var Promise = require('bluebird')

var logger = require('../../util/logger')
var wire = require('../../wire')
var wireutil = require('../../wire/util')
var wirerouter = require('../../wire/router')
var dbapi = require('../../db/api')
var lifecycle = require('../../util/lifecycle')
var srv = require('../../util/srv')
var TtlSet = require('../../util/ttlset')
var zmqutil = require('../../util/zmqutil')

module.exports = function(options) {
  var log = logger.createLogger('reaper')
  var ttlset = new TtlSet(options.heartbeatTimeout)

  if (options.name) {
    logger.setGlobalIdentifier(options.name)
  }

  // Input
  var sub = zmqutil.socket('sub')
  Promise.map(options.endpoints.sub, function(endpoint) {
    return srv.resolve(endpoint).then(function(records) {
      return srv.attempt(records, function(record) {
        log.info('Receiving input from "%s"', record.url)
        sub.connect(record.url)
        return Promise.resolve(true)
      })
    })
  })
  .catch(function(err) {
    log.fatal('Unable to connect to sub endpoint', err)
    lifecycle.fatal()
  })

  // Establish always-on channels
  ;[wireutil.global].forEach(function(channel) {
    log.info('Subscribing to permanent channel "%s"', channel)
    sub.subscribe(channel)
  })

  // Output
  var push = zmqutil.socket('push')
  Promise.map(options.endpoints.push, function(endpoint) {
    return srv.resolve(endpoint).then(function(records) {
      return srv.attempt(records, function(record) {
        log.info('Sending output to "%s"', record.url)
        push.connect(record.url)
        return Promise.resolve(true)
      })
    })
  })
  .catch(function(err) {
    log.fatal('Unable to connect to push endpoint', err)
    lifecycle.fatal()
  })

  ttlset.on('insert', function(serial) {
    log.info('Device "%s" is present', serial)
    push.send([
      wireutil.global
    , wireutil.envelope(new wire.DevicePresentMessage(
        serial
      ))
    ])
  })

  ttlset.on('drop', function(serial) {
    log.info('Reaping device "%s" due to heartbeat timeout', serial)
    push.send([
      wireutil.global
    , wireutil.envelope(new wire.DeviceAbsentMessage(
        serial
      ))
    ])
  })

  function loadInitialState() {
    return dbapi.loadPresentDevices()
      .then(function(cursor) {
        return Promise.promisify(cursor.toArray, cursor)()
          .then(function(list) {
            var now = Date.now()
            list.forEach(function(device) {
              ttlset.bump(device.serial, now, TtlSet.SILENT)
            })
          })
      })
  }

  function listenToChanges() {
    sub.on('message', wirerouter()
      .on(wire.DeviceIntroductionMessage, function(channel, message) {
        ttlset.drop(message.serial, TtlSet.SILENT)
        ttlset.bump(message.serial, Date.now())
      })
      .on(wire.DeviceHeartbeatMessage, function(channel, message) {
        ttlset.bump(message.serial, Date.now())
      })
      .on(wire.DeviceAbsentMessage, function(channel, message) {
        ttlset.drop(message.serial, TtlSet.SILENT)
      })
      .handler())
  }

  log.info('Reaping devices with no heartbeat')

  lifecycle.observe(function() {
    [push, sub].forEach(function(sock) {
      try {
        sock.close()
      }
      catch (err) {
        // No-op
      }
    })

    ttlset.stop()
  })

  loadInitialState().then(listenToChanges).catch(function(err) {
    log.fatal('Unable to load initial state', err)
    lifecycle.fatal()
  })
}