import java.io.*;
import java.util.IllegalFormatException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.swing.JFileChooser;
import javax.swing.JOptionPane;

/**
 * TextIO provides a set of static methods for reading and writing text.  By default, it reads
 * from standard input and writes to standard output, but it is possible to redirect the input
 * and output to files or to other input and output streams.  When the standard input and output
 * streams are being used, the input methods will not produce an error; instead, the user is
 * repeatedly prompted for input until a legal input is entered.  (If standard input has been
 * changed externally, as by file redirection on the command line, this is not a reasonable
 * behavior; to handle this case, TextIO will give up after 10 consecutive illegal inputs and
 * will throw an IllegalArgumentException.)  For the most part, any other
 * error will be translated into an IllegalArguementException.
 * <p>For writing to standard output, the output methods in this class pretty much
 * duplicate the functionality of System.out, and System.out can be used interchangeably with them.
 * <p>This class does not use optimal Java programming practices.  It is designed specifically to be easily
 * usable even by a beginning programmer who has not yet learned about objects and exceptions.  Therefore, 
 * everything is in a single source file that compiles into a single class file, all the methods are
 * static methods, and none of the methods throw exceptions that would require try...catch statements.
 * Also for this reason, all exceptions are converted into IllegalArgumentExceptions, even when this
 * exception type doesn't really make sense.
 * <p>This class requires Java 5.0 or higher. (A previous version of TextIO required only Java 1.1;
 * this version should work with any source code that used the previous version, but it has some new
 * features, including the type of formatted output that was introduced in Java 5 and the ability to
 * use files and streams.)
 */
public class TextIO {

    /* Modified November 2007 to empty the TextIO input buffer when switching from one
     * input source to another. This fixes a bug that allows input from the previous input
     * source to be read after the new source has been selected.
     */

    /**
     * The value returned by the peek() method when the input is at end-of-file.
     * (The value of this constant is (char)0xFFFF.)
     */
    public final static char EOF = (char)0xFFFF; 

    /**
     * The value returned by the peek() method when the input is at end-of-line.
     * The value of this constant is the character '\n'.
     */
    public final static char EOLN = '\n';          // The value returned by peek() when at end-of-line.
    

    /**
     * After this method is called, input will be read from standard input (as it 
     * is in the default state).  If a file or stream was previously the input source, that file
     * or stream is closed.
     */
    public static void readStandardInput() {
        if (readingStandardInput)
            return;
        try {
            in.close();
        }
        catch (Exception e) {
        }
        emptyBuffer();  // Added November 2007
        in = standardInput;
        inputFileName = null;
        readingStandardInput = true;
        inputErrorCount = 0;
    }
    
    /**
     * After this method is called, input will be read from inputStream, provided it
     * is non-null.  If inputStream is null, then this method has the same effect
     * as calling readStandardInput(); that is, future input will come from the
     * standard input stream.
     */
    public static void readStream(InputStream inputStream) {
        if (inputStream == null)
            readStandardInput();
        else
            readStream(new InputStreamReader(inputStream));
    }
    
    /**
     * After this method is called, input will be read from inputStream, provided it
     * is non-null.  If inputStream is null, then this method has the same effect
     * as calling readStandardInput(); that is, future input will come from the
     * standard input stream.
     */
    public static void readStream(Reader inputStream) {
        if (inputStream == null)
            readStandardInput();
        else {
            if ( inputStream instanceof BufferedReader)
                in = (BufferedReader)inputStream;
            else
                in = new BufferedReader(inputStream);
            emptyBuffer();  // Added November 2007
            inputFileName = null;
            readingStandardInput = false;
            inputErrorCount = 0;
        }
    }
    
