import java.util.ArrayList;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Lexer {
  public static enum TokenType {
    // Definitions of accepted tokens
    IF("if"), WHILE("while"), PRINT("print"), TYPE("int|string|boolean"), BOOLOP("==|!="), BOOLVAL("false|true"), INTOP("[+]"), CHAR("[a-z]"), DIGIT("[0-9]"), WHITESPACE("[ \t\f\r\n]+"), LPAREN("[(]"), RPAREN("[)]");
    public final String pattern;

    private TokenType(String pattern) {
      this.pattern = pattern;
    }
  }

  public static class Token {
    public TokenType type;
    public String data;

    public Token(TokenType type, String data) {
      this.type = type;
      this.data = data;
    }
  }

  public static ArrayList<Token> lex(String input) {
    // The tokens to return
    ArrayList<Token> tokens = new ArrayList<Token>();

    // allows us to work with a mutable string
    StringBuffer tokenPatternsBuffer = new StringBuffer();

    for (TokenType tokenType : TokenType.values()) {
      tokenPatternsBuffer.append(String.format("|(?<%s>%s)", tokenType.name(), tokenType.pattern));
    }
    Pattern tokenPatterns = Pattern.compile(new String(tokenPatternsBuffer.substring(1)));

    // Begin matching tokens
    Matcher matcher = tokenPatterns.matcher(input);
      while (matcher.find()) {
        if (matcher.group(TokenType.DIGIT.name()) != null) {
          tokens.add(new Token(TokenType.DIGIT, matcher.group(TokenType.DIGIT.name())));
          continue;
      } else if (matcher.group(TokenType.IF.name()) != null) {
          tokens.add(new Token(TokenType.IF, matcher.group(TokenType.IF.name())));
          continue;
      } else if (matcher.group(TokenType.WHILE.name()) != null) {
          tokens.add(new Token(TokenType.WHILE, matcher.group(TokenType.WHILE.name())));
          continue;
      } else if (matcher.group(TokenType.TYPE.name()) != null) {
          tokens.add(new Token(TokenType.TYPE, matcher.group(TokenType.TYPE.name())));
          continue;
      } else if (matcher.group(TokenType.PRINT.name()) != null) {
          tokens.add(new Token(TokenType.PRINT, matcher.group(TokenType.PRINT.name())));
          continue;
      } else if (matcher.group(TokenType.BOOLOP.name()) != null) {
          tokens.add(new Token(TokenType.BOOLOP, matcher.group(TokenType.BOOLOP.name())));
          continue;
      } else if (matcher.group(TokenType.BOOLVAL.name()) != null) {
          tokens.add(new Token(TokenType.BOOLVAL, matcher.group(TokenType.BOOLVAL.name())));
          continue;
      } else if (matcher.group(TokenType.INTOP.name()) != null) {
          tokens.add(new Token(TokenType.INTOP, matcher.group(TokenType.INTOP.name())));
          continue;
      } else if (matcher.group(TokenType.CHAR.name()) != null) {
        tokens.add(new Token(TokenType.CHAR, matcher.group(TokenType.CHAR.name())));
        continue;
      } else if (matcher.group(TokenType.LPAREN.name()) != null) {
          tokens.add(new Token(TokenType.LPAREN, matcher.group(TokenType.LPAREN.name())));
          continue;
      } else if (matcher.group(TokenType.RPAREN.name()) != null) {
          tokens.add(new Token(TokenType.RPAREN, matcher.group(TokenType.RPAREN.name())));
          continue;
      } else if (matcher.group(TokenType.WHITESPACE.name()) != null) {
          continue;
      }
    }
    return tokens;
  }

  public static void main(String[] args) {
    String input = "if (int 5) abc @";
    // Create tokens and print them
    ArrayList<Token> tokens = lex(input);
    for (Token token : tokens)
      System.out.println("DEBUG Lexer - " + token.type + " [ " + token.data + " ] " + "found at " + "linenumber");
  }
}