08-fact-comparison.js

'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')
const { Engine } = require('json-rules-engine')

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

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

  // first run, user can afford a gift card
  await engine.run(facts)

  // second run; a user that cannot afford a gift card
  userFacts = {
    userId: 'jefferson',
    accounts: [{
      type: 'customer',
      balance: 30
    }]
  }
  facts = Object.assign({}, userFacts, productList)
  await engine.run(facts)
}
start()
/*
 * 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.
 */