    /**
     * Opens a file with a specified name for input.  If the file name is null, this has
     * the same effect as calling readStandardInput(); that is, input will be read from standard
     * input.  If an
     * error occurs while trying to open the file, an exception of type IllegalArgumentException
     * is thrown, and the input source is not changed.  If the file is opened 
     * successfully, then after this method is called, all of the input routines will read 
     * from the file, instead of from standard input.
     */
    public static void readFile(String fileName) {
        if (fileName == null) // Go back to reading standard input
            readStandardInput();
        else {
            BufferedReader newin;
            try {
                newin = new BufferedReader( new FileReader(fileName) );
            }
            catch (Exception e) {
                throw new IllegalArgumentException("Can't open file \"" + fileName + "\" for input.\n"
                                 + "(Error :" + e + ")");
            }
            if (! readingStandardInput) { // close current input stream
                try {
                    in.close();
                }
                catch (Exception e) {
                }
            }
            emptyBuffer();  // Added November 2007
            in = newin;
            readingStandardInput = false;
            inputErrorCount = 0;
            inputFileName = fileName;
        }
    }

    /**
     * Puts a GUI file-selection dialog box on the screen in which the user can select
     * an input file.  If the user cancels the dialog instead of selecting a file, it is
     * not considered an error, but the return value of the subroutine is false.
     * If the user does select a file, but there is an error while trying to open the
     * file, then an exception of type IllegalArgumentException is thrown.  Finally, if
     * the user selects a file and it is successfully opened, then the return value of the
     * subroutine is true, and  the input routines will read from the file, instead of 
     * from standard input.   If the user cancels, or if any error occurs, then the
     * previous input source is not changed.
     * <p>NOTE: Calling this method starts a GUI user interface thread, which can continue
     * to run even if the thread that runs the main program ends.  If you use this method
     * in a non-GUI program, it might be necessary to call System.exit(0) at the end of the main() 
     * routine to shut down the Java virtual machine completely.
     */
    public static boolean readUserSelectedFile() {
        if (fileDialog == null)
            fileDialog = new JFileChooser();
        fileDialog.setDialogTitle("Select File for Input");
        int option = fileDialog.showOpenDialog(null);
        if (option != JFileChooser.APPROVE_OPTION)
            return false;
        File selectedFile = fileDialog.getSelectedFile();
        BufferedReader newin;
        try {
            newin = new BufferedReader( new FileReader(selectedFile) );
        }
        catch (Exception e) {
            throw new IllegalArgumentException("Can't open file \"" + selectedFile.getName() + "\" for input.\n"
                             + "(Error :" + e + ")");
        }
        if (!readingStandardInput) { // close current file
            try {
                in.close();
            }
            catch (Exception e) {
            }
        }
        emptyBuffer();  // Added November 2007
        in = newin;
        inputFileName = selectedFile.getName();
        readingStandardInput = false;
        inputErrorCount = 0;
        return true;
    }
    
    /**
     * After this method is called, output will be written to standard output (as it 
     * is in the default state).  If a file or stream was previously open for output, it
     * will be closed.
     */
    public static void writeStandardOutput() {
        if (writingStandardOutput)
            return;
        try {
            out.close();
        }
        catch (Exception e) {
        }
        outputFileName = null;
        outputErrorCount = 0;
        out = standardOutput;
        writingStandardOutput = true;
    }
    

    /**
     * After this method is called, output will be sent to outputStream, provided it
     * is non-null.  If outputStream is null, then this method has the same effect
     * as calling writeStandardOutput(); that is, future output will be sent to the
     * standard output stream.
     */
    public static void writeStream(OutputStream outputStream) {
        if (outputStream == null)
            writeStandardOutput();
        else
            writeStream(new PrintWriter(outputStream));
    }
    
    /**
     * After this method is called, output will be sent to outputStream, provided it
     * is non-null.  If outputStream is null, then this method has the same effect
     * as calling writeStandardOutput(); that is, future output will be sent to the
     * standard output stream.
     */
    public static void writeStream(PrintWriter outputStream) {
        if (outputStream == null)
            writeStandardOutput();
        else {
            out = outputStream;
            outputFileName = null;
            outputErrorCount = 0;
            writingStandardOutput = false;
        }
    }
    

