flowchart TD
    A[Start Program] --> B[Display Welcome Message]
    B --> C{Read User Command}
    C -->|pwd| D[Show Current Directory]
    C -->|ls| E[List Files & Directories]
    C -->|mkdir| F[Create Directory]
    C -->|touch| G[Create Empty File]
    C -->|rm| H[Delete File]
    C -->|cat| I[Read & Display File]
    C -->|nano| J[Edit File Content]
    C -->|nano-append| K[Append to File]
    C -->|exit| L[Exit Program]
    C -->|invalid| M[Show Error]
    D --> C
    E --> C
    F --> C
    G --> C
    H --> C
    I --> C
    J --> C
    K --> C
    M --> C
    L --> N[End Program]

while (!exit)
{
    Console.Write("mmabas@SDOps:~$ ");
    string input = Console.ReadLine() ?? "";
    // Command processing via switch statement
}

public static void Pwd()
{
    var currentDir = Directory.GetCurrentDirectory();
    DirectoryInfo dirinfo = new DirectoryInfo(currentDir);
    Console.WriteLine(dirinfo.FullName);
    Console.WriteLine("Full Name of the directory is : {0}", dirinfo.FullName);
    Console.WriteLine("The directory was last accesses on: {0}", dirinfo.LastAccessTime.ToString());
}

public static void Ls()
{
    var currentDir = Directory.GetCurrentDirectory();
    DirectoryInfo dirinfo = new DirectoryInfo(currentDir);
    
    FileInfo[] filesInDir = dirinfo.GetFiles();
    DirectoryInfo[] dirsInDir = dirinfo.GetDirectories();
    
    foreach (var directoryInfo in dirsInDir)
    {
        Console.WriteLine("{0}      -----      {1}", directoryInfo.Name, directoryInfo.LastAccessTime);
    }
    foreach (FileInfo file in filesInDir)
    {
        Console.WriteLine("{0}      {1}      {2}", file.Name, file.Length, file.LastAccessTime);
    }
}

public static void MkDir()
{
    Console.Write("Enter the name of the directory: ");
    var name = Console.ReadLine();
    
    if (string.IsNullOrEmpty(name))
    {
        Console.WriteLine("Directory name cannot be empty.");
        return;
    }
    
    if (Directory.Exists(name))
    {
        Console.WriteLine("Directory already exists.");
        return;
    }
    
    Directory.CreateDirectory(name);
}

public static void Touch()
{
    Console.Write("Enter the name of the file: ");
    var name = Console.ReadLine();
    
    if (string.IsNullOrEmpty(name))
    {
        Console.WriteLine("File name cannot be empty.");
        return;
    }
    
    if (File.Exists(name))
    {
        Console.WriteLine("File already exists.");
        return;
    }
    
    var fs = File.Create(name);
    fs.Close();  // Important: Always close the stream after use
}

private static void Rm()
{
    Console.Write("Enter the name of the file: ");
    var name = Console.ReadLine();
    if (!ValidateExists(name)) return;
    
    File.Delete(name);
}

private static void Cat()
{
    Console.Write("Enter the name of the file: ");
    var name = Console.ReadLine();
    if (!ValidateExists(name)) return;
    
    var content = File.ReadAllText(name);
    Console.WriteLine(content);
}

private static void NanoAppend()
{
    Console.Write("Enter the name of the file: ");
    var name = Console.ReadLine();
    if (!ValidateExists(name)) return;
    
    Console.Write("Enter the text to append: ");
    var text = Console.ReadLine();
    
    if (string.IsNullOrEmpty(text))
    {
        Console.WriteLine("Text cannot be empty.");
        return;
    }
    
    File.AppendAllText(name, text);
}

private static void Nano()
{
    Console.Write("Enter the name of the file: ");
    var name = Console.ReadLine();
    if (!ValidateExists(name)) return;
    
    Console.WriteLine("----- ------ ----- [Old Content] ----- ------ -----");
    ReadFileData(name);
    
    Console.WriteLine("----- ------ ----- [Please write the new content] ----- ------ -----");
    WriteFileData(name);
}

private static void ReadFileData(string? name)
{
    FileStream fs = new FileStream(name, FileMode.OpenOrCreate, FileAccess.ReadWrite);
    StreamReader sr = new StreamReader(fs);
    sr.BaseStream.Seek(0, SeekOrigin.Begin);  // Move to start of file
    
    string str = sr.ReadLine();
    while (str != null)
    {
        Console.WriteLine("{0}", str);
        str = sr.ReadLine();
    }
    
    sr.Close();
    fs.Close();
}

private static void WriteFileData(string? name)
{
    FileStream fs = new FileStream(name, FileMode.Create, FileAccess.ReadWrite);
    StreamWriter w = new StreamWriter(fs);
    
    var text = Console.ReadLine();
    if (string.IsNullOrEmpty(text))
    {
        Console.WriteLine("Text cannot be empty.");
        return;
    }
    
    w.Write(text);
    w.Flush();  // Ensures data is written to disk
    w.Close();
    fs.Close();
}

sequenceDiagram
    participant App as Application
    participant FS as FileStream
    participant SR as StreamReader/Writer
    participant File as Physical File
    
    App->>FS: Create FileStream(path, mode, access)
    FS->>File: Open file handle
    App->>SR: Create StreamReader/Writer(FileStream)
    SR->>FS: Connect to stream
    
    alt Reading
        App->>SR: ReadLine()
        SR->>FS: Read bytes
        FS->>File: Read from disk
        File-->>FS: Return bytes
        FS-->>SR: Return bytes
        SR-->>App: Return string
    else Writing
        App->>SR: Write(text)
        SR->>FS: Write bytes to buffer
        App->>SR: Flush()
        SR->>FS: Force write
        FS->>File: Write to disk
    end
    
    App->>SR: Close()
    SR->>FS: Release stream
    App->>FS: Close()
    FS->>File: Release file handle

private static bool ValidateExists(string? name)
{
    if (string.IsNullOrEmpty(name))
    {
        Console.WriteLine("File name cannot be empty.");
        return false;
    }
    
    if (!File.Exists(name))
    {
        Console.WriteLine("File does not exist.");
        return false;
    }
    
    return true;
}

Welcome to Linux emulation on Windows!
 
mmabas@SDOps:~$ pwd
C:\Users\Student\Projects
Full Name of the directory is : C:\Users\Student\Projects
The directory was last accesses on: 10/26/2025 2:30:00 PM
 
mmabas@SDOps:~$ touch myfile.txt
 
mmabas@SDOps:~$ nano
Enter the name of the file: myfile.txt
----- ------ ----- [Old Content] ----- ------ -----
----- ------ ----- [Please write the new content] ----- ------ -----
Hello, this is my first file!
 
mmabas@SDOps:~$ cat
Enter the name of the file: myfile.txt
Hello, this is my first file!
 
mmabas@SDOps:~$ nano-append
Enter the name of the file: myfile.txt
Enter the text to append: This is appended text.
 
mmabas@SDOps:~$ cat
Enter the name of the file: myfile.txt
Hello, this is my first file!This is appended text.
 
mmabas@SDOps:~$ exit