import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class FTP2server {

	final static String CRLF = "\r\n";
	static int retrCount = 0;
	static boolean user = false;
	static boolean needPass = false;
	static boolean loggedIn = false;
	static boolean pass = false;
	static String type = "";
	static boolean syst = false;
	static String hostaddress = "";
	static int portnumber = 0;
	static boolean needRetr = false;
	static boolean validRetr = false;

	// Program-Class overview: The purpose of FTP1Server is to determine if a received command is a valid FTP command.
	// My approach was to first read the input from the console and then parse the string in order to check for validity.

	public static void main(String[] args) throws IOException {  // input is saved and passed to "parse"

		BufferedReader b = new BufferedReader(new InputStreamReader(System.in));  // declare and instantiate a BufferedReader
		ArrayList<String> inputList = new ArrayList<String>();  // declare and instantiate an ArrayList
		String input = ""; // declare and instantiate input
		int i = 0;
		i = b.read();

		while (i != -1) {  // read input from the console and compile it into inputList
			input += (char) i;  // scan characters into input string
			if ((char) i == '\r') { // check for the end of input
				i = b.read();
				if ((char) i == '\n') {
					input += (char) i;
					inputList.add(input);
					input = "";
					i = b.read();
				}
				else {
					inputList.add(input);
					input = "";
				}
			} else if ((char) i == '\n') {
				inputList.add(input);
				input = "";
				i = b.read();
			} else {
				i = b.read();
			}
		}

		System.out.printf("220 COMP 431 FTP server ready.%s", CRLF);

		for (int j = 0; j < inputList.size(); j++) {  // loop through the inputList in order to pass each input to "parse"
			input = inputList.get(j);
			System.out.print(input);
			parse(input);
		}
	}

	static void parse(String inputline) throws IOException {  // takes input from the console and checks each string for valid FTP characteristics

		String token = ""; // The current token

		StringTokenizer tokenizedLine = new StringTokenizer(inputline, " \n\r", true); // declare and instantiate a
		// StringTokenizer with delimiters

		if (tokenizedLine.hasMoreTokens()) {  // check if string has more tokens
			token = tokenizedLine.nextToken(); // Get the token

			if (token.equalsIgnoreCase("user")) {  // see if the string representing the token matches "user"
				if (tokenizedLine.hasMoreTokens()) {  // check if string has more tokens
					token = tokenizedLine.nextToken();

					if (!token.equals(" ")) {  // make sure there is a space between "user" and the username
						System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
						return;
					}

					while (token.equals(" ")) {  // loop through the spaces between "user" and the username
						token = tokenizedLine.nextToken();
					}

					String username = "";

					while (tokenizedLine.hasMoreTokens() && !token.equals("\r")) {  // store the username from the remaining tokens
						username += token;  // add token to username variable
						token = tokenizedLine.nextToken();
					}

					char[] characters = username.toCharArray();  // convert the username to a character array
					for (int x = 0; x < characters.length; x++) {  // loop through each character of the username
						if ((int) characters[x] <= 127 && (int) characters[x] >= 0) {
							// check if character is one of the 128 ASCII characters
							continue;
						} else {  // the username characters were invalid
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					}

					if (token.equals("\r")) {  // check for <CR>
						if(tokenizedLine.hasMoreTokens()) { // check if token has more tokens
							if (tokenizedLine.nextToken().equals("\n")) {  // check for <LF>
								if (username.length() > 0) { // make sure there was a username entered
									checkOrder("user");
									return;
								} else { // no username was entered
									System.out.printf("501 Syntax error in parameter.%s", CRLF);
									return;
								}
							} else {  // there was no <LF>
								System.out.printf("501 Syntax error in parameter.%s", CRLF);
								return;
							}
						} else {  // there was no <LF>
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					} else {  // there was no <CR>
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
						return;
					}
				}

				else {  // there were no more tokens after the command
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}
			}

			else if (token.equalsIgnoreCase("pass")) { // see if the string representing the token matches "pass"
				if (tokenizedLine.hasMoreTokens()) {  // check if token has more tokens
					token = tokenizedLine.nextToken();

					if (!token.equals(" ")) {  // make sure there is a space between "pass" and the password
						System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
						return;
					}

					while (token.equals(" ")) { // loop through the spaces between "pass" and the password
						token = tokenizedLine.nextToken();
					}