    /**
     * Opens a file with a specified name for output.  If the file name is null, this has
     * the same effect as calling writeStandardOutput(); that is, output will be sent to standard
     * output.  If an
     * error occurs while trying to open the file, an exception of type IllegalArgumentException
     * is thrown.  If the file is opened successfully, then after this method is called,
     * all of the output routines will write to the file, instead of to  standard output.
     * If an error occurs, the output destination is not changed.
     * <p>NOTE: Calling this method starts a GUI user interface thread, which can continue
     * to run even if the thread that runs the main program ends.  If you use this method
     * in a non-GUI program, it might be necessary to call System.exit(0) at the end of the main() 
     * routine to shut down the Java virtual machine completely.
     */
    public static void writeFile(String fileName) {
        if (fileName == null)  // Go back to reading standard output
            writeStandardOutput();
        else {
            PrintWriter newout;
            try {
                newout = new PrintWriter(new FileWriter(fileName));
            }
            catch (Exception e) {
                throw new IllegalArgumentException("Can't open file \"" + fileName + "\" for output.\n"
                                 + "(Error :" + e + ")");
            }
            if (!writingStandardOutput) {
                try {
                    out.close();
                }
                catch (Exception e) {
                }
            }
            out = newout;
            writingStandardOutput = false;
            outputFileName = fileName;
            outputErrorCount = 0;
        }
    }
    
    /**
     * Puts a GUI file-selection dialog box on the screen in which the user can select
     * an output file.  If the user cancels the dialog instead of selecting a file, it is
     * not considered an error, but the return value of the subroutine is false.
     * If the user does select a file, but there is an error while trying to open the
     * file, then an exception of type IllegalArgumentException is thrown.  Finally, if
     * the user selects a file and it is successfully opened, then the return value of the
     * subroutine is true, and  the output routines will write to the file, instead of 
     * to standard output.  If the user cancels, or if an error occurs, then the current
     * output destination is not changed.
     */
    public static boolean writeUserSelectedFile() {
        if (fileDialog == null)
            fileDialog = new JFileChooser();
        fileDialog.setDialogTitle("Select File for Output");
        File selectedFile;
        while (true) {
            int option = fileDialog.showSaveDialog(null);
            if (option != JFileChooser.APPROVE_OPTION)
                return false;  // user canceled
            selectedFile = fileDialog.getSelectedFile();
            if (selectedFile.exists()) {
                int response = JOptionPane.showConfirmDialog(null,
                        "The file \"" + selectedFile.getName() + "\" already exists.  Do you want to replace it?",
                        "Replace existing file?",
                        JOptionPane.YES_NO_OPTION, JOptionPane.WARNING_MESSAGE);
                if (response == JOptionPane.YES_OPTION)
                    break;
            }
            else {
                break;
            }
        }
        PrintWriter newout;
        try {
            newout = new PrintWriter(new FileWriter(selectedFile));
        }
        catch (Exception e) {
            throw new IllegalArgumentException("Can't open file \"" + selectedFile.getName() + "\" for output.\n"
                             + "(Error :" + e + ")");
        }
        if (!writingStandardOutput) {
            try {
                out.close();
            }
            catch (Exception e) {
            }
        }
        out = newout;
        writingStandardOutput = false;
        outputFileName = selectedFile.getName();
        outputErrorCount = 0;
        return true;
    }
    

    /**
     * If TextIO is currently reading from a file, then the return value is the name of the file.  
     * If the class is reading from standard input or from a stream, then the return value is null.
     */
    public static String getInputFileName() {
        return inputFileName;
    }
    

    /**
     * If TextIO is currently writing to a file, then the return value is the name of the file.  
     * If the class is writing to standard output or to a stream, then the return value is null.
     */
    public static String getOutputFileName() {
        return outputFileName;
    }
    

