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   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
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   distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.poi.examples.xssf.usermodel;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

import org.apache.commons.compress.archivers.zip.ZipArchiveEntry;
import org.apache.commons.compress.archivers.zip.ZipArchiveOutputStream;
import org.apache.commons.compress.archivers.zip.ZipFile;
import org.apache.poi.openxml4j.opc.internal.ZipHelper;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.usermodel.FillPatternType;
import org.apache.poi.ss.usermodel.HorizontalAlignment;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.ss.util.CellReference;
import org.apache.poi.util.LocaleUtil;
import org.apache.poi.xssf.usermodel.XSSFCellStyle;
import org.apache.poi.xssf.usermodel.XSSFDataFormat;
import org.apache.poi.xssf.usermodel.XSSFFont;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

/**
 * Demonstrates a workaround you can use to generate large workbooks and avoid OutOfMemory exception.
 * <p>
 * Note - You probably <em>don't want to use this approach any more</em>! POI
 *  now includes the SXSSF which handles all of this for you, you should
 *  be using that instead! This code remains mostly for historical interest.
 * <p>
 * If you really want to use this approach, which is also the one that SXSSF
 * does for you, it works as follows:
 * <ol>
 * <li>create a template workbook, create sheets and global objects such as cell styles, number formats, etc.</li>
 * <li>create an application that streams data in a text file</li>
 * <li>Substitute the sheet in the template with the generated data</li>
 * </ol>
 *
 *  Since 3.8 POI provides a low-memory footprint SXSSF API, which implements
 *  ths "BigGridDemo" strategy. SXSSF is an API-compatible streaming extension
 *  of XSSF to be used when very large spreadsheets have to be produced, and
 *  heap space is limited. SXSSF achieves its low memory footprint by limiting
 *  access to the rows that are within a sliding window, while XSSF gives access
 *  to all rows in the document. Older rows that are no longer in the window
 *  become inaccessible, as they are written to the disk.
 *
 * @see <a href="https://poi.apache.org/spreadsheet/how-to.html#sxssf">SXSSF (Streaming Usermodel API)</a>.
 */
public final class BigGridDemo {
    private static final String XML_ENCODING = "UTF-8";

    private static final Random rnd = new Random();

    private BigGridDemo() {}

    public static void main(String[] args) throws Exception {

        // Step 1. Create a template file. Setup sheets and workbook-level objects such as
        // cell styles, number formats, etc.

        try (XSSFWorkbook wb = new XSSFWorkbook()) {
            XSSFSheet sheet = wb.createSheet("Big Grid");

            Map<String, XSSFCellStyle> styles = createStyles(wb);
            //name of the zip entry holding sheet data, e.g. /xl/worksheets/sheet1.xml
            String sheetRef = sheet.getPackagePart().getPartName().getName();

            //save the template
            try (FileOutputStream os = new FileOutputStream("template.xlsx")) {
                wb.write(os);
            }

            //Step 2. Generate XML file.
            File tmp = File.createTempFile("sheet", ".xml");
            try (
                    FileOutputStream stream = new FileOutputStream(tmp);
                    Writer fw = new OutputStreamWriter(stream, XML_ENCODING)
                ) {
                generate(fw, styles);
            }

            //Step 3. Substitute the template entry with the generated data
            try (FileOutputStream out = new FileOutputStream("big-grid.xlsx")) {
                substitute(new File("template.xlsx"), tmp, sheetRef.substring(1), out);
            }
        }
    }

    /**
     * Create a library of cell styles.
     */
    private static Map<String, XSSFCellStyle> createStyles(XSSFWorkbook wb){
        Map<String, XSSFCellStyle> styles = new HashMap<>();
        XSSFDataFormat fmt = wb.createDataFormat();

        XSSFCellStyle style1 = wb.createCellStyle();
        style1.setAlignment(HorizontalAlignment.RIGHT);
        style1.setDataFormat(fmt.getFormat("0.0%"));
        styles.put("percent", style1);

        XSSFCellStyle style2 = wb.createCellStyle();
        style2.setAlignment(HorizontalAlignment.CENTER);
        style2.setDataFormat(fmt.getFormat("0.0X"));
        styles.put("coeff", style2);

        XSSFCellStyle style3 = wb.createCellStyle();
        style3.setAlignment(HorizontalAlignment.RIGHT);
        style3.setDataFormat(fmt.getFormat("$#,##0.00"));
        styles.put("currency", style3);

        XSSFCellStyle style4 = wb.createCellStyle();
        style4.setAlignment(HorizontalAlignment.RIGHT);
        style4.setDataFormat(fmt.getFormat("mmm dd"));
        styles.put("date", style4);

        XSSFCellStyle style5 = wb.createCellStyle();
        XSSFFont headerFont = wb.createFont();
        headerFont.setBold(true);
        style5.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        style5.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        style5.setFont(headerFont);
        styles.put("header", style5);

        return styles;
    }

    private static void generate(Writer out, Map<String, XSSFCellStyle> styles) throws Exception {

        Calendar calendar = LocaleUtil.getLocaleCalendar();

