var http = require('http')
var os = require('os')
var path = require('path')
var fs = require('fs')
var crypto = require('crypto')
var pkg = require('./package')
var semver = require('semver')
var toPull = require('stream-to-pull-stream')
var pull = require('pull-stream')
var tar = require('tar-stream')
var zlib = require('zlib')
var cat = require('pull-cat')
var hash = require('pull-hash')
var multicb = require('multicb')
var memo = require('asyncmemo')
var lru = require('hashlru')

function escapeHTML(str) {
  return String(str)
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
}

function idToHex(id) {
  var b64 = String(id).replace(/^[%#&]|\.[a-z0-9]*$/g, '')
  return new Buffer(b64, 'base64').toString('hex')
}

function onceify(fn, self) {
  var cbs = [], err, data
  return function (cb) {
    if (fn) {
      cbs.push(cb)
      fn.call(self, function (_err, _data) {
        err = _err, data = _data
        var _cbs = cbs
        cbs = null
        while (_cbs.length) _cbs.shift()(err, data)
      })
      fn = null
    } else if (cbs) {
      cbs.push(cb)
    } else {
      cb(err, data)
    }
  }
}

function once(cb) {
  var done
  return function (err, result) {
    if (done) {
      if (err) console.trace(err)
    } else {
      done = true
      cb(err, result)
    }
  }
}

function npmLogin(registryAddress, cb) {
  var tokenLine = registryAddress.replace(/^http:/, '') + ':_authToken=1'
  var filename = path.join(os.homedir(), '.npmrc')
  fs.readFile(filename, 'utf8', function (err, data) {
    if (err && err.code === 'ENOENT') data = ''
    else if (err) return cb(new Error(err.stack))
    var lines = data ? data.split('\n') : []
    if (lines.indexOf(tokenLine) > -1) return cb()
    var trailingNewline = (lines.length === 0 || lines[lines.length-1] === '')
    var line = trailingNewline ? tokenLine + '\n' : '\n' + tokenLine
    fs.appendFile(filename, line, cb)
  })
}

function formatHost(host) {
  return /^[^\[]:.*:.*:/.test(host) ? '[' + host + ']' : host
}

exports.name = 'npm-registry'
exports.version = '1.0.0'
exports.manifest = {
  getAddress: 'async'
}
exports.init = function (sbot, config) {
  var conf = config.npm || {}
  var port = conf.port || 8043
  var host = conf.host || null
  var autoAuth = conf.autoAuth !== false

  var server = http.createServer(exports.respond(sbot, config))
  var getAddress = onceify(function (cb) {
    server.on('error', cb)
    server.listen(port, host, function () {
      server.removeListener('error', cb)
      var regHost = formatHost(host || 'localhost')
      var regPort = this.address().port
      var regUrl = 'http://' + regHost + ':' + regPort + '/'
      if (autoAuth) npmLogin(regUrl, next)
      else next()
      function next(err) {
        cb(err, regUrl)
      }
    })
    sbot.on('close', function () {
      server.close()
    })
  })

  getAddress(function (err, addr) {
    if (err) return console.error('[npm-registry]', err.stack || err)
    console.log('[npm-registry] Listening on ' + addr)
  })

  return {
    getAddress: getAddress
  }
}

exports.respond = function (sbot, config) {
  var reg = new SsbNpmRegistryServer(sbot, config)
  return function (req, res) {
    new Req(reg, req, res).serve()
  }
}

function publishMsg(sbot, value, cb) {
  var gotExpectedPrevious = false
  sbot.publish(value, function next(err, msg) {
    if (err && /^expected previous:/.test(err.message)) {
      // retry once on this error
      if (gotExpectedPrevious) return cb(err)
      gotExpectedPrevious = true
      return sbot.publish(value, next)
    }
    cb(err, msg)
  })
}

function getDependencyBranches(sbot, link, cb) {
  var id = link.link

  // get ids of heads of tree of dependencyBranch message links to include all
  // the dependencies of the given tarball id.
  var getPackageJsonCached = memo(getPackageJsonFromTarballBlob, sbot)
  var msgs = {}
  var branched = {}
  var blobs = {}

  function addPkgById(id, cb) {
    if (blobs[id]) return cb()
    blobs[id] = true
    getPackageJsonCached(id, function (err, pkg) {
      if (err) return cb(err)
      var done = multicb()
      for (var name in pkg.dependencies || {}) {
        addPkgBySpec(name, pkg.dependencies[name], done())
      }
      done(cb)
    })
  }

  function addPkgBySpec(name, spec, cb) {
    var versions = {}
    var distTags = {}
    pull(
      getMentions(sbot.links2, {$prefix: 'npm:' + name + ':'}),
      pull.filter(mentionMatches(null, name, spec)),
      pull.map(function (mention) {
        // query to get the messages since links2 does not include the msg id
        return sbot.links({
          source: mention.author,
          dest: mention.link,
          rel: 'mentions',
          values: true,
        })
      }),
      pull.flatten(),
      pull.drain(function (msg) {
        var c = msg && msg.value && msg.value.content
        if (!c || !Array.isArray(c.mentions)) return
        c.mentions.forEach(function (link) {
          var data = link && link.name && decodeName(link.name)
          if (!data || data.name !== name) return
          versions[data.version] = {msg: msg, mention: link, mentionData: data}
          if (data.distTag) distTags[data.distTag] = data.version
        })
      }, function (err) {
        if (err) return cb(err)
        var version = distTags[spec]
          || semver.maxSatisfying(Object.keys(versions), spec)
        var item = versions[version]
        if (!item) return cb(new Error('Dependency version not found: ' + name + '@' + spec))
        addDepBranchMsg(item.msg)
        // console.log('add', item.msg.key, item.mentionData.name, item.mentionData.version)
        addPkgById(item.mention.link, cb)
      })
    )
  }

