11-using-facts-in-events.js

'use strict'
/*
 * This is an advanced example demonstrating an event that emits the value
 * of a fact in it's parameters.
 *
 * Usage:
 *   node ./examples/11-using-facts-in-events.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/11-using-facts-in-events.js
 */

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

async function start () {
  /**
   * Setup a new engine
   */
  const engine = new Engine([], { replaceFactsInEventParams: true })

  // in-memory "database"
  let currentHighScore = null
  const currentHighScoreFact = new Fact('currentHighScore', () => currentHighScore)

  /**
   * Rule for when you've gotten the high score
   * event will include your score and initials.
   */
  const highScoreRule = {
    conditions: {
      any: [
        {
          fact: 'currentHighScore',
          operator: 'equal',
          value: null
        },
        {
          fact: 'score',
          operator: 'greaterThan',
          value: {
            fact: 'currentHighScore',
            path: '$.score'
          }
        }
      ]
    },
    event: {
      type: 'highscore',
      params: {
        initials: { fact: 'initials' },
        score: { fact: 'score' }
      }
    }
  }

  /**
   * Rule for when the game is over and you don't have the high score
   * event will include the previous high score
   */
  const gameOverRule = {
    conditions: {
      all: [
        {
          fact: 'score',
          operator: 'lessThanInclusive',
          value: {
            fact: 'currentHighScore',
            path: '$.score'
          }
        }
      ]
    },
    event: {
      type: 'gameover',
      params: {
        initials: {
          fact: 'currentHighScore',
          path: '$.initials'
        },
        score: {
          fact: 'currentHighScore',
          path: '$.score'
        }
      }
    }
  }
  engine.addRule(highScoreRule)
  engine.addRule(gameOverRule)
  engine.addFact(currentHighScoreFact)

  /**
   * Register listeners with the engine for rule success
   */
  engine
    .on('success', async ({ params: { initials, score } }) => {
      console.log(`HIGH SCORE\n${initials} - ${score}`)
    })
    .on('success', ({ type, params }) => {
      if (type === 'highscore') {
        currentHighScore = params
      }
    })

  let facts = {
    initials: 'DOG',
    score: 968
  }

  // first run, without a high score
  await engine.run(facts)

  console.log('\n')

  // new player
  facts = {
    initials: 'AAA',
    score: 500
  }

  // new player hasn't gotten the high score yet
  await engine.run(facts)

  console.log('\n')

  facts = {
    initials: 'AAA',
    score: 1000
  }

  // second run, with a high score
  await engine.run(facts)
}

start()

/*
 * OUTPUT:
 *
 * NEW SCORE:
 * DOG - 968
 *
 * HIGH SCORE:
 * DOG - 968
 *
 * HIGH SCORE:
 * AAA - 1000
 */