package main

import (
    "io"
    "fmt"
    "os"
)

// copy file using os package
func copyFileUsingOsPackage(src, dst string) error {
    bytesRead, err := os.ReadFile(src)
    if err != nil {
        return err
    }

    return os.WriteFile(dst, bytesRead, 0644)
}

// copy file using io package
func copyFileUsingIoPackage(src, dst string) (int64, error) {
        source, err := os.Open(src)
        if err != nil {
                return 0, err
        }
        defer source.Close()

        destination, err := os.Create(dst)
        if err != nil {
                return 0, err
        }
        defer destination.Close()
        
        nBytes, err := io.Copy(destination, source)
        
        return nBytes, err
}

func main() {
    src := "/tmp/file-src.txt"
    dst := "/tmp/file-dst.txt"

    n, err := copyFileUsingIoPackage(src, dst)

    if err != nil {
        panic(err)
    }

    fmt.Printf("Copied %d bytes", n)
    fmt.Println()

    err = copyFileUsingOsPackage(src, dst)

    if err != nil {
        panic(err)
    }
}

package main

import (
    "fmt"
    "path/filepath"
    "strings"
)

func main() {
    filePath := "/tmp/file.ext"

    // get file name with extension
    fileName := filepath.Base(filePath)

    // get file extension
    fileExt := filepath.Ext(filePath)

    // truncate file name extension
    fileNameWithoutExt := strings.TrimSuffix(fileName, fileExt)

    fmt.Println("File name without extension: " + fileNameWithoutExt)
}

// $ go run main.go
// File name without extension: file

package main

import (
	b64 "encoding/base64"
	"fmt"
)

func main() {
	str := "text123321!?$*&()'-=@~"

	// Encode using the standard encoder
	strEnc := b64.StdEncoding.EncodeToString([]byte(str))
	fmt.Println(strEnc)

	strDec, err := b64.StdEncoding.DecodeString(strEnc)

	if err != nil {
		panic(err)
	}

	fmt.Println(string(strDec))
	fmt.Println()

	// Encode using a URL-compatible base64 format
	strEnc = b64.URLEncoding.EncodeToString([]byte(str))
	fmt.Println(strEnc)

	strDec, err = b64.URLEncoding.DecodeString(strEnc)

	if err != nil {
		panic(err)
	}

	fmt.Println(string(strDec))
}

// $ go run main.go
// dGV4dDEyMzMyMSE/JComKCknLT1Afg==
// text123321!?$*&()'-=@~

// dGV4dDEyMzMyMSE_JComKCknLT1Afg==
// text123321!?$*&()'-=@~

package main

import (
	"fmt"
	"net"
	"net/url"
)

func main() {
	s := "mysql://user:pass@host.com:3306/path?key=value#fragment"

	u, err := url.Parse(s)

	if err != nil {
		panic(err)
	}

	fmt.Println("Scheme: " + u.Scheme)

	fmt.Println("Username: " + u.User.Username())
	p, _ := u.User.Password()
	fmt.Println("Password: " + p)

	fmt.Println("Host with port: " + u.Host)

	host, port, err := net.SplitHostPort(u.Host)

	if err != nil {
		panic(err)
	}

	fmt.Println("Host: " + host)
	fmt.Println("Port: " + port)

	fmt.Println("Path: " + u.Path)
	fmt.Println("Fragment: " + u.Fragment)

	fmt.Println("Raw query: " + u.RawQuery)

	m, err := url.ParseQuery(u.RawQuery)

	if err != nil {
		panic(err)
	}

	fmt.Println("Value: " + m["key"][0])
}

// $ go run main.go 
// Scheme: mysql
// Username: user
// Password: pass
// Host with port: host.com:3306
// Host: host.com
// Port: 3306
// Path: /path
// Fragment: fragment
// Raw query: key=value
// Value: value

package main

import (
	"fmt"
	"time"
)

func print(from string) {
	for i := 0; i < 3; i++ {
		fmt.Println(from, ":", i)
	}
}

func main() {
	// Synchronous function call
	print("synchronous call")