    // *************************** Output Methods *********************************
        
    /**
     * Write a single value to the current output destination, using the default format
     * and no extra spaces.  This method will handle any type of parameter, even one
     * whose type is one of the primitive types.
     */
    public static void put(Object x) { 
        out.print(x); 
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }
    
    /**
     * Write a single value to the current output destination, using the default format
     * and outputting at least minChars characters (with extra spaces added before the
     * output value if necessary).  This method will handle any type of parameter, even one
     * whose type is one of the primitive types.
     * @param x The value to be output, which can be of any type.
     * @param minChars The minimum number of characters to use for the output.  If x requires fewer
     * then this number of characters, then extra spaces are added to the front of x to bring
     * the total up to minChars.  If minChars is less than or equal to zero, then x will be printed
     * in the minimum number of spaces possible.
     */
    public static void put(Object x, int minChars)  { 
        if (minChars <= 0)
            out.print(x);
        else
            out.printf("%" + minChars + "s", x);
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }
        
    /**
     * This is equivalent to put(x), followed by an end-of-line.
     */
    public static void putln(Object x) { 
        out.println(x);
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }
    
    /**
     * This is equivalent to put(x,minChars), followed by an end-of-line.
     */
    public static void putln(Object x, int minChars) {
        put(x,minChars);
        out.println();
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }

    /**
     * Write an end-of-line character to the current output destination.
     */
    public static void putln() {
        out.println();
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }
    
    /**
     * Writes formatted output values to the current output destination.  This method has the
     * same function as System.out.printf(); the details of formatted output are not discussed
     * here.  The first parameter is a string that describes the format of the output.  There
     * can be any number of additional parameters; these specify the values to be output and
     * can be of any type.  This method will throw an IllegalArgumentException if the
     * format string is null or if the format string is illegal for the values that are being
     * output.
     */
    public static void putf(String format, Object... items) {
        if (format == null)
            throw new IllegalArgumentException("Null format string in TextIO.putf() method.");
        try {
            out.printf(format,items);
        }
        catch (IllegalFormatException e) {
            throw new IllegalArgumentException("Illegal format string in TextIO.putf() method.");
        }
        out.flush();
        if (out.checkError())
            outputError("Error while writing output.");
    }
    
    // *************************** Input Methods *********************************

    /**
     * Test whether the next character in the current input source is an end-of-line.  Note that
     * this method does NOT skip whitespace before testing for end-of-line -- if you want to do
     * that, call skipBlanks() first.
     */
    public static boolean eoln() { 
        return peek() == '\n'; 
    }

    /**
     * Test whether the next character in the current input source is an end-of-file.  Note that
     * this method does NOT skip whitespace before testing for end-of-line -- if you want to do
     * that, call skipBlanks() or skipWhitespace() first.
     */
    public static boolean eof()  { 
        return peek() == EOF; 
    }
    
    /**
     * Reads the next character from the current input source.  The character can be a whitespace
     * character; compare this to the getChar() method, which skips over whitespace and returns the
     * next non-whitespace character.  An end-of-line is always returned as the character '\n', even
     * when the actual end-of-line in the input source is something else, such as '\r' or "\r\n".
     * This method will throw an IllegalArgumentException if the input is at end-of-file (which will 
     * not ordinarily happen if reading from standard input).
     */
    public static char getAnyChar() { 
        return readChar(); 
    }

    /**
     * Returns the next character in the current input source, without actually removing that
     * character from the input.  The character can be a whitespace character and can be the
     * end-of-file character (specified by the constant TextIO.EOF).An end-of-line is always returned 
     * as the character '\n', even when the actual end-of-line in the input source is something else, 
     * such as '\r' or "\r\n".  This method never causes an error.
     */
    public static char peek() { 
        return lookChar();
    }
    
