//set up:


//Basics:

console.log(__dirname);
  //It will return the absolute path for current folder.
console.log(__filename);  //It will return the absolute path for current folder  with file name.
---------------------------------------------------

// Modeles | Require
let data = require("./script");
/* :> './' will look for relative to current path,
'require(".fileName") Will return the object.'
*/

module.exports = { var1, var2 }
// We can export multiple things/variables.

let { people } = require("./totalPeople");
// It will only return the 'people' variable in 'totalPeople'.

let { people, age } = require("./totalPeople");
// It will only return the 'people' and 'age' variables in 'totalPeople'.

// Also called Destructuring.
    ---------------------------------------------------
  
let os = require("os");
//Will provide built in Operating System module( object).

console.log(os.platform());
//Will return the type of OS ( windows/Linux...);

console.log(os.homedir());
//It will provide the HOME directory
      ---------------------------------------------------

const fs = require("fs");
 //Built in module, Used to read/write the files. ( FILE SYSTEM )
        
                       // Reading Files
fs.readFile(('./R/text.txt'), ( error, data ) => {
   console.log("Data: ", data); // It will return a package as a Buffer. 
   console.log(data.toString()); // It will provide the data (text.txt) in readable format.
});
//'readFile' is an async function and will not block the execution.

                      // Writing Files
fs.writeFile('./R/text.txt', " This is new replaced data,  ", ( ) => {
  //If the address is not valid, It will create the file.
  // It will replace the old data.
  //Since it's Async function, Call back function is required.
  console.log("Data updated");
});
//'writeField' is an asyn function and will not block the execution.


                      // Directories
//create
fs.mkdir('./assets',(err)=>{
    if(err) { console.log("Error: ",err) }
    console.log("Folder created");
})
//Remove
fs.rmdir('./assets',(err)=>{
    if(err) { console.log("Error: ",err) }
    console.log("Folder Removed");
})

//Check if specific 'folder' exist or not.
if(fs.existSync("./Resources")){
  //Check if 'Resources' folder is there or not.
  //'existSync' is a sync function and will block the code. 
  //code
}

**
  //Check for folder 'R' using '!'.
if(!fs.existsSync('./R')){
    console.log(" R Folder does not exists");

 //Create Folder.
 fs.mkdir('./R',(err)=>{
     if(err){ console.log("Issue with creatin Folder") };
     console.log("Folder R created")
 })
}else {
    //If already there, then deleting 'R' Folder
    fs.rmdir("./R",(err)=>{
        if(err){ console.log("issue with deleting Folder") }
        console.log("Folder R Deleted.")
    })
}

**  

                      // Deleting Files        
fs.unlink("./R/text.txt", (err)=>{
    console.log("Issue with deleting File");
    console.log("File has been deleted.")
})


//We should always check first if 'folder'/'files' exist or not.
if(fs.existsSync("./R")){
  console.log("Folder 'R' does exist");
  //Code
}

if(fs.existsSync("./R/file.txt")){
  console.log("File 'file.txt' does exist");
  //Code
}
** //Summary
  //Import Modules
const http = require("http");
const fs = require("fs");

//Creating Server
const server = http.createServer((req, res)=>{})

//Read File.
fs.readFile("./R/blogData.txt",(err,data)=>{ })

//Writing Files
fs.writeFile("./R/newFile4", "To a worm in horseradish, The world is horseradish.", (error)=>{
 // console.log("File Updated.")
})

//Create Directories.
fs.mkdir("./R/newFile5",(error)=>{})

//Check the Folder/File
console.log(fs.existsSync("./R/newFile2"));

//Remove Folder
fs.rmdir("./R/NewFolderCreated",(error)=>{ })

//Deleting File
fs.unlink("./R/newFile2",(error) =>{ })

//Server Configuration.
server.listen(8080 ,"localhost",()=>{});

**


      ---------------------------------------------------
      
 //Streams and Buffers.       
 Stream : Start using data, Before it has finished loading. Data will be transferred as 'Buffers'.
 