        SpreadsheetWriter sw = new SpreadsheetWriter(out);
        sw.beginSheet();

        //insert header row
        sw.insertRow(0);
        int styleIndex = styles.get("header").getIndex();
        sw.createCell(0, "Title", styleIndex);
        sw.createCell(1, "% Change", styleIndex);
        sw.createCell(2, "Ratio", styleIndex);
        sw.createCell(3, "Expenses", styleIndex);
        sw.createCell(4, "Date", styleIndex);

        sw.endRow();

        //write data rows
        for (int rownum = 1; rownum < 100000; rownum++) {
            sw.insertRow(rownum);

            sw.createCell(0, "Hello, " + rownum + "!");
            sw.createCell(1, (double)rnd.nextInt(100)/100, styles.get("percent").getIndex());
            sw.createCell(2, (double)rnd.nextInt(10)/10, styles.get("coeff").getIndex());
            sw.createCell(3, rnd.nextInt(10000), styles.get("currency").getIndex());
            sw.createCell(4, calendar, styles.get("date").getIndex());

            sw.endRow();

            calendar.roll(Calendar.DAY_OF_YEAR, 1);
        }
        sw.endSheet();
    }

    /**
     *
     * @param zipfile the template file
     * @param tmpfile the XML file with the sheet data
     * @param entry the name of the sheet entry to substitute, e.g. xl/worksheets/sheet1.xml
     * @param out the stream to write the result to
     */
    private static void substitute(File zipfile, File tmpfile, String entry, OutputStream out) throws IOException {
        try (ZipFile zip = ZipHelper.openZipFile(zipfile)) {
            try (ZipArchiveOutputStream zos = new ZipArchiveOutputStream(out)) {
                Enumeration<? extends ZipArchiveEntry> en = zip.getEntries();
                while (en.hasMoreElements()) {
                    ZipArchiveEntry ze = en.nextElement();
                    if (!ze.getName().equals(entry)) {
                        zos.putArchiveEntry(new ZipArchiveEntry(ze.getName()));
                        try (InputStream is = zip.getInputStream(ze)) {
                            copyStream(is, zos);
                        }
                        zos.closeArchiveEntry();
                    }
                }
                zos.putArchiveEntry(new ZipArchiveEntry(entry));
                try (InputStream is = new FileInputStream(tmpfile)) {
                    copyStream(is, zos);
                }
                zos.closeArchiveEntry();
            }
        }
    }

    private static void copyStream(InputStream in, OutputStream out) throws IOException {
        byte[] chunk = new byte[1024];
        int count;
        while ((count = in.read(chunk)) >=0 ) {
          out.write(chunk,0,count);
        }
    }

    /**
     * Writes spreadsheet data in a Writer.
     * (YK: in future it may evolve in a full-featured API for streaming data in Excel)
     */
    public static class SpreadsheetWriter {
        private final Writer _out;
        private int _rownum;

        SpreadsheetWriter(Writer out){
            _out = out;
        }

        void beginSheet() throws IOException {
            _out.write("<?xml version=\"1.0\" encoding=\""+XML_ENCODING+"\"?>" +
                    "<worksheet xmlns=\"http://schemas.openxmlformats.org/spreadsheetml/2006/main\">" );
            _out.write("<sheetData>\n");
        }

        void endSheet() throws IOException {
            _out.write("</sheetData>");
            _out.write("</worksheet>");
        }

        /**
         * Insert a new row
         *
         * @param rownum 0-based row number
         */
        void insertRow(int rownum) throws IOException {
            _out.write("<row r=\""+(rownum+1)+"\">\n");
            this._rownum = rownum;
        }

        /**
         * Insert row end marker
         */
        void endRow() throws IOException {
            _out.write("</row>\n");
        }

        public void createCell(int columnIndex, String value, int styleIndex) throws IOException {
            String ref = new CellReference(_rownum, columnIndex).formatAsString();
            _out.write("<c r=\""+ref+"\" t=\"inlineStr\"");
            if(styleIndex != -1) {
                _out.write(" s=\""+styleIndex+"\"");
            }
            _out.write(">");
            _out.write("<is><t>"+value+"</t></is>");
            _out.write("</c>");
        }

        public void createCell(int columnIndex, String value) throws IOException {
            createCell(columnIndex, value, -1);
        }

        public void createCell(int columnIndex, double value, int styleIndex) throws IOException {
            String ref = new CellReference(_rownum, columnIndex).formatAsString();
            _out.write("<c r=\""+ref+"\" t=\"n\"");
            if(styleIndex != -1) {
                _out.write(" s=\""+styleIndex+"\"");
            }
            _out.write(">");
            _out.write("<v>"+value+"</v>");
            _out.write("</c>");
        }

        public void createCell(int columnIndex, double value) throws IOException {
            createCell(columnIndex, value, -1);
        }

        public void createCell(int columnIndex, Calendar value, int styleIndex) throws IOException {
            createCell(columnIndex, DateUtil.getExcelDate(value, false), styleIndex);
        }
    }
}