    /**
     * Skips over any whitespace characters, except for end-of-lines.  After this method is called,
     * the next input character is either an end-of-line, an end-of-file, or a non-whitespace character.
     * This method never causes an error.  (Ordinarily, end-of-file is not possible when reading from
     * standard input.)
     */
    public static void skipBlanks() { 
        char ch=lookChar();
        while (ch != EOF && ch != '\n' && Character.isWhitespace(ch)) {
            readChar();
            ch = lookChar();
        }
    }

    /**
     * Skips over any whitespace characters, including for end-of-lines.  After this method is called,
     * the next input character is either an end-of-file or a non-whitespace character.
     * This method never causes an error. (Ordinarily, end-of-file is not possible when reading from
     * standard input.)
     */
    private static void skipWhitespace() {
        char ch=lookChar();
        while (ch != EOF && Character.isWhitespace(ch)) {
            readChar();
            if (ch == '\n' && readingStandardInput && writingStandardOutput) {
                out.print("? ");
                out.flush();
            }
            ch = lookChar();
        }
    }

    /**
     * Skips whitespace characters and then reads a value of type byte from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static byte getlnByte() { 
        byte x=getByte(); 
        emptyBuffer(); 
        return x; 
    }
    
    /**
     * Skips whitespace characters and then reads a value of type short from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static short getlnShort() {
        short x=getShort();
        emptyBuffer(); 
        return x; 
    }
    
    /**
     * Skips whitespace characters and then reads a value of type int from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static int getlnInt() { 
        int x=getInt(); 
        emptyBuffer(); 
        return x; 
    }
    
    /**
     * Skips whitespace characters and then reads a value of type long from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static long getlnLong() {
        long x=getLong(); 
        emptyBuffer(); 
        return x;
    }
    
    /**
     * Skips whitespace characters and then reads a value of type float from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static float getlnFloat() {
        float x=getFloat(); 
        emptyBuffer(); 
        return x;
    }
    
    /**
     * Skips whitespace characters and then reads a value of type double from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static double getlnDouble() { 
        double x=getDouble(); 
        emptyBuffer(); 
        return x; 
    }
    
    /**
     * Skips whitespace characters and then reads a value of type char from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  Note that the value
     * that is returned will be a non-whitespace character; compare this with the getAnyChar() method.
     * When using standard IO, this will not produce an error.  In other cases, an error can occur if
     * an end-of-file is encountered.
     */
    public static char getlnChar() {
        char x=getChar(); 
        emptyBuffer(); 
        return x;
    }
    
    /**
     * Skips whitespace characters and then reads a value of type boolean from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     * <p>Legal inputs for a boolean input are: true, t, yes, y, 1, false, f, no, n, and 0; letters can be
     * either upper case or lower case. One "word" of input is read, using the getWord() method, and it
     * must be one of these; note that the "word"  must be terminated by a whitespace character (or end-of-file).
     */
    public static boolean getlnBoolean() { 
        boolean x=getBoolean(); 
        emptyBuffer();
        return x; 
    }
    
    /**
     * Skips whitespace characters and then reads one "word" from input, discarding the rest of 
     * the current line of input (including the next end-of-line character, if any).  A word is defined as
     * a sequence of non-whitespace characters (not just letters!).   When using standard IO,
     * this will not produce an error.  In other cases, an IllegalArgumentException will be thrown
     * if an end-of-file is encountered.
     */
    public static String getlnWord() {
        String x=getWord(); 
        emptyBuffer(); 
        return x; 
    }
    
    /**
     * This is identical to getln().
     */
    public static String getlnString() {
        return getln();
    } 
    
    /**
     * Reads all the characters from the current input source, up to the next end-of-line.  The end-of-line
     * is read but is not included in the return value.  Any other whitespace characters on the line are retained,
     * even if they occur at the start of input.  The return value will be an empty string if there are
     * no characters before the end-of-line.  When using standard IO, this will not produce an error.  
     * In other cases, an IllegalArgumentException will be thrown if an end-of-file is encountered.
     */
    public static String getln() {
        StringBuffer s = new StringBuffer(100);
        char ch = readChar();
        while (ch != '\n') {
            s.append(ch);
            ch = readChar();
        }
        return s.toString();
    }
    
