index.js

const fs = require("fs");
const { Tail } = require("tail");
const { EventEmitter } = require("events");

const JSON_FILE = "./theFile.json";

const controller = new EventEmitter();
const Services = {};

// controller.on("test", payload => console.log(`This is a test: ${payload}`));
// controller.emit("test", "is this thing on?");

// Register Trigger
controller.on("jsonFile:newLine", function(payload) {
  const found = recipeList.filter(
    ({ trigger: { service, name } }) =>
      service === "jsonFile" && name === "newLine"
  );
  // console.log({ found });
  // Find all matching recipes
  found.forEach(({ action, trigger }) => {
    const actionService = Services[action.service];
    const actionMethod = actionService[action.method];
    actionMethod({ action, trigger, payload });
  });
});

const recipeList = [
  {
    user: "sure!",
    trigger: {
      service: "jsonFile",
      name: "newLine"
    },
    action: {
      service: "console",
      method: "log",
      payload: { message: "line" }
    }
  }
];

// Trigger setup, ingest
// could be a server route
const theFile = new Tail(JSON_FILE);
theFile.on("line", data => {
  console.log("yo update");
  controller.emit("jsonFile:newLine", { line: data });
});
theFile.on("error", err => console.log(err));
// Services.jsonFile = theFile;

// Action setup
const consoleService = {
  log: ({ action, trigger, payload }) => {
    // prolly shouldnt interpolate so late in the pipeline
    const interpolatedMessage = payload[action.payload.message];
    // logging to console is the final action
    console.log(interpolatedMessage);
  }
};
Services.console = consoleService;