/*
 * 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.commons.csv;

import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;

import static org.apache.commons.csv.Token.Type.*;

/**
 * Parses CSV files according to the specified format.
 *
 * Because CSV appears in many different dialects, the parser supports many formats by allowing the
 * specification of a {@link CSVFormat}.
 *
 * The parser works record wise. It is not possible to go back, once a record has been parsed from the input stream.
 *
 * <h2>Creating instances</h2>
 * <p>
 * There are several static factory methods that can be used to create instances for various types of resources:
 * </p>
 * <ul>
 *     <li>{@link #parse(java.io.File, Charset, CSVFormat)}</li>
 *     <li>{@link #parse(String, CSVFormat)}</li>
 *     <li>{@link #parse(java.net.URL, java.nio.charset.Charset, CSVFormat)}</li>
 * </ul>
 * <p>
 * Alternatively parsers can also be created by passing a {@link Reader} directly to the sole constructor.
 *
 * For those who like fluent APIs, parsers can be created using {@link CSVFormat#parse(java.io.Reader)} as a shortcut:
 * </p>
 * <pre>
 * for(CSVRecord record : CSVFormat.EXCEL.parse(in)) {
 *     ...
 * }
 * </pre>
 *
 * <h2>Parsing record wise</h2>
 * <p>
 * To parse a CSV input from a file, you write:
 * </p>
 *
 * <pre>
 * File csvData = new File(&quot;/path/to/csv&quot;);
 * CSVParser parser = CSVParser.parse(csvData, CSVFormat.RFC4180);
 * for (CSVRecord csvRecord : parser) {
 *     ...
 * }
 * </pre>
 *
 * <p>
 * This will read the parse the contents of the file using the
 * <a href="http://tools.ietf.org/html/rfc4180" target="_blank">RFC 4180</a> format.
 * </p>
 *
 * <p>
 * To parse CSV input in a format like Excel, you write:
 * </p>
 *
 * <pre>
 * CSVParser parser = CSVParser.parse(csvData, CSVFormat.EXCEL);
 * for (CSVRecord csvRecord : parser) {
 *     ...
 * }
 * </pre>
 *
 * <p>
 * If the predefined formats don't match the format at hands, custom formats can be defined. More information about
 * customising CSVFormats is available in {@link CSVFormat CSVFormat JavaDoc}.
 * </p>
 *
 * <h2>Parsing into memory</h2>
 * <p>
 * If parsing record wise is not desired, the contents of the input can be read completely into memory.
 * </p>
 *
 * <pre>
 * Reader in = new StringReader(&quot;a;b\nc;d&quot;);
 * CSVParser parser = new CSVParser(in, CSVFormat.EXCEL);
 * List&lt;CSVRecord&gt; list = parser.getRecords();
 * </pre>
 *
 * <p>
 * There are two constraints that have to be kept in mind:
 * </p>
 *
 * <ol>
 *     <li>Parsing into memory starts at the current position of the parser. If you have already parsed records from
 *     the input, those records will not end up in the in memory representation of your CSV data.</li>
 *     <li>Parsing into memory may consume a lot of system resources depending on the input. For example if you're
 *     parsing a 150MB file of CSV data the contents will be read completely into memory.</li>
 * </ol>
 *
 * <h2>Notes</h2>
 * <p>
 * Internal parser state is completely covered by the format and the reader-state.
 * </p>
 *
 * @version $Id: CSVParser.java 1695167 2015-08-10 21:08:58Z ggregory $
 *
 * @see <a href="package-summary.html">package documentation for more details</a>
 */
public final class CSVParser implements Iterable<CSVRecord>, Closeable {

    /**
     * Creates a parser for the given {@link File}.
     *
     * <p><strong>Note:</strong> This method internally creates a FileReader using
     * {@link java.io.FileReader#FileReader(java.io.File)} which in turn relies on the default encoding of the JVM that
     * is executing the code. If this is insufficient create a URL to the file and use
     * {@link #parse(URL, Charset, CSVFormat)}</p>
     *
     * @param file
     *            a CSV file. Must not be null.
     * @param charset
     *            A charset
     * @param format
     *            the CSVFormat used for CSV parsing. Must not be null.
     * @return a new parser
     * @throws IllegalArgumentException
     *             If the parameters of the format are inconsistent or if either file or format are null.
     * @throws IOException
     *             If an I/O error occurs
     */
    public static CSVParser parse(final File file, final Charset charset, final CSVFormat format) throws IOException {
        Assertions.notNull(file, "file");
        Assertions.notNull(format, "format");
        return new CSVParser(new InputStreamReader(new FileInputStream(file), charset), format);
    }