**
                //Create/Read new Stream
let createStream1 = fs.createReadStream("./R/sampleData.txt");
//Address should be mentioned.
/* We can pass the 2nd argument as '{ encoding: "utf8" }', and this we don't have to use 'toString()'.
let createStream1 = fs.createReadStream("./R/sampleData.txt",{encoding:"utf8"});
*/

createStream1.on("data",(bufferData)=>{
  //'on' is event listener, 
  //'data' is type of event. ( example 'click','scroll')
    console.log(bufferData.toString());
  //Every time we get new buffer, This 'bufferData' will be called ( call back function.)
})
**        
                          //Write Stream       
** 
let createStream = fs.createReadStream("./R/sampleData.txt", { encoding:'utf8'});
let writeStream = fs.createWriteStream('./R/blogData.txt');//if address does not exist, It will create new one.

writeStream.write('First Line Here...'); 
// It will write the provided text in './R/blogData.txt'

createStream.on("data",(buffer)=>{
  //For every 'buffer' generated, It will passed on to 'writeStream' 
    writeStream.write('\n'); 
    writeStream.write("Some Data");
    writeStream.write('\n');
    writeStream.write('\n');
    writeStream.write( buffer );
})    
 writeStream.write('Last Line Here....'); 
**
  //OR
**
  //Streams and buffers.
let createStream = fs.createReadStream("./R/sampleData.txt", { encoding:'utf8'});
let writeStream = fs.createWriteStream('./R/blogData.txt');

writeStream.write("First Line...");

//Using 'PIPE'
createStream.pipe(writeStream);
 //It will automatically pass all the data to './R/blogData.txt'. from "./R/sampleData.txt".
**  
        
      ---------------------------------------------------
                 //Client and Servers
const http = require("http");

const server = http.createServer((req, res)=>{
      console.log("Request Made")
});

server.listen( 3000 , 'localhost' ,()=>{
  // 'localhost' is by default.
    console.log("Server is Live on Port 3000")
})

      ---------------------------------------------------
            //Requests and Responses.
**  
  const server = http.createServer((req, res)=>{
      console.log("Request Made")
      
    console.log(req.url);
    //It will provide the 'url'. Root url is '/'.
    
    console.log(req.method);
    //It will return the method used. 
});
**    

 
**
const server = http.createServer((req, res)=>{

  //Set Header Content Type.
  res.setHeader("Content-type", "text/plain");
  //It will tell browser what kind of content to      expect. It can '"text/html"', If we want to pass     on HTML content/tags. 
  
  res.write(" Hello Karan");
  res.end(); //Manually end it. This will send the response to the browser. 
});
**
  
**
//Linking HTML file to the Code. 
 let fs = require("fs");

const server = http.createServer((req, res)=>{

  res.setHeader("Content-type", "text/html");
  //'text/html' is used, This time we will passing data as a HTML content ( with Tags nd all);
  
  fs.readFile('./home/Index.html',(err, data)=>{
    if(err){
      console.log("Koi Panga", err);
      res.end();
      //If err then we want to end the response, So that browser will move with next step ( other wise it will struck on loading )
    }else {
      res.write(data); //We are passing 'index.html' as the data.
      res.end();
      
      //We can also use 'res.end(data)'(for single file). ( res.write() will not be needed. )
    }
  })

  
  res.write(" Hello Karan");
  res.end(); //This will send the response to the browser. 
});
  
 **
   
                //Routes
   
**
 const server = http.createServer((req, res)=>{   
 console.log("URL: ", req.url)
   
 let path = "./"; // Root will always be './'
 switch( req.url ){
  
  case '/':
  path += 'index.html'
  break;

  case '/about':
  path += "about.html";
  break;
  default :
  path += "404.html";
     //This we can add specific page
}

 //Header Content.
 res.setHeader("Content-type", "text/html");
 fs.readFile(path,(err, data )=>{
   //Depending upon the URL, It will return the required HTML/plain page.
 res.write(data);
 res.end();
  })
});
**   
                  //Status Codes
   200 - OK
   301  Resource moved
   404  Not Found
   500  Internal serval error
  
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