/**
 * @author Abhishek Prakash
 * @filename excelExportUtility.js
 * @description Reusable excel worksheet generator
 */
import { LightningElement, api } from "lwc";
import { loadScript } from "lightning/platformResourceLoader";
import workbook from "@salesforce/resourceUrl/xlsjs";

export default class ExportExcelUtility extends LightningElement {
    @api headerList; //List of header columns for all the sheets
    @api apiNameList; //List of Api name for corresponding to header column
    @api filename; //File name of the excel workbook
    @api worksheetNameList; //List of all the worksheet names
    @api sheetData; //List of data for all the worksheets
    librariesLoaded = false;

    /**
     * @description load external library when component is rendered
     */
    renderedCallback() {
        if (this.librariesLoaded) return;
        this.librariesLoaded = true;

        Promise.all([loadScript(this, workbook + "/xlsx.full.min.js")])
            .then(() => {
                console.log("success");
            })
            .catch(error => {
                console.log("failure");
            });
    }

    /**
     * @description this button can be called from parent component to download the file
     */
    @api download() {
        const XLSX = window.XLSX;
        let xlsData = this.sheetData;
        let xlsHeader = this.headerList;
        let ws_name = this.worksheetNameList;
        let createXLSLFormatObj = Array(xlsData.length).fill([]);

        /* form header list */
        xlsHeader.forEach((item, index) => createXLSLFormatObj[index] = [item])

        /* form data key list */
        xlsData.forEach((item, selectedRowIndex) => {
            let xlsRowKey = this.apiNameList[selectedRowIndex];

            item.forEach((value, index) => {
                var innerRowData = [];
                xlsRowKey.forEach(item => {
                    innerRowData.push(value[item]);
                })
                createXLSLFormatObj[selectedRowIndex].push(innerRowData);
            })
        });

        /* creating new Excel */
        var wb = XLSX.utils.book_new();

        /* creating new worksheet */
        var ws = Array(createXLSLFormatObj.length).fill([]);
        
        for (let i = 0; i < ws.length; i++) {
            /* converting data to excel format and puhing to worksheet */
            let data = XLSX.utils.aoa_to_sheet(createXLSLFormatObj[i]);
            ws[i] = [...ws[i], data];

            /* Add worksheet to Excel */
            XLSX.utils.book_append_sheet(wb, ws[i][0], ws_name[i]);
        }

        /* Write Excel and Download */
        XLSX.writeFile(wb, this.filename);

        //Fire file download completion Event
        const customEvent = new CustomEvent('downloadcomplete', {});
        this.dispatchEvent(customEvent);
    }
}

<!--
/**
 * @author Abhishek Prakash
 * @filename parentComponent.html
 * @description Calling export excel component
 */
-->
<template>
    <!-- START: Spinner -->
    <div if:true={showSpinner}>
        <lightning-spinner class="loadingSpinner" variant="brand" size="medium"
            alternative-text="Loading"></lightning-spinner>
    </div>
    
    <template for:each={items} for:item="item">
      <c-export-excel-utility 
          header-list={columnHeader}
          filename={filename}
          worksheet-name-list={workSheetNameList}
          sheet-data={xlsData}
          api-name-list={apiNameList}
          ondownloadcomplete={handleDownloadComplete}
      ></c-export-excel-utility>

      <lightning-button 
        variant="brand" 
        label="Export" 
        title="Brand" 
        data-id={item.Id}
        onclick={exportExcelData}
      ></lightning-button>
    </template>
</template>

/**
 * @author Abhishek Prakash
 * @filename parentComponent.js
 * @description Calling export excel component
 */
import { LightningElement, api, wire } from 'lwc';

export default class ParentComponent extends LightningElement {
    workSheetNameList; // store all the sheets name of the the tables
    xlsData; // store all tables data
    filename;
    columnHeader = [['Col 1', 'Col 2', 'Col 3']];
    apiNameList = [['Name', 'Email', 'count']];
    items = [
      {
        'Id' : '1',
        'Name' : 'Abhishek',
        'Email' : 'abskpr@gmail.com',
        'count' : 1
      },
      {
        Id : '2',
        'Name' : 'Prakash',
        'Email' : 'abskpr@yopmail.com',
        'count' : 2
      }
    ];
  
  /**
   * @description excel hotel data on button click
   */
  exportExcelData(event) {
      this.showSpinner = true;
      let recordId = event.currentTarget.dataset.id;
      let parentRecord = this.items.find(item => item.Id === recordId);

      if (parentRecord) {
          this.filename = parentRecord.Name + '.xlsx';
          this.xlsData = [parentRecord];
          this.workSheetNameList = [this.filename];

          //Call download method on exportExcelUtility
          setTimeout(() => {
              this.template.querySelector("c-export-excel-utility").download();
          }, 100);
      }
  }
  
  /**
   * @description handle file download completion;
   */
  handleDownloadComplete() {
      this.showSpinner = false;
  }
}