[ERC998] NFTが他のNFTやERC20トークンを所有する仕組みを理解しよう！

address rootOwner = address(rootOwnerOf(_tokenId));
require(
  rootOwner == msg.sender || 
  isApprovedForAll(rootOwner, msg.sender) ||
  getApproved(tokenId) == msg.sender
);

function approve(address _approved, uint256 _tokenId) external {
  address rootOwner = address(rootOwnerOf(_tokenId));	
  require(rootOwner == msg.sender || isApprovedForAll(rootOwner,msg.sender));

  rootOwnerAndTokenIdToApprovedAddress[rootOwner][_tokenId] = _approved;
  emit Approval(rootOwner, _approved, _tokenId);
}

function getApproved(uint256 _tokenId) public view returns (address)  {
  address rootOwner = address(rootOwnerOf(_tokenId));
  return rootOwnerAndTokenIdToApprovedAddress[rootOwner][_tokenId];
}

// Logic for calling rootOwnerOfChild for a tokenId
address tokenOwner = ownerOf(tokenId);
address childContract = address(this);
bytes32 rootOwner = ERC998ERC721(tokenOwner).rootOwnerOfChild(childContract, tokenId);

uint256 tokenId = 6;
bytes memory tokenIdBytes = new bytes(32);
assembly { mstore(add(tokenIdBytes, 32), tokenId) }
ERC721(contractAddress).safeTransferFrom(userAddress, composableAddress, 3, tokenIdBytes);

pragma solidity ^0.4.24;

/// @title `ERC998ERC721` Top-Down Composable Non-Fungible Token
/// @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-998.md
///  Note: the ERC-165 identifier for this interface is 0xcde244d9
interface ERC998ERC721TopDown {

  /// @dev This emits when a token receives a child token.
  /// @param _from The prior owner of the token.
  /// @param _toTokenId The token that receives the child token.
  event ReceivedChild(
    address indexed _from, 
    uint256 indexed _toTokenId, 
    address indexed _childContract, 
    uint256 _childTokenId
  );
  
  /// @dev This emits when a child token is transferred from a token to an address.
  /// @param _fromTokenId The parent token that the child token is being transferred from.
  /// @param _to The new owner address of the child token.
  event TransferChild(
    uint256 indexed _fromTokenId, 
    address indexed _to, 
    address indexed _childContract, 
    uint256 _childTokenId
  );

  /// @notice Get the root owner of tokenId.
  /// @param _tokenId The token to query for a root owner address
  /// @return rootOwner The root owner at the top of tree of tokens and ERC-998 magic value.
  function rootOwnerOf(uint256 _tokenId) public view returns (bytes32 rootOwner);
  
  /// @notice Get the root owner of a child token.
  /// @param _childContract The contract address of the child token.
  /// @param _childTokenId The tokenId of the child.
  /// @return rootOwner The root owner at the top of tree of tokens and ERC-998 magic value.
  function rootOwnerOfChild(
    address _childContract, 
    uint256 _childTokenId
  ) 
    public 
    view
    returns (bytes32 rootOwner);
  
  /// @notice Get the parent tokenId of a child token.
  /// @param _childContract The contract address of the child token.
  /// @param _childTokenId The tokenId of the child.
  /// @return parentTokenOwner The parent address of the parent token and ERC-998 magic value
  /// @return parentTokenId The parent tokenId of _tokenId
  function ownerOfChild(
    address _childContract, 
    uint256 _childTokenId
  ) 
    external 
    view 
    returns (
      bytes32 parentTokenOwner, 
      uint256 parentTokenId
    );
  
  /// @notice A token receives a child token
  /// @param _operator The address that caused the transfer.
  /// @param _from The owner of the child token.
  /// @param _childTokenId The token that is being transferred to the parent.
  /// @param _data Up to the first 32 bytes contains an integer which is the receiving parent tokenId.  
  function onERC721Received(
    address _operator, 
    address _from, 
    uint256 _childTokenId, 
    bytes _data
  ) 
    external 
    returns(bytes4);
    
