }

        /**
         * Cursor <em>view</em> on a character buffer.
         *
         * @since 8.2
         * @version 8.2
         */
        static final class CharBufferCharCursor implements CharCursor {
                private final CharBuffer buffer;

                CharBufferCharCursor(final CharBuffer buffer) {
                        this.buffer = requireNonNull(buffer);
                }

                @Override
                public int next() {
                        if (!buffer.hasRemaining()) {
                                return -1;
                        }
                        return buffer.get();
                }
        }

        /**
         * Allows appending chars in bulks to {@link StringBuilder}.
         *
         * @since 8.2
         * @version 8.2
         */
        static final class CharAppender {
                private static final int SIZE = 32;

                private char[] buffer = new char[SIZE];
                private int index = 0;

                CharAppender() {
                }

                boolean nonEmpty() {
                        return index != 0;
                }

                void append(final char c) {
                        if (index == buffer.length) {
                                increaseSize(buffer.length*2);
                        }

                        buffer[index++] = c;
                }

                @Override
                public String toString() {
                        return String.valueOf(buffer, 0, index);
                }

                void reset() {
                        index = 0;
                }

                private void increaseSize(final int newSize) {
                        final char[] newBuffer = new char[newSize];
                        System.arraycopy(buffer, 0, newBuffer, 0, index);
                        buffer = newBuffer;
                }
        }

        /**
         * Simple growing list of strings.
         *
         * @since 8.2
         * @version 8.2
         */
        static final class StringList {
                private static final int SIZE = 16;
                private String[] elements;
                private int size;

                StringList() {
                        size = 0;
                        elements = new String[SIZE];
                }

                public int size() {
                        return size;
                }

                public void add(final String value) {
                        if (size == elements.length) {
                                increaseSize(elements.length*2);
                        }
                        elements[size++] = value;
                }

                public void set(final int index, final String value) {
                        elements[index] = value;
                }

                public void clear() {
                        size = 0;
                }

                public String[] toArray() {
                        final var result = new String[size];
                        System.arraycopy(elements, 0, result, 0, size);
                        return result;
                }

                private void increaseSize(final int newSize) {
                        final String[] newElements = new String[newSize];
                        System.arraycopy(elements, 0, newElements, 0, size);
                        elements = newElements;
                }

        }

}