	// Asynchronous function call
	// To run this function in a goroutine, use go f(s)
	// This new goroutine will execute concurrently with the calling main goroutine
	go print("asynchronous call")

	// Goroutine can also be execute as an anonymous function
	go func(msg string) {
		fmt.Println(msg)
	}("asynchronous anonymous call")

	// Two previous function calls are now running asynchronously in separate goroutines
	// Wait for them to finish
	time.Sleep(time.Second)
	fmt.Println("done")
}

// $ go run main.go
// synchronous call : 0
// synchronous call : 1
// synchronous call : 2
// asynchronous anonymous call
// asynchronous call : 0
// asynchronous call : 1
// asynchronous call : 2
// done

package main

import "fmt"

func main() {
    // Create unbuffered channel
	unbufferedChannel := make(chan string)

	go func() {
        // Send a value into a channel using the channel<- syntax
		unbufferedChannel <- "unbuffered channel"
	}()

    // The <-channel syntax receives a value from the channel
	fmt.Println(<-unbufferedChannel)

    // Create buffered channel with size 2
	bufferedChannel := make(chan string, 2)

    // Send a value to a buffered channel. The operation in non blocking
	bufferedChannel <- "buffered"
	bufferedChannel <- "channel"

	fmt.Println(<-bufferedChannel)
	fmt.Println(<-bufferedChannel)
}

// go run main.go 
// unbuffered channel
// buffered
// channel

package main

import (
	"fmt"
	"os"
	"strings"
)

func main() {
	os.Setenv("FOO", "1")
	fmt.Println("FOO:", os.Getenv("FOO"))
	fmt.Println("BAR:", os.Getenv("BAR"))

	fmt.Println("----------------------")

	for _, env := range os.Environ() {
		pair := strings.SplitN(env, "=", 2)
		fmt.Println(pair[0])
	}
}

// FOO: 1
// BAR: 
// ----------------------
// HOSTNAME
// PWD
// HOME
// LANG
// SHLVL
// PATH
// _
// FOO

<?php 

$folderPath = "/tmp/test-folder"; 

// List of files inside the folder 
$files = glob($folderPath.'/*'); 
 
foreach($files as $file) { 
	if(is_file($file)) 
		// Delete the given file 
		unlink($file); 
} 

echo "Files deleted";

// php main.php
// Files deleted

package main

import "fmt"

func factorial(n int) int {
	if n == 0 {
		return 1
	}

	return n * factorial(n-1)
}

func main() {
	fmt.Println(factorial(5))
}

// $ go run main.go 
// 120

package main

import "fmt"

// The function createCounter returns anonymous function defined within its body.
// The returned function encapsulates the variable count, creating a closure.
func createCounter() func() int {
	count := 0

	return func() int {
		count++

		return count
	}
}

func main() {
    // We invoke createCounter, storing the result (a function) in counter variable.
    // This function captures and retains its own count value,
    // which updates with each subsequent invocation of createCounter.
	counter := createCounter()

	fmt.Println(counter())
	fmt.Println(counter())
	fmt.Println(counter())

	newCounter := createCounter()
	
    fmt.Println(newCounter())
}

// $ go run main.go 
// 1
// 2
// 3
// 1

package main

import (
    "fmt"
    "runtime"
)

func main() {
    // The runtime.GOOS constant can be used to detect the OS at runtime,
    // since this constant is only set at runtime.
    os := runtime.GOOS

    switch os {
    case "windows":
        fmt.Println("Windows")
    case "darwin":
        fmt.Println("MacOS")
    case "linux":
        fmt.Println("Linux")
    default:
        fmt.Printf("%s.\n", os)
    }

    // The runtime.GOARCH constant can be used to determine the target architecture of a running program.
    fmt.Println(runtime.GOARCH)
}

