12-using-custom-almanac.js

'use strict'

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

/**
 * Almanac that support piping values through named functions
 */
class PipedAlmanac extends Almanac {
  constructor (options) {
    super(options)
    this.pipes = new Map()
  }

  addPipe (name, pipe) {
    this.pipes.set(name, pipe)
  }

  factValue (factId, params, path) {
    let pipes = []
    if (params && 'pipes' in params && Array.isArray(params.pipes)) {
      pipes = params.pipes
      delete params.pipes
    }
    return super.factValue(factId, params, path).then(value => {
      return pipes.reduce((value, pipeName) => {
        const pipe = this.pipes.get(pipeName)
        if (pipe) {
          return pipe(value)
        }
        return value
      }, value)
    })
  }
}

async function start () {
  const engine = new Engine()
    .addRule({
      conditions: {
        all: [
          {
            fact: 'age',
            params: {
              // the addOne pipe adds one to the value
              pipes: ['addOne']
            },
            operator: 'greaterThanInclusive',
            value: 21
          }
        ]
      },
      event: {
        type: 'Over 21(ish)'
      }
    })

  engine.on('success', async (event, almanac) => {
    const name = await almanac.factValue('name')
    const age = await almanac.factValue('age')
    console.log(`${name} is ${age} years old and ${'is'.green} ${event.type}`)
  })

  engine.on('failure', async (event, almanac) => {
    const name = await almanac.factValue('name')
    const age = await almanac.factValue('age')
    console.log(`${name} is ${age} years old and ${'is not'.red} ${event.type}`)
  })

  const createAlmanacWithPipes = () => {
    const almanac = new PipedAlmanac()
    almanac.addPipe('addOne', (v) => v + 1)
    return almanac
  }

  // first run Bob who is less than 20
  await engine.run({ name: 'Bob', age: 19 }, { almanac: createAlmanacWithPipes() })

  // second run Alice who is 21
  await engine.run({ name: 'Alice', age: 21 }, { almanac: createAlmanacWithPipes() })

  // third run Chad who is 20
  await engine.run({ name: 'Chad', age: 20 }, { almanac: createAlmanacWithPipes() })
}

start()

/*
 * OUTPUT:
 *
 * Bob is 19 years old and is not Over 21(ish)
 * Alice is 21 years old and is Over 21(ish)
 * Chad is 20 years old and is Over 21(ish)
 */