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A domain service for Apache Isis', allowing collections of (view model) objects to be exported/imported to/from an Excel spreadsheet.
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/*
 *  Copyright 2014 Dan Haywood
 *
 *  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 org.isisaddons.module.excel.dom.util;

import java.io.File;
import java.io.IOException;
import java.util.Collections;
import java.util.List;

import org.apache.poi.openxml4j.exceptions.InvalidFormatException;

import org.apache.isis.applib.DomainObjectContainer;
import org.apache.isis.applib.annotation.Programmatic;
import org.apache.isis.applib.services.bookmark.BookmarkService;
import org.apache.isis.applib.value.Blob;
import org.apache.isis.core.metamodel.specloader.SpecificationLoader;
import org.apache.isis.core.runtime.system.persistence.PersistenceSession;
import org.apache.isis.core.runtime.system.session.IsisSessionFactory;

import org.isisaddons.module.excel.dom.ExcelService;
import org.isisaddons.module.excel.dom.WorksheetContent;
import org.isisaddons.module.excel.dom.WorksheetSpec;

public class ExcelServiceImpl {

    private final ExcelFileBlobConverter excelFileBlobConverter = new ExcelFileBlobConverter();


    /**
     * Creates a Blob holding a single-sheet spreadsheet of the domain objects.  The sheet name is derived from the
     * class name.
     *
     * 
     *     There are no specific restrictions on the domain objects; they can be either persistable entities or
     *     view models.  Do be aware though that if imported back using {@link #fromExcel(Blob, Class)},
     *     then new instances are always created.  It is generally better therefore to work with view models than to
     *     work with entities.  This also makes it easier to maintain backward compatibility in the future if the
     *     persistence model changes; using view models represents a stable API for import/export.
     * 
     */
    @Programmatic
    public  Blob toExcel(
            final List domainObjects,
            final Class cls,
            final String fileName) throws ExcelService.Exception {
        return toExcel(domainObjects, cls, null, fileName);
    }

    /**
     * As {@link #toExcel(List, Class, String)}, but specifying the sheet name.
     */
    @Programmatic
    public  Blob toExcel(
            final List domainObjects,
            final Class cls,
            final String sheetName,
            final String fileName) {
        return toExcel(new WorksheetContent(domainObjects, new WorksheetSpec(cls, sheetName)), fileName);
    }

    /**
     * As {@link #toExcel(List, Class, String)}, but with the domain objects, class and sheet name provided using a
     * {@link WorksheetContent}.
     */
    @Programmatic
    public  Blob toExcel(WorksheetContent worksheetContent, final String fileName) {
        return toExcel(Collections.singletonList(worksheetContent), fileName);
    }

    /**
     * As {@link #toExcel(WorksheetContent, String)}, but with multiple sheets.
     */
    @Programmatic
    public Blob toExcel(final List worksheetContents, final String fileName) {
        try {
            final File file = newExcelConverter().appendSheet(worksheetContents);
            return excelFileBlobConverter.toBlob(fileName, file);
        } catch (final IOException ex) {
            throw new ExcelService.Exception(ex);
        }
    }


    // //////////////////////////////////////

    /**
     * Returns a list of objects for each line in the spreadsheet, of the specified type.  The objects are read
     * from a sheet taken as the simple name of the class.
     *
     * 
     *     If the class is a view model then the objects will be properly instantiated (that is, using
     *     {@link org.apache.isis.applib.DomainObjectContainer#newViewModelInstance(Class, String)}, with the correct
     *     view model memento); otherwise the objects will be simple transient objects (that is, using
     *     {@link org.apache.isis.applib.DomainObjectContainer#newTransientInstance(Class)}).
     * 
     */
    @Programmatic
    public  List fromExcel(
            final Blob excelBlob,
            final Class cls) throws ExcelService.Exception {
        return fromExcel(excelBlob, cls, null);
    }

    /**
     * As {@link #fromExcel(Blob, Class)}, but specifying the sheet name.
     */
    @Programmatic
    public  List fromExcel(
            final Blob excelBlob,
            final Class cls,
            final String sheetName) throws ExcelService.Exception {
        final WorksheetSpec worksheetSpec = new WorksheetSpec(cls, sheetName);
        return fromExcel(excelBlob, worksheetSpec);
    }

    /**
     * As {@link #fromExcel(Blob, Class, String)}, but specifying the class name and sheet name by way of a
     * {@link WorksheetSpec}.
     */
    @Programmatic
    public  List fromExcel(
            final Blob excelBlob,
            final WorksheetSpec worksheetSpec) throws ExcelService.Exception {
        final List> listOfList =
                fromExcel(excelBlob, Collections.singletonList(worksheetSpec));
        return (List) listOfList.get(0);
    }

    /**
     * As {@link #fromExcel(Blob, WorksheetSpec)}, but reading multiple sheets (and returning a list of lists of
     * domain objects).
     */
    @Programmatic
    public List> fromExcel(
            final Blob excelBlob,
            final List worksheetSpecs) throws ExcelService.Exception {
        try {
            return newExcelConverter().fromBytes(worksheetSpecs, excelBlob.getBytes(), container);
        } catch (final IOException | InvalidFormatException e) {
            throw new ExcelService.Exception(e);
        }
    }

    private ExcelConverter newExcelConverter() {
        return new ExcelConverter(getSpecificationLoader(), getPersistenceSession(), bookmarkService);
    }


    // //////////////////////////////////////


    @javax.inject.Inject
    private DomainObjectContainer container;

    @javax.inject.Inject
    private BookmarkService bookmarkService;

    @javax.inject.Inject
    IsisSessionFactory isisSessionFactory;

    private SpecificationLoader getSpecificationLoader() {
        return isisSessionFactory.getSpecificationLoader();
    }

    private PersistenceSession getPersistenceSession() {
        return isisSessionFactory.getCurrentSession().getPersistenceSession();
    }

}