var pull = require('pull-stream')

// Reduce a feed's own contact and channel-subscription messages into the sets
// they describe. createUserStream runs oldest-first, so a later unfollow
// correctly undoes an earlier follow.
//
// Both /user-feed/ and /items are built on this: "who does this feed listen
// to" is the whole selection rule, which is what lets a new kiosk show up by
// being followed rather than by being added to a list somewhere.
module.exports = function getFollows (sbot, feedId, cb) {
  var following = Object.create(null)
  var channelSubscriptions = Object.create(null)

  pull(
    sbot.createUserStream({ id: feedId }),
    pull.filter(function (msg) {
      var c = msg && msg.value && msg.value.content
      if (!c || typeof c !== 'object') return false   // also skips private (string) content
      return c.type === 'contact' ||
        (c.type === 'channel' && typeof c.subscribed !== 'undefined')
    }),
    pull.drain(function (msg) {
      var c = msg.value.content
      if (c.type === 'contact') {
        if (!c.contact) return
        if (c.following) following[c.contact] = true
        else delete following[c.contact]
      } else {
        if (!c.channel) return
        if (c.subscribed) channelSubscriptions[c.channel] = true
        else delete channelSubscriptions[c.channel]
      }
    }, function (err) {
      if (err) return cb(err)
      cb(null, { following: following, channelSubscriptions: channelSubscriptions })
    })
  )
}