  /// @notice Transfer child token from top-down composable to address.
  /// @param _fromTokenId The owning token to transfer from.
  /// @param _to The address that receives the child token
  /// @param _childContract The ERC-721 contract of the child token.
  /// @param _childTokenId The tokenId of the token that is being transferred.
  function transferChild(
    uint256 _fromTokenId,
    address _to, 
    address _childContract, 
    uint256 _childTokenId
  ) 
    external;
  
  /// @notice Transfer child token from top-down composable to address.
  /// @param _fromTokenId The owning token to transfer from.
  /// @param _to The address that receives the child token
  /// @param _childContract The ERC-721 contract of the child token.
  /// @param _childTokenId The tokenId of the token that is being transferred.
  function safeTransferChild(
    uint256 _fromTokenId,
    address _to, 
    address _childContract, 
    uint256 _childTokenId
  ) 
    external;
  
  /// @notice Transfer child token from top-down composable to address.
  /// @param _fromTokenId The owning token to transfer from.
  /// @param _to The address that receives the child token
  /// @param _childContract The ERC-721 contract of the child token.
  /// @param _childTokenId The tokenId of the token that is being transferred.
  /// @param _data Additional data with no specified format
  function safeTransferChild(
    uint256 _fromTokenId,
    address _to, 
    address _childContract, 
    uint256 _childTokenId, 
    bytes _data
  ) 
    external;
  
  /// @notice Transfer bottom-up composable child token from top-down composable to other ERC-721 token.
  /// @param _fromTokenId The owning token to transfer from.
  /// @param _toContract The ERC-721 contract of the receiving token
  /// @param _toTokenId The receiving token  
  /// @param _childContract The bottom-up composable contract of the child token.
  /// @param _childTokenId The token that is being transferred.
  /// @param _data Additional data with no specified format
  function transferChildToParent(
    uint256 _fromTokenId, 
    address _toContract, 
    uint256 _toTokenId, 
    address _childContract, 
    uint256 _childTokenId, 
    bytes _data
  ) 
    external;
  
  /// @notice Get a child token from an ERC-721 contract.
  /// @param _from The address that owns the child token.
  /// @param _tokenId The token that becomes the parent owner
  /// @param _childContract The ERC-721 contract of the child token
  /// @param _childTokenId The tokenId of the child token
  function getChild(
    address _from, 
    uint256 _tokenId, 
    address _childContract, 
    uint256 _childTokenId
  ) 
    external;
}

// Get the root owner of tokenId.
function rootOwnerOf(uint256 _tokenId) public view returns (bytes32 rootOwner);

0xcd740db5 = this.rootOwnerOf.selector ^ this.rootOwnerOfChild.selector ^ this.tokenOwnerOf.selector ^ this.ownerOfChild.selector;

// Get the root owner of a child token.
function rootOwnerOfChild(
  address _childContract, 
  uint256 _childTokenId
) 
  public 
  view 
  returns (bytes32 rootOwner);

0xcd740db5 = this.rootOwnerOf.selector ^ this.rootOwnerOfChild.selector ^ this.tokenOwnerOf.selector ^ this.ownerOfChild.selector;

// Get the parent tokenId of a child token and the owner address of the parent token.
function ownerOfChild(
  address _childContract, 
  uint256 _childTokenId
) 
  external 
  view 
  returns (
    address parentTokenOwner, 
    uint256 parentTokenId
  );

0xcd740db5 = this.rootOwnerOf.selector ^ this.rootOwnerOfChild.selector ^ this.tokenOwnerOf.selector ^ this.ownerOfChild.selector;

// A token receives a child token
function onERC721Received(
  address _operator, 
  address _from, 
  uint256 _childTokenId, 
  bytes _data
) 
  external 
  returns(bytes4);

// Transfer child token from top-down composable to address.
function transferChild(
  uint256 _fromTokenId,
  address _to, 
  address _childContract, 
  uint256 _childTokenId
) 
  external;

ERC721(_childContract).transferFrom(this, _to, _childTokenId);

