public boolean isAvailable(int dayIndex) {
        int nDex = this.getNumberWith1InBinaryForIndex(dayIndex);
        return (availableDex & nDex) != 0;
    }

    /**
     * @param dayIndex    [0..6], 0 - monday, ..., 6 - sunday
     * @param isAvailable boolean value
     */
    public void setAvailableDay(int dayIndex, boolean isAvailable) {

        boolean isAvailableInitially = this.isAvailable(dayIndex);

        if (isAvailableInitially == isAvailable) {
            return;
        }

        if (isAvailableInitially) {
            // we should turn off
            availableDex = availableDex & this.getNumberWith0InBinaryForIndex(dayIndex);
        } else {
            // we should turn on
            availableDex = availableDex | this.getNumberWith1InBinaryForIndex(dayIndex);
        }
    }

    private int getNumberWith1InBinaryForIndex(int dayIndex) {
        switch (dayIndex) {
            case 0: // mon
                return 64; // 1000000
            case 1: // tue
                return 32; // 100000
            case 2: // wed
                return 16; // 10000
            case 3: // thu
                return 8;  // 1000
            case 4: // fri
                return 4;  // 100
            case 5: // sat
                return 2;  // 10
            case 6: // sun
                return 1;  // 1
        }
        throw new IllegalArgumentException("Day index should be in [0..6] range");
    }

    private int getNumberWith0InBinaryForIndex(int dayIndex) {
        switch (dayIndex) {
            case 0: // mon
                return 63;  // 0111111
            case 1: // tue
                return 95;  // 1011111
            case 2: // wed
                return 111; // 1101111
            case 3: // thu
                return 119; // 1110111
            case 4: // fri
                return 123; // 1111011
            case 5: // sat
                return 125; // 1111101
            case 6: // sun
                return 126; // 1111110
        }
        throw new IllegalArgumentException("Day index should be in [0..6] range");
    }