package kr.wisestone.owl.web.view;

import org.apache.poi.xssf.usermodel.XSSFCell;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.LocalizedResourceHelper;
import org.springframework.web.servlet.support.RequestContextUtils;
import org.springframework.web.servlet.view.AbstractView;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Locale;
import java.util.Map;

public abstract class AbstractExcelView extends AbstractView {

    /** The content type for an Excel response */
    private static final String CONTENT_TYPE = "application/vnd.ms-excel";

    /** The extension to look for existing templates */
    private static final String EXTENSION = ".xls";


    private String url;


    /**
     * Default Constructor.
     * Sets the content type of the view to "application/vnd.ms-excel".
     */
    public AbstractExcelView() {
        setContentType(CONTENT_TYPE);
    }

    /**
     * Set the URL of the Excel workbook source, without localization part nor extension.
     */
    public void setUrl(String url) {
        this.url = url;
    }


    @Override
    protected boolean generatesDownloadContent() {
        return true;
    }

    /**
     * Renders the Excel view, given the specified model.
     */
    @Override
    protected final void renderMergedOutputModel(
            Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

        XSSFWorkbook workbook;
        if (this.url != null) {
            workbook = getTemplateSource(this.url, request);
        }
        else {
            workbook = new XSSFWorkbook();
            logger.debug("Created Excel Workbook from scratch");
        }

        buildExcelDocument(model, workbook, request, response);

        // Set the content type.
        response.setContentType(getContentType());

        // Should we set the content length here?
        // response.setContentLength(workbook.getBytes().length);

        // Flush byte array to servlet output stream.
        ServletOutputStream out = response.getOutputStream();
        workbook.write(out);
        out.flush();
    }

    /**
     * Creates the workbook from an existing XLS document.
     * @param url the URL of the Excel template without localization part nor extension
     * @param request current HTTP request
     * @return the HSSFWorkbook
     * @throws Exception in case of failure
     */
    protected XSSFWorkbook getTemplateSource(String url, HttpServletRequest request) throws Exception {
        LocalizedResourceHelper helper = new LocalizedResourceHelper(getApplicationContext());
        Locale userLocale = RequestContextUtils.getLocale(request);
        Resource inputFile = helper.findLocalizedResource(url, EXTENSION, userLocale);

        // Create the Excel document from the source.
        if (logger.isDebugEnabled()) {
            logger.debug("Loading Excel workbook from " + inputFile);
        }
        return new XSSFWorkbook(inputFile.getInputStream());
    }

    /**
     * Subclasses must implement this method to create an Excel HSSFWorkbook document,
     * given the model.
     * @param model the model Map
     * @param workbook the Excel workbook to complete
     * @param request in case we need locale etc. Shouldn't look at attributes.
     * @param response in case we need to set cookies. Shouldn't write to it.
     */
    protected abstract void buildExcelDocument(
            Map<String, Object> model, XSSFWorkbook workbook, HttpServletRequest request, HttpServletResponse response)
            throws Exception;


    /**
     * Convenient method to obtain the cell in the given sheet, row and column.
     * <p>Creates the row and the cell if they still doesn't already exist.
     * Thus, the column can be passed as an int, the method making the needed downcasts.
     * @param sheet a sheet object. The first sheet is usually obtained by workbook.getSheetAt(0)
     * @param row the row number
     * @param col the column number
     * @return the HSSFCell
     */
    protected XSSFCell getCell(XSSFSheet sheet, int row, int col) {
        XSSFRow sheetRow = sheet.getRow(row);
        if (sheetRow == null) {
            sheetRow = sheet.createRow(row);
        }
        XSSFCell cell = sheetRow.getCell(col);
        if (cell == null) {
            cell = sheetRow.createCell(col);
        }
        return cell;
    }

    /**
     * Convenient method to set a String as text content in a cell.
     * @param cell the cell in which the text must be put
     * @param text the text to put in the cell
     */
    protected void setText(XSSFCell cell, String text) {
        cell.setCellType(XSSFCell.CELL_TYPE_STRING);
        cell.setCellValue(text);
    }
}