/*
 * 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.freemarker.generator.tools.excel;

import org.apache.freemarker.generator.base.datasource.DataSource;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.DataFormatter;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;

import java.io.IOException;
import java.io.InputStream;
import java.text.SimpleDateFormat;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Collectors;

import static org.apache.poi.ss.usermodel.Row.MissingCellPolicy.CREATE_NULL_AS_BLANK;

/**
 * Parse Excel documents (XLS &amp; XLSX) using Apache POI.
 */
public class ExcelTool {

    private static final boolean EMULATE_CSV = true;
    private static final SimpleDateFormat TIME_DATE_FORMAT = new SimpleDateFormat("HH:mm:ss");
    private static final SimpleDateFormat YEAR_TIME_FORMAT = new SimpleDateFormat("yyyy");

    public Workbook parse(DataSource dataSource) {
        try (InputStream is = dataSource.getUnsafeInputStream()) {
            final Workbook workbook = WorkbookFactory.create(is);
            // make sure that the workbook is closed together with the data source
            return dataSource.addClosable(workbook);
        } catch (IOException e) {
            throw new RuntimeException("Failed to parse Excel data source: " + dataSource, e);
        }
    }

    public List<Workbook> parse(Collection<DataSource> dataSources) {
        return dataSources.stream()
                .map(this::parse)
                .collect(Collectors.toList());
    }

    /**
     * Get all sheets of a workbook.
     *
     * @param workbook The workbook
     * @return Sheets of the workbook
     */
    public List<Sheet> getSheets(Workbook workbook) {
        final List<Sheet> result = new ArrayList<>();
        for (int i = 0; i < workbook.getNumberOfSheets(); i++) {
            result.add(workbook.getSheetAt(i));
        }
        return result;
    }

    /**
     * Transform the Excel sheet into a table. Please not that locales are mostly
     * ignored by Apache POI (see https://poi.apache.org/apidocs/dev/org/apache/poi/ss/usermodel/DataFormatter.html)
     *
     * @param sheet Excel sheet
     * @return Table containing formatted cell values as strings
     */
    public List<List<Object>> toTable(Sheet sheet) {
        final DataFormatter dataFormatter = dataFormatter();
        final Iterator<Row> iterator = sheet.iterator();
        final List<List<Object>> result = new ArrayList<>();

        while (iterator.hasNext()) {
            final Row row = iterator.next();
            result.add(toColumns(row, dataFormatter));
        }

        return result;
    }

    /**
     * EXPERIMENTAL FEATURE
     * <p>
     * Transform the sheet to table containing raw Java objects, e.g. Date, Double, ...
     *
     * @param sheet Excel sheet
     * @return Table containing cells as raw Java objects
     */
    public List<List<Object>> toRawTable(Sheet sheet) {
        final DataFormatter dataFormatter = dataFormatter();
        final Iterator<Row> iterator = sheet.iterator();
        final List<List<Object>> result = new ArrayList<>();

        while (iterator.hasNext()) {
            final Row row = iterator.next();
            result.add(toRawColumns(row, dataFormatter));
        }

        return result;
    }

    @Override
    public String toString() {
        return "Process Excels files (XLS, XLSX) using Apache POI (see https://poi.apache.org)";
    }

    private static List<Object> toColumns(Row row, DataFormatter dataFormatter) {
        final List<Object> columnValues = new ArrayList<>();
        for (int columnIndex = 0; columnIndex < row.getLastCellNum(); columnIndex++) {
            final Cell cell = row.getCell(columnIndex, CREATE_NULL_AS_BLANK);
            final String formattedCellValue = dataFormatter.formatCellValue(cell).trim();
            columnValues.add(formattedCellValue);
        }
        return columnValues;
    }

    private static List<Object> toRawColumns(Row row, DataFormatter dataFormatter) {
        final List<Object> columnValues = new ArrayList<>();
        for (int columnIndex = 0; columnIndex < row.getLastCellNum(); columnIndex++) {
            final Cell cell = row.getCell(columnIndex, CREATE_NULL_AS_BLANK);
            final Object cellValue = toCellValue(cell, dataFormatter);
            columnValues.add(cellValue);
        }
        return columnValues;
    }

    private static Object toCellValue(Cell cell, DataFormatter formatter) {
        final CellType cellType = cell.getCellType();
        switch (cellType) {
            case BOOLEAN:
                return cell.getBooleanCellValue();
            case NUMERIC:
                return DateUtil.isCellDateFormatted(cell) ? toDateCellValue(cell) : cell.getNumericCellValue();
            default:
                return formatter.formatCellValue(cell);
        }
    }

    /**
     * Try desperately to make sense out of Excel and its handling of dates.
     * See https://stackoverflow.com/questions/15710888/reading-time-values-from-spreadsheet-using-poi-api.
     *
     * @param cell Cell containing some sort of date or time
     * @return The corresponding Java instance
     */
    private static synchronized Object toDateCellValue(Cell cell) {
        final Date date = cell.getDateCellValue();

        // "Time-only" values have date set to 31-Dec-1899 so if year is "1899"
        // you can assume it is a "time-only" value
        final String year = YEAR_TIME_FORMAT.format(date);

        if (year.equals("1899")) {
            // handle "Time-only" value
            return LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()).toLocalTime();
        } else {
            // here you may have a date-only or date-time value
            final String timeStamp = TIME_DATE_FORMAT.format(date);
            if (timeStamp.equals("00:00:00")) {
                // if time is 00:00:00 you can assume it is a date only value (but it could be midnight)
                return new java.sql.Date(date.getTime()).toLocalDate();
            } else {
                return date;
            }
        }
    }

    private static DataFormatter dataFormatter() {
        return new DataFormatter(EMULATE_CSV);
    }
}