import java.util.*;
import java.io.*;

public class Parse
{
  private String line; // our input buffer
  private int [] vars;
  private Scanner scan;
  private boolean eval;

  public Parse()
  {
    line = "";

    vars = new int[26];
    for (int i=0; i<26; i++)
    vars[i] = 0;

    scan = new Scanner(System.in);
  }

  public void run() throws IOException
  {
    String token;

    System.out.print("> ");

    token = getToken();
    parseCode(token);                        // ::= <code> .

  }

  public void parseCode(String token) throws IOException
  {
    do {
      parseStmt(token);                    // ::= <statement> <code> | <statment>
      token = getToken();
    } while (!token.equals("."));
  }

  public void parseStmt(String token) throws IOException
  {
    int val;
    String text;
      if (token.equals("load"))                 // ::= load <string>
      {
        token = getToken();
        text = parseString(token);

        line = loadFile(text) + line;
      }
      else if (token.equals("print"))            // ::= print <string> | print <expr>
      {
        token = getToken();

        if (token.charAt(0) == '"')
        {
          text = parseString (token);

          // execute part
          if (eval == true)
            System.out.println(text);
        }
        else
        {
          val = parseExpr(token);

          // execute part
          if (eval == true)
            System.out.println(val);
        }
      }
      else if (token.equals("input"))            // ::= input <var>
      {
        token = getToken();
        val = parseVar(token);

        // execute part
        if (eval == true)
        {
          System.out.print("? ");
          val = scan.nextInt();
          storeVar(token, val);
        }
      }
      else if (token.equals("if"))
      {
        token = getToken();
        // determines whether the condition was true or not
        boolean cond = parseCond(token);
        // assigns the boolean value (true or false) to the global eval boolean
        eval = cond;
        token = getToken();
        parseStmt(token);
      }
      else if (isVar(token))
      {
      }
      else
      {
        reportError(token);
      }
      eval = true;
  }

  public int parseExpr(String token)
  {
    int val;

    val = parseVal(token);
    token = getToken();

    switch(token.charAt(0))
    {
      case '+':
      token = getToken();
      val = val + parseVal(token);        // ::= <val> + <val>
      break;
      case '-':
      token = getToken();
      val = val - parseVal(token);        // ::= <val> - <val>
      break;
      case '*':
      token = getToken();
      val = val * parseVal(token);        // ::= <val> * <val>
      break;
      case '/':
      token = getToken();
      val = val / parseVal(token);        // ::= <val> / <val>
      break;
      default:    // oops, a unary experssion
      line = token + line;
    }

    return val;
  }

  public String parseString(String token)
  {
    String text = "";

    if (!token.equals("\""))
    reportError(token);

    int i;
    for (i=0; i<line.length(); i++)
    if (line.charAt(i) != '"')
    {
      if (line.charAt(i) == '\n' || line.charAt(i) == '\r')
      reportError(text);
      text += line.charAt(i);
    }
    else
    {
      line = line.substring(i+1); // removes string including "
      break;
    }

    if (i == line.length())
    reportError(text);

    return text;
  }

  public boolean parseCond(String token)
  {
    int val;
    boolean cond = false;
    val = parseVal(token);
    token = getToken();
    switch(token.charAt(0))
    {
      case '=':
      token = getToken(); // skip extra equals sign
      token = getToken();
      cond = val == parseVal(token);        // ::= <val> + <val>
      break;
      case '<':
      token = getToken();
      cond = val < parseVal(token);        // ::= <val> - <val>
      break;
      case '>':
      token = getToken();
      cond = val > parseVal(token);        // ::= <val> * <val>
      break;
      default:
      line = token + line;
    }

    return cond;
  }

  public String loadFile(String name) throws IOException
  {
    String text = "";

    Scanner fileScan = new Scanner(new File(name));

    while (fileScan.hasNext())
    text += fileScan.nextLine() + "\n";

    fileScan.close();

    return text;
  }

  public int parseVal(String token)
  {
    if (isNumeric(token))
    return Integer.parseInt(token);            // ::= <num>
    else if (isVar(token))
    return parseVar(token);                    // ::= <var>
    else
    reportError(token);

    return -1;  // should never happen
  }

  public int parseVar(String token)
  {
    if (!isVar(token))
    reportError(token);

    return vars [ ((int)(token.charAt(0))) - 97 ];
  }

  public void storeVar(String token, int val)
  {
    vars[ ((int)(token.charAt(0))) - 97 ] = val;
  }

  public boolean isNumeric(String token)
  {
    for (int i=0; i<token.length(); i++)
    if(!Character.isDigit(token.charAt(i)))
    return false;

    return true;
  }

  public boolean isVar(String token)
  {
    return (token.length() == 1) && isAlpha(token.charAt(0));
  }

  public boolean isAlpha(char ch)
  {
    return ((int) ch) >= 97 && ((int) ch) <= 122;
  }

  public void reportError(String token)
  {
    line += "\n";
    System.out.println("ERROR: " + token + line.substring(0, line.indexOf('\n')));

    for (int i = 0; i< token.length()+7; i++)
    System.out.print(" ");
    System.out.println("^");
    System.exit(-1);
  }

  public boolean isBlank(char ch)
  {
    switch (ch)
    {
      case ' ':
      case '\t':
      case '\r': case '\n':
      return true;
    }
    return false;
  }

  public boolean isSymbol(char ch)
  {
    switch (ch)
    {
      case '.':
      case '+': case '-': case '*' : case '/':
      case '=': case '>': case '<':
      case '"':
      return true;
    }
    return false;
  }

  public boolean isDelim(char ch)
  {
    return isBlank(ch) || isSymbol(ch);
  }

  public String skipBlanks(String buffer)
  {
    int i;
    for (i = 0; i<buffer.length(); i++)
    if (!isBlank(buffer.charAt(i)))
    break;
    return line.substring(i);
  }

  public String getToken()
  {
    int i;
    String token;

    line = skipBlanks(line);
    while (line.length() == 0)
    {
      line = scan.nextLine();
      line = skipBlanks(line);
    }

    for (i=0; i<line.length(); i++)
    if (isDelim(line.charAt(i)))
    {
      if (i == 0)
      i++;
      break;
    }

    token = line.substring(0, i);
    line = line.substring(i);

    return token;
  }
}