SR-SYSTEM/backend/src/main/java/com/srsystem/util/ExcelParser.java

package com.srsystem.util;

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddressList;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.springframework.web.multipart.MultipartFile;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.*;
import java.util.function.Function;

public class ExcelParser {

    public static <T> ParseResult<T> parse(MultipartFile file, RowMapper<T> mapper, List<Validator<T>> validators) throws IOException {
        List<T> data = new ArrayList<>();
        List<ParseFailure> failures = new ArrayList<>();

        try (InputStream is = file.getInputStream(); Workbook wb = new XSSFWorkbook(is)) {
            Sheet sheet = wb.getSheetAt(0);
            if (sheet.getPhysicalNumberOfRows() < 2) {
                return new ParseResult<>(List.of(), List.of(new ParseFailure(0, "데이터 행이 없습니다")));
            }

            Row headerRow = sheet.getRow(0);
            int colCount = headerRow.getPhysicalNumberOfCells();
            String[] headers = new String[colCount];
            for (int i = 0; i < colCount; i++) {
                headers[i] = getCellValue(headerRow.getCell(i)).trim().toLowerCase();
            }

            for (int r = 1; r <= sheet.getLastRowNum(); r++) {
                Row row = sheet.getRow(r);
                if (row == null) continue;

                try {
                    Map<String, String> rowData = new HashMap<>();
                    for (int c = 0; c < colCount; c++) {
                        String val = getCellValue(row.getCell(c));
                        if (!val.isEmpty()) {
                            rowData.put(headers[c], val);
                        }
                    }

                    if (rowData.isEmpty()) continue;

                    T item = mapper.map(rowData);
                    for (Validator<T> v : validators) {
                        String err = v.validate(item, rowData);
                        if (err != null) {
                            throw new ValidationException(err);
                        }
                    }
                    data.add(item);
                } catch (Exception e) {
                    failures.add(new ParseFailure(r + 1, e.getMessage()));
                }
            }
        }

        return new ParseResult<>(data, failures);
    }

    public static byte[] generateTemplate(String[] headers, String sheetName, Map<Integer, String[]> dropdowns) throws IOException {
        try (Workbook wb = new XSSFWorkbook(); ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
            Sheet sheet = wb.createSheet(sheetName);
            Row headerRow = sheet.createRow(0);

            CellStyle headerStyle = wb.createCellStyle();
            Font headerFont = wb.createFont();
            headerFont.setBold(true);
            headerFont.setColor(IndexedColors.WHITE.getIndex());
            headerStyle.setFont(headerFont);
            headerStyle.setFillForegroundColor(IndexedColors.INDIGO.getIndex());
            headerStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
            headerStyle.setBorderBottom(BorderStyle.THIN);
            headerStyle.setBorderLeft(BorderStyle.THIN);
            headerStyle.setBorderRight(BorderStyle.THIN);
            headerStyle.setBorderTop(BorderStyle.THIN);

            for (int i = 0; i < headers.length; i++) {
                Cell cell = headerRow.createCell(i);
                cell.setCellValue(headers[i]);
                cell.setCellStyle(headerStyle);
                sheet.autoSizeColumn(i);
            }

            if (dropdowns != null) {
                for (Map.Entry<Integer, String[]> entry : dropdowns.entrySet()) {
                    int col = entry.getKey();
                    String[] values = entry.getValue();
                    DataValidationHelper helper = sheet.getDataValidationHelper();
                    DataValidationConstraint constraint = helper.createExplicitListConstraint(values);
                    CellRangeAddressList range = new CellRangeAddressList(1, 1000, col, col);
                    DataValidation validation = helper.createValidation(constraint, range);
                    validation.setShowErrorBox(true);
                    validation.createErrorBox("유효성 검사", "허용된 값만 입력 가능합니다.");
                    sheet.addValidationData(validation);
                }
            }

            wb.write(bos);
            return bos.toByteArray();
        }
    }

    private static String getCellValue(Cell cell) {
        if (cell == null) return "";
        return switch (cell.getCellType()) {
            case STRING -> cell.getStringCellValue().trim();
            case NUMERIC -> {
                double val = cell.getNumericCellValue();
                if (val == Math.floor(val) && !Double.isInfinite(val)) {
                    yield String.valueOf((long) val);
                }
                yield String.valueOf(val);
            }
            case BOOLEAN -> String.valueOf(cell.getBooleanCellValue());
            case FORMULA -> {
                try { yield String.valueOf((int) cell.getNumericCellValue()); }
                catch (Exception e) { yield cell.getStringCellValue(); }
            }
            default -> "";
        };
    }

    public record ParseResult<T>(List<T> data, List<ParseFailure> failures) {
        public boolean hasFailures() { return !failures.isEmpty(); }
    }

    public record ParseFailure(int row, String reason) {}

    @FunctionalInterface
    public interface RowMapper<T> {
        T map(Map<String, String> rowData) throws Exception;
    }

    @FunctionalInterface
    public interface Validator<T> {
        String validate(T item, Map<String, String> rawData);
    }

    private static class ValidationException extends RuntimeException {
        public ValidationException(String message) { super(message); }
    }
}