This contract is a correct implementation of an ERC1155 token. It is mostly copied from @openzeppelin's implementation, but with slight modifications to URI related items. Firstly, this implementation allows querying different URI's for specific tokenIds, Openzeppelin only allowed a single stored URI. Secondly, this implementation emits an event whenever a URI is updated. For some reason Openzeppelin left this functionality out of there implementation entirely, even though the EIP defining the token standard clearly states that changing the URI MUST emit the URI() event.
<3 Belvis