					String password = "";

					while (tokenizedLine.hasMoreTokens() && !token.equals("\r")) { //store the password from the remaining tokens
						password += token;
						token = tokenizedLine.nextToken();
					}

					char[] characters = password.toCharArray();  // create a character array of the password
					for (int x = 0; x < characters.length; x++) {  // loop through every character of the password
						if ((int) characters[x] <= 127 && (int) characters[x] >= 0) {
							// check that every character is one of the 128 ASCII characters
							continue;
						} else {  // the password characters were invalid
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					}

					if (token.equals("\r")) {  // check for <CR>
						if(tokenizedLine.hasMoreTokens()) { // check if token has more tokens
							if (tokenizedLine.nextToken().equals("\n")) {  // check for <LF>
								if (password.length() > 0) { // make sure there was a password entered
									checkOrder("pass");
									return;
								} else { // no password was entered
									System.out.printf("501 Syntax error in parameter.%s", CRLF);
									return;
								}
							} else {  // there was no <LF>
								System.out.printf("501 Syntax error in parameter.%s", CRLF);
								return;
							}
						} else {  // there was no <LF>
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					} else {  // there was no <CR>
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
						return;
					}
				} else {  // there were no more tokens after the command
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}
			}

			else if (token.equalsIgnoreCase("type")) {  // see if the string representing the token matches "type"
				token = tokenizedLine.nextToken();

				if (!token.equals(" ")) {  // make sure there is a space between "type" and the character chosen
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}

				while (token.equals(" ")) {  // loop through the spaces between type and the character
					token = tokenizedLine.nextToken();
				}

				if (tokenizedLine.hasMoreTokens()) { // check if there are more tokens
					if (token.equals("A") || token.equals("I")) {  // check that those tokens are either 'A' or 'I'
						if (token.equals("A")) {
							type = "a";
						}
						if (token.equals("I")) {
							type = "i";
						}
						if (tokenizedLine.hasMoreTokens()) { // check if there are more tokens
							token = tokenizedLine.nextToken();
							if (token.equals("\r")) {  // check for <CR>
								if(tokenizedLine.hasMoreTokens()) { // check if token has more tokens
									if (tokenizedLine.nextToken().equals("\n")) {  // check for <LF>
										checkOrder("type");
										return;
									} else {  // there was no <LF>
										System.out.printf("501 Syntax error in parameter.%s", CRLF);
										return;
									}
								} else {  // there was no <LF>
									System.out.printf("501 Syntax error in parameter.%s", CRLF);
									return;
								}
							} else {  // there was no <CR>
								System.out.printf("501 Syntax error in parameter.%s", CRLF);
								return;
							}
						} else {  // there were no more tokens after the command
							System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
							return;
						}
					} else { // the type-code was invalid
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
					}
				} else {  // there were no more tokens after the command
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}
			}

			else if (token.equalsIgnoreCase("noop") || token.equalsIgnoreCase("syst") || token.equalsIgnoreCase("quit")) {
				// see if the string representing the token matches "noop", "syst", or "quit"
				if (tokenizedLine.hasMoreTokens() && tokenizedLine.nextToken().equals("\r")) {  // checks if next token is <CR>
					if (tokenizedLine.hasMoreTokens() && tokenizedLine.nextToken().equals("\n")) { // check if next token is <LF>
						if (token.equalsIgnoreCase("noop")) {
							checkOrder("noop");
						} else if (token.equalsIgnoreCase("syst")) {
							checkOrder("syst");
						} else {
							checkOrder("quit");
						}
						return;
					} else { // there was no <LF>
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
						return;
					}
				} else { // there was no <CR>
					System.out.printf("501 Syntax error in parameter.%s", CRLF);
					return;
				}
			}

