package parser;

import java.io.*;

public class Lexer {
	public static final int EOF = -1;
	public static final int PLUS = 1;
	public static final int MULT = 2;
	public static final int INT = 3;
	public static final int ID = 4;
	public static final int PRINT = 5;
	public static final int EQUALS = 6;
	public static final int NEWLINE = 7;

	public static String[] tokenNames = {
		null,
		"PLUS",
		"MULT",
		"INT",
		"ID",
		"PRINT",
		"EQUALS",
		"NEWLINE"
	};

	/** Current char of lookahead */
	int c;

	/** Where to pull char from */
	InputStream in;

	public Lexer(InputStream in) throws IOException {
		this.in = in;
		consume();
	}

	public Token nextToken() throws IOException {
		while ( c!=EOF ) {
			if ( c==' ' || c=='\t' ) {
				consume();
				continue;
			}
			if ( c>='0' && c<='9' ) {
				StringBuffer buf = new StringBuffer();
				while ( c>='0' && c<='9' ) {
					buf.append((char)c);
					consume();
				}
				return new Token(INT, buf.toString());
			}
			if ( c>='a' && c<='z' ) {
				StringBuffer buf = new StringBuffer();
				while ( c>='a' && c<='z' ) {
					buf.append((char)c);
					consume();
				}
				String text = buf.toString();
				if ( text.equals("print") ) {
					return new Token(PRINT);
				}
				return new Token(ID, text);
			}
			if ( c=='+' ) {
				consume();
				return new Token(PLUS);
			}
			if ( c=='*' ) {
				consume();
				return new Token(MULT);
			}
			if ( c=='=' ) {
				consume();
				return new Token(EQUALS);
			}
			if ( c=='\n' || c=='\r' ) {
				consume();
				return new Token(NEWLINE);
			}
			throw new IllegalArgumentException("invalid char");
		}
		return new Token(EOF);
	}

	public void consume() throws IOException {
		c = in.read();
	}
}