json-rules-engine/examples/09-rule-results.js

Rules Engine expressed in simple json

'use strict'

/*
 * This is a basic example demonstrating how to leverage the metadata supplied by rule results
 *
 * Usage:
 *   node ./examples/09-rule-results.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/09-rule-results.js
 */
require('colors')
let Engine = require('../dist').Engine

/**
 * Setup a new engine
 */
let engine = new Engine()

// rule for determining honor role student atheletes (student has GPA >= 3.5 AND is an athlete)
engine.addRule({
  conditions: {
    all: [{
      fact: 'athlete',
      operator: 'equal',
      value: true
    }, {
      fact: 'GPA',
      operator: 'greaterThanInclusive',
      value: 3.5
    }]
  },
  event: {  // define the event to fire when the conditions evaluate truthy
    type: 'honor-roll',
    params: {
      message: 'Student made the athletics honor-roll'
    }
  }
})

function render (message, ruleResult) {
  // if rule succeeded, render success message
  if (ruleResult.result) {
    return console.log(`${message}`.green)
  }
  // if rule failed, iterate over each failed condition to determine why the student didn't qualify for athletics honor roll
  let detail = ruleResult.conditions.all.filter(condition => !condition.result)
  .map(condition => {
    switch (condition.operator) {
      case 'equal':
        return `was not an ${condition.fact}`
      case 'greaterThanInclusive':
        return `${condition.fact} of ${condition.factResult} was too low`
    }
  }).join(' and ')
  console.log(`${message} ${detail}`.red)
}

/**
 * On success, retrieve the student's username for display purposes, and render
 */
engine.on('success', (event, almanac, ruleResult) => {
  almanac.factValue('username').then(username => {
    render(`${username.bold} succeeded! ${event.params.message}`, ruleResult)
  })
})

/**
 * On failure, retrieve the student's username for display purposes, and render
 */
engine.on('failure', (event, almanac, ruleResult) => {
  almanac.factValue('username').then(username => {
    render(`${username.bold} failed - `, ruleResult)
  })
})

// Run the engine for 5 different students
Promise.all([
  engine.run({ athlete: false, GPA: 3.9, username: 'joe' }),
  engine.run({ athlete: true, GPA: 3.5, username: 'larry' }),
  engine.run({ athlete: false, GPA: 3.1, username: 'jane' }),
  engine.run({ athlete: true, GPA: 4.0, username: 'janet' }),
  engine.run({ athlete: true, GPA: 1.1, username: 'sarah' })
])

/*
 * OUTPUT:
 *
 * joe failed -  was not an athlete
 * larry succeeded! Student made the athletics honor-roll
 * jane failed -  was not an athlete and GPA of 3.1 was too low
 * janet succeeded! Student made the athletics honor-roll
 * sarah failed -  GPA of 1.1 was too low
 */