private void updateProgress(Progress progress, int[] cubesInStage, int finished, int skipped) {
        int[] actualStages = new int[cubesInStage.length + 1];
        System.arraycopy(cubesInStage, 0, actualStages, 0, cubesInStage.length);
        actualStages[actualStages.length - 1] = finished + skipped;
        int totalKnownUnfinished = 0;
        //the amount of cubes that went through 0-th stage
        totalKnownUnfinished += cubesInStage[0];
        for (int n = 1; n < cubesInStage.length; n++) {
            //the amount if cubes that went through n-th stage but didn't go through (n-1)-th stage.
            //TODO: is it accurate enough?
            totalKnownUnfinished += Math.max(0, cubesInStage[n] - cubesInStage[n - 1]);
        }
        int unknown = toUpdate.size() + finished + skipped - totalKnownUnfinished;
        if (unknown < 0) {
            unknown = 0;
        }
        //if unknown, assume 0
        actualStages[0] += unknown;
        for (int i = 0; i < actualStages.length; i++) {
            int currentStage = (i == actualStages.length - 1) ?
                    actualStages[i] :
                    actualStages[i] - actualStages[i + 1];
            if (currentStage < 0) {
                currentStage = 0;
            }
            actualStages[i] = currentStage;
        }
        int total = 0;
        for (int num : actualStages) {
            total += num;
        }
        double totalProgress = 0;
        for (int i = 0; i < actualStages.length; i++) {
            double progressPart = actualStages[i]/(double) total;
            double weightedProgress = progressPart*i/(double) (actualStages.length - 1);
            totalProgress += weightedProgress;
        }
        assert totalProgress < 1.00001 && totalProgress >= 0;
        if (totalProgress > 1) {
            totalProgress = 1;
        }
        int progressInt = (int) (totalProgress*Integer.MAX_VALUE);
        progress.setProgress(progressInt);
    }