Creating and displaying key pairs

NuGet packages:

Programming elements:

using System;
using System.Threading.Tasks;
using System.IO;
using Amazon.EC2;
using Amazon.EC2.Model;
using System.Collections.Generic;

namespace EC2CreateKeyPair
{
  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class to create and store a key pair
  class Program
  {
    static async Task Main(string[] args)
    {
      // Create the EC2 client
      var ec2Client = new AmazonEC2Client();

      // Parse the command line and show help if necessary
      var parsedArgs = CommandLine.Parse(args);
      if(parsedArgs.Count == 0)
      {
        // In the case of no command-line arguments,
        // just show help and the existing key pairs
        PrintHelp();
        Console.WriteLine("\nNo arguments specified.");
        Console.Write(
          "Do you want to see a list of the existing key pairs? ((y) or n): ");
        string response = Console.ReadLine();
        if((string.IsNullOrEmpty(response)) || (response.ToLower() == "y"))
          await EnumerateKeyPairs(ec2Client);
        return;
      }

      // Get the application arguments from the parsed list
      string keyPairName =
        CommandLine.GetArgument(parsedArgs, null, "-k", "--keypair-name");
      string pemFileName =
        CommandLine.GetArgument(parsedArgs, null, "-p", "--pem-filename");
      if(string.IsNullOrEmpty(keyPairName))
        CommandLine.ErrorExit("\nNo key pair name specified." +
          "\nRun the command with no arguments to see help.");
      if(string.IsNullOrEmpty(pemFileName) || !pemFileName.EndsWith(".pem"))
        CommandLine.ErrorExit("\nThe PEM filename is missing or incorrect." +
          "\nRun the command with no arguments to see help.");

      // Create the key pair
      await CreateKeyPair(ec2Client, keyPairName, pemFileName);
      await EnumerateKeyPairs(ec2Client);
    }


    //
    // Method to create a key pair and save the key material in a PEM file
    private static async Task CreateKeyPair(
      IAmazonEC2 ec2Client, string keyPairName, string pemFileName)
    {
      // Create the key pair
      CreateKeyPairResponse response =
        await ec2Client.CreateKeyPairAsync(new CreateKeyPairRequest{
          KeyName = keyPairName
        });
      Console.WriteLine($"\nCreated new key pair: {response.KeyPair.KeyName}");

      // Save the private key in a PEM file
      using (var s = new FileStream(pemFileName, FileMode.Create))
      using (var writer = new StreamWriter(s))
      {
        writer.WriteLine(response.KeyPair.KeyMaterial);
      }
    }


    //
    // Method to show the key pairs that are available
    private static async Task EnumerateKeyPairs(IAmazonEC2 ec2Client)
    {
      DescribeKeyPairsResponse response = await ec2Client.DescribeKeyPairsAsync();
      Console.WriteLine("Available key pairs:");
      foreach (KeyPairInfo item in response.KeyPairs)
        Console.WriteLine($"  {item.KeyName}");
    }


    //
    // Command-line help
    private static void PrintHelp()
    {
      Console.WriteLine(
        "\nUsage: EC2CreateKeyPair -k <keypair-name> -p <pem-filename>" +
        "\n  -k, --keypair-name: The name you want to assign to the key pair." +
        "\n  -p, --pem-filename: The name of the PEM file to create, with a \".pem\" extension.");
    }
  }


  // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  // Class that represents a command line on the console or terminal.
  // (This is the same for all examples. When you have seen it once, you can ignore it.)
  static class CommandLine
  {
    //
    // Method to parse a command line of the form: "--key value" or "-k value".
    //
    // Parameters:
    // - args: The command-line arguments passed into the application by the system.
    //
    // Returns:
    // A Dictionary with string Keys and Values.
    //
    // If a key is found without a matching value, Dictionary.Value is set to the key
    //  (including the dashes).
    // If a value is found without a matching key, Dictionary.Key is set to "--NoKeyN",
    //  where "N" represents sequential numbers.
    public static Dictionary<string,string> Parse(string[] args)
    {
      var parsedArgs = new Dictionary<string,string>();
      int i = 0, n = 0;
      while(i < args.Length)
      {
        // If the first argument in this iteration starts with a dash it's an option.
        if(args[i].StartsWith("-"))
        {
          var key = args[i++];
          var value = key;

          // Check to see if there's a value that goes with this option?
          if((i < args.Length) && (!args[i].StartsWith("-"))) value = args[i++];
          parsedArgs.Add(key, value);
        }

        // If the first argument in this iteration doesn't start with a dash, it's a value
        else
        {
          parsedArgs.Add("--NoKey" + n.ToString(), args[i++]);
          n++;
        }
      }

      return parsedArgs;
    }

    //
    // Method to get an argument from the parsed command-line arguments
    //
    // Parameters:
    // - parsedArgs: The Dictionary object returned from the Parse() method (shown above).
    // - defaultValue: The default string to return if the specified key isn't in parsedArgs.
    // - keys: An array of keys to look for in parsedArgs.
    public static string GetArgument(
      Dictionary<string,string> parsedArgs, string defaultReturn, params string[] keys)
    {
      string retval = null;
      foreach(var key in keys)
        if(parsedArgs.TryGetValue(key, out retval)) break;
      return retval ?? defaultReturn;
    }

    //
    // Method to exit the application with an error.
    public static void ErrorExit(string msg, int code=1)
    {
      Console.WriteLine("\nError");
      Console.WriteLine(msg);
      Environment.Exit(code);
    }
  }

}