contract ERC1155 is IERC1155, ERC165, CommonConstants
{
    using SafeMath for uint256;
    using Address for address;

    // id => (owner => balance)
    mapping (uint256 => mapping(address => uint256)) internal balances;

    // owner => (operator => approved)
    mapping (address => mapping(address => bool)) internal operatorApproval;

/////////////////////////////////////////// ERC165 //////////////////////////////////////////////

    /*
        bytes4(keccak256("safeTransferFrom(address,address,uint256,uint256,bytes)")) ^
        bytes4(keccak256("safeBatchTransferFrom(address,address,uint256[],uint256[],bytes)")) ^
        bytes4(keccak256("balanceOf(address,uint256)")) ^
        bytes4(keccak256("balanceOfBatch(address[],uint256[])")) ^
        bytes4(keccak256("setApprovalForAll(address,bool)")) ^
        bytes4(keccak256("isApprovedForAll(address,address)"));
    */
    bytes4 constant private INTERFACE_SIGNATURE_ERC1155 = 0xd9b67a26;

/////////////////////////////////////////// CONSTRUCTOR //////////////////////////////////////////

    constructor() public {
        _registerInterface(INTERFACE_SIGNATURE_ERC1155);
    }

/////////////////////////////////////////// ERC1155 //////////////////////////////////////////////

    /**
        @notice Transfers `_value` amount of an `_id` from the `_from` address to the `_to` address specified (with safety call).
        @dev Caller must be approved to manage the tokens being transferred out of the `_from` account (see "Approval" section of the standard).
        MUST revert if `_to` is the zero address.
        MUST revert if balance of holder for token `_id` is lower than the `_value` sent.
        MUST revert on any other error.
        MUST emit the `TransferSingle` event to reflect the balance change (see "Safe Transfer Rules" section of the standard).
        After the above conditions are met, this function MUST check if `_to` is a smart contract (e.g. code size > 0). If so, it MUST call `onERC1155Received` on `_to` and act appropriately (see "Safe Transfer Rules" section of the standard).
        @param _from    Source address
        @param _to      Target address
        @param _id      ID of the token type
        @param _value   Transfer amount
        @param _data    Additional data with no specified format, MUST be sent unaltered in call to `onERC1155Received` on `_to`
    */
    function safeTransferFrom(address _from, address _to, uint256 _id, uint256 _value, bytes calldata _data) external {

        require(_to != address(0x0), "_to must be non-zero.");
        require(_from == msg.sender || operatorApproval[_from][msg.sender] == true, "Need operator approval for 3rd party transfers.");

        // SafeMath will throw with insuficient funds _from
        // or if _id is not valid (balance will be 0)
        balances[_id][_from] = balances[_id][_from].sub(_value);
        balances[_id][_to]   = _value.add(balances[_id][_to]);

        // MUST emit event
        emit TransferSingle(msg.sender, _from, _to, _id, _value);

        // Now that the balance is updated and the event was emitted,
        // call onERC1155Received if the destination is a contract.
        if (_to.isContract()) {
            _doSafeTransferAcceptanceCheck(msg.sender, _from, _to, _id, _value, _data);
        }
    }

    /**
        @notice Transfers `_values` amount(s) of `_ids` from the `_from` address to the `_to` address specified (with safety call).
        @dev Caller must be approved to manage the tokens being transferred out of the `_from` account (see "Approval" section of the standard).
        MUST revert if `_to` is the zero address.
        MUST revert if length of `_ids` is not the same as length of `_values`.
        MUST revert if any of the balance(s) of the holder(s) for token(s) in `_ids` is lower than the respective amount(s) in `_values` sent to the recipient.
        MUST revert on any other error.
        MUST emit `TransferSingle` or `TransferBatch` event(s) such that all the balance changes are reflected (see "Safe Transfer Rules" section of the standard).
        Balance changes and events MUST follow the ordering of the arrays (_ids[0]/_values[0] before _ids[1]/_values[1], etc).
        After the above conditions for the transfer(s) in the batch are met, this function MUST check if `_to` is a smart contract (e.g. code size > 0). If so, it MUST call the relevant `ERC1155TokenReceiver` hook(s) on `_to` and act appropriately (see "Safe Transfer Rules" section of the standard).
        @param _from    Source address
        @param _to      Target address
        @param _ids     IDs of each token type (order and length must match _values array)
        @param _values  Transfer amounts per token type (order and length must match _ids array)
        @param _data    Additional data with no specified format, MUST be sent unaltered in call to the `ERC1155TokenReceiver` hook(s) on `_to`
    */
    function safeBatchTransferFrom(address _from, address _to, uint256[] calldata _ids, uint256[] calldata _values, bytes calldata _data) external {