			else if (token.equalsIgnoreCase("port")) {
				if (tokenizedLine.hasMoreTokens()) {  // check if string has more tokens
					token = tokenizedLine.nextToken();

					if (!token.equals(" ")) {  // make sure there is a space between "user" and the pathname
						System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
						return;
					}

					while (token.equals(" ")) {  // loop through the spaces between "user" and the pathname
						token = tokenizedLine.nextToken();
					}

					String hostport = "";

					while (tokenizedLine.hasMoreTokens() && !token.equals("\r")) {  // store the pathname from the remaining tokens
						hostport += token;  // add token to pathname variable
						token = tokenizedLine.nextToken();
					}

					char[] hostChar = hostport.toCharArray();

					for (int i = 0; i < hostChar.length; i++) {
						if ((int) hostChar[i] <= 255 && (int) hostChar[i] > 0) {
							continue;
						} else {
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					}

					String[] parts = hostport.split(",",6);

					if (parts.length == 6) {

						String ha1 = parts[0];
						String ha2 = parts[1];
						String ha3 = parts[2];
						String ha4 = parts[3];
						int pa1 = Integer.parseInt(parts[4]);
						int pa2 = Integer.parseInt(parts[5]);

						if (token.equals("\r")) {  // check for <CR>
							if(tokenizedLine.hasMoreTokens()) { // check if token has more tokens
								if (tokenizedLine.nextToken().equals("\n")) {  // check for <LF>
									processPort(ha1,ha2,ha3,ha4,pa1,pa2);
									checkOrder("port");
									return;
								} else { // no pathname was entered
									System.out.printf("501 Syntax error in parameter.%s", CRLF);
									return;
								}
							} else {  // there was no <LF>
								System.out.printf("501 Syntax error in parameter.%s", CRLF);
								return;
							}
						} else {  // there was no <CR>
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					} else {
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
						return;
					}
				} else {
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}
			}

			else if (token.equalsIgnoreCase("retr")) {
				if (tokenizedLine.hasMoreTokens()) {  // check if string has more tokens
					token = tokenizedLine.nextToken();

					if (!token.equals(" ")) {  // make sure there is a space between "user" and the pathname
						System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
						return;
					}

					while (token.equals(" ")) {  // loop through the spaces between "user" and the pathname
						token = tokenizedLine.nextToken();
					}

					while (token.charAt(0) == '/' || token.charAt(0) == '\\') {
						token = token.substring(1, token.length());
					}

					String pathname = "";

					while (tokenizedLine.hasMoreTokens() && !token.equals("\r")) {  // store the pathname from the remaining tokens
						pathname += token;  // add token to pathname variable
						token = tokenizedLine.nextToken();
					}

					char[] characters = pathname.toCharArray();  // convert the pathname to a character array
					for (int x = 0; x < characters.length; x++) {  // loop through each character of the pathname
						if ((int) characters[x] <= 127 && (int) characters[x] >= 0) {
							// check if character is one of the 128 ASCII characters
							continue;
						} else {  // the pathname characters were invalid
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					}

					if (token.equals("\r")) {  // check for <CR>
						if(tokenizedLine.hasMoreTokens()) { // check if token has more tokens
							if (tokenizedLine.nextToken().equals("\n")) {  // check for <LF>
								if (pathname.length() > 0) { // make sure there was a pathname entered
									retrCount++;
									processRetr(pathname);
									checkOrder("retr");
									return;
								} else { // no pathname was entered
									System.out.printf("501 Syntax error in parameter.%s", CRLF);
									return;
								}
							} else {  // there was no <LF>
								System.out.printf("501 Syntax error in parameter.%s", CRLF);
								return;
							}
						} else {  // there was no <LF>
							System.out.printf("501 Syntax error in parameter.%s", CRLF);
							return;
						}
					} else {  // there was no <CR>
						System.out.printf("501 Syntax error in parameter.%s", CRLF);
						return;
					}
				}