// Output:
// Linux
// amd64

package main

import (
    "fmt"
    "os"
    "path/filepath"
)

func checkErr(err error) {
    if err != nil {
        panic(err)
    }
}

func main() {
    // The simplest way to create a temporary file is to call os.CreateTemp.
    // It will create and open the file for reading and writing.
    // We used "" as the first argument, so os.CreateTemp will create a file in the default directory.
    tmpFile, err := os.CreateTemp("", "tmpfile")
    checkErr(err)
    defer os.Remove(tmpFile.Name())

    fmt.Println("Temp file name:", tmpFile.Name())

    // Write some data to the temporary file
    _, err = tmpFile.Write([]byte{1, 2, 3, 4, 5})
    checkErr(err)

    // If we intend to write a lot of temporary files, we may prefer to create a temporary directory.
    // The arguments to os.MkdirTemp are the same as for os.CreateTemp, but it returns the directory name rather than the opened file.
    dName, err := os.MkdirTemp("", "tmpdir")
    checkErr(err)
    defer os.RemoveAll(dName)
    
    fmt.Println("Temp directory name:", dName)

    fName := filepath.Join(dName, "testFile")
    err = os.WriteFile(fName, []byte{1, 2, 3, 4, 5}, 0666)
    checkErr(err)
    defer os.Remove(fName)
}

// Output:
// Temp file name: /tmp/tmpfile3400905374
// Temp directory name: /tmp/tmpdir2812568099

package main

import "fmt"

func main() {
    // Recover function must be called inside a deferred function.
    // When the enclosing function panics, defer is activated and the restore call inside it catches the panic.
    defer func() {
        if r := recover(); r != nil {
            fmt.Printf("recovered: %s\n", r)
        }
    }()

    panic("some fatal error")
    
    // This code won't run because of panic.
    // Basic operations stop during a panic and resume during a deferred close.
    fmt.Println("after panic")
}

import json
import os
import uuid

filename = str(uuid.uuid4()) # create random file name

# JSON data to be written
jsonDict ={
    "firstname" : "John",
    "lastname" : "Doe",
    "age" : 30,
    "phonenumber" : "9976770500"
}

# write JSON to file
with open(filename, "w") as f:
    json.dump(jsonDict, f)

# read JSON string from file
f = open(filename, "r")
print(f.read())
f.close()
os.remove(filename)

# Output:
# {"firstname": "John", "lastname": "Doe", "age": 30, "phonenumber": "9976770500"}

import json
import uuid
 
jsonString = '{"firstname": "John", "lastname": "Doe"}'

# Create random file name and write json to file
filename = str(uuid.uuid4())

with open(filename, "w") as f:
    f.write(jsonString)

# Parse JSON string
# Deserializes json string into dict
print("Parse JSON string")
jsonDict = json.loads(jsonString)

# Iterating through the json
for key, value in jsonDict.items():
    print(key, value)

print()
#----------------------------------------------------#

print("Read JSON file")
f = open (filename, "r")
 
# Reading from file
jsonDict = json.loads(f.read())
 
# Iterating through the json
for key, value in jsonDict.items():
    print(key, value)
 
# Closing file
f.close()

# Output
# Parse JSON string
# firstname John
# lastname Doe
#
# Read JSON file
# firstname John
# lastname Doe

import os
import uuid

filename = str(uuid.uuid4()) # create random file name
wLines = ["First line\n", "Second line\n", "Third line\n"]

# writing lines to file
f = open(filename, 'w')
f.writelines(wLines)
f.close()

#--------------------------------------------------------#

print("-----Read lines using 'readlines' method-----")
f = open(filename, 'r')
rLines = f.readlines()

for lineNumber, line in enumerate(rLines, 1):
	print("Line {}: {}".format(lineNumber, line.strip()))

#--------------------------------------------------------#

print("-----Read lines using 'readline' method-----")
f = open(filename, 'r')
lineNumber = 1
 
while True:
    lineNumber += 1
 
    # Get next line from file
    line = f.readline()
 
    # if line is empty
    # end of file is reached
    if not line:
        break
    print("Line {}: {}".format(lineNumber, line.strip()))
 
f.close()

