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pragma solidity ^0.5.2;
import "./IERC721Enumerable.sol";
import "./ERC721.sol";
import "../../introspection/ERC165.sol";
/**
* @title ERC-721 Non-Fungible Token with optional enumeration extension logic
* @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
contract ERC721Enumerable is ERC165, ERC721, IERC721Enumerable {
// Mapping from owner to list of owned token IDs
mapping(address => uint256[]) private _ownedTokens;
// Mapping from token ID to index of the owner tokens list
mapping(uint256 => uint256) private _ownedTokensIndex;
// Array with all token ids, used for enumeration
uint256[] private _allTokens;
// Mapping from token id to position in the allTokens array
mapping(uint256 => uint256) private _allTokensIndex;
bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;
/*
* 0x780e9d63 ===
* bytes4(keccak256('totalSupply()')) ^
* bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) ^
* bytes4(keccak256('tokenByIndex(uint256)'))
*/
/**
* @dev Constructor function
*/
constructor () public {
// register the supported interface to conform to ERC721 via ERC165
_registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
}
/**
* @dev Gets the token ID at a given index of the tokens list of the requested owner
* @param owner address owning the tokens list to be accessed
* @param index uint256 representing the index to be accessed of the requested tokens list
* @return uint256 token ID at the given index of the tokens list owned by the requested address
*/
function tokenOfOwnerByIndex(address owner, uint256 index) public view returns (uint256) {
require(index < balanceOf(owner));
return _ownedTokens[owner][index];
}
/**
* @dev Gets the total amount of tokens stored by the contract
* @return uint256 representing the total amount of tokens
*/
function totalSupply() public view returns (uint256) {
return _allTokens.length;
}
/**
* @dev Gets the token ID at a given index of all the tokens in this contract
* Reverts if the index is greater or equal to the total number of tokens
* @param index uint256 representing the index to be accessed of the tokens list
* @return uint256 token ID at the given index of the tokens list
*/
function tokenByIndex(uint256 index) public view returns (uint256) {
require(index < totalSupply());
return _allTokens[index];
}
/**
* @dev Internal function to transfer ownership of a given token ID to another address.
* As opposed to transferFrom, this imposes no restrictions on msg.sender.
* @param from current owner of the token
* @param to address to receive the ownership of the given token ID
* @param tokenId uint256 ID of the token to be transferred
*/
function _transferFrom(address from, address to, uint256 tokenId) internal {
super._transferFrom(from, to, tokenId);
_removeTokenFromOwnerEnumeration(from, tokenId);
_addTokenToOwnerEnumeration(to, tokenId);
}
/**
* @dev Internal function to mint a new token
* Reverts if the given token ID already exists
* @param to address the beneficiary that will own the minted token
* @param tokenId uint256 ID of the token to be minted
*/
function _mint(address to, uint256 tokenId) internal {
super._mint(to, tokenId);
_addTokenToOwnerEnumeration(to, tokenId);
_addTokenToAllTokensEnumeration(tokenId);
}
/**
* @dev Internal function to burn a specific token
* Reverts if the token does not exist
* Deprecated, use _burn(uint256) instead
* @param owner owner of the token to burn
* @param tokenId uint256 ID of the token being burned
*/
function _burn(address owner, uint256 tokenId) internal {
super._burn(owner, tokenId);
_removeTokenFromOwnerEnumeration(owner, tokenId);
// Since tokenId will be deleted, we can clear its slot in _ownedTokensIndex to trigger a gas refund
_ownedTokensIndex[tokenId] = 0;
_removeTokenFromAllTokensEnumeration(tokenId);
}
/**
* @dev Gets the list of token IDs of the requested owner
* @param owner address owning the tokens
* @return uint256[] List of token IDs owned by the requested address
*/
function _tokensOfOwner(address owner) internal view returns (uint256[] storage) {
return _ownedTokens[owner];
}
/**
* @dev Private function to add a token to this extension's ownership-tracking data structures.
* @param to address representing the new owner of the given token ID
* @param tokenId uint256 ID of the token to be added to the tokens list of the given address
*/
function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
_ownedTokensIndex[tokenId] = _ownedTokens[to].length;
_ownedTokens[to].push(tokenId);
}
/**
* @dev Private function to add a token to this extension's token tracking data structures.
* @param tokenId uint256 ID of the token to be added to the tokens list
*/
function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
_allTokensIndex[tokenId] = _allTokens.length;
_allTokens.push(tokenId);
}
/**
* @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
* while the token is not assigned a new owner, the _ownedTokensIndex mapping is _not_ updated: this allows for
* gas optimizations e.g. when performing a transfer operation (avoiding double writes).
* This has O(1) time complexity, but alters the order of the _ownedTokens array.
* @param from address representing the previous owner of the given token ID
* @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
*/
function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
// To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
// then delete the last slot (swap and pop).
uint256 lastTokenIndex = _ownedTokens[from].length.sub(1);
uint256 tokenIndex = _ownedTokensIndex[tokenId];
// When the token to delete is the last token, the swap operation is unnecessary
if (tokenIndex != lastTokenIndex) {
uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];
_ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
_ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
}
// This also deletes the contents at the last position of the array
_ownedTokens[from].length--;
// Note that _ownedTokensIndex[tokenId] hasn't been cleared: it still points to the old slot (now occcupied by
// lasTokenId, or just over the end of the array if the token was the last one).
}
/**
* @dev Private function to remove a token from this extension's token tracking data structures.
* This has O(1) time complexity, but alters the order of the _allTokens array.
* @param tokenId uint256 ID of the token to be removed from the tokens list
*/
function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
// To prevent a gap in the tokens array, we store the last token in the index of the token to delete, and
// then delete the last slot (swap and pop).
uint256 lastTokenIndex = _allTokens.length.sub(1);
uint256 tokenIndex = _allTokensIndex[tokenId];
// When the token to delete is the last token, the swap operation is unnecessary. However, since this occurs so
// rarely (when the last minted token is burnt) that we still do the swap here to avoid the gas cost of adding
// an 'if' statement (like in _removeTokenFromOwnerEnumeration)
uint256 lastTokenId = _allTokens[lastTokenIndex];
_allTokens[tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
_allTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
// This also deletes the contents at the last position of the array
_allTokens.length--;
_allTokensIndex[tokenId] = 0;
}
}