using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;

namespace dpapicmd {
    class Program {

        static void showHelp(string err = null) {
            if (err != null) {
                var color = Console.ForegroundColor;
                Console.ForegroundColor = ConsoleColor.DarkRed;
                Console.Error.WriteLine("Error: " + err + "\r\n");
                Console.ForegroundColor = color;
            }
            Console.Error.WriteLine("dpapicmd [/user] [/decrypt] [/utf8] [/entropy:<entropy>] {/clipboard|<text>}");
            Console.Error.WriteLine("Text is read as Base64 bytes unless /utf8 is used. Decrypted input and encrypted output is always Base64.");
            Environment.Exit(1);
        }
        static bool user = false;
        static bool dec = false;
        static bool utf8 = false;
        static bool clip = false;
        static string entropy = null;
        static string text;

        [STAThread]
        static void Main(string[] args) {
            if (args.Length == 0 || args[0] == "/?") {
                showHelp();
            }
            Array.Reverse(args);
            var argsl = new List<string>(args);
            var texts = argsl.FindAll(s => !s.StartsWith("/"));
            if (texts.Count > 1) {
                showHelp("Too many inputs.");
            }
            text = texts.Count == 0 ? null : texts[0];
            var options = new Stack<string>(argsl.FindAll(s => s.StartsWith("/")));
            while (options.Count > 0){
                var opt = options.Pop();
                if (opt.Length < 4) {
                    showHelp("Invalid option: " + opt + ".");
                }
                processOption(opt);
            }
            if ((clip && dec) || (clip && !dec && text == null)) {
                if (options.Count != 0) {
                    showHelp("Cannot specify /clipboard and provide input text.");
                }
                text = System.Windows.Forms.Clipboard.GetText();
                if (dec) text = text.Trim();
                if (string.IsNullOrEmpty(text)) {
                    showHelp("No text on clipboard.");
                }
            } else {
                if (options.Count != 0) {
                    showHelp("Too many arguments.");
                }
            }

            try {
                var entBytes = entropy == null ? null :
                    utf8 ? Encoding.UTF8.GetBytes(entropy) : Convert.FromBase64String(entropy);
                var target = (utf8 & !dec) ? Encoding.UTF8.GetBytes(text) : Convert.FromBase64String(text);
                var res = dec ?
                    ProtectedData.Unprotect(target, entBytes, user ? DataProtectionScope.CurrentUser : DataProtectionScope.LocalMachine) :
                    ProtectedData.Protect(target, entBytes, user ? DataProtectionScope.CurrentUser : DataProtectionScope.LocalMachine);
                var strout = (utf8 & dec) ? Encoding.UTF8.GetString(res) : Convert.ToBase64String(res);
                if (clip) {
                    System.Windows.Forms.Clipboard.SetText(strout);
                    Console.WriteLine("Output copied to clipboard.");
                } else {
                    Console.WriteLine(strout);
                }
            } catch(Exception ex) {
                showHelp(ex.ToString());
            }
        }
        static void processOption(string opt) {
            switch(opt.ToLowerInvariant().Substring(0,4)){
                case "/use": 
                    user = true;
                    break;
                case "/dec":
                    dec = true;
                    break;
                case "/utf":
                    utf8 = true;
                    break;
                case "/ent":
                    var col = opt.IndexOf(':');
                    if (col == -1 || col == opt.Length - 1) showHelp();
                    entropy = opt.Substring(col + 1);
                    break;
                case "/cli":
                    clip = true;
                    break;
                default:
                    showHelp("Unknown option: " + opt + ".");
                    break;
            }
        }
    }
}