git ssb

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module.exports = function (onFirst, through, onLast, onEmpty) {
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  var ended, last, first = true, queue = []
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  return function (read) {
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    var mappedRead = through(function (end, cb) {
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      if (ended = end) return read(ended, cb)
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      if (queue.length)
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        return cb(null, queue.shift())
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      read(null, function (end, data) {
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        if (end) return cb(end)
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        last = data
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        cb(null, data)
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      })
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    })
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    return function (end, cb) {
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      var tmp
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      if (ended) return cb(ended)
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      if (ended = end) return read(ended, cb)
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      if (first)
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        return read(null, function (end, data) {
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          if (ended = end) {
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            if (end === true && onEmpty)
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              return onEmpty(cb)
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            return cb(ended)
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          }
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          first = false
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          last = data
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          queue.push(data)
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          if (onFirst)
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            onFirst(data, cb)
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          else
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            mappedRead(null, cb)
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        })
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      mappedRead(null, function (end, data) {
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        if (ended = end) {
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          if (end === true && last)
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            return onLast(last, cb)
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        }
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        cb(end, data)
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      })
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    }
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  }
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}
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