package calculator.antlr;
   
   import org.antlr.v4.runtime.CharStream;
   import org.antlr.v4.runtime.CharStreams;
   import org.antlr.v4.runtime.CommonTokenStream;
   import org.antlr.v4.runtime.tree.ParseTree;
   
   import calculator.Expression;
   import calculator.calculatorLexer;
  import calculator.calculatorParser;
  
  import org.antlr.v4.runtime.ANTLRErrorListener;
  import org.antlr.v4.runtime.BaseErrorListener;
  import org.antlr.v4.runtime.RecognitionException;
  import org.antlr.v4.runtime.Recognizer;
  
  public class Parser {
  
  	/**
  	 * Analyze a string input and return an Expression object representing the
  	 * parsed expression.
  	 * 
  	 */
  	public Expression parse(String inputStr) {
  		// Creation of a CharStream from the input string
  		CharStream input = CharStreams.fromString(inputStr);
  
  		// Lexer generated by ANTLR (calculatorLexer) to tokenize the input
  		calculatorLexer lexer = new calculatorLexer(input);
  
  		// Add error listener to throw exceptions on syntax error
  		lexer.removeErrorListeners();
  		lexer.addErrorListener(getBaseErrrorListener());
  
  		CommonTokenStream tokens = new CommonTokenStream(lexer);
  
  		// Parser generated by ANTLR (calculatorParser) to create a parse tree from the
  		// tokens
  		calculatorParser parser = new calculatorParser(tokens);
  
  		parser.removeErrorListeners();
  		parser.addErrorListener(getBaseErrrorListener());
  
  		ParseTree tree = parser.complete();
  
  		// Visit the tree to build the Expression
  		ParserVisitor visitor = new ParserVisitor();
  		return visitor.visit(tree);
  	}
  
  	private ANTLRErrorListener getBaseErrrorListener() {
  		return new BaseErrorListener() {
  			@Override
  			public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol, int line,
  					int charPositionInLine, String msg, RecognitionException e) {
  				throw new IllegalArgumentException(
  						"Invalid expression at line " + line + ":" + charPositionInLine + " - " + msg);
  			}
  		};
  	}
  }