example.js

const kappa = require('kappa-core')
const Query = require('./')
const ram = require('random-access-memory')

const memdb = require('memdb')
const level = require('level')

const pull = require('pull-stream')

const core = kappa(ram, { valueEncoding: 'json'  })

const db = memdb() || level('/tmp/db')

function validator (msg) {
  if (typeof msg !== 'object') return null
  if (typeof msg.value !== 'object') return null
  if (typeof msg.value.timestamp !== 'number') return null
  if (typeof msg.value.type !== 'string') return null
  return msg
}

const indexes = [
  { key: 'log', value: ['value', 'timestamp'] },
  { key: 'typ', value: [['value', 'type'], ['value', 'timestamp']] },
  { key: 'cha', value: [['value', 'type'], ['value', 'content', 'channel'], ['value', 'timestamp']] }
]

core.use('query', Query(db, core, { indexes, validator })) 

core.ready(() => {
  core.writer('local', (err, feed) => {
    const data = [{
      type: 'chat/message',
      timestamp: 1561996331739,
      content: { body: 'First message' }
    }, {
      type: 'user/about',
      timestamp: 1561996331740,
      content: { name: 'Grace' }
    }, {
    }, {
      type: 'chat/message',
      timestamp: 1561996331742,
      content: { body: 'Third message' }
    }, {
      type: 'chat/message',
      timestamp: 1561996331743,
      content: { channel: 'dogs', body: 'Lurchers rule' }
    }, {
      type: 'chat/message',
      timestamp: 1561996331741,
      content: { body: 'Second message' }
    }, {
      type: 'user/about',
      timestamp: 1561996331754,
      content: { name: 'Poison Ivy' }
    }]

    feed.append(data)
  })

  const query = [{ $filter: { value: { type: 'chat/message', content: { channel: 'dogs' } } } }]

  pull(
    core.api.query.read({ live: true, query }),
    pull.drain(console.log)
  )
})