json-rules-engine/examples/08-fact-comparison.js

Rules Engine expressed in simple json

'use strict'

/*
 * This is a basic example demonstrating a condition that compares two facts
 *
 * Usage:
 *   node ./examples/08-fact-comparison.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/08-fact-comparison.js
 */

require('colors')
let Engine = require('../dist').Engine

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

/**
 * Rule for determining if account has enough money to purchase a $50 gift card product
 *
 * customer-account-balance >= $50 gift card
 */
let rule = {
  conditions: {
    all: [{
      // extract 'balance' from the 'customer' account type
      fact: 'account',
      path: '.balance',
      params: {
        accountType: 'customer'
      },

      operator: 'greaterThanInclusive',  // >=

      // "value" in this instance is an object containing a fact definition
      // fact helpers "path" and "params" are supported here as well
      value: {
        fact: 'product',
        path: '.price',
        params: {
          productId: 'giftCard'
        }
      }
    }]
  },
  event: { type: 'customer-can-afford-gift-card' }
}
engine.addRule(rule)

engine.addFact('account', (params, almanac) => {
  // get account list
  return almanac.factValue('accounts')
    .then(accounts => {
      // use "params" to filter down to the type specified, in this case the "customer" account
      let customerAccount = accounts.filter(account => account.type === params.accountType)
      // return the customerAccount object, which "path" will use to pull the "balance" property
      return customerAccount[0]
    })
})

engine.addFact('product', (params, almanac) => {
  // get product list
  return almanac.factValue('products')
    .then(products => {
      // use "params" to filter down to the product specified, in this case the "giftCard" product
      let product = products.filter(product => product.productId === params.productId)
      // return the product object, which "path" will use to pull the "price" property
      return product[0]
    })
})

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

// define fact(s) known at runtime
let productList = {
  products: [
    {
      productId: 'giftCard',
      price: 50
    }, {
      productId: 'widget',
      price: 45
    }, {
      productId: 'widget-plus',
      price: 800
    }
  ]
}

let userFacts = {
  userId: 'washington',
  accounts: [{
    type: 'customer',
    balance: 500
  }, {
    type: 'partner',
    balance: 0
  }]
}

// compile facts to be fed to the engine
facts = Object.assign({}, userFacts, productList)

engine
  .run(facts)  // first run, user can afford a gift card
  .then(() => {
    // second run; a user that cannot afford a gift card
    userFacts = {
      userId: 'jefferson',
      accounts: [{
        type: 'customer',
        balance: 30
      }]
    }
    facts = Object.assign({}, userFacts, productList)
    return engine.run(facts)
  })
  .catch(console.log)

/*
 * OUTPUT:
 *
 * washington DID meet conditions for the customer-can-afford-gift-card rule.
 * jefferson did NOT meet conditions for the customer-can-afford-gift-card rule.
 */