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contracts...Lootbox.sol

pragma solidity >=0.7.0 <0.9.0;

/** 
 * @title Lootbox
 * @dev Matrix lootbox contract
 */
 
 contract Lootbox {

    // NULL is for depleted items; fungible tokens not yet implemented     
    enum TokenType{ NULL, NONFUNGIBLE, SEMIFUNGIBLE, FUNGIBLE }
     
    
    // pity indicates whether an item is in the pity pool
    struct LootboxItem {
        TokenType tokenType;
        string name;
        uint32 unitWeight;
        bool pity;
    }
     
     
    // maps id to rate ranges
    // width of range, inclusive. is the total weight (i.e. unit weight for NFTs, unit weight * qty for SFTs)
    // open function generates a random int and checks which range it falls in
    mapping(uint => uint32[2]) public normalRates;
    mapping(uint => uint32[2]) public pityRates;
     
     
    // list of LootboxItems is the Lootbox pool
    LootboxItem[] public pool;
     
    // random integer between 1 and rangeEnd, inclusive
    function _fakeRandint(uint rangeEnd) private view returns (uint randint_) {
        randint_ = (uint(keccak256(abi.encodePacked(block.timestamp, block.difficulty))) % rangeEnd) + 1;
    }
    
    function _rangeEnd() public view returns (uint rangeEnd_) {
        if (pool.length == 0) return 0;
        for (uint i=pool.length-1; i>=0; i--) {
            if (i==0 && pool[0].tokenType == TokenType.NULL) return 0;
            if (pool[i].tokenType == TokenType.NULL) continue;
            rangeEnd_ = normalRates[i][1];
            break;
        }
    }
    
    function _pityRangeEnd() public view returns (uint rangeEnd_) {
        if (pool.length == 0) return 0;
        for (uint i=pool.length-1; i>=0; i--) {
            if (i==0 && pool[0].tokenType == TokenType.NULL) return 0;
            if (i==0 && !pool[0].pity) return 0;
            if (pool[i].tokenType == TokenType.NULL) continue;
            if (!pool[i].pity) continue;
            rangeEnd_ = pityRates[i][1];
            break;
        }
    }
    
    function addNft(string memory _name, uint32 _weight, bool _pity) public {
        uint32 rangeEnd = uint32(_rangeEnd()+1);
        uint32 pityRangeEnd = uint32(_pityRangeEnd()+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) {
            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 = uint32(_rangeEnd()+1);
        uint32 pityRangeEnd = uint32(_pityRangeEnd()+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) {
            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 _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 _open() private returns (LootboxItem memory item_) {
        uint rangeEnd = _rangeEnd();
        if (rangeEnd == 0) revert("Box empty");
        uint32 randIndex = uint32(_fakeRandint(rangeEnd));
        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);
                break;
            }
        }
    }
    
    function _pityOpen() private returns (LootboxItem memory item_) {
        uint rangeEnd = _pityRangeEnd();
        if (rangeEnd == 0) revert("Pity pool empty");
        uint32 randIndex = uint32(_fakeRandint(rangeEnd));
        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);
                break;
            }
        }
    }
    
    function open() public returns (LootboxItem memory item_) {
        item_ = _open();
    }
    
    function pityOpen() public returns (LootboxItem memory item_) {
        item_ = _pityOpen();
    }
 }