git ssb

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// read stream to get events
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// for each item, check to see if already rendered root
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// accept prioritized list (render these first)
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var pull = require('pull-stream')
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var nest = require('depnest')
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var extend = require('xtend')
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var HLRU = require('hashlru')
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var resolve = require('mutant/resolve')
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var onceTrue = require('mutant/once-true')
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exports.needs = nest({
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  'backlinks.obs.for': 'first',
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  'sbot.async.get': 'first',
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  'message.sync.isBlocked': 'first',
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  'message.sync.root': 'first',
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  'message.sync.unbox': 'first',
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})
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exports.gives = nest('feed.pull.rollup', true)
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exports.create = function (api) {
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  // cache mostly just to avoid reading the same roots over and over again
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  // not really big enough for multiple refresh cycles
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  var cache = HLRU(100)
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  return nest('feed.pull.rollup', function (rootFilter) {
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    var seen = new Set()
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    return pull(
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      pull.map(msg => {
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        if (msg.value) {
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          var root = api.message.sync.root(msg)
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          if (!root) {
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            // already a root, pass thru!
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            return msg
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          } else {
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            return root
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          }
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        }
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      }),
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      // UNIQUE
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      pull.filter(idOrMsg => {
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        if (idOrMsg) {
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          if (idOrMsg.key) idOrMsg = idOrMsg.key
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          if (typeof idOrMsg === 'string') {
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            var key = idOrMsg
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            if (!seen.has(key)) {
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              seen.add(key)
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              return true
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            }
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          }
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        }
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      }),
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      // LOOKUP (if needed)
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      pull.asyncMap((keyOrMsg, cb) => {
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        if (keyOrMsg.value) {
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          cb(null, keyOrMsg)
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        } else {
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          var key = keyOrMsg
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          if (cache.has(key)) {
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            cb(null, cache.get(key))
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          } else {
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            api.sbot.async.get(key, (_, value) => {
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              var msg = {key, value}
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              if (msg.value) {
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                cache.set(key, msg)
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              }
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              cb(null, msg)
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            })
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          }
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        }
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      }),
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      // UNBOX (if needed)
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      pull.map(msg => {
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        if (msg.value && typeof msg.value.content === 'string') {
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          var unboxed = api.message.sync.unbox(msg)
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          if (unboxed) return unboxed
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        }
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        return msg
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      }),
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      // FILTER
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      pull.filter(msg => msg && msg.value && !api.message.sync.root(msg)),
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      pull.filter(rootFilter || (() => true)),
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      pull.filter(msg => !api.message.sync.isBlocked(msg)),
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      // ADD REPLIES
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      pull.asyncMap((rootMessage, cb) => {
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        // use global backlinks cache
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        var backlinks = api.backlinks.obs.for(rootMessage.key)
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        onceTrue(backlinks.sync, () => {
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          var replies = resolve(backlinks).filter(msg => {
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            return api.message.sync.root(msg) === rootMessage.key && !api.message.sync.isBlocked(msg)
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          })
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          cb(null, extend(rootMessage, { replies }))
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        })
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      })
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    )
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  })
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}
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