/// @notice Transfer child token from top-down composable to address.
/// @param _fromTokenId The owning token to transfer from.
/// @param _to The address that receives the child token
/// @param _childContract The ERC-721 contract of the child token.
/// @param _childTokenId The tokenId of the token that is being transferred.
function safeTransferChild(
  uint256 _fromTokenId,
  address _to, 
  address _childContract, 
  uint256 _childTokenId
) 
  external;

ERC721(_childContract).safeTransferFrom(this, _to, _childTokenId);

ERC721(_childContract).safeTransferFrom(this, _to, _childTokenId, _data);

ERC998ERC721BottomUp(_childContract).transferToParent(address(this), _toContract, _toTokenId, _childTokenId, _data);

///  @dev The ERC-165 identifier for this interface is 0xa344afe4
interface ERC998ERC721TopDownEnumerable {

  /// @notice Get the total number of child contracts with tokens that are owned by tokenId.
  /// @param _tokenId The parent token of child tokens in child contracts
  /// @return uint256 The total number of child contracts with tokens owned by tokenId.
  function totalChildContracts(uint256 _tokenId) external view returns(uint256);
  
  /// @notice Get child contract by tokenId and index
  /// @param _tokenId The parent token of child tokens in child contract
  /// @param _index The index position of the child contract
  /// @return childContract The contract found at the tokenId and index.
  function childContractByIndex(
    uint256 _tokenId, 
    uint256 _index
  ) 
    external 
    view 
    returns (address childContract);
  
  /// @notice Get the total number of child tokens owned by tokenId that exist in a child contract.
  /// @param _tokenId The parent token of child tokens
  /// @param _childContract The child contract containing the child tokens
  /// @return uint256 The total number of child tokens found in child contract that are owned by tokenId.
  function totalChildTokens(
    uint256 _tokenId, 
    address _childContract
  ) 
    external 
    view 
    returns(uint256);
  
  /// @notice Get child token owned by tokenId, in child contract, at index position
  /// @param _tokenId The parent token of the child token
  /// @param _childContract The child contract of the child token
  /// @param _index The index position of the child token.
  /// @return childTokenId The child tokenId for the parent token, child token and index
  function childTokenByIndex(
    uint256 _tokenId, 
    address _childContract, 
    uint256 _index
  )
    external 
    view 
    returns (uint256 childTokenId);
}

/// @title `ERC998ERC20` Top-Down Composable Non-Fungible Token
/// @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-998.md
///  Note: the ERC-165 identifier for this interface is 0x7294ffed
interface ERC998ERC20TopDown {

  /// @dev This emits when a token receives ERC-20 tokens.
  /// @param _from The prior owner of the token.
  /// @param _toTokenId The token that receives the ERC-20 tokens.
  /// @param _erc20Contract The ERC-20 contract.
  /// @param _value The number of ERC-20 tokens received.
  event ReceivedERC20(
    address indexed _from, 
    uint256 indexed _toTokenId, 
    address indexed _erc20Contract, 
    uint256 _value
  );
  
  /// @dev This emits when a token transfers ERC-20 tokens.
  /// @param _tokenId The token that owned the ERC-20 tokens.
  /// @param _to The address that receives the ERC-20 tokens.
  /// @param _erc20Contract The ERC-20 contract.
  /// @param _value The number of ERC-20 tokens transferred.
  event TransferERC20(
    uint256 indexed _fromTokenId, 
    address indexed _to, 
    address indexed _erc20Contract, 
    uint256 _value
  );

  /// @notice A token receives ERC-20 tokens
  /// @param _from The prior owner of the ERC-20 tokens
  /// @param _value The number of ERC-20 tokens received
  /// @param _data Up to the first 32 bytes contains an integer which is the receiving tokenId.  
  function tokenFallback(address _from, uint256 _value, bytes _data) external;
  