    /**
     * Skips whitespace characters and then reads a value of type byte from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static byte getByte()   { 
        return (byte)readInteger(-128L,127L); 
    }

    /**
     * Skips whitespace characters and then reads a value of type short from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static short getShort() { 
        return (short)readInteger(-32768L,32767L);
    }   
    
    /**
     * Skips whitespace characters and then reads a value of type int from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static int getInt()     { 
        return (int)readInteger(Integer.MIN_VALUE, Integer.MAX_VALUE);
    }
    
    /**
     * Skips whitespace characters and then reads a value of type long from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static long getLong()   { 
        return readInteger(Long.MIN_VALUE, Long.MAX_VALUE); 
    }
    
    /**
     * Skips whitespace characters and then reads a single non-whitespace character from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error.  In other cases, an IllegalArgumentException will be thrown if an end-of-file
     * is encountered.
     */
    public static char getChar() { 
        skipWhitespace();
        return readChar();
    }
    
    /**
     * Skips whitespace characters and then reads a value of type float from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static float getFloat() {
        float x = 0.0F;
        while (true) {
            String str = readRealString();
            if (str == null) {
                errorMessage("Floating point number not found.",
                        "Real number in the range " + (-Float.MAX_VALUE) + " to " + Float.MAX_VALUE);
            }
            else {
                try { 
                    x = Float.parseFloat(str); 
                }
                catch (NumberFormatException e) {
                    errorMessage("Illegal floating point input, " + str + ".",
                            "Real number in the range " +  (-Float.MAX_VALUE) + " to " + Float.MAX_VALUE);
                    continue;
                }
                if (Float.isInfinite(x)) {
                    errorMessage("Floating point input outside of legal range, " + str + ".",
                            "Real number in the range " +  (-Float.MAX_VALUE) + " to " + Float.MAX_VALUE);
                    continue;
                }
                break;
            }
        }
        inputErrorCount = 0;
        return x;
    }
    
    /**
     * Skips whitespace characters and then reads a value of type double from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     */
    public static double getDouble() {
        double x = 0.0;
        while (true) {
            String str = readRealString();
            if (str == null) {
                errorMessage("Floating point number not found.",
                        "Real number in the range " + (-Double.MAX_VALUE) + " to " + Double.MAX_VALUE);
            }
            else {
                try { 
                    x = Double.parseDouble(str); 
                }
                catch (NumberFormatException e) {
                    errorMessage("Illegal floating point input, " + str + ".",
                            "Real number in the range " + (-Double.MAX_VALUE) + " to " + Double.MAX_VALUE);
                    continue;
                }
                if (Double.isInfinite(x)) {
                    errorMessage("Floating point input outside of legal range, " + str + ".",
                            "Real number in the range " + (-Double.MAX_VALUE) + " to " + Double.MAX_VALUE);
                    continue;
                }
                break;
            }
        }
        inputErrorCount = 0;
        return x;
    }
    
    /**
     * Skips whitespace characters and then reads one "word" from input. Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  A word is defined as
     * a sequence of non-whitespace characters (not just letters!).   When using standard IO,
     * this will not produce an error.  In other cases, an IllegalArgumentException will be thrown
     * if an end-of-file is encountered.
     */
    public static String getWord() {
        skipWhitespace();
        StringBuffer str = new StringBuffer(50);
        char ch = lookChar();
        while (ch == EOF || !Character.isWhitespace(ch)) {
            str.append(readChar());
            ch = lookChar();
        }
        return str.toString();
    }
    
