A process that restarts the local registrant when needed

needed = require './needed'
install = require './install'

most = require 'most'

max_delta = 200

run = (restart,config,limit = most.never()) ->

  host = process.env.ROYAL_THING_HOST ? config.host
  db = new CouchDB config.provisioning

  debug 'Calling install()'
  {save} = await install host, db
    .catch (error) ->
      debug.dev "install failed: #{error.stack ? error}"
      throw error

  debug 'Starting.'

Restarting the process & saving the update sequence

  restart_needed = false
  new_seq = null

  save_new_seq = ->
    if new_seq?
      debug "Save new seq #{new_seq}."
      await save new_seq
      new_seq = null

Only restart at intervals, not on every change.

  on_interval = ->
    debug 'on_interval'
    if restart_needed
      debug "Calling `restart`."
      await restart config
      restart_needed = false
      await save_new_seq()
      debug "Restart completed."
    else
      await save_new_seq()
    return

Start the on_interval function.

  interval = setInterval (->
    try
      await on_interval()
    catch error
      debug.dev "Error: #{error}"
  ), config.interval ? 61*second

  limit.observe ->
    debug 'No longer monitoring'
    clearInterval interval

Force a restart if the database is too far away from our own sequence number.

  {update_seq} = await db.info()
  our_seq = (await save())?.update_seq ? 0

  debug 'Analyzing', {update_seq,our_seq}

  if update_seq isnt our_seq
    new_seq = update_seq
    restart_needed = true

  await on_interval()

Monitoring changes

  debug 'Monitoring changes'

  map_function = (emit) ->
    (doc) ->
      if doc._id.match /^number:\d+$/
        emit null

  handle_changes = ({id,seq,doc}) ->
    debug "Change on #{id} (seq #{seq})", doc
    new_doc = doc

We need to provide needed with both the previous record and the current record. Let's try to retrieve the previous record by querying for revs_info.

    doc = await db
      .get id,
        revs_info: true

If we can't access the current record for whatever reason, simply re-use the document provided by change.

      .catch (error) ->
        new_doc

    old_rev = doc._revs_info?[1]?.rev

Finally, retrieve the previous revision of the document,

    if old_rev?
      debug 'Retrieving previous version', old_rev
      old_doc = await db
        .get id, rev: old_rev
        .catch (error) ->
          debug.dev "Failed to gather data about #{id}: #{error.stack ? error}"
          null

If none is specified, assumes that the document was just created (it's normal that there is no former revisions), or deleted (we weren't able to obtain revs_info).

    unless old_doc?
      debug 'Constructing previous document'
      old_doc = {}
      old_doc[k] = v for own k,v of new_doc
      old_doc._deleted = not (new_doc._deleted ? false)

then use needed to decide whether it was modified in a way that requires a restart.

    if needed host, old_doc, new_doc
      restart_needed = true
      debug.csr "Triggering restart because of #{id}"
    new_seq = seq

    return

  completed = db
    .query_changes map_function, since: our_seq, include_docs: true
    .until limit
    .observe ({id,seq,doc}) ->
      try
        await handle_changes {id,seq,doc}
      catch error
        debug.dev 'handle_changes', error
      return

This function will return as soon as processing can start.

  debug 'Started.'

It return an object containing a Promise that will complete when a complete run is finished.

  return {completed}

debug = (require 'tangible') 'royal-thing'

second = 1000

CouchDB = require 'most-couchdb'

module.exports = run