LookAheadSet.java

package com.sap.ide.cts.parser.incremental;

import java.util.ArrayList;
import java.util.List;

import com.sap.furcas.metamodel.FURCAS.textblocks.AbstractToken;

public class LookAheadSet {

    private final List<Entry> list = new ArrayList<Entry>();

    // private Entry currentEntry;

    public void advance(int offset) {
        // replace <tok,cla,cnt> in list with <tok,cla - offset,cnt + 1>
        for (Entry currentEntry : list) {
            currentEntry.characterLookahead = currentEntry.characterLookahead - offset;
            currentEntry.tokenLookback++;
        }
    }

    public void addItem(AbstractToken tok) {
        list.add(new Entry(tok, tok.getLookahead(), 0));
    }

    public int computeLookback() {
        /*
         * remove <tok,cla,cnt> s.t. cla <= 0 from list if (list == empty) return 0; else return max cnt j <tok,cla,cnt> in list
         */
        List<Entry> removeObjects = new ArrayList<Entry>();
        for (Entry entry : list) {
            if (entry.characterLookahead <= 0) {
                removeObjects.add(entry);
            }
        }
        list.removeAll(removeObjects);
        if (list.isEmpty()) {
            return 0;
        }

        // TODO this is a hack re-check algorithm then change to maxLookback =0;
        int maxLookback = 1;
        for (Entry entry2 : list) {
            if (entry2.tokenLookback > maxLookback) {
                maxLookback = entry2.tokenLookback;
            }
        }
        return maxLookback;
    }

    public boolean allItemsDiscardable() {
        /*
         * forall <tok,cla,cnt> in list, !was_re_lexed(tok)
         */
        boolean result = true;
        for (Entry entry : list) {
            result = wasReLexed(entry.token) && result;
        }
        return result;
    }

    private boolean wasReLexed(AbstractToken token) {
        return token.isRelexingNeeded();
    }

    private class Entry {
        private final AbstractToken token;
        private int characterLookahead;
        private int tokenLookback;

        public Entry(AbstractToken token, int characterLookahead, int tokenLookback) {
            super();
            this.token = token;
            this.characterLookahead = characterLookahead;
            this.tokenLookback = tokenLookback;
        }

        @Override
        public boolean equals(Object other) {
            if (other instanceof Entry) {
                Entry otherEntry = (Entry) other;
                return token.equals(otherEntry.token) && characterLookahead == otherEntry.characterLookahead
                        && tokenLookback == otherEntry.tokenLookback;
            } else {
                return false;
            }
        }
    }
}