				else {  // there were no more tokens after the command
					System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
					return;
				}
			}

			else { // the command entered did not match "user", "pass", "type", "syst", "noop", or "quit"
				System.out.printf("500 Syntax error, command unrecognized.%s", CRLF);
				return;
			}
		}
	}

	public static void checkOrder(String command) {
		if (command.equals("user")) {
			if (user == false) {
				user = true;
				needPass = true;
				System.out.printf("331 Guest access OK, send password.%s", CRLF);
				return;
			} else {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			}
		} else if (command.equals("pass")) {
			if (user && needPass) {
				needPass = false;
				loggedIn = true;
				System.out.printf("230 Guest login OK.%s", CRLF);
				return;
			} else {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			}
		} else if (command.equals("type")) {
			if (needPass) {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			} else if (!loggedIn) {
				System.out.printf("530 Not logged in.%s", CRLF);
				return;
			} else {
				if (type.equalsIgnoreCase("a")) {
					System.out.printf("200 Type set to A.%s", CRLF);
					return;
				} else {
					System.out.printf("200 Type set to I.%s", CRLF);
					return;
				}
			}
		} else if (command.equals("noop")) {
			if (needPass) {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			} else if (!loggedIn) {
				System.out.printf("530 Not logged in.%s", CRLF);
				return;
			} else {
				System.out.printf("200 Command OK.%s", CRLF);
				return;
			}
		} else if (command.equals("syst")) {
			if (needPass) {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			} else if (!loggedIn) {
				System.out.printf("530 Not logged in.%s", CRLF);
				return;
			} else {
				System.out.printf("215 UNIX Type: L8.%s", CRLF);
				return;
			}
		} else if (command.equals("port")) {
			if (needPass) {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			} else if (!loggedIn) {
				System.out.printf("530 Not logged in.%s", CRLF);
				return;
			} else {
				needRetr = true;
				System.out.printf("200 Port command successful (" + hostaddress + portnumber + ").%s", CRLF);
				return;
			}
		} else if (command.equals("retr")) {
			if (needPass) {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			} else if (!loggedIn) {
				System.out.printf("530 Not logged in.%s", CRLF);
				return;
			} else if (needRetr) {
				if (validRetr) {
					System.out.printf("250 Requested file action completed.%s", CRLF);
					validRetr = false;
					needRetr = false;
					return;
				} else {
					return;
				}
			} else {
				System.out.printf("503 Bad sequence of commands.%s", CRLF);
				return;
			}
		} else {
			System.out.printf("200 Command OK.%s", CRLF);
			System.exit(1);
		}
	}

	public static void processPort(String ha1, String ha2, String ha3, String ha4, int pa1, int pa2) {
		hostaddress = ha1 + "." + ha2 + "." + ha3 + "." + ha4 + ",";
		portnumber = (pa1 * 256) + pa2;
	}

	public static void processRetr(String pathname) throws IOException {
		String filename = "retr_files/file" + retrCount;
		FileInputStream in = null;
		FileOutputStream out = null;

		File pathnameFile = new File(pathname);
		if (needRetr) {
			if (pathnameFile.exists()) {
				System.out.printf("150 File status okay.%s", CRLF);
				validRetr = true;
			}
		}

		try {
			in = new FileInputStream(pathname);
			out = new FileOutputStream(filename);

			int x;

			while ((x = in.read()) != -1) {
				out.write(x);
			}

			if (in != null) {
				in.close();
			}

			if (out != null) {
				out.close();
			}
		} catch (IOException e) {
			System.out.printf("550 File not found or access denied.%s", CRLF);
			validRetr = false;
			return;
		}
	}


	public static void fail(Exception e, String msg) {  // handle exceptions
		System.err.println(msg + ": " + e);
		System.exit(1);
	}
}