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contracts...Lootbox.sol

pragma solidity >=0.7.0 <0.9.0;

/** 
 * @title Lootbox
 * @dev Matrix lootbox contract
 */
 
 contract Lootbox {
     enum TokenType{ NULL, NONFUNGIBLE, SEMIFUNGIBLE, FUNGIBLE }
     
     struct LootboxItem {
         TokenType tokenType;
         string name;
         uint32 unitWeight;
         bool pity;
     }
     
     
     // maps id to rate ranges
     mapping(uint => uint32[2]) public normalRates;
     mapping(uint => uint32[2]) public pityRates;
     LootboxItem[] public pool;
     
    function _fakeRandint(uint range_end) private view returns (uint randint_) {
        randint_ = uint(keccak256(abi.encodePacked(block.timestamp, block.difficulty))) % (range_end + 1);
    }
    
    function _removeItem(uint _index) private {
        LootboxItem storage toRemove = pool[_index];
        
        // change ranges of all other items first because unitWeight may be deleted
        for (uint i=_index+1; i<pool.length; i++) {
            if (pool[i].tokenType == TokenType.NULL) continue;
            normalRates[_index][0] -= toRemove.unitWeight;
            normalRates[_index][1] -= toRemove.unitWeight;
            
            if (pool[i].pity) {
                pityRates[_index][0] -= toRemove.unitWeight;
                pityRates[_index][1] -= toRemove.unitWeight;
            }
        }
        
        // remove relevant item
        if (toRemove.tokenType == TokenType.SEMIFUNGIBLE) {
            if (normalRates[_index][1] >= normalRates[_index][0] + toRemove.unitWeight) {
                normalRates[_index][1] -= toRemove.unitWeight;
                if (toRemove.pity) pityRates[_index][1] -= toRemove.unitWeight;
            } else {
                pool[_index].tokenType = TokenType.NULL;
            }
        } else if (toRemove.tokenType == TokenType.NONFUNGIBLE) {
           pool[_index].tokenType = TokenType.NULL;
        } else revert("Trying to remove null item");
    }
    
    function addNft(string memory _name, uint32 _weight, bool _pity) public {
        uint32 rangeEnd = (pool.length>0) ? normalRates[pool.length-1][1] + 1 : 1;
        LootboxItem memory item = LootboxItem({tokenType: TokenType.NONFUNGIBLE, name: _name, unitWeight: _weight, pity: _pity});
        pool.push(item);
        normalRates[pool.length-1] = [rangeEnd, rangeEnd+_weight-1];
        
        if (_pity) {
            uint32 pityRangeEnd = (pool.length>0) ? pityRates[pool.length-1][1] + 1 : 1;
            pityRates[pool.length-1] = [pityRangeEnd, pityRangeEnd+_weight-1];
        }
    }
    
    function addNft(string memory _name, uint32 _weight) public {
        addNft(_name, _weight, false);
    }
    
    function addSft(string memory _name, uint32 _weight, uint32 _qty, bool _pity) public {
        uint32 rangeEnd = (pool.length>0) ? normalRates[pool.length-1][1] + 1 : 1;
        LootboxItem memory item = LootboxItem({tokenType: TokenType.SEMIFUNGIBLE, name: _name, unitWeight: _weight, pity: _pity});
        pool.push(item);
        normalRates[pool.length-1] = [rangeEnd, rangeEnd+(_weight*_qty)-1];
        
        if (_pity) {
            uint32 pityRangeEnd = (pool.length>0) ? pityRates[pool.length-1][1] + 1 : 1;
            pityRates[pool.length-1] = [pityRangeEnd, pityRangeEnd+(_weight*_qty)-1];
        }
    }
    
    function addSft(string memory _name, uint32 _weight, uint32 _qty) public {
        addSft(_name, _weight, _qty, false);
    }
    
    function _open() private returns (LootboxItem memory item_) {
        uint rangeEnd;
        for (uint i=pool.length-1; i>=0; i--) {
            if (pool[i].tokenType == TokenType.NULL) continue;
            if (i==0 && pool[0].tokenType == TokenType.NULL) revert("Box empty");
            rangeEnd = normalRates[i][1];
            break;
        }
        
        uint32 randIndex = uint32(_fakeRandint(rangeEnd-1)) + 1;
        for (uint i=0; i<pool.length; i++) {
            if (pool[i].tokenType == TokenType.NULL) continue;
            if (randIndex <= normalRates[i][1]) {
                item_ = pool[i];
                _removeItem(i);
            }
        }
    }
    
    function _pityOpen() private returns (LootboxItem memory item_) {
        uint rangeEnd;
        for (uint i=pool.length-1; i>=0; i--) {
            if (pool[i].tokenType == TokenType.NULL) continue;
            if (!pool[i].pity) continue;
            rangeEnd = pityRates[i][1];
            break;
        }
        
        uint32 randIndex = uint32(_fakeRandint(rangeEnd-1)) + 1;
        for (uint i=0; i<pool.length; i++) {
            if (pool[i].tokenType == TokenType.NULL) continue;
            if (!pool[i].pity) continue;
            if (randIndex <= pityRates[i][1]) {
                item_ = pool[i];
                _removeItem(i);
            }
        }
  
    }
    
    function open() public returns (LootboxItem memory item_) {
        item_ = _open();
    }
     
 }