import { saveAs } from 'file-saver'
import XLSX from 'xlsx'

function datenum (v, date1904) {
    if (date1904) v += 1462;
    let epoch = Date.parse(v);
    return (epoch - new Date(Date.UTC(1899, 11, 30))) / (24 * 60 * 60 * 1000)
}

function data2ws (data) {
    const ws = {};
    const range = { s: { c: 10000000, r: 10000000 }, e: { c: 0, r: 0 } };
    for (let R = 0; R !== data.length; ++R) {
        for (let C = 0; C !== data[R].length; ++C) {
            if (range.s.r > R) range.s.r = R;
            if (range.s.c > C) range.s.c = C;
            if (range.e.r < R) range.e.r = R;
            if (range.e.c < C) range.e.c = C;
            const cell = { v: data[R][C] };
            if (cell.v == null) continue;
            const cellRef = XLSX.utils.encode_cell({ c: C, r: R });

            if (typeof cell.v === 'number') cell.t = 'n';
            else if (typeof cell.v === 'boolean') cell.t = 'b';
            else if (cell.v instanceof Date) {
                cell.t = 'n';
                cell.z = XLSX.SSF._table[14];
                cell.v = datenum(cell.v)
            } else cell.t = 's';

            ws[cellRef] = cell
        }
    }
    if (range.s.c < 10000000) ws['!ref'] = XLSX.utils.encode_range(range);
    return ws
}
function Workbook () {
    if (!(this instanceof Workbook)) return new Workbook();
    this.SheetNames = [];
    this.Sheets = {}
}

function s2ab (s) {
    const buf = new ArrayBuffer(s.length);
    const view = new Uint8Array(buf);
    for (let i = 0; i !== s.length; ++i) view[i] = s.charCodeAt(i) & 0xFF
    return buf
}

/*
* th => 表头
* data => 数据
* fileName => 文件名
* fileType => 文件类型
* sheetName => sheet页名
*/
export default function toExcel ({ th, data, fileName, fileType, sheetName }) {
    data.unshift(th);
    let wb = new Workbook();
    let ws = data2ws(data);
    sheetName = sheetName || 'sheet1';
    wb.SheetNames.push(sheetName);
    wb.Sheets[sheetName] = ws;
    fileType = fileType || 'xlsx';
    let wbout = XLSX.write(wb, { bookType: fileType, bookSST: false, type: 'binary' });
    fileName = fileName || '列表';
    saveAs(new Blob([s2ab(wbout)], { type: 'application/octet-stream' }), `${fileName}.${fileType}`)
}
