04-fact-dependency.js

'use strict'
/*
 * This is an advanced example that demonstrates facts with dependencies
 * on other facts.  In addition, it demonstrates facts that load data asynchronously
 * from outside sources (api's, databases, etc)
 *
 * Usage:
 *   node ./examples/04-fact-dependency.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/04-fact-dependency.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()

  /**
   * Rule for identifying microsoft employees that have been terminated.
   * - Demonstrates re-using a same fact with different parameters
   * - Demonstrates calling a base fact, which serves to load data once and reuse later
   */
  const microsoftRule = {
    conditions: {
      all: [{
        fact: 'account-information',
        operator: 'equal',
        value: 'microsoft',
        path: '$.company'
      }, {
        fact: 'account-information',
        operator: 'equal',
        value: 'terminated',
        path: '$.status'
      }]
    },
    event: { type: 'microsoft-terminated-employees' }
  }
  engine.addRule(microsoftRule)

  /**
   * Rule for identifying accounts older than 5 years
   * - Demonstrates calling a base fact, also shared by the account-information-field fact
   * - Demonstrates performing computations on data retrieved by base fact
   */
  const tenureRule = {
    conditions: {
      all: [{
        fact: 'employee-tenure',
        operator: 'greaterThanInclusive',
        value: 5,
        params: {
          unit: 'years'
        }
      }]
    },
    event: { type: 'five-year-tenure' }
  }
  engine.addRule(tenureRule)

  /**
   * Register listeners with the engine for rule success and failure
   */
  let facts
  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.')
    })

  /**
   * 'account-information' fact executes an api call and retrieves account data
   * - Demonstrates facts called only by other facts and never mentioned directly in a rule
   */
  engine.addFact('account-information', (params, almanac) => {
    return almanac.factValue('accountId')
      .then(accountId => {
        return accountClient.getAccountInformation(accountId)
      })
  })

  /**
   * 'employee-tenure' fact retrieves account-information, and computes the duration of employment
   * since the account was created using 'accountInformation.createdAt'
   */
  engine.addFact('employee-tenure', (params, almanac) => {
    return almanac.factValue('account-information')
      .then(accountInformation => {
        const created = new Date(accountInformation.createdAt)
        const now = new Date()
        switch (params.unit) {
          case 'years':
            return now.getFullYear() - created.getFullYear()
          case 'milliseconds':
          default:
            return now.getTime() - created.getTime()
        }
      })
      .catch(console.log)
  })

  // first run, using washington's facts
  console.log('-- FIRST RUN --')
  facts = { accountId: 'washington' }
  await engine.run(facts)

  console.log('-- SECOND RUN --')
  // second run, using jefferson's facts; facts & evaluation are independent of the first run
  facts = { accountId: 'jefferson' }
  await engine.run(facts)

  /*
  * NOTES:
  *
  * - Notice that although a total of 6 conditions were evaluated using
  *   account-information (3 rule conditions x 2 accounts), the account-information api call
  *   is only called twice -- once for each account.  This is due to the base fact caching the results
  *   for washington and jefferson after the initial data load.
  */
}
start()

/*
 * OUTPUT:
 *
 * loading account information for "washington"
 * washington DID meet conditions for the microsoft-terminated-employees rule.
 * washington did NOT meet conditions for the five-year-tenure rule.
 * loading account information for "jefferson"
 * jefferson did NOT meet conditions for the microsoft-terminated-employees rule.
 * jefferson DID meet conditions for the five-year-tenure rule.
 */