git ssb

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var nest = require('depnest')
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var MutantPullReduce = require('mutant-pull-reduce')
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var ref = require('ssb-ref')
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exports.needs = nest({
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  'sbot.pull.query': 'first',
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  'keys.sync.id': 'first'
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})
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exports.gives = nest({
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  'contact.obs': ['following', 'followers'],
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  'sbot.hook.feed': true
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})
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exports.create = function (api) {
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  var followingCache = {}
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  var followerCache = {}
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  return nest({
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    'contact.obs': { following, followers },
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    'sbot.hook.feed': function (msg) {
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      if (isContact(msg) && msg.timestamp) {
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        var author = msg.value.author
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        var contact = msg.value.content.contact
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        var following = msg.value.content.following
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        var from = followingCache[author]
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        var to = followerCache[contact]
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        if (from) from.push({id: contact, value: following, timestamp: msg.timestamp})
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        if (to) to.push({id: author, value: following, timestamp: msg.timestamp})
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      }
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    }
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  })
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  function following (id) {
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    if (!ref.isFeed(id)) throw new Error('a feed id must be specified')
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    if (!followingCache[id]) {
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      followingCache[id] = reduce(api.sbot.pull.query({
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        query: [
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          makeQuery(id, { $prefix: '@' }),
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          {'$map': {
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            id: ['value', 'content', 'contact'],
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            value: ['value', 'content', 'following'],
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            timestamp: 'timestamp'
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          }}
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        ],
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        live: true
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      }))
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    }
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    return followingCache[id]
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  }
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  function followers (id) {
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    if (!ref.isFeed(id)) throw new Error('a feed id must be specified')
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    if (!followerCache[id]) {
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      followerCache[id] = reduce(api.sbot.pull.query({
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        query: [
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          makeQuery({ $prefix: '@' }, id),
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          {'$map': {
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            id: ['value', 'author'],
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            value: ['value', 'content', 'following'],
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            timestamp: 'timestamp'
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          }}
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        ],
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        live: true
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      }))
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    }
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    return followerCache[id]
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  }
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}
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function reduce (stream) {
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  var newestValues = {}
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  return MutantPullReduce(stream, (result, item) => {
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    if (!ref.isFeed(item.id)) return result // invalid message, skip this item
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    newestValues[item.id] = newestValues[item.id] || 0
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    if (newestValues[item.id] < item.timestamp) {
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      newestValues[item.id] = item.timestamp
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      if (item.value != null) {
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        if (item.value) {
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          result.add(item.id)
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        } else {
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          result.delete(item.id)
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        }
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      }
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    }
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    return result
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  }, {
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    startValue: new Set()
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  })
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}
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function makeQuery (a, b) {
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  return {'$filter': {
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    value: {
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      author: a,
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      content: {
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        type: 'contact',
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        contact: b
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      }
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    }
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  }}
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}
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function isContact (msg) {
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  return msg.value && msg.value.content && msg.value.content.type === 'contact'
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}
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