git ssb

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const pull = require('pull-stream')
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const sort = require('ssb-sort')
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const { isMsg } = require('ssb-ref')
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const { isGathering } = require('ssb-gathering-schema')
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module.exports = function getBacklinks (server) {
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  if (arguments.length !== 1 || typeof arguments[0] !== 'object') throw new Error('getBacklinks needs a server as it\'s first argument!')
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  return function (gathering, cb) {
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    if (!isGathering(gathering)) return cb(new Error('getBacklinks requires a valid gathering message'))
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    const key = gathering.key
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    if (!isMsg(key)) return cb(new Error('getBacklinks requires a valid gathering message'))
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    const query = [{
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      $filter: { dest: key }
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    }]
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    pull(
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      server.backlinks.read({ query }),
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      pull.filter(m => {
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        return (m.value.content.about === key) || (m.value.content.root === key)
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      }),
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      pull.collect((err, backlinks) => {
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        if (err) return cb(err)
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        const sorted = sort([ gathering, ...backlinks ])
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        sorted.shift()
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        // remove gathering after sort
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        // putting gathering into the sort is paranoid and is thinking ahead to a time without timestamps
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        cb(null, sorted)
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      })
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    )
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  }
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}
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