state-action style for force-move

state-action-style-game.sol

pragma solidity ^0.5.2;
pragma experimental ABIEncoderV2;

import "fmg-core/contracts/Commitment.sol";

library StateActionStyle {
  using Commitment for Commitment.CommitmentStruct;

  struct StateActionAttributes {
    address stateActionLibrary;
    bytes methodName;
    bytes actionData;
    bytes stateData;
  }

  function validTransition(Commitment memory state1, Commitment memory state2) external pure returns (bool) {
    StateActionAttributes memory attrs1 = abi.decode(state1.appAttributes, (StateActionAttributes));
    StateActionAttributes memory attrs2 = abi.decode(state2.appAttributes, (StateActionAttributes));

    require(attrs1.stateActionLibrary == attrs2.stateActionLibrary, "App definition must not change");

    // call stateAction.methodName(stateData, actionData) => n
    bytes calculatedStateData = static_call_magic(attrs2.stateActionLibrary, attrs2.methodName, attrs1.stateData, attrs2.actionData);

    require(hash(calculatedStateData) == hash(attrs2.stateData), "Action must be correctly applied");
  }
}