git ssb

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var nest = require('depnest')
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var ref = require('ssb-ref')
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var MutantArray = require('mutant/array')
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var concat = require('mutant/concat')
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var { computed } = require('mutant')
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exports.needs = nest({
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  'message.sync.unbox': 'first',
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  'backlinks.obs.for': 'first'
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})
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exports.gives = nest({
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  'sbot.hook.publish': true,
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  'message.obs.shares': true
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})
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exports.create = function (api) {
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  var activeShares = new Set()
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  return nest({
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    'sbot.hook.publish': (msg) => {
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      if (!(msg && msg.value && msg.value.content)) return
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      if (typeof msg.value.content === 'string') {
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        msg = api.message.sync.unbox(msg)
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        if (!msg) return
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      }
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      var c = msg.value.content
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      if (c.type !== 'share') return
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      if (!c.share || !c.share.link || !c.share.text) return
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      activeShares.forEach((shares) => {
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        if (shares.id === c.share.link) {
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          shares.push(msg)
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        }
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      })
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    },
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    'message.obs.shares': (id) => {
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      if (!ref.isLink(id)) throw new Error('an id must be specified')
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      var obs = get(id)
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      obs.id = id
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      var result = computed(obs, getShares, {
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        // allow manual append for simulated realtime
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        onListen: () => activeShares.add(obs),
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        onUnlisten: () => activeShares.delete(obs)
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      })
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      result.sync = obs.sync
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      return result
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    }
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  })
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  function get(id) {
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    var backlinks = api.backlinks.obs.for(id)
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    var merge = MutantArray()
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    var shares = computed([backlinks.sync, concat([backlinks, merge])], (sync, backlinks) => {
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      if (sync) {
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        return backlinks.reduce((result, msg) => {
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          var c = msg.value.content
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          if (c.type === 'share' && c.share && c.share.text && c.share.link === id) {
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            var value = result[msg.value.author]
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            if (!value || value[0] < msg.value.timestamp) {
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              result[msg.value.author] = [msg.value.timestamp, c.share.text]
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            }
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          }
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          return result
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        }, {})
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      } else {
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        return {}
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      }
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    })
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    shares.push = merge.push
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    shares.sync = backlinks.sync
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    return shares
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  }
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}
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function getShares(shares) {
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  return Object.keys(shares).reduce((result, id) => {
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    if (shares[id].length >= 1) {
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      result.push(id)
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    }
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    return result
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  }, [])
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}