    /**
     * Skips whitespace characters and then reads a value of type boolean from input.  Any additional characters on
     * the current line of input are retained, and will be read by the next input operation.  When using standard IO,
     * this will not produce an error; the user will be prompted repeatedly for input until a legal value
     * is input.  In other cases, an IllegalArgumentException will be thrown if a legal value is not found.
     * <p>Legal inputs for a boolean input are: true, t, yes, y, 1, false, f, no, n, and 0; letters can be
     * either upper case or lower case. One "word" of input is read, using the getWord() method, and it
     * must be one of these; note that the "word"  must be terminated by a whitespace character (or end-of-file).
     */
    public static boolean getBoolean() {
        boolean ans = false;
        while (true) {
            String s = getWord();
            if ( s.equalsIgnoreCase("true") || s.equalsIgnoreCase("t") ||
                    s.equalsIgnoreCase("yes")  || s.equalsIgnoreCase("y") ||
                    s.equals("1") ) {
                ans = true;
                break;
            }
            else if ( s.equalsIgnoreCase("false") || s.equalsIgnoreCase("f") ||
                    s.equalsIgnoreCase("no")  || s.equalsIgnoreCase("n") ||
                    s.equals("0") ) {
                ans = false;
                break;
            }
            else
                errorMessage("Illegal boolean input value.",
                "one of:  true, false, t, f, yes, no, y, n, 0, or 1");
        }
        inputErrorCount = 0;
        return ans;
    }
    
    // ***************** Everything beyond this point is private implementation detail *******************
    
    private static String inputFileName;  // Name of file that is the current input source, or null if the source is not a file.
    private static String outputFileName; // Name of file that is the current output destination, or null if the destination is not a file.
    
    private static JFileChooser fileDialog; // Dialog used by readUserSelectedFile() and writeUserSelectedFile()
    
    private final static BufferedReader standardInput = new BufferedReader(new InputStreamReader(System.in));  // wraps standard input stream
    private final static PrintWriter standardOutput = new PrintWriter(System.out);  // wraps standard output stream

    private static BufferedReader in = standardInput;  // Stream that data is read from; the current input source.
    private static PrintWriter out = standardOutput;   // Stream that data is written to; the current output destination.
    
    private static boolean readingStandardInput = true;
    private static boolean writingStandardOutput = true;
    
    private static int inputErrorCount;  // Number of consecutive errors on standard input; reset to 0 when a successful read occurs.
    private static int outputErrorCount;  // Number of errors on standard output since it was selected as the output destination.
    
    private static Matcher integerMatcher;  // Used for reading integer numbers; created from the integer Regex Pattern.
    private static Matcher floatMatcher;   // Used for reading floating point numbers; created from the floatRegex Pattern.
    private final static Pattern integerRegex = Pattern.compile("(\\+|-)?[0-9]+");
    private final static Pattern floatRegex = Pattern.compile("(\\+|-)?(([0-9]+(\\.[0-9]*)?)|(\\.[0-9]+))((e|E)(\\+|-)?[0-9]+)?");
    
    private static String buffer = null;  // One line read from input.
    private static int pos = 0;           // Position of next char in input line that has not yet been processed.
    
    private static String readRealString() {   // read chars from input following syntax of real numbers
        skipWhitespace();
        if (lookChar() == EOF)
            return null;
        if (floatMatcher == null)
            floatMatcher = floatRegex.matcher(buffer);
        floatMatcher.region(pos,buffer.length());
        if (floatMatcher.lookingAt()) {
            String str = floatMatcher.group();
            pos = floatMatcher.end();
            return str;
        }
        else 
            return null;
    }
    
    private static String readIntegerString() {  // read chars from input following syntax of integers
        skipWhitespace();
        if (lookChar() == EOF)
            return null;
        if (integerMatcher == null)
            integerMatcher = integerRegex.matcher(buffer);
        integerMatcher.region(pos,buffer.length());
        if (integerMatcher.lookingAt()) {
            String str = integerMatcher.group();
            pos = integerMatcher.end();
            return str;
        }
        else 
            return null;
    }
    