  /// @notice Look up the balance of ERC-20 tokens for a specific token and ERC-20 contract
  /// @param _tokenId The token that owns the ERC-20 tokens
  /// @param _erc20Contract The ERC-20 contract
  /// @return The number of ERC-20 tokens owned by a token from an ERC-20 contract
  function balanceOfERC20(
    uint256 _tokenId, 
    address _erc20Contract
  ) 
    external 
    view 
    returns(uint256);
  
  /// @notice Transfer ERC-20 tokens to address
  /// @param _tokenId The token to transfer from
  /// @param _value The address to send the ERC-20 tokens to
  /// @param _erc20Contract The ERC-20 contract
  /// @param _value The number of ERC-20 tokens to transfer
  function transferERC20(
    uint256 _tokenId, 
    address _to, 
    address _erc20Contract, 
    uint256 _value
  ) 
    external;
  
  /// @notice Transfer ERC-20 tokens to address or ERC-20 top-down composable
  /// @param _tokenId The token to transfer from
  /// @param _value The address to send the ERC-20 tokens to
  /// @param _erc223Contract The `ERC-223` token contract
  /// @param _value The number of ERC-20 tokens to transfer
  /// @param _data Additional data with no specified format, can be used to specify tokenId to transfer to
  function transferERC223(
    uint256 _tokenId, 
    address _to, 
    address _erc223Contract, 
    uint256 _value, 
    bytes _data
  )
    external;
  
  /// @notice Get ERC-20 tokens from ERC-20 contract.
  /// @param _from The current owner address of the ERC-20 tokens that are being transferred.
  /// @param _tokenId The token to transfer the ERC-20 tokens to.
  /// @param _erc20Contract The ERC-20 token contract
  /// @param _value The number of ERC-20 tokens to transfer  
  function getERC20(
    address _from, 
    uint256 _tokenId, 
    address _erc20Contract, 
    uint256 _value
  ) 
    external;
}

function tokenFallback(address _from, uint256 _value, bytes _data) external;

function balanceOfERC20(uint256 _tokenId, address _erc20Contract) external view returns(uint256);

function transferERC20(uint256 _tokenId, address _to, address _erc20Contract, uint256 _value) external;

function transferERC223(
  uint256 _tokenId, 
  address _to, 
  address _erc223Contract, 
  uint256 _value, 
  bytes _data
) 
external;

function getERC20(
  address _from, 
  uint256 _tokenId, 
  address _erc20Contract, 
  uint256 _value
) 
external;

/// @dev The ERC-165 identifier for this interface is 0xc5fd96cd
interface ERC998ERC20TopDownEnumerable {
  
  /// @notice Get the number of ERC-20 contracts that token owns ERC-20 tokens from
  /// @param _tokenId The token that owns ERC-20 tokens.
  /// @return uint256 The number of ERC-20 contracts
  function totalERC20Contracts(uint256 _tokenId) external view returns(uint256);
  
  /// @notice Get an ERC-20 contract that token owns ERC-20 tokens from by index
  /// @param _tokenId The token that owns ERC-20 tokens.
  /// @param _index The index position of the ERC-20 contract.
  /// @return address The ERC-20 contract
  function erc20ContractByIndex(
    uint256 _tokenId, 
    uint256 _index
  ) 
    external 
    view 
    returns(address);
}

/// @title `ERC998ERC721` Bottom-Up Composable Non-Fungible Token
/// @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-998.md
///  Note: the ERC-165 identifier for this interface is 0xa1b23002
interface ERC998ERC721BottomUp {

  /// @dev This emits when a token is transferred to an ERC-721 token
  /// @param _toContract The contract the token is transferred to
  /// @param _toTokenId The token the token is transferred to
  /// @param _tokenId The token that is transferred  
  event TransferToParent(
    address indexed _toContract, 
    uint256 indexed _toTokenId, 
    uint256 _tokenId
  );
  
  /// @dev This emits when a token is transferred from an ERC-721 token
  /// @param _fromContract The contract the token is transferred from
  /// @param _fromTokenId The token the token is transferred from
  /// @param _tokenId The token that is transferred  
  event TransferFromParent(
    address indexed _fromContract, 
    uint256 indexed _fromTokenId, 
    uint256 _tokenId
  );
  