    /**
     * Creates a parser for the given {@link String}.
     *
     * @param string
     *            a CSV string. Must not be null.
     * @param format
     *            the CSVFormat used for CSV parsing. Must not be null.
     * @return a new parser
     * @throws IllegalArgumentException
     *             If the parameters of the format are inconsistent or if either string or format are null.
     * @throws IOException
     *             If an I/O error occurs
     */
    public static CSVParser parse(final String string, final CSVFormat format) throws IOException {
        Assertions.notNull(string, "string");
        Assertions.notNull(format, "format");

        return new CSVParser(new StringReader(string), format);
    }

    /**
     * Creates a parser for the given URL.
     *
     * <p>
     * If you do not read all records from the given {@code url}, you should call {@link #close()} on the parser, unless
     * you close the {@code url}.
     * </p>
     *
     * @param url
     *            a URL. Must not be null.
     * @param charset
     *            the charset for the resource. Must not be null.
     * @param format
     *            the CSVFormat used for CSV parsing. Must not be null.
     * @return a new parser
     * @throws IllegalArgumentException
     *             If the parameters of the format are inconsistent or if either url, charset or format are null.
     * @throws IOException
     *             If an I/O error occurs
     */
    public static CSVParser parse(final URL url, final Charset charset, final CSVFormat format) throws IOException {
        Assertions.notNull(url, "url");
        Assertions.notNull(charset, "charset");
        Assertions.notNull(format, "format");

        return new CSVParser(new InputStreamReader(url.openStream(), charset), format);
    }

    // the following objects are shared to reduce garbage

    private final CSVFormat format;

    /** A mapping of column names to column indices */
    private final Map<String, Integer> headerMap;

    private final Lexer lexer;

    /** A record buffer for getRecord(). Grows as necessary and is reused. */
    private final List<String> record = new ArrayList<String>();

    /**
     * The next record number to assign.
     */
    private long recordNumber;

    /**
     * Lexer offset when the parser does not start parsing at the beginning of the source. Usually used in combination
     * with {@link #recordNumber}.
     */
    private final long characterOffset;

    private final Token reusableToken = new Token();

    /**
     * Customized CSV parser using the given {@link CSVFormat}
     *
     * <p>
     * If you do not read all records from the given {@code reader}, you should call {@link #close()} on the parser,
     * unless you close the {@code reader}.
     * </p>
     *
     * @param reader
     *            a Reader containing CSV-formatted input. Must not be null.
     * @param format
     *            the CSVFormat used for CSV parsing. Must not be null.
     * @throws IllegalArgumentException
     *             If the parameters of the format are inconsistent or if either reader or format are null.
     * @throws IOException
     *             If there is a problem reading the header or skipping the first record
     */
    public CSVParser(final Reader reader, final CSVFormat format) throws IOException {
        this(reader, format, 0, 1);
    }

    /**
     * Customized CSV parser using the given {@link CSVFormat}
     *
     * <p>
     * If you do not read all records from the given {@code reader}, you should call {@link #close()} on the parser,
     * unless you close the {@code reader}.
     * </p>
     *
     * @param reader
     *            a Reader containing CSV-formatted input. Must not be null.
     * @param format
     *            the CSVFormat used for CSV parsing. Must not be null.
     * @param characterOffset
     *            Lexer offset when the parser does not start parsing at the beginning of the source.
     * @param recordNumber
     *            The next record number to assign
     * @throws IllegalArgumentException
     *             If the parameters of the format are inconsistent or if either reader or format are null.
     * @throws IOException
     *             If there is a problem reading the header or skipping the first record
     * @since 1.1
     */
    public CSVParser(final Reader reader, final CSVFormat format, final long characterOffset, final long recordNumber)
            throws IOException {
        Assertions.notNull(reader, "reader");
        Assertions.notNull(format, "format");

        this.format = format;
        this.lexer = new Lexer(format, new ExtendedBufferedReader(reader));
        this.headerMap = this.initializeHeader();
        this.characterOffset = characterOffset;
        this.recordNumber = recordNumber - 1;
    }

    private void addRecordValue() {
        final String input = this.reusableToken.content.toString();
        final String nullString = this.format.getNullString();
        if (nullString == null) {
            this.record.add(input);
        } else {
            this.record.add(input.equalsIgnoreCase(nullString) ? null : input);
        }
    }

    /**
     * Closes resources.
     *
     * @throws IOException
     *             If an I/O error occurs
     */
    @Override
    public void close() throws IOException {
        if (this.lexer != null) {
            this.lexer.close();
        }
    }

    /**
     * Returns the current line number in the input stream.
     *
     * <p>
     * <strong>ATTENTION:</strong> If your CSV input has multi-line values, the returned number does not correspond to
     * the record number.
     * </p>
     *
     * @return current line number
     */
    public long getCurrentLineNumber() {
        return this.lexer.getCurrentLineNumber();
    }

    /**
     * Returns a copy of the header map that iterates in column order.
     * <p>
     * The map keys are column names. The map values are 0-based indices.
     * </p>
     * @return a copy of the header map that iterates in column order.
     */
    public Map<String, Integer> getHeaderMap() {
        return this.headerMap == null ? null : new LinkedHashMap<String, Integer>(this.headerMap);
    }

    /**
     * Returns the current record number in the input stream.
     *
     * <p>
     * <strong>ATTENTION:</strong> If your CSV input has multi-line values, the returned number does not correspond to
     * the line number.
     * </p>
     *
     * @return current record number
     */
    public long getRecordNumber() {
        return this.recordNumber;
    }

