/*
 * File: tokenscanner.h
 * --------------------
 * This file exports a <code>TokenScanner</code> class that divides
 * a string into individual logical units called <b><i>tokens</i></b>.
 */

#ifndef _tokenscanner_h
#define _tokenscanner_h

#include <iostream>
#include <string>
#include "private/tokenpatch.h"

/*
 * Type: TokenType
 * ---------------
 * This enumerated type defines the values of the
 * <code>getTokenType</code> method.
 */

#ifdef _WIN32
#  define TokenType TokenTypeT
#  define WORD WORD_TC
#endif

enum TokenType { SEPARATOR, WORD, NUMBER, STRING, OPERATOR };

/*
 * Class: TokenScanner
 * -------------------
 * This class divides a string into individual tokens.  The typical
 * use of the <code>TokenScanner</code> class is illustrated by the
 * following pattern, which reads the tokens in the string variable
 * <code>input</code>:
 *
 *<pre>
 *    TokenScanner scanner(input);
 *    while (scanner.hasMoreTokens()) {
 *       string token = scanner.nextToken();
 *       ... process the token ...
 *    }
 *</pre>
 *
 * The <code>TokenScanner</code> class exports several additional methods
 * that give clients more control over its behavior.  Those methods are
 * described individually in the documentation.
 */
class TokenScanner {
public:
    /*
     * Constructor: TokenScanner
     * Usage: TokenScanner scanner;
     *        TokenScanner scanner(str);
     *        TokenScanner scanner(infile);
     * ------------------------------------
     * Initializes a scanner object.  The initial token stream comes from
     * the specified string or input stream, if supplied.  The default
     * constructor creates a scanner with an empty token stream.
     */
    TokenScanner();
    TokenScanner(std::string str);
    TokenScanner(std::istream & infile);

    /*
     * Destructor: ~TokenScanner
     * -------------------------
     * Deallocates the storage associated with this scanner.
     */
    virtual ~TokenScanner();

    /*
     * Method: setInput
     * Usage: scanner.setInput(str);
     *        scanner.setInput(infile);
     * --------------------------------
     * Sets the token stream for this scanner to the specified string or
     * input stream.  Any previous token stream is discarded.
     */
    void setInput(std::string str);
    void setInput(std::istream & infile);

    /*
     * Method: hasMoreTokens
     * Usage: if (scanner.hasMoreTokens()) ...
     * ---------------------------------------
     * Returns <code>true</code> if there are additional tokens for this
     * scanner to read.
     */
    bool hasMoreTokens();

    /*
     * Method: nextToken
     * Usage: token = scanner.nextToken();
     * -----------------------------------
     * Returns the next token from this scanner.  If <code>nextToken</code>
     * is called when no tokens are available, it returns the empty string.
     */
    std::string nextToken();

    /*
     * Method: saveToken
     * Usage: scanner.saveToken(token);
     * --------------------------------
     * Pushes the specified token back into this scanner's input stream.
     * On the next call to <code>nextToken</code>, the scanner will return
     * the saved token without reading any additional characters from the
     * token stream.
     */
    void saveToken(std::string token);

    /*
     * Method: getPosition
     * Usage: int pos = scanner.getPosition();
     * ---------------------------------------
     * Returns the current position of the scanner in the input stream.
     * If <code>saveToken</code> has been called, this position corresponds
     * to the beginning of the saved token.  If <code>saveToken</code> is
     * called more than once, <code>getPosition</code> returns -1.
     */
    int getPosition() const;

    /*
     * Method: ignoreWhitespace
     * Usage: scanner.ignoreWhitespace();
     * ----------------------------------
     * Tells the scanner to ignore whitespace characters.  By default,
     * the <code>nextToken</code> method treats whitespace characters
     * (typically spaces and tabs) just like any other punctuation mark
     * and returns them as single-character tokens.
     * Calling
     *
     *<pre>
     *    scanner.ignoreWhitespace();
     *</pre>
     *
     * changes this behavior so that the scanner ignore whitespace characters.
     */
    void ignoreWhitespace();

    /*
     * Method: ignoreComments
     * Usage: scanner.ignoreComments();
     * --------------------------------
     * Tells the scanner to ignore comments.  The scanner package recognizes
     * both the slash-star and slash-slash comment format from the C-based
     * family of languages.  Calling
     *
     *<pre>
     *    scanner.ignoreComments();
     *</pre>
     *
     * sets the parser to ignore comments.
     */
    void ignoreComments();

    /*
     * Method: scanNumbers
     * Usage: scanner.scanNumbers();
     * -----------------------------
     * Controls how the scanner treats tokens that begin with a digit.  By
     * default, the <code>nextToken</code> method treats numbers and letters
     * identically and therefore does not provide any special processing for
     * numbers.  Calling
     *
     *<pre>
     *    scanner.scanNumbers();
     *</pre>
     *
     * changes this behavior so that <code>nextToken</code> returns the
     * longest substring that can be interpreted as a real number.
     */
    void scanNumbers();

