var pull = require('pull-stream')
var pullDefer = require('pull-defer')
var pullNext = require('pull-next')
var SortedArray = require('sorted-array-functions')
var nest = require('depnest')
var ref = require('ssb-ref')
var sustained = require('../../../lib/sustained')
var Value = require('mutant/value')

exports.gives = nest({
  'feed.pull': [ 'summary' ]
})

exports.create = function () {
  return nest({
    'feed.pull': { summary }
  })
}

function summary (source, opts, cb) {
  var bumpFilter = opts && opts.bumpFilter
  var windowSize = opts && opts.windowSize || 1000
  var prioritized = opts && opts.prioritized || {}

  var loading = Value(true)

  var last = null
  var returned = false
  var done = false

  var result = pullNext(() => {
    if (!done) {
      loading.set(true)
      var next = {reverse: true, limit: windowSize, live: false}
      if (last) {
        next.lt = last
      }
      var deferred = pullDefer.source()
      pull(
        source(next),
        pull.collect((err, values) => {
          loading.set(false)
          if (err) throw err
          if (!values.length) {
            done = true
            deferred.resolve(pull.values([]))
            if (!returned) cb && cb()
            returned = true
          } else {
            var fromTime = last && last.timestamp || Date.now()
            last = values[values.length - 1]
            groupMessages(values, fromTime, {bumpFilter, prioritized}, (err, result) => {
              if (err) throw err
              deferred.resolve(
                pull.values(result)
              )
              if (!returned) cb && cb()
              returned = true
            })
          }
        })
      )
    }
    return deferred
  })

  // switch to loading state immediately, only revert after no loading for > 200 ms
  result.loading = sustained(loading, 500, x => x)

  return result
}

function groupMessages (messages, fromTime, opts, cb) {
  var subscribes = {}
  var follows = {}
  var messageUpdates = {}
  reverseForEach(messages, function (msg) {
    if (!msg.value) return
    var c = msg.value.content
    if (c.type === 'contact') {
      updateContact(msg, follows, opts)
    } else if (c.type === 'channel') {
      updateChannel(msg, subscribes, opts)
    } else if (c.type === 'vote') {
      if (c.vote && c.vote.link) {
        // only show likes of posts added in the current window
        // and only for the main post
        const group = messageUpdates[c.vote.link]
        if (group) {
          if (c.vote.value > 0) {
            group.likes.add(msg.value.author)
            group.relatedMessages.push(msg)
          } else {
            group.likes.delete(msg.value.author)
            group.relatedMessages.push(msg)
          }
        }
      }
    } else {
      if (c.root) {
        const group = ensureMessage(c.root, messageUpdates)
        group.fromTime = fromTime
        group.repliesFrom.add(msg.value.author)
        SortedArray.add(group.replies, msg, compareUserTimestamp)
        group.channel = group.channel || msg.value.content.channel
        group.relatedMessages.push(msg)
      } else {
        const group = ensureMessage(msg.key, messageUpdates)
        group.fromTime = fromTime
        group.lastUpdateType = 'post'
        group.updated = msg.timestamp || msg.value.sequence
        group.author = msg.value.author
        group.channel = msg.value.content.channel
        group.message = msg
        group.boxed = typeof msg.value.content === 'string'
      }
    }
  }, () => {
    var result = []
    Object.keys(follows).forEach((key) => {
      bumpIfNeeded(follows[key], opts)
      if (follows[key].updated) {
        SortedArray.add(result, follows[key], compareUpdated)
      }
    })
    Object.keys(subscribes).forEach((key) => {
      bumpIfNeeded(subscribes[key], opts)
      if (subscribes[key].updated) {
        SortedArray.add(result, subscribes[key], compareUpdated)
      }
    })
    Object.keys(messageUpdates).forEach((key) => {
      bumpIfNeeded(messageUpdates[key], opts)
      if (messageUpdates[key].updated) {
        SortedArray.add(result, messageUpdates[key], compareUpdated)
      }
    })
    cb(null, result)
  })
}

function bumpIfNeeded (group, {bumpFilter, prioritized}) {
  group.relatedMessages.forEach(msg => {
    if (prioritized[msg.key] && group.priority < prioritized[msg.key]) {
      group.priority = prioritized[msg.key]
    }

    var shouldBump = !bumpFilter || bumpFilter(msg, group)

    // only bump when filter passes
    var newUpdated = msg.timestamp || msg.value.sequence
    if (!group.updated || (shouldBump && newUpdated > group.updated)) {
      group.updated = newUpdated
      if (msg.value.content.type === 'vote') {
        if (group.likes.size) {
          group.lastUpdateType = 'like'
        } else if (group.repliesFrom.size) {
          group.lastUpdateType = 'reply'
        } else if (group.message) {
          group.lastUpdateType = 'post'
        }
      }

      if (msg.value.content.type === 'post') {
        if (msg.value.content.root) {
          group.lastUpdateType = 'reply'
        } else {
          group.lastUpdateType = 'post'
        }
      }
    }
  })
}

function compareUpdated (a, b) {
  // highest priority first
  // then most recent date
  return b.priority - a.priority || b.updated - a.updated
}

function reverseForEach (items, fn, cb) {
  var i = items.length - 1
  nextBatch()

  function nextBatch () {
    var start = Date.now()
    while (i >= 0) {
      fn(items[i], i)
      i -= 1
      if (Date.now() - start > 10) break
    }

    if (i > 0) {
      setImmediate(nextBatch)
    } else {
      cb && cb()
    }
  }
}

function updateContact (msg, groups, opts) {
  var c = msg.value.content
  var id = msg.value.author
  var group = groups[id]
  if (ref.isFeed(c.contact)) {
    if (c.following) {
      if (!group) {
        group = groups[id] = {
          type: 'follow',
          priority: 0,
          relatedMessages: [],
          lastUpdateType: null,
          contacts: new Set(),
          updated: 0,
          author: id,
          id: id
        }
      }
      group.contacts.add(c.contact)
      group.relatedMessages.push(msg)
    } else {
      if (group) {
        group.contacts.delete(c.contact)
        if (!group.contacts.size) {
          delete groups[id]
        }
      }
    }
  }
}

function updateChannel (msg, groups, opts) {
  var c = msg.value.content
  var channel = c.channel
  var group = groups[channel]
  if (typeof channel === 'string') {
    if (c.subscribed) {
      if (!group) {
        group = groups[channel] = {
          type: 'subscribe',
          priority: 0,
          relatedMessages: [],
          lastUpdateType: null,
          subscribers: new Set(),
          updated: 0,
          channel
        }
      }
      group.subscribers.add(msg.value.author)
      group.relatedMessages.push(msg)
    } else {
      if (group) {
        group.subscribers.delete(msg.value.author)
        if (!group.subscribers.size) {
          delete groups[channel]
        }
      }
    }
  }
}

function ensureMessage (id, groups) {
  var group = groups[id]
  if (!group) {
    group = groups[id] = {
      type: 'message',
      priority: 0,
      repliesFrom: new Set(),
      relatedMessages: [],
      replies: [],
      message: null,
      messageId: id,
      likes: new Set(),
      updated: 0
    }
  }
  return group
}

function compareUserTimestamp (a, b) {
  var isClose = !a.timestamp || !b.timestamp || Math.abs(a.timestamp - b.timestamp) < (10 * 60e3)
  if (isClose) {
    // recieved close together, use provided timestamps
    return a.value.timestamp - b.value.timestamp
  } else {
    return a.timestamp - b.timestamp
  }
}