/**
 * File: LexState.java
 * 
 * Figure 7.35 of "Computer Systems", J. Stanley Warford,
 * Fourth Edition, Jones & Bartlett, Publishers, 2010.
 */

public enum LexState {
    eLS_START, eLS_IDENT, eLS_SIGN, eLS_INTEGER, eLS_STOP
}


/**
 * File: Tokenizer.java
 * 
 * Figure 7.35 of "Computer Systems", J. Stanley Warford,
 * Fourth Edition, Jones & Bartlett, Publishers, 2010.
 */

public class Tokenizer {
    private InBuffer b;

    public Tokenizer(InBuffer inBuffer) {
        b = inBuffer;
    }

    public AToken getToken() {
        char nextChar;
        int sign = +1;
        int localIntValue = 0;
        StringBuffer localIdentValue = new StringBuffer("");
        AToken aToken = new TEmpty();
        LexState state = LexState.eLS_START;
        do {
            nextChar = b.advanceInput();
            switch (state) {
            case eLS_START:
                if (Util.isAlpha(nextChar)) {
                    localIdentValue.append(nextChar);
                    state = LexState.eLS_IDENT;
                } else if (nextChar == '-') {
                    sign = -1;
                    state = LexState.eLS_SIGN;
                } else if (nextChar == '+') {
                    sign = +1;
                    state = LexState.eLS_SIGN;
                } else if (Util.isDigit(nextChar)) {
                    localIntValue = nextChar - '0';
                    sign = +1;
                    state = LexState.eLS_INTEGER;
                } else if (nextChar == ',') {
                    aToken = new TComma();
                    state = LexState.eLS_STOP;
                } else if (nextChar == '(') {
                    aToken = new TLeftParen();
                    state = LexState.eLS_STOP;
                } else if (nextChar == ')') {
                    aToken = new TRightParen();
                    state = LexState.eLS_STOP;
                } else if (nextChar == '\n') {
                    state = LexState.eLS_STOP;
                } else if (nextChar != ' ') {
                    aToken = new TInvalid();
                }
                break;
            case eLS_IDENT:
                if (Util.isAlpha(nextChar) || Util.isDigit(nextChar)) {
                    localIdentValue.append(nextChar);
                } else {
                    b.backUpInput();
                    aToken = new TIdentifier(localIdentValue);
                    state = LexState.eLS_STOP;
                }
                break;
            case eLS_SIGN:
                if (Util.isDigit(nextChar)) {
                    localIntValue = nextChar - '0';
                    state = LexState.eLS_INTEGER;
                } else {
                    aToken = new TInvalid();
                }
                break;
            case eLS_INTEGER:
                if (Util.isDigit(nextChar)) {
                    localIntValue = 10 * localIntValue + nextChar - '0';
                } else {
                    b.backUpInput();
                    aToken = new TInteger(sign * localIntValue);
                    state = LexState.eLS_STOP;
                }
                break;
            }
        } while ((state != LexState.eLS_STOP) && !(aToken instanceof TInvalid));
        return aToken;
    }
}