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Unicalc.java

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// file:    Unicalc.java
// author:  Robert Keller
// purpose: Shell for Unicalc application

import java.io.*;
import OpenList;
import Quantity;
import UnicalcParser;
import LineBufferInputStream;

/**
 * Unicalc defines one Unicalc application, with database readable from
 * a file.  Unicalc derives the conversion factor for converting one
 * kind of Quantity to another.  Quantities are multiplicative and 
 * conversions are defined by a database of equations.  
 *
 * Class Quantity does most of the work.  Class Unicalc is primarily a
 * shell for using Quantities.
 */

class Unicalc
{
/** the default name of the database file */

static String defaultDBfilename = "/cs/cs60/bin/unicalc.db";


/** the first prompt string */

static String promptString1 = "convert from: ";


/** the second prompt string */

static String promptString2 = "convert to: ";


/** 
 * the Unicalc database in association list form
 *
 * Each element of the list is a list of two objects: a String and
 * a Quantity, denoting the left- and right-hand sides of a conversion
 * equation.
 */

OpenList DB;                    


/**
 * Read a database from the named file.  Each line of the file is a
 * string defining the left-hand unit and a corresponding expression
 * to which the unit is converted.
 */

void readDB(String DBfilename)
  {
  DB = OpenList.nil;                            // Initialize database.

  FileInputStream filein = null;                // to keep compiler happy

  try
    {
    filein = new FileInputStream(DBfilename);   // Open databasefile.
    }
  catch( FileNotFoundException e )
    {
    System.out.println("*** Database file " + DBfilename + " not found.");
    System.exit(1);                             // Exit if no DB.
    }

  LineBufferInputStream in = new LineBufferInputStream(filein);

  while( !in.eof() )
    {
    String LHS = in.getString();                     // Read LHS of equation.

    String line = in.getNonBlankLine();              // Read RHS of equation.

    Object input = new UnicalcParser(line).parse();  // Parse the RHS

    Quantity RHS = Quantity.makeQuantity(input);     // Make Quantity from RHS.

    DB = OpenList.cons(OpenList.list(LHS, RHS), DB); // cons eqn to A-list.
    }
  }


/**
 * Parse a Quantity from the input/
 */

static Quantity getQuantity(LineBufferInputStream in, PrintStream out)
  {
  // Parse input to a tree, constructed using OpenList

  Object input;

  do
    {
    String line = in.getNonBlankLine();         // Get something to parse.
    input = new UnicalcParser(line).parse();    // Parse it to a tree.
    if( input == null )
      {
      out.println("Invalid input, please try again");
      }
    }
  while( input == null );                       // Make sure it is sensible.

  return Quantity.makeQuantity(input);          // Make Quantity from tree.
  }


/**
 * Provide shell loop, reading from inStream and printing to out.
 * On each iteration, the user is prompted for "to" and "from" 
 * Quantity expressions, which are parsed to create trees, and then
 * Quantities.  One Quantity is converted to the other and the result
 * printed.
 */

void loop(InputStream inStream, PrintStream out)
  {
  LineBufferInputStream in = new LineBufferInputStream(inStream);

  while( true )
    {
    prompt(promptString1, out);                    // First prompt.
    if( in.eof() ) break;                          // Make sure we have input.

    Quantity fromQuantity = getQuantity(in, out);  // Get "from" Quantity.

    prompt(promptString2, out);                    // Second prompt.
    if( in.eof() ) break;                          // Make sure we have input.

    Quantity toQuantity = getQuantity(in, out);    // Get "to" Quantity.

    Quantity conversion =                          // Convert "from" to "to"
        Quantity.convert(fromQuantity, toQuantity, DB);

    out.println("multiply by: " + conversion);     // Display results
    out.println("or divide by: " + Quantity.invert(conversion));
    out.println();
    }
  out.println();
  }


/**
 * Prompt with a string on the output stream.
 */

static void prompt(String promptString, PrintStream out)
  {
  out.print(promptString);
  out.flush();
  }


/**
 * the Unicalc application program
 */

static public void main(String arg[])
  {
  String DBfilename = defaultDBfilename;        // Use default database.

  Unicalc unicalc = new Unicalc();              // Create Unicalc instance.

  unicalc.readDB(DBfilename);                   // Populate database.

  unicalc.loop(System.in, System.out);          // Run shell.
  }

}

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