    private static long readInteger(long min, long max) {  // read long integer, limited to specified range
        long x=0;
        while (true) {
            String s = readIntegerString();
            if (s == null){
                errorMessage("Integer value not found in input.",
                        "Integer in the range " + min + " to " + max);
            }
            else {
                String str = s.toString();
                try { 
                    x = Long.parseLong(str);
                }
                catch (NumberFormatException e) {
                    errorMessage("Illegal integer input, " + str + ".",
                            "Integer in the range " + min + " to " + max);
                    continue;
                }
                if (x < min || x > max) {
                    errorMessage("Integer input outside of legal range, " + str + ".",
                            "Integer in the range " + min + " to " + max);
                    continue;
                }
                break;
            }
        }
        inputErrorCount = 0;
        return x;
    }
    
    
    private static void errorMessage(String message, String expecting) {  // Report error on input.
        if (readingStandardInput && writingStandardOutput) {
                // inform user of error and force user to re-enter.
            out.println();
            out.print("  *** Error in input: " + message + "\n");
            out.print("  *** Expecting: " + expecting + "\n");
            out.print("  *** Discarding Input: ");
            if (lookChar() == '\n')
                out.print("(end-of-line)\n\n");
            else {
                while (lookChar() != '\n')    // Discard and echo remaining chars on the current line of input.
                    out.print(readChar());
                out.print("\n\n");
            }
            out.print("Please re-enter: ");
            out.flush();
            readChar();  // discard the end-of-line character
            inputErrorCount++;
            if (inputErrorCount >= 10)
                throw new IllegalArgumentException("Too many input consecutive input errors on standard input.");
        }
        else if (inputFileName != null)
            throw new IllegalArgumentException("Error while reading from file \"" + inputFileName + "\":\n" 
                    + message + "\nExpecting " + expecting);
        else
            throw new IllegalArgumentException("Error while reading from inptu stream:\n" 
                    + message + "\nExpecting " + expecting);
    }
    
    private static char lookChar() {  // return next character from input
        if (buffer == null || pos > buffer.length())
            fillBuffer();
        if (buffer == null)
            return EOF;
        else if (pos == buffer.length())
            return '\n';
        else 
            return buffer.charAt(pos);
    }
    
    private static char readChar() {  // return and discard next character from input
        char ch = lookChar();
        if (buffer == null) {
            if (readingStandardInput)
                throw new IllegalArgumentException("Attempt to read past end-of-file in standard input???");
            else
                throw new IllegalArgumentException("Attempt to read past end-of-file in file \"" + inputFileName + "\".");
        }
        pos++;
        return ch;
    }
        
    private static void fillBuffer() {    // Wait for user to type a line and press return,
        try {
            buffer = in.readLine();
        }
        catch (Exception e) {
            if (readingStandardInput)
                throw new IllegalArgumentException("Error while reading standard input???");
            else if (inputFileName != null)
                throw new IllegalArgumentException("Error while attempting to read from file \"" + inputFileName + "\".");
            else
                throw new IllegalArgumentException("Errow while attempting to read form an input stream.");
        }
        pos = 0;
        floatMatcher = null;
        integerMatcher = null;
    }
    
    private static void emptyBuffer() {   // discard the rest of the current line of input
        buffer = null;
    }
    
    private static void outputError(String message) {  // Report an error on output.
        if (writingStandardOutput) {
            System.err.println("Error occurred in TextIO while writing to standard output!!");
            outputErrorCount++;
            if (outputErrorCount >= 10) {
                outputErrorCount = 0;
                throw new IllegalArgumentException("Too many errors while writing to standard output.");
            }
        }
        else if (outputFileName != null){
            throw new IllegalArgumentException("Error occurred while writing to file \"" 
                    + outputFileName+ "\":\n   " + message);
        }
        else {
            throw new IllegalArgumentException("Error occurred while writing to output stream:\n   " + message);
        }
    }
        
} // end of class TextIO