        // MUST Throw on errors
        require(_to != address(0x0), "destination address must be non-zero.");
        require(_ids.length == _values.length, "_ids and _values array lenght must match.");
        require(_from == msg.sender || operatorApproval[_from][msg.sender] == true, "Need operator approval for 3rd party transfers.");

        for (uint256 i = 0; i < _ids.length; ++i) {
            uint256 id = _ids[i];
            uint256 value = _values[i];

            // SafeMath will throw with insuficient funds _from
            // or if _id is not valid (balance will be 0)
            balances[id][_from] = balances[id][_from].sub(value);
            balances[id][_to]   = value.add(balances[id][_to]);
        }

        // Note: instead of the below batch versions of event and acceptance check you MAY have emitted a TransferSingle
        // event and a subsequent call to _doSafeTransferAcceptanceCheck in above loop for each balance change instead.
        // Or emitted a TransferSingle event for each in the loop and then the single _doSafeBatchTransferAcceptanceCheck below.
        // However it is implemented the balance changes and events MUST match when a check (i.e. calling an external contract) is done.

        // MUST emit event
        emit TransferBatch(msg.sender, _from, _to, _ids, _values);

        // Now that the balances are updated and the events are emitted,
        // call onERC1155BatchReceived if the destination is a contract.
        if (_to.isContract()) {
            _doSafeBatchTransferAcceptanceCheck(msg.sender, _from, _to, _ids, _values, _data);
        }
    }

    /**
        @notice Get the balance of an account's Tokens.
        @param _owner  The address of the token holder
        @param _id     ID of the Token
        @return        The _owner's balance of the Token type requested
     */
    function balanceOf(address _owner, uint256 _id) external view returns (uint256) {
        // The balance of any account can be calculated from the Transfer events history.
        // However, since we need to keep the balances to validate transfer request,
        // there is no extra cost to also privide a querry function.
        return balances[_id][_owner];
    }


    /**
        @notice Get the balance of multiple account/token pairs
        @param _owners The addresses of the token holders
        @param _ids    ID of the Tokens
        @return        The _owner's balance of the Token types requested (i.e. balance for each (owner, id) pair)
     */
    function balanceOfBatch(address[] calldata _owners, uint256[] calldata _ids) external view returns (uint256[] memory) {

        require(_owners.length == _ids.length);

        uint256[] memory balances_ = new uint256[](_owners.length);

        for (uint256 i = 0; i < _owners.length; ++i) {
            balances_[i] = balances[_ids[i]][_owners[i]];
        }

        return balances_;
    }

    /**
        @notice Enable or disable approval for a third party ("operator") to manage all of the caller's tokens.
        @dev MUST emit the ApprovalForAll event on success.
        @param _operator  Address to add to the set of authorized operators
        @param _approved  True if the operator is approved, false to revoke approval
    */
    function setApprovalForAll(address _operator, bool _approved) external {
        operatorApproval[msg.sender][_operator] = _approved;
        emit ApprovalForAll(msg.sender, _operator, _approved);
    }

    /**
        @notice Queries the approval status of an operator for a given owner.
        @param _owner     The owner of the Tokens
        @param _operator  Address of authorized operator
        @return           True if the operator is approved, false if not
    */
    function isApprovedForAll(address _owner, address _operator) external view returns (bool) {
        return operatorApproval[_owner][_operator];
    }

/////////////////////////////////////////// Internal //////////////////////////////////////////////

    function _doSafeTransferAcceptanceCheck(address _operator, address _from, address _to, uint256 _id, uint256 _value, bytes memory _data) internal {

        // If this was a hybrid standards solution you would have to check ERC165(_to).supportsInterface(0x4e2312e0) here but as this is a pure implementation of an ERC-1155 token set as recommended by
        // the standard, it is not necessary. The below should revert in all failure cases i.e. _to isn't a receiver, or it is and either returns an unknown value or it reverts in the call to indicate non-acceptance.


