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Selcukes Databind helps to parser JSON, YML, XML, CSV, Properties and Excel files.
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/*
 *  Copyright (c) Ramesh Babu Prudhvi.
 *
 *  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.
 */

package io.github.selcukes.databind.excel;

import io.github.selcukes.collections.DataTable;
import io.github.selcukes.collections.Maps;
import io.github.selcukes.collections.Resources;
import io.github.selcukes.collections.Streams;
import io.github.selcukes.databind.annotation.DataFile;
import io.github.selcukes.databind.converters.Converter;
import io.github.selcukes.databind.exception.DataMapperException;
import lombok.SneakyThrows;
import org.apache.poi.ss.usermodel.Cell;
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.nio.file.Path;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static io.github.selcukes.collections.Reflections.newInstance;
import static io.github.selcukes.databind.converters.Converters.defaultConverters;
import static java.lang.String.format;
import static java.util.Optional.ofNullable;

class ExcelParser {

    private final Class entityClass;
    private final List> defaultConverters;

    public ExcelParser(final Class entityClass) {
        this.entityClass = entityClass;
        this.defaultConverters = defaultConverters();
    }

    public Stream parse(Path filePath) {
        try (var workbook = ExcelParser.getWorkbook(filePath.toString())) {
            var startIndex = 0;
            var skip = 1;

            var sheet = ofNullable(entityClass.getDeclaredAnnotation(DataFile.class))
                    .map(annotation -> workbook.getSheet(annotation.sheetName()))
                    .orElse(workbook.getSheetAt(startIndex));

            var headers = Streams.of(sheet.getRow(startIndex).cellIterator())
                    .collect(Maps.ofIgnoreCase(ExcelCell::getCellData, Cell::getColumnIndex));

            var cellMappers = Stream.of(entityClass.getDeclaredFields())
                    .map(field -> new ExcelCell<>(field, headers, defaultConverters))
                    .toList();

            return Streams.of(sheet.iterator())
                    .skip(skip)
                    .map(row -> cellMappers.stream().map(cellMapper -> cellMapper.parse(row))
                            .toList())
                    .map(this::initEntity);
        } catch (Exception ex) {
            throw new DataMapperException(format("Unable to parse Excel data to %s.", entityClass), ex);
        }
    }

    public T initEntity(final List> mappers) {
        var hasDefaultConstructor = Stream.of(entityClass.getDeclaredConstructors())
                .anyMatch(constructor -> constructor.getParameterCount() == 0);
        if (!hasDefaultConstructor) {
            throw new IllegalStateException(format("%s must have default constructor.", entityClass.getSimpleName()));
        }

        var entity = newInstance(entityClass);
        mappers.forEach(mapper -> mapper.assignValue(entity));

        return entity;
    }

    public static DataTable parseSheet(Sheet sheet) {
        return Streams.of(sheet.iterator())
                .skip(1)
                .map(ExcelParser::readRow)
                .collect(Collectors.toCollection(DataTable::new));
    }

    public static Map readRow(Row row) {
        return Streams.of(row.cellIterator())
                .collect(Maps.of(cell -> cell.getSheet().getRow(0)
                        .getCell(cell.getColumnIndex()).getStringCellValue(),
                    ExcelCell::getCellData));
    }

    @SneakyThrows
    public static Workbook getWorkbook(String filePath) {
        var workbook = WorkbookFactory.create(Resources.fileStream(filePath));
        ExcelCell.setFormulaEvaluator(workbook.getCreationHelper().createFormulaEvaluator());
        return workbook;
    }

}