#--------------------------------------------------------#

print("-----Read lines via file object iteration-----")
f = open(filename, 'r')

for lineNumber, line in enumerate(f, 1):
    print("Line {}: {}".format(lineNumber, line.strip()))

#--------------------------------------------------------#

print("-----Read lines via file contex manager-----")
with open(filename, "r") as f:
    for lineNumber, line in enumerate(f, 1):
        print("Line {}: {}".format(lineNumber, line.strip()))

os.remove(filename) # remove file

# Output example:

# Read lines using 'readlines' method
# Line 1: First line
# Line 2: Second line
# Line 3: Third line

# File management using context manager
class FileManager():
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode
        self.file = None
  
    # The __enter__ method opens the file and returns a file object
    def __enter__(self):
        print('Open file: {}'.format(self.filename))
        self.file = open(self.filename, self.mode)
        return self.file

    # The __exit__ method takes care of closing the file on exiting the with block 
    def __exit__(self, etype, value, traceback):
        print('Close file: {}'.format(self.filename))
        self.file.close()

# A FileManager object is created with test.txt as the filename and "write" mode
# when __init__ method is executed
with FileManager('test.txt', 'w') as f:
    f.write('First line\n')
    f.write('Second line\n')

# The file is already closed thanks to the automatic call to the __exit__ method
print('File closed: {}\n'.format(f.closed))

with FileManager('test.txt', 'r') as f:
    for line in f:
        print(line.rstrip())

# Output
#Open file: test.txt
#Close file: test.txt
#File closed: True
#
#Open file: test.txt
#First line
#Second line
#Close file: test.txt

package main

import (
    "bufio"
    "fmt"
    "os"
)

func checkErr(err error) {
    if err != nil {
        panic(err)
    }
}

func main() {
    content := "Some content"
    // write a string (or just bytes) into a file
    err := os.WriteFile("/tmp/dfile1", []byte(content), 0644)
    checkErr(err)

    // open a file for writing
    file, err := os.Create("/tmp/dfile2")
    checkErr(err)
    // defer a Close immediately after opening a file
    defer file.Close()

    bytesCount, err := file.Write([]byte(content))
    checkErr(err)
    fmt.Printf("wrote %d bytes\n", bytesCount)

    bytesCount, err = file.WriteString("Some other content\n")
    checkErr(err)
    fmt.Printf("wrote %d bytes\n", bytesCount)
    // flush writes to a stable storage (file system for example)
    file.Sync()

    // bufio provides buffered writers
    writer := bufio.NewWriter(file)
    bytesCount, err = writer.WriteString("Some othe buffered content\n")
    checkErr(err)
    fmt.Printf("wrote %d bytes\n", bytesCount)
    // ensure all buffered operations have been applied to the underlying writer
    writer.Flush()
}

package main

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
)

func GenerateRandomHash(n int) (string, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)

	// Note that err == nil only if we read len(b) bytes.
	if err != nil {
		return "", err
	}

	hasher := sha256.New()
	hasher.Write(b)
	sha := hex.EncodeToString(hasher.Sum(nil))

	return sha, nil
}

func main() {
	hash, err := GenerateRandomHash(512)

	if err != nil {
		panic(err)
	}

	fmt.Println(hash)
}

// go run main.go 
// 34c0fb393623843e56719b5d9d66385a55b4b4d3393187b7b1a76aee46c421c5

package main

import (
    "crypto/sha256"
    "fmt"
)

func main() {
    str := "some string to calculate hash"
    hash := sha256.New()

    hash.Write([]byte(str))
    sum := hash.Sum(nil) // the argument can be used to append to an existing byte slice

    fmt.Println(str)
    fmt.Printf("%x\n", sum)
}

// go run main.go 
// some string to calculate hash
// 7aad383b9ad516fa67057adc283ce2cf71858aff317a5e267adebfdbd5dda5fd