tz payment channel contract

channel.tz

parameter (pair mutez signature);
storage
  (pair :storage
     (or :status %status (unit %Open) (unit %Closed))
     (pair (key %signingKey) (pair (key %sender2) (key %recipient))));
code { DUP ;
       DIP { CDR @storage_slash_1 } ;
       CAR @action_slash_2 ;
       DUP @action ;
       DUP ;
       CAR @value ;
       DUP @value ;
       PACK @bytes ;
       DUUUP ;
       CDR @signature2 ;
       DUUUUUUP @storage ;
       CDAR %signingKey ;
       CHECK_SIGNATURE ;
       NOT ;
       IF { PUSH string "Invalid signature" ; FAILWITH } { UNIT } ;
       DROP ;
       DUUUUP @storage ;
       CDDAR %sender2 ;
       HASH_KEY ;
       IMPLICIT_ACCOUNT ;
       DUUP @value ;
       UNIT ;
       TRANSFER_TOKENS @senderTransfer ;
       DUUUUUP @storage ;
       CDDDR %recipient ;
       HASH_KEY ;
       IMPLICIT_ACCOUNT ;
       DUUUP @value ;
       BALANCE ;
       SUB ;
       UNIT ;
       TRANSFER_TOKENS @recipientTransfer ;
       DUUUUUUP @storage ;
       NIL operation ;
       DUUUP @recipientTransfer ;
       DIIIP { DROP } ;
       DIIIIP { DROP ; DROP ; DROP ; DROP } ;
       CONS ;
       DUUUP ;
       DIIIP { DROP } ;
       CONS ;
       PAIR };