// DeviceGroup protocol for p≡p

 // Copyleft (c) 2016, p≡p foundation

 // Written by Volker Birk

 include ./fsm.yml2

 protocol DeviceGroup {

     // all messages have a timestamp, time out and are removed after timeout

     broadcast sendBeacon;

     unencrypted sendBeacon;

     fsm DeviceState filename=sync {

         condition storedGroupKeys();

         condition keyElectionWon(Identity partner);

         state InitState {

             on Init {

                 if storedGroupKeys()

                     go Grouped;

                 go Sole;

             }

         }

         state Sole {

             on KeyGen // injected by generate_keypair()

                 do sendBeacon;

             on CannotDecrypt

                 do sendBeacon;  // cry, baby

             on Beacon(Identity partner) // this event will not happen for already

                                         // rejected partners

                 do sendHandshakeRequest(partner);

             on HandshakeRequest(Identity partner) {

                 do sendHandshakeRequest(partner);

                 go HandshakingSole(partner);

             }

         }

         state HandshakingSole(Identity partner) {

             on Init

                 do showHandshake(partner);

             on HandshakeRejected(Identity partner) {

                 do rejectHandshake(partner);             // stores rejection of partner

                 go Sole;

             }

             on HandshakeAccepted(Identity partner) {

                 do acceptHandshake(partner); 

                 if keyElectionWon(partner) {    // an already existing group

                                                 // always wins

                     do sendGroupKeys(partner);

                     go Grouped;

                 }

                 go WaitForGroupKeysSole(Identity partner);

             }

         }

         state WaitForGroupKeysSole(Identity partner) {

             on GroupKeys(Identity partner, Stringlist keys) {

                 do storeGroupKeys(partner, keys);

                 // TODO : add a callback to signal finished waiting for group keys

                 go Grouped;

             }

             on Cancel go Sole;

             on Reject(Identity partner) {

                 do rejectHandshake(partner);

                 go Sole;

             }

         }

         state Grouped {

             on KeyGen

                 do sendGroupKeys; // always send all keys

             on Beacon(Identity partner)

                 do sendHandshakeRequest(partner);

             on HandshakeRequest(Identity partner) {

                 do sendHandshakeRequest(partner);

                 go HandshakingGrouped(partner);

             }

         }

         state HandshakingGrouped(Identity partner) {

             on Init

                 do showHandshake(partner);

             on HandshakeRejected(Identity partner) {

                 do rejectHandshake(partner);             // stores rejection of partner

                 go Grouped;

             }

             on HandshakeAccepted(Identity partner) {

                 do acceptHandshake(partner); 

                 // an already existing group always wins

                 do sendGroupKeys(partner);

                 go Grouped;

             }

         }

         tag Init 1;

         tag Beacon 2;

         tag HandshakeRequest 3;

         tag GroupKeys 4;

     }

 }