  /// @notice Get the root owner of tokenId.
  /// @param _tokenId The token to query for a root owner address
  /// @return rootOwner The root owner at the top of tree of tokens and ERC-998 magic value.
  function rootOwnerOf(uint256 _tokenId) external view returns (bytes32 rootOwner);

  /// @notice Get the owner address and parent token (if there is one) of a token
  /// @param _tokenId The tokenId to query.
  /// @return tokenOwner The owner address of the token
  /// @return parentTokenId The parent owner of the token and ERC-998 magic value
  /// @return isParent True if parentTokenId is a valid parent tokenId and false if there is no parent tokenId
  function tokenOwnerOf(
    uint256 _tokenId
  )
    external 
    view
    returns (
      bytes32 tokenOwner, 
      uint256 parentTokenId, 
      bool isParent
    );
 
  /// @notice Transfer token from owner address to a token
  /// @param _from The owner address
  /// @param _toContract The ERC-721 contract of the receiving token
  /// @param _toToken The receiving token
  /// @param _data Additional data with no specified format
  function transferToParent(
    address _from, 
    address _toContract, 
    uint256 _toTokenId, 
    uint256 _tokenId, 
    bytes _data
  )
    external;
   
  /// @notice Transfer token from a token to an address
  /// @param _fromContract The address of the owning contract
  /// @param _fromTokenId The owning token
  /// @param _to The address the token is transferred to.
  /// @param _tokenId The token that is transferred
  /// @param _data Additional data with no specified format
  function transferFromParent(
    address _fromContract, 
    uint256 _fromTokenId, 
    address _to, 
    uint256 _tokenId, 
    bytes _data
  )
    external;
  
  /// @notice Transfer a token from a token to another token
  /// @param _fromContract The address of the owning contract
  /// @param _fromTokenId The owning token
  /// @param _toContract The ERC-721 contract of the receiving token
  /// @param _toToken The receiving token
  /// @param _tokenId The token that is transferred
  /// @param _data Additional data with no specified format
  function transferAsChild(
    address _fromContract, 
    uint256 _fromTokenId, 
    address _toContract, 
    uint256 _toTokenId, 
    uint256 _tokenId, 
    bytes _data
  )
    external;
}

function rootOwnerOf(uint256 _tokenId) public view returns (bytes32 rootOwner);

this.rootOwnerOf.selector ^ this.rootOwnerOfChild.selector ^ 
this.tokenOwnerOf.selector ^ this.ownerOfChild.selector;

function tokenOwnerOf(uint256 _tokenId) external view returns (bytes32 tokenOwner, uint256 parentTokenId, bool isParent);

function transferToParent(address _from, address _toContract, uint256 _toTokenId, uint256 _tokenId, bytes _data) external;

function transferFromParent(address _fromContract, uint256 _fromTokenId, address _to, uint256 _tokenId, bytes _data) external;

function transferAsChild(address _fromContract, uint256 _fromTokenId, address _toContract, uint256 _toTokenId, uint256 _tokenId, bytes _data) external;

/// @dev The ERC-165 identifier for this interface is 0x8318b539
interface ERC998ERC721BottomUpEnumerable {
  
  /// @notice Get the number of ERC-721 tokens owned by parent token.
  /// @param _parentContract The contract the parent ERC-721 token is from.
  /// @param _parentTokenId The parent tokenId that owns tokens
  //  @return uint256 The number of ERC-721 tokens owned by parent token.
  function totalChildTokens(
    address _parentContract, 
    uint256 _parentTokenId
  ) 
    external 
    view 
    returns (uint256);
  
  /// @notice Get a child token by index
  /// @param _parentContract The contract the parent ERC-721 token is from.
  /// @param _parentTokenId The parent tokenId that owns the token
  /// @param _index The index position of the child token
  /// @return uint256 The child tokenId owned by the parent token
  function childTokenByIndex(
    address _parentContract, 
    uint256 _parentTokenId, 
    uint256 _index
  ) 
    external 
    view 
    returns (uint256);
}

