pragma solidity ^0.5.0;


/*
@notice: Library used in assessments for clustering, score- and payout computation
*/
library Math {


    /*
      @return: a random number between 0 and a given upper limit (included) based on the last blockhash
      @dev based on a function by alexvandesande
    */
    function getRandomNumber(uint _seed, uint _max) public view returns(uint) {
        return(uint(keccak256(abi.encodePacked(blockhash(block.number-1), _seed)))%(_max+1));
    }

    /**
       @notice Creates clusters of a given radius around all scores.
       @param _data Array of scores submitted by assessors
       @param _consentRadius Distance under which two scores are taken to be in consensus.
       @return finalScore The average of all scores in the largest cluster
       @return largestClusterSize the number of scores in the largest cluster
       @dev in case of a two clusters of equal size, the one with a lower score
        is chosen
    */
    function getFinalScore(int[] memory _data, uint _consentRadius)
        public
        pure
        returns(int finalScore, uint largestClusterSize)
    {
        //get largest Cluster and its score
        int largestClusterScore;
        for (uint i = 0; i < _data.length; i++) {
            uint clusterSize = 0;
            int clusterScore = 0;
            for (uint j = 0; j < _data.length; j++) {
                if (abs(_data[i] - _data[j]) <= _consentRadius) {
                    clusterScore += _data[j];
                    clusterSize++;
                }
            }
            if (clusterSize > largestClusterSize ||
                (clusterSize == largestClusterSize && clusterScore < largestClusterScore)) {
                largestClusterSize = clusterSize;
                largestClusterScore = clusterScore;

            }
        }
        finalScore = largestClusterScore/int(largestClusterSize);
    }

    /*
      @param _distance: Absolute difference between the assessor's score and the final score
      @param _stake: Amount of tokens paid by the assessor to participate
      @param _consentRadius: Distance under which two scores are taken to be in consensus.
      @return payout: Sum of reward and the proportion of stake an assessors gets back
      @return dissenting: Flag whether or not an assessor is part of the majority
      @dev The reward always is the same amount as the stake.

    */
    function getPayout(uint _distance, uint _stake, uint _consentRadius
    )
        public
        pure
        returns(uint payout, bool dissenting)
    {
        uint distanceAsPercentageOfRadius = (_distance*10000) / _consentRadius;
        // if in rewardCluster
        if (_distance <= _consentRadius) {
            payout = (_stake * (10000 - distanceAsPercentageOfRadius)) / 10000 + _stake;
        } else {
            // cap it to 20000 to prevent underflow
            //solhint-disable-next-line max-line-length
            uint distanceAsPercentageOf2RadiusCapped = distanceAsPercentageOfRadius > 20000 ? 20000 : distanceAsPercentageOfRadius;
            payout = (_stake * (20000 - distanceAsPercentageOf2RadiusCapped)) / 20000;
            dissenting = true;
        }
    }

    function abs(int x) public pure returns(uint) {
        return uint(x < 0 ? -x : x);
    }
}