git ssb

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var nest = require('depnest')
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var pull = require('pull-stream')
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var Value = require('mutant/value')
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var onceTrue = require('mutant/once-true')
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var defer = require('pull-defer')
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exports.needs = nest({
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  'sbot.obs.connection': 'first'
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})
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exports.gives = nest('blob.obs.has', true)
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exports.create = function (api) {
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  var cbs = null
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  return nest('blob.obs.has', function (id) {
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    var value = Value()
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    onceTrue(api.sbot.obs.connection, sbot => {
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      sbot.blobs.has(id, (_, has) => {
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        if (has) {
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          value.set(true)
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        } else {
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          value.set(false)
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          waitFor(id, () => value.set(true))
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        }
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      })
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    })
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    return value
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  })
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  function waitFor (id, cb) {
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    if (!cbs) {
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      cbs = {}
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      pull(
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        StreamWhenConnected(api.sbot.obs.connection, sbot => sbot.blobs.ls({old: false})),
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        pull.drain(blob => {
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          if (cbs[blob]) {
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            while (cbs[blob].length) {
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              cbs[blob].pop()()
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            }
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            delete cbs[blob]
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          }
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        })
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      )
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    }
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    if (!cbs[id]) cbs[id] = []
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    cbs[id].push(cb)
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  }
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}
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function StreamWhenConnected (connection, fn) {
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  var stream = defer.source()
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  onceTrue(connection, function (connection) {
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    stream.resolve(fn(connection))
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  })
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  return stream
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}
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