05-optimizing-runtime-with-fact-priorities.js

'use strict'
/*
 * This is an advanced example that demonstrates using fact priorities to optimize the rules engine.
 *
 * Usage:
 *   node ./examples/05-optimizing-runtime-with-fact-priorities.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/05-optimizing-runtime-with-fact-priorities.js
 */

require('colors')
const { Engine } = require('json-rules-engine')
const accountClient = require('./support/account-api-client')

async function start () {
  /**
   * Setup a new engine
   */
  const engine = new Engine()

  /**
   * - Demonstrates setting high performance (cpu) facts higher than low performing (network call) facts.
   */
  const microsoftRule = {
    conditions: {
      all: [{
        fact: 'account-information',
        operator: 'equal',
        value: true
      }, {
        fact: 'date',
        operator: 'lessThan',
        value: 1467331200000 // unix ts for 2016-07-01; truthy when current date is prior to 2016-07-01
      }]
    },
    event: { type: 'microsoft-employees' }
  }
  engine.addRule(microsoftRule)

  /**
   * Register listeners with the engine for rule success and failure
   */
  const facts = { accountId: 'washington' }
  engine
    .on('success', event => {
      console.log(facts.accountId + ' DID '.green + 'meet conditions for the ' + event.type.underline + ' rule.')
    })
    .on('failure', event => {
      console.log(facts.accountId + ' did ' + 'NOT'.red + ' meet conditions for the ' + event.type.underline + ' rule.')
    })

  /**
   * Low and High Priorities.
   * Facts that do not have a priority set default to 1
   * @type {Integer} - Facts are run in priority from highest to lowest.
   */
  const HIGH = 100
  const LOW = 1

  /**
   * 'account-information' fact executes an api call - network calls are expensive, so
   * we set this fact to be LOW priority; it will only be evaluated after all higher priority facts
   * evaluate truthy
   */
  engine.addFact('account-information', (params, almanac) => {
    // this fact will not be evaluated, because the "date" fact will fail first
    console.log('Checking the "account-information" fact...') // this message will not appear
    return almanac.factValue('accountId')
      .then((accountId) => {
        return accountClient.getAccountInformation(accountId)
      })
  }, { priority: LOW })

  /**
   * 'date' fact returns the current unix timestamp in ms.
   * Because this is cheap to compute, we set it to "HIGH" priority
   */
  engine.addFact('date', (params, almanac) => {
    console.log('Checking the "date" fact...')
    return Date.now()
  }, { priority: HIGH })

  // define fact(s) known at runtime
  await engine.run()
}
start()

/*
 * OUTPUT:
 *
 * Checking the "date" fact first..
 * washington did NOT meet conditions for the microsoft-employees rule.
 */

/*
 * NOTES:
 *
 * - Notice that the "account-information" fact was never evaluated, saving a network call and speeding up
 * the engine by an order of magnitude(or more!).  Swap the priorities of the facts to see both run.
 */