import { Injectable } from '@angular/core';
import { saveAs } from 'file-saver';
import * as XLSX from 'xlsx';
import { TranslateService } from '@ngx-translate/core';
import { EXCEL_FILE_EXTENSION, EXCEL_FILE_TYPE } from '../../utils/app.constants';

@Injectable({
  providedIn: 'root'
})
export class ExcelExportService {

  private fileType = EXCEL_FILE_TYPE;
  private fileExtension = EXCEL_FILE_EXTENSION;

  constructor(private translate: TranslateService) {}

  public exportExcel(jsonData: any[], fileName: string): void {

    // 🔑 Translate headers here (single place)
    const translatedData = this.translateHeaders(jsonData);

    const ws: XLSX.WorkSheet = XLSX.utils.json_to_sheet(translatedData);
    const wb: XLSX.WorkBook = { Sheets: { data: ws }, SheetNames: ['data'] };
    const excelBuffer: any = XLSX.write(wb, { bookType: 'xlsx', type: 'array' });

    this.saveExcelFile(excelBuffer, fileName);
  }

  private translateHeaders(data: any[]): any[] {
    if (!data || !data.length) return data;

    return data.map(row => {
      const newRow: any = {};
      Object.keys(row).forEach(key => {
        // Convention: translation keys == property names
        const translatedKey = this.translate.instant(key);
        newRow[translatedKey] = row[key];
      });
      return newRow;
    });
  }

  private saveExcelFile(buffer: any, fileName: string): void {
    const data: Blob = new Blob([buffer], { type: this.fileType });
    saveAs(data, fileName + this.fileExtension);
  }
}