Architecture

The Big Picture

Actors

When a user invokes an action on a Fismo machine, they must do so through that machine’s configured Operator contract.
Rules about who can interact with a given machine can be enforced at this level.
To let any user interact with the machine, simply pass through the invokeAction call with no checks.
To target only holders of a given token, verify ownership first, reverting for non-holders.
Deployed operator contracts can be reused between machines where the access control logic is suitable.

The Fismo contract’s owner is set at deployment time.
Privileged operations such as adding or updating machines, states, and transitions can only be performed by the contract’s owner.
Storage shared with Guards.
Anyone can call view functions to check things like a user’s current state in a given machine.
When a user invokes an action on a Fismo machine via an Operator, the state transition can be performed automatically if valid and unguarded.

When Fismo is performing a state transition and finds that either the current state has an exit guard or the next state has an entrance guard, then the Guard contracts become involved.
Fismo delegates a call to a deterministcally defined function on the configured guard logic contract for the state in question.
The name of the function is composed of the machine name, the state name, and the guard direction, i.e., exit, enter.
Guard functions can revert to stop the transition or return a success message.