Docket
Docket uses postal, a node.js event bus and a javascript finite state machine to show how simple event pattern matching can work using state machines. The state machine changes are animated in the browser using D3.
A series of items are added to an imaginary shopping basket. As the state machine checks each one (coffee, sugar, dog food, etc.) it's looking for clues that it's Christmas (a complex event, implied by other events).
The state changes that trigger the state machine are the appearance of party crackers, sprouts and mince pies (in any order). As each trigger product is seen in the basket the state of the machine changes until the final one appears which triggers the "it's Christmas" event. Any other products have no effect on the state machine and the appearance of the same product more than once (mince pies followed by mince pies) simply causes the state machine to remain in the same state.
The demo can easily be updated to represent other simple and complex events or modified to represent typical christmas purchases in other countries.
To run the demo download the repository:
git clone https://github.com/julianbrowne/docket.git
(all npm package dependencies are included)
And run it
node docket
The console output should look like this:
Starting HTTP server
Starting WS server on 9000
Waiting for browser to connect at http://127.0.0.1:9000
Browser connected
listening to sales / new
Sold - 1 bottles of olive oil
Sold - 2 loaves of bread
Sold - 1 packs of butter
Sold - 1 litres of fabric conditioner
Sold - 3 grams of cheese
Sold - 1 boxes of crackers << state change
Sold - 1 jars of coffee
Sold - 2 lbs of rice
Sold - 2 bottles of port
Sold - 3 packets of mince pies << state change
Sold - 1 whole of chicken
Sold - 2 bottles of milk
Sold - 1 cans of air freshener
Sold - 2 packets of twiglets
Sold - 5 lbs of potatoes
Sold - 4 boxes of chocolate orange
Sold - 1 bottles of washing-up liquid
Sold - 1 whole of goose
Sold - 1 bottles of mulled wine
Sold - 1 lbs of brocolli
Sold - 2 lbs of sugar
Sold - 4 lbs of sprouts << state change
Woot - It's Christmas! << complex event matched
Sold - 3 packets of kitchen roll
Sold - 1 lbs of tea
Sold - 4 cans of dog food
Each sales event published to the bus is also emitted on a "sale" channel on a websocket. Connecting the browser to http://127.0.0.1:9000 will load a page to watch these.
Similarly, for each state change, a web socket message is pushed on the "state-change" channel. This is used in the html page to animate a D3 state machine diagram showing the matching progress.
