package org.kohsuke.rngom.binary;

final class PatternInterner {
    private static final int INIT_SIZE = 256;
    private static final float LOAD_FACTOR = 0.3f;
    private Pattern[] table;
    private int used;
    private int usedLimit;

    PatternInterner() {
        table = null;
        used = 0;
        usedLimit = 0;
    }

    PatternInterner(PatternInterner parent) {
        table = parent.table;
        if (table != null)
            table = (Pattern[]) table.clone();
        used = parent.used;
        usedLimit = parent.usedLimit;
    }

    Pattern intern(Pattern p) {
        int h;

        if (table == null) {
            table = new Pattern[INIT_SIZE];
            usedLimit = (int) (INIT_SIZE * LOAD_FACTOR);
            h = firstIndex(p);
        } else {
            for (h = firstIndex(p); table[h] != null; h = nextIndex(h)) {
                if (p.samePattern(table[h]))
                    return table[h];
            }
        }
        if (used >= usedLimit) {
            // rehash
            Pattern[] oldTable = table;
            table = new Pattern[table.length << 1];
            for (int i = oldTable.length; i > 0;) {
                --i;
                if (oldTable[i] != null) {
                    int j;
                    for (j = firstIndex(oldTable[i]);
                        table[j] != null;
                        j = nextIndex(j));
                    table[j] = oldTable[i];
                }
            }
            for (h = firstIndex(p); table[h] != null; h = nextIndex(h));
            usedLimit = (int) (table.length * LOAD_FACTOR);
        }
        used++;
        table[h] = p;
        return p;
    }

    private int firstIndex(Pattern p) {
        return p.patternHashCode() & (table.length - 1);
    }

    private int nextIndex(int i) {
        return i == 0 ? table.length - 1 : i - 1;
    }
}