    /*
     * Method: scanStrings
     * Usage: scanner.scanStrings();
     * -----------------------------
     * Controls how the scanner treats tokens enclosed in quotation marks.  By
     * default, quotation marks (either single or double) are treated just like
     * any other punctuation character.  Calling
     *
     *<pre>
     *    scanner.scanStrings();
     *</pre>
     *
     * changes this assumption so that <code>nextToken</code> returns a single
     * token consisting of all characters through the matching quotation mark.
     * The quotation marks are returned as part of the scanned token so that
     * clients can differentiate strings from other token types.
     */
    void scanStrings();

    /*
     * Method: addWordCharacters
     * Usage: scanner.addWordCharacters(str);
     * --------------------------------------
     * Adds the characters in <code>str</code> to the set of characters
     * legal in a <code>WORD</code> token.  For example, calling
     * <code>addWordCharacters("_")</code> adds the underscore to the
     * set of characters that are accepted as part of a word.
     */
    void addWordCharacters(std::string str);

    /*
     * Method: isWordCharacter
     * Usage: if (scanner.isWordCharacter(ch)) ...
     * -------------------------------------------
     * Returns <code>true</code> if the character is valid in a word.
     */
    bool isWordCharacter(char ch) const;

    /*
     * Method: addOperator
     * Usage: scanner.addOperator(op);
     * -------------------------------
     * Defines a new multicharacter operator.  Whenever you call
     * <code>nextToken</code> when the input stream contains operator
     * characters, the scanner returns the longest possible operator
     * string that can be read at that point.
     */
    void addOperator(std::string op);

    /*
     * Method: verifyToken
     * Usage: scanner.verifyToken(expected);
     * -------------------------------------
     * Reads the next token and makes sure it matches the string
     * <code>expected</code>.  If it does not, <code>verifyToken</code>
     * throws an error.
     */
    void verifyToken(std::string expected);

    /*
     * Method: getTokenType
     * Usage: TokenType type = scanner.getTokenType(token);
     * ----------------------------------------------------
     * Returns the type of this token.  This type will match one of the
     * following enumerated type constants: <code>EOF</code>,
     * <code>SEPARATOR</code>, <code>WORD</code>, <code>NUMBER</code>,
     * <code>STRING</code>, or <code>OPERATOR</code>.
     */
    TokenType getTokenType(std::string token) const;

    /*
     * Method: getChar
     * Usage: int ch = scanner.getChar();
     * ----------------------------------
     * Reads the next character from the scanner input stream.
     */
    int getChar();

    /*
     * Method: ungetChar
     * Usage: scanner.ungetChar(ch);
     * -----------------------------
     * Pushes the character <code>ch</code> back into the scanner stream.
     * The character must match the one that was read.
     */
    void ungetChar(int ch);

    /*
     * Method: getStringValue
     * Usage: string str = scanner.getStringValue(token);
     * --------------------------------------------------
     * Returns the string value of a token.  This value is formed by removing
     * any surrounding quotation marks and replacing escape sequences by the
     * appropriate characters.
     */
    std::string getStringValue(std::string token) const;

    /* Private section */

    /**********************************************************************/
    /* Note: Everything below this point in the file is logically part    */
    /* of the implementation and should not be of interest to clients.    */
    /**********************************************************************/

private:
    /*
     * Private type: StringCell
     * ------------------------
     * This type is used to construct linked lists of cells, which are used
     * to represent both the stack of saved tokens and the set of defined
     * operators.  These types cannot use the Stack and Lexicon classes
     * directly because tokenscanner.h is an extremely low-level interface,
     * and doing so would create circular dependencies in the .h files.
     */
    struct StringCell {
        std::string str;
        StringCell *link;
    };

    enum NumberScannerState {
        INITIAL_STATE,
        BEFORE_DECIMAL_POINT,
        AFTER_DECIMAL_POINT,
        STARTING_EXPONENT,
        FOUND_EXPONENT_SIGN,
        SCANNING_EXPONENT,
        FINAL_STATE
    };

    std::string buffer;              /* The original argument string */
    std::istream *isp;               /* The input stream for tokens  */
    bool stringInputFlag;            /* Flag indicating string input */
    bool ignoreWhitespaceFlag;       /* Scanner ignores whitespace   */
    bool ignoreCommentsFlag;         /* Scanner ignores comments     */
    bool scanNumbersFlag;            /* Scanner parses numbers       */
    bool scanStringsFlag;            /* Scanner parses strings       */
    std::string wordChars;           /* Additional word characters   */
    StringCell *savedTokens;         /* Stack of saved tokens        */
    StringCell *operators;           /* List of multichar operators  */

    /* Private method prototypes */
    void initScanner();
    void skipSpaces();
    std::string scanWord();
    std::string scanNumber();
    std::string scanString();
    bool isOperator(std::string op);
    bool isOperatorPrefix(std::string op);
};

#endif
