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ERC721 token with ERC20 adapter to allow for doping of ERC20 value into ERC721 NON FUNGIABLE unique assets.

SkySolutionsSkySilo, the ERC721SmartToken contract implements non-fungible tokens based on ERC721 standard that also supports ERC20 interface. The main idea is to create a token that can be both non-fungible and has transferable value.

Inside ERC721 contract each not fungible token represented as a NFT structure where there is a member element called value .

struct NFT {
        uint256 value;          // NFT value 
        string  metadata;       // ... metadata: IPFS path
        uint256 kind;           // ... type
        uint256 level;          // ... activities level
        uint256 state;          // ... state
    }

This element holds ERC20 token inside ERC721 token.

To work with ERC721 token as normal ERC20 token we need to create a ERC20Adapter that implements standard ERC20 methods, as for example balanceOf method.

function balanceOf(address _owner) public view returns (uint256)

But in our case due to ERC721 structure for each _owner there can be many non-fungible tokens belong to this particular address. To select particular token for ERC20 compatible operations like transfer token value to another address we need to implement new methods that will accept address and token ID as parameters.

function approveFrom(uint256 _fromId, address _spender, uint256 _toId, uint256 _value) public returns (bool success)

This method calls ERC20Controller method implemented by ERC721SmartToken contract that will use the following mappings to store information abount NFT tokens:

mapping (address => mapping (address => uint256)) public allowanceIds; // transfer allowance
mapping (address => mapping (address => uint256)) public allowanceAmt; // transfer allowance

Now we can use ERC20 standard methods transfer and transferFrom to transfer values between two NFT tokens.

ERC20Controller implements defaultId methods that provides a default NFT id for the _owner address.

function defaultId(address _owner) internal returns (uint256 id);

So, we can use ERC20 standard method approve to approve transfer between two NFT default tokens for msg.sender and _spender.

See Help for events description.

TokenContainer

TokenContainer smart contract implements hierarchical structure for token pools. Now one NFT token can be a container for other NFT tokens in the same smart contract. Each token can belong only one container, token-container relationship supported by the following mapping:

mapping (uint256 => uint256) public tokenIndexToPoolToken;

The public variable maxLevel defines the maximum number of levelels in hierarchical structure where the root must be al level 0 and a token with level maxLevel-1 will be terminal node in the structure.

For each token we can find the path from this token to the root token using the following method:

function getPath(uint256 _nodeId) external view returns(uint256[] path);

The path could contain number of token IDs starting from the first pool token that _nodeId belongs to. Plase note that NFT ID 0 is reserved and equal to null value. So, only not zeto IDs are counted as pool token IDs.

For each pool token we can check the pool size and recieve pool members array:

function _getPoolSize(uint256 _nodeId) view internal returns(uint256 size);
function _getPool(uint256 _nodeId) view internal returns(uint256[] pool);

A NFT token can be added to pool token or can be removed from pool. In removal we will check if removing token nodeId does not have any pool members _getPoolSize(_nodeId) == 0 and if not we will rise an exception.

function addToken(uint256 _nodeId, uint256 _parentId) public;
function removeToken(uint256 _nodeId) public;

The TokenContainer constructur calls ERC721SmartToken constructur with token name and token symbol.

TokenPool

TokenPool is TokenContainer with 4 level pool structure:

Level     Container / Member
--------------------------------------------
  0       SuperPool
  1           |_____.Pool
  2                   |_____.SubPool
  3                             |_____.Token

The pool schema described by the following structure:

struct Pool {
        uint8   level;      // Pool level: 0,1,2,3
        uint256 maxNumber;  // Maximum number of pools on this lavel
        uint256 maxMember;  // Maximum number of members for the pool
        uint256 number;     // Pool number for this level
        uint256 last;       // NFT ID for last availible pool (with member capacity)
        uint256 share;      // Pool share from token investment
 }

Use insertPool method to insert token in the pool structure:

function insertPool(uint256 _id) public returns(bool);

This function calls _insertPool to insert the token and if needed also insert new pool in the structure:

function _insertPool(uint256 _id, uint8 _level) internal returns (bool);

After the token is inserted in the pool structure the function insertPool calls the value distribution function:

function _distributeValue(uint256 _id) internal returns (bool);

than distrubutes the token value between SuperPool, Pool and SubPool based on Pool.share. The rest of the token value after the pool distribution will go to commission. Use the following methods to get collected commission and current pool values:

function getComission() public view returns(uint256 commission);

function getDistribution() public view returns(uint256[4] distribution)

The last function returns the following values:

distribution[0];         // Super Pool Value
distribution[1];         // Pool Value
distribution[2];         // SubPool Value
distribution[3];         // Tokens Value (must be 0)

To pay value the smart contract uses the following function:

function _payValue(uint256 _id, uint256 _value) internal returns(uint256[4] distribution);

__payValue returns distribution for the payment based on the same structure as getDistribution but in this case only one array element can have non zero value equal to _value. For example, if Pool has made a payment then distribution[1] == _value and the rest of distribution[0,2,3] == 0. If all elements have zero value then payment is not successful and all pool does not have enough value to pay requested amount. In this case _payValue emits SecondTierCall event. If the payment went through then event PaymentValue was emited:

 event PaymentValue(uint256 id, uint256 value, uint8 level);

and it will return the pool level that has made the payment, in our example it will be level == 1.