    /**
     * Parses the CSV input according to the given format and returns the content as a list of
     * {@link CSVRecord CSVRecords}.
     *
     * <p>
     * The returned content starts at the current parse-position in the stream.
     * </p>
     *
     * @return list of {@link CSVRecord CSVRecords}, may be empty
     * @throws IOException
     *             on parse error or input read-failure
     */
    public List<CSVRecord> getRecords() throws IOException {
        CSVRecord rec;
        final List<CSVRecord> records = new ArrayList<CSVRecord>();
        while ((rec = this.nextRecord()) != null) {
            records.add(rec);
        }
        return records;
    }

    /**
     * Initializes the name to index mapping if the format defines a header.
     *
     * @return null if the format has no header.
     * @throws IOException if there is a problem reading the header or skipping the first record
     */
    private Map<String, Integer> initializeHeader() throws IOException {
        Map<String, Integer> hdrMap = null;
        final String[] formatHeader = this.format.getHeader();
        if (formatHeader != null) {
            hdrMap = new LinkedHashMap<String, Integer>();

            String[] headerRecord = null;
            if (formatHeader.length == 0) {
                // read the header from the first line of the file
                final CSVRecord nextRecord = this.nextRecord();
                if (nextRecord != null) {
                    headerRecord = nextRecord.values();
                }
            } else {
                if (this.format.getSkipHeaderRecord()) {
                    this.nextRecord();
                }
                headerRecord = formatHeader;
            }

            // build the name to index mappings
            if (headerRecord != null) {
                for (int i = 0; i < headerRecord.length; i++) {
                    final String header = headerRecord[i];
                    final boolean containsHeader = hdrMap.containsKey(header);
                    final boolean emptyHeader = header == null || header.trim().isEmpty();
                    if (containsHeader &&
                            (!emptyHeader || (emptyHeader && !this.format.getAllowMissingColumnNames()))) {
                        throw new IllegalArgumentException("The header contains a duplicate name: \"" + header +
                                "\" in " + Arrays.toString(headerRecord));
                    }
                    hdrMap.put(header, Integer.valueOf(i));
                }
            }
        }
        return hdrMap;
    }

    /**
     * Gets whether this parser is closed.
     *
     * @return whether this parser is closed.
     */
    public boolean isClosed() {
        return this.lexer.isClosed();
    }

    /**
     * Returns an iterator on the records.
     *
     * <p>IOExceptions occurring during the iteration are wrapped in a
     * RuntimeException.
     * If the parser is closed a call to {@code next()} will throw a
     * NoSuchElementException.</p>
     */
    @Override
    public Iterator<CSVRecord> iterator() {
        return new Iterator<CSVRecord>() {
            private CSVRecord current;

            private CSVRecord getNextRecord() {
                try {
                    return CSVParser.this.nextRecord();
                } catch (final IOException e) {
                    // TODO: This is not great, throw an ISE instead?
                    throw new RuntimeException(e);
                }
            }

            @Override
            public boolean hasNext() {
                if (CSVParser.this.isClosed()) {
                    return false;
                }
                if (this.current == null) {
                    this.current = this.getNextRecord();
                }

                return this.current != null;
            }

            @Override
            public CSVRecord next() {
                if (CSVParser.this.isClosed()) {
                    throw new NoSuchElementException("CSVParser has been closed");
                }
                CSVRecord next = this.current;
                this.current = null;

                if (next == null) {
                    // hasNext() wasn't called before
                    next = this.getNextRecord();
                    if (next == null) {
                        throw new NoSuchElementException("No more CSV records available");
                    }
                }

                return next;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    /**
     * Parses the next record from the current point in the stream.
     *
     * @return the record as an array of values, or {@code null} if the end of the stream has been reached
     * @throws IOException
     *             on parse error or input read-failure
     */
    CSVRecord nextRecord() throws IOException {
        CSVRecord result = null;
        this.record.clear();
        StringBuilder sb = null;
        final long startCharPosition = lexer.getCharacterPosition() + this.characterOffset;
        do {
            this.reusableToken.reset();
            this.lexer.nextToken(this.reusableToken);
            switch (this.reusableToken.type) {
            case TOKEN:
                this.addRecordValue();
                break;
            case EORECORD:
                this.addRecordValue();
                break;
            case EOF:
                if (this.reusableToken.isReady) {
                    this.addRecordValue();
                }
                break;
            case INVALID:
                throw new IOException("(line " + this.getCurrentLineNumber() + ") invalid parse sequence");
            case COMMENT: // Ignored currently
                if (sb == null) { // first comment for this record
                    sb = new StringBuilder();
                } else {
                    sb.append(Constants.LF);
                }
                sb.append(this.reusableToken.content);
                this.reusableToken.type = TOKEN; // Read another token
                break;
            default:
                throw new IllegalStateException("Unexpected Token type: " + this.reusableToken.type);
            }
        } while (this.reusableToken.type == TOKEN);

        if (!this.record.isEmpty()) {
            this.recordNumber++;
            final String comment = sb == null ? null : sb.toString();
            result = new CSVRecord(this.record.toArray(new String[this.record.size()]), this.headerMap, comment,
                    this.recordNumber, startCharPosition);
        }
        return result;
    }

}