/// @dev This mapping tracks standard ERC20/`ERC-223` ownership, where an address owns
///  a particular amount of tokens.
mapping(address => uint) userBalances;

/// @dev This additional mapping tracks ERC-998 ownership, where an ERC-721 token owns
///  a particular amount of tokens. This tracks contractAddres => tokenId => balance
mapping(address => mapping(uint => uint)) nftBalances;

/// @title `ERC998ERC20` Bottom-Up Composable Fungible Token
/// @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-998.md
/// Note: The ERC-165 identifier for this interface is 0xffafa991
interface ERC998ERC20BottomUp {
  
  /// @dev This emits when a token is transferred to an ERC-721 token
  /// @param _toContract The contract the token is transferred to
  /// @param _toTokenId The token the token is transferred to
  /// @param _amount The amount of tokens transferred
  event TransferToParent(
    address indexed _toContract, 
    uint256 indexed _toTokenId, 
    uint256 _amount
  );

  /// @dev This emits when a token is transferred from an ERC-721 token
  /// @param _fromContract The contract the token is transferred from
  /// @param _fromTokenId The token the token is transferred from
  /// @param _amount The amount of tokens transferred
  event TransferFromParent(
    address indexed _fromContract, 
    uint256 indexed _fromTokenId, 
    uint256 _amount
  );

  /// @notice Get the balance of a non-fungible parent token
  /// @param _tokenContract The contract tracking the parent token
  /// @param _tokenId The ID of the parent token
  /// @return amount The balance of the token
  function balanceOfToken(
    address _tokenContract, 
    uint256 _tokenId
  )
    external
    view
    returns (uint256 amount);

  /// @notice Transfer tokens from owner address to a token
  /// @param _from The owner address
  /// @param _toContract The ERC-721 contract of the receiving token
  /// @param _toToken The receiving token
  /// @param _amount The amount of tokens to transfer
  function transferToParent(
    address _from, 
    address _toContract, 
    uint256 _toTokenId, 
    uint256 _amount
  )
    external;

  /// @notice Transfer token from a token to an address
  /// @param _fromContract The address of the owning contract
  /// @param _fromTokenId The owning token
  /// @param _to The address the token is transferred to
  /// @param _amount The amount of tokens to transfer
  function transferFromParent(
    address _fromContract, 
    uint256 _fromTokenId, 
    address _to, 
    uint256 _amount
  )
    external;

  /// @notice Transfer token from a token to an address, using `ERC-223` semantics
  /// @param _fromContract The address of the owning contract
  /// @param _fromTokenId The owning token
  /// @param _to The address the token is transferred to
  /// @param _amount The amount of tokens to transfer
  /// @param _data Additional data with no specified format, can be used to specify the sender tokenId
  function transferFromParentERC223(
    address _fromContract, 
    uint256 _fromTokenId, 
    address _to, 
    uint256 _amount, 
    bytes _data
  )
    external;

  /// @notice Transfer a token from a token to another token
  /// @param _fromContract The address of the owning contract
  /// @param _fromTokenId The owning token
  /// @param _toContract The ERC-721 contract of the receiving token
  /// @param _toToken The receiving token
  /// @param _amount The amount tokens to transfer
  function transferAsChild(
    address _fromContract, 
    uint256 _fromTokenId, 
    address _toContract, 
    uint256 _toTokenId, 
    uint256 _amount
   )
    external;
}

function balanceOfToken(address _tokenContract, uint256 _tokenId) external view returns (uint256 amount);

function transferToParent(address _from, address _toContract, uint256 _toTokenId, uint256 _amount) external;

function transferFromParent(address _fromContract, uint256 _fromTokenId, address _to, uint256 _amount) external;

function transferFromParentERC223(address _fromContract, uint256 _fromTokenId, address _to, uint256 _amount, bytes _data) external;

function transferAsChild(address _fromContract, uint256 _fromTokenId, address _toContract, uint256 _toTokenId, uint256 _amount) external;