const fs = require("fs");
const path = require("path");
// 方法1 直接使用原生的来
(async () => {
    console.time('方式1')
    const fileName = path.resolve(__dirname, './fsModule/复制文件1.docx');
    const fileCont = await fs.promises.readFile(path.resolve(__dirname, './fsModule/100MB大文件.docx'), 'utf-8');
    await fs.promises.writeFile(fileName, fileCont, {encoding: 'utf-8', flag: 'w'});
    console.timeEnd('方式1') //方式1: 1318.309ms
})()


// 方法2 通过流的方法来读取
(() => {
    console.time('用流的方式读取文件')
    const fromFileName = path.resolve(__dirname, './fsModule/100MB大文件.docx');
    const toFileName = path.resolve(__dirname, './fsModule/复制文件2.docx');
    const rs = fs.createReadStream(fromFileName, {
        autoClose: true,
        encoding: 'utf-8',
        highWaterMark: 64 * 1024 * 1024,
        flags: 'r'
    })
    const ws = fs.createWriteStream(toFileName, {
        encoding: 'utf-8',
        flags: 'a',
        highWaterMark: 16 * 1024 * 1024,
        autoClose: true
    })
    rs.on('data', chunk => {
        ws.write(chunk, 'utf-8');
    })


    rs.on('end', () => {
        console.log('文件写入完毕!!')

    })
    console.timeEnd('用流的方式读取文件') //用流的方式读取文件: 4.218ms
})()


// 方式3 优化用流读取 解决背压问题
(() => {
    console.time('优化用流的方式读取文件')
    const fromFileName = path.resolve(__dirname, './fsModule/100MB大文件.docx');
    const toFileName = path.resolve(__dirname, './fsModule/复制文件3.docx');
    const rs = fs.createReadStream(fromFileName, {
        autoClose: true,
        encoding: 'utf-8',
        highWaterMark: 64 * 1024 * 1024,
        flags: 'r'
    })
    const ws = fs.createWriteStream(toFileName, {
        encoding: 'utf-8',
        flags: 'a',
        highWaterMark: 16 * 1024 * 1024,
        autoClose: true
    })
    rs.on('data', chunk => {
        const wsFlag = ws.write(chunk, 'utf-8');
        if (!wsFlag) {
            rs.pause();
        }
    })
    ws.on('drain', () => {
        // 继续读取
        rs.resume();
    })

    rs.on('end', () => {
        console.log('文件写入完毕!!')
        ws.end();

    })
    console.timeEnd('优化用流的方式读取文件') //用流的方式读取文件:  3.006ms
})()


// 方法四: pipe
(() => {
    console.time('优化用流的方式读取文件')
    const fromFileName = path.resolve(__dirname, './fsModule/100MB大文件.docx');
    const toFileName = path.resolve(__dirname, './fsModule/复制文件4.docx');
    const rs = fs.createReadStream(fromFileName, {
        autoClose: true,
        encoding: 'utf-8',
        highWaterMark: 64 * 1024 * 1024,
        flags: 'r'
    })
    const ws = fs.createWriteStream(toFileName, {
        encoding: 'utf-8',
        flags: 'a',
        highWaterMark: 16 * 1024 * 1024,
        autoClose: true
    })
    // 直接解决背压问题
    rs.pipe(ws);
    console.timeEnd('优化用流的方式读取文件') // 7.967ms
})()

// 方法五 copyFile 
const fromFileName = path.resolve(__dirname, './fsModule/100MB大文件.docx');
const toFileName = path.resolve(__dirname, './fsModule/复制文件5.docx');
fs.copyFile(fromFileName, toFileName,0, ()=>{
    console.log('复制完成')
})