First implementation of redux-trigger middleware.

This is the first trial of an implementation for the redux-trigger
concept. It relies on adding triggers that stay resident until you
explicitly remove them.

Things I've learned from this approach:
* It's really risky to leave a trigger after it fires.
  - Because it's likely to trigger again on the same state unless you do
    something.
  - It leaves the responsibility to the trigger to remove itself.
  - Triggers can be a performance hit because they run every time the
    state changes.

To this end, the next update will move triggers to be temporary and
one-time use only.

Author: coderkevin

src/index.js

@@ -0,0 +1,95 @@
+
+const REDUX_TRIGGER_ADD = 'REDUX_TRIGGER_ADD';
+const REDUX_TRIGGER_REMOVE = 'REDUX_TRIGGER_REMOVE';
+
+/**
+ * Middleware creator.
+ */
+function createTriggerMiddleware() {
+	let triggers = [];
+
+	return ( store ) => ( next ) => ( action ) => {
+		switch ( action.type ) {
+			case REDUX_TRIGGER_ADD:
+				triggers.unshift( action.payload );
+
+				console.log("** redux-trigger add! **");
+				console.log( triggers );
+				return true;
+			case REDUX_TRIGGER_REMOVE:
+				triggers.splice( triggers.indexOf( action.payload ), 1 );
+
+				console.log("** redux-trigger remove! **");
+				console.log( triggers );
+				return true;
+			default:
+				let res = next( action );
+				checkTriggers( store, triggers );
+				return res;
+		}
+	}
+}
+
+function checkTriggers( store, triggers ) {
+	for ( let index = triggers.length - 1; index >= 0; index-- ) {
+		let trigger = triggers[ index ];
+		let match = trigger.matcher( store.getState() );
+
+		if ( match ) {
+			// Remove the trigger first, so it doesn't get run again.
+			triggers.splice( index, 1 );
+
+			// Then dispatch the trigger's action.
+			let action = trigger.actionCreator( match );
+			store.dispatch( action );
+		}
+	}
+}
+
+
+/**
+ * Convenience function to create a trigger object.
+ *
+ * @param Function matcher ( state )
+ * 	return match object when trigger should fire, or null if no match.
+ * @param Function actionCreator ( match )
+ *  create action using match object.
+ * @return Object The trigger object.
+ */
+export function createTrigger( matcher, actionCreator ) {
+	return {
+		matcher,
+		actionCreator
+	};
+}
+
+/**
+ * Trigger add action creator.
+ *
+ * @param Object trigger
+ *   The trigger object to be added. Must be in the format:
+ *   { matcher, actionCreator }
+ * @return Object The trigger action to be dispatched.
+ */
+export function addTrigger( trigger ) {
+	return {
+		type: REDUX_TRIGGER_ADD,
+		payload: trigger
+	};
+}
+
+/**
+ * Trigger remove action creator.
+ *
+ * @param Object trigger The trigger object to be removed.
+ * @return Object The trigger action to be dispatched.
+ */
+export function removeTrigger( trigger ) {
+	return {
+		type: REDUX_TRIGGER_REMOVE,
+		payload: trigger
+	};
+}
+
+export default createTriggerMiddleware;
+