// Syner.java Oct.6, 1998   By Gregor v. Bochmann & Yaoping Wang
import java.io.*;
import java.util.*;

class Lexer {
	public final int BEGIN = 1;
	public final int END = 2;
	public final int ASSIGN = 3;
	public final int PLUS = 4;
	public final int MINUS = 5;
	public final int IDENT = 6;
	public final int SEMICOLON = 7;
	
	// -------------------------------------- //
	// PORTION BELOW CREATED FOR ASSIGNMENT 3 //
	// -------------------------------------- //
	
	public final int MULTIPLY = 8;
	public final int DIVIDE = 9;
	public final int GREATER = 10;
	public final int GREATEQ = 11;
	public final int LESSER = 12;
	public final int LESSEQ = 13;
	public final int OPENB = 14;
	public final int CLOSEB = 15;
	public final int OPENC = 16;
	public final int CLOSEC = 17;
	public final int NUMBER = 18;
	public final int WHILE = 19;
	public final int EQUAL = 20;
	
	private int n; // holds next digit
	
	// -------------------------------------- //
	// PORTION ABOVE CREATED FOR ASSIGNMENT 3 //
	// -------------------------------------- //
	
	public String idName;  // identifier name
	public int token;  //holds the next token

	private BufferedReader input; // input file buffer
	private char c;  //holds the next character

	public Lexer(String inputFile){
		try{input = new BufferedReader(new FileReader(inputFile));} 
		catch(IOException ee) {ee.printStackTrace();}
	}

	public void start() throws IOException, EndOfFileEncountered{
		nextChar(); 
		getNextToken();
	}

	public void getNextToken()throws IOException, EndOfFileEncountered {
		disposeSpace();
		String terminalString ="";
		int terminalNum = 0;			// created for assignment 3
		
		if(Character.isLetter(c)){ //first character is a letter, get whole alphanumeric string
			terminalString += c;
			nextChar();
			while(Character.isLetterOrDigit(c)){terminalString += c; nextChar();}
			idName = terminalString;
			if(terminalString.equals("BEGIN")) token = BEGIN;
			else if(terminalString.equals("END")) token = END;
			else if(terminalString.equals("WHILE")) token = WHILE; //created for assignment 3
			else token = IDENT;
				} 
		else if (c == '+') {token = PLUS; nextChar();} 
		else if (c == '-') {token = MINUS; nextChar();} 
		else if (c == ';') {token = SEMICOLON; nextChar();} 
		else if (c == ':') { //check that next char is '=' to find assignment token ":=" 
						nextChar(); 
						if (c == '=') {token = ASSIGN; nextChar();}
						else {System.out.println("lexical error: '=' expected after ':'; skip to end of program");
						       skipToEndOfFile();}
		}
		
		// -------------------------------------- //
		// PORTION BELOW CREATED FOR ASSIGNMENT 3 //
		// -------------------------------------- //

		
		else if (Character.isDigit(c)){ //first digit is a letter, get whole value
			terminalNum = terminalNum*10 + (Integer.valueOf(c)-48);
			nextChar();
			while(Character.isDigit(c))
			{
				terminalNum = terminalNum*10 + (Integer.valueOf(c)-48);
				nextChar();
			}
			idName = Integer.toString(terminalNum);
			token = NUMBER;
		}
		
		else if (c == '=') {token = EQUAL; nextChar();}
		
		else if (c == '<') {//check whether or not the relop is < or <=
			nextChar();
			if (c == '=') {token = LESSEQ; nextChar();}
			else {token = LESSER; nextChar();}
		}
		
		else if (c == '>') {
			nextChar();
			if (c == '=') {token = GREATEQ; nextChar();}
			else {token = GREATER; nextChar();}
		}
		
		else if (c == '*') { token = MULTIPLY; nextChar();}
		else if (c == '/') { token = DIVIDE; nextChar();}
		else if (c == '(') { token = OPENB; nextChar();}
		else if (c == ')') { token = CLOSEB; nextChar();}
		else if (c == '{') { token = OPENC; nextChar();}
		else if (c == '}') { token = CLOSEC; nextChar();}
		
		
		// -------------------------------------- //
		// PORTION ABOVE CREATED FOR ASSIGNMENT 3 //
		// -------------------------------------- //
		
		
		else {System.out.println("invalid lexical unit; skip to end of program"); skipToEndOfFile();}
		}
		
	public void disposeSpace() throws IOException, EndOfFileEncountered{
		//get rid of all space like \t, \n, and blank space
		while(Character.isWhitespace(c)) {nextChar();}
		}

	public void nextChar() throws IOException, EndOfFileEncountered{//get next character
		int i;
		if((i = input.read()) == -1)//hit the end of file, exception thrown
			throw new EndOfFileEncountered();
		c = (char) i;
		System.out.print(c);
		}
	
	public void skipToEndOfFile() throws IOException, EndOfFileEncountered {
		while (true) {nextChar();}
		}
	
}