        // Note: if the below reverts in the onERC1155Received function of the _to address you will have an undefined revert reason returned rather than the one in the require test.
        // If you want predictable revert reasons consider using low level _to.call() style instead so the revert does not bubble up and you can revert yourself on the ERC1155_ACCEPTED test.
        require(ERC1155TokenReceiver(_to).onERC1155Received(_operator, _from, _id, _value, _data) == ERC1155_ACCEPTED, "contract returned an unknown value from onERC1155Received");
    }

    function _doSafeBatchTransferAcceptanceCheck(address _operator, address _from, address _to, uint256[] memory _ids, uint256[] memory _values, bytes memory _data) internal {

        // If this was a hybrid standards solution you would have to check ERC165(_to).supportsInterface(0x4e2312e0) here but as this is a pure implementation of an ERC-1155 token set as recommended by
        // the standard, it is not necessary. The below should revert in all failure cases i.e. _to isn't a receiver, or it is and either returns an unknown value or it reverts in the call to indicate non-acceptance.

        // Note: if the below reverts in the onERC1155BatchReceived function of the _to address you will have an undefined revert reason returned rather than the one in the require test.
        // If you want predictable revert reasons consider using low level _to.call() style instead so the revert does not bubble up and you can revert yourself on the ERC1155_BATCH_ACCEPTED test.
        require(ERC1155TokenReceiver(_to).onERC1155BatchReceived(_operator, _from, _ids, _values, _data) == ERC1155_BATCH_ACCEPTED, "contract returned an unknown value from onERC1155BatchReceived");
    }
}
// A sample implementation of core ERC1155 function.
function safeTransferFrom(address _from, address _to, uint256 _id, uint256 _value, bytes calldata _data) external {

        require(_to != address(0x0), "_to must be non-zero.");
        require(_from == msg.sender || operatorApproval[_from][msg.sender] == true, "Need operator approval for 3rd party transfers.");

        // SafeMath will throw with insuficient funds _from
        // or if _id is not valid (balance will be 0)
        balances[_id][_from] = balances[_id][_from].sub(_value);
        balances[_id][_to]   = _value.add(balances[_id][_to]);

        // MUST emit event
        emit TransferSingle(msg.sender, _from, _to, _id, _value);

        // Now that the balance is updated and the event was emitted,
        // call onERC1155Received if the destination is a contract.
        if (_to.isContract()) {
            _doSafeTransferAcceptanceCheck(msg.sender, _from, _to, _id, _value, _data);
        }
    }
/**
 @notice Transfers `_value` amount of an `_id` from the `_from` address to the `_to` address specified (with safety call).
 @dev Caller must be approved to manage the tokens being transferred out of the `_from` account (see "Approval" section of the standard).
 MUST revert if `_to` is the zero address.
 MUST revert if balance of holder for token `_id` is lower than the `_value` sent.
 MUST revert on any other error.
 MUST emit the `TransferSingle` event to reflect the balance change (see "Safe Transfer Rules" section of the standard).
 After the above conditions are met, this function MUST check if `_to` is a smart contract (e.g. code size > 0). If so, it MUST call `onERC1155Received` on `_to` and act appropriately (see "Safe Transfer Rules" section of the standard).
 @param _from    Source address
 @param _to      Target address
 @param _id      ID of the token type
 @param _value   Transfer amount
 @param _data    Additional data with no specified format, MUST be sent unaltered in call to `onERC1155Received` on `_to`
 */