  function addDepBranchMsg(msg) {
    var c = msg && msg.value && msg.value.content
    if (!c) return
    if (msgs[msg.key]) return
    msgs[msg.key] = msg.value
    if (Array.isArray(c.dependencyBranch)) {
      for (var k = 0; k < c.dependencyBranch.length; k++) {
        branched[c.dependencyBranch[k]] = true
      }
    }
    if (Array.isArray(c.versionBranch)) {
      for (var k = 0; k < c.versionBranch.length; k++) {
        branched[c.versionBranch[k]] = true
      }
    }
  }

  function addPkgsByName(name, cb) {
    var data = decodeName(name)
    pull(
      getMentions(sbot.links2, {$prefix: 'npm:' + data.name + ':'}),
      pull.map(function (mention) {
        return packageLinks(sbot, mention.author, mention.link, data.name)
      }),
      pull.flatten(),
      pull.drain(addDepBranchMsg, cb)
    )
  }

  var done = multicb()
  addPkgsByName(link.name, done())
  addPkgById(id, done())
  done(function (err) {
    if (err) return cb(err)
    var ids = []
    for (var key in msgs) {
      if (!branched[key]) ids.push(key)
    }
    cb(null, ids)
  })
}

function packageLinks(sbot, feed, id, name, spec) {
  var matches = mentionMatches(id, name, spec)
  return pull(
    sbot.links({
      source: feed,
      dest: id,
      rel: 'mentions',
      values: true,
    }),
    pull.filter(function (msg) {
      var c = msg && msg.value && msg.value.content
      return c && Array.isArray(c.mentions) && c.mentions.some(matches)
    })
  )
}

// For each dependency that is not a bundledDependency, get message ids for
// that dependency name + version.
function publishSingleMention(sbot, mention, cb) {
  if (!sbot.links2) return cb(new Error('ssb-links scuttlebot plugin is required to publish ssb-npm packages'))
  // Calculate dependencyBranch message ids.
  var value = {
    type: 'npm-packages',
    mentions: [mention]
  }
  var done = multicb({pluck: 1, spread: true})
  getDependencyBranches(sbot, mention, function (err, branches) {
    if (err) return cb(err)
    value.dependencyBranch = branches || undefined
    publishMsg(sbot, value, cb)
  })
}

function publishMentions(sbot, mentions, cb) {
  // console.error("publishing %s mentions", mentions.length)
  if (mentions.length === 0) return cb(new Error('Empty mentions list'))
  // if it is just one mention, fetch and add useful metadata
  if (mentions.length === 1) return publishSingleMention(sbot, mentions[0], cb)
  publishMsg(sbot, {
    type: 'npm-packages',
    mentions: mentions,
  }, cb)
}

exports.publishPkgMentions = function (sbot, mentions, cb) {
  // try to fit the mentions into as few messages as possible,
  // while fitting under the message size limit.
  var msgs = []
  ;(function next(i, chunks) {
    if (i >= mentions.length) return cb(null, msgs)
    var chunkLen = Math.ceil(mentions.length / chunks)
    publishMentions(sbot, mentions.slice(i, i + chunkLen), function (err, msg) {
      if (err && /must not be large/.test(err.message)) return next(i, chunks + 1)
      if (err && msgs.length) return onPartialPublish(err)
      if (err) return cb(err)
      msgs.push(msg)
      next(i + chunkLen, chunks)
    })
  })(0, 1)
  function onPartialPublish(err) {
    var remaining = mentions.length - i
    return cb(new Error('Published messages ' +
      msgs.map(function (msg) { return msg.key }).join(', ') + ' ' +
      'but failed to publish remaining ' + remaining + ': ' + (err.stack || err)))
  }
}

exports.expandPkgMentions = function (sbot, mentions, props, cb) {
  cb = once(cb)
  var waiting = 0
  var expandedMentions = mentions.map(function (link) {
    var id = link && link.link
    if (!id) return link
    waiting++
    var newLink = {}
    for (var k in link) newLink[k] = link[k]
    getPackageJsonFromTarballBlob(sbot, id, function (err, pkg) {
      if (err) return cb(err)
      for (var k in props) newLink[k] = pkg[k]
      if (props.shasum && !pkg.shasum) newLink.shasum = pkg._shasum
      if (!--waiting) next()
    })
    return newLink
  })
  if (!waiting) next()
  function next() {
    cb(null, expandedMentions)
  }
}

function SsbNpmRegistryServer(sbot, config) {
  this.sbot = sbot
  this.config = config
  this.npmConfig = config.npm || {}
  this.host = this.npmConfig.host || 'localhost'
  this.fetchAll = this.npmConfig.fetchAll
  this.needShasum = this.npmConfig.needShasum
  var wsPort = config.ws && Number(config.ws.port) || '8989'
  this.wsLink = this.npmConfig.wsLink
    || ('http://' + (config.host || 'localhost') + ':' + wsPort)
  this.getMsg = memo({cache: lru(100)}, this.getMsg)
}

SsbNpmRegistryServer.prototype = Object.create(http.Server.prototype)
SsbNpmRegistryServer.prototype.constructor = SsbNpmRegistryServer

SsbNpmRegistryServer.prototype.pushBlobs = function (ids, cb) {
  var self = this
  if (!self.sbot.blobs.push) return cb(new Error('missing blobs.push'))
  ;(function next(i) {
    if (i >= ids.length) return cb()
    self.sbot.blobs.push(ids[i], function (err) {
      if (err) return cb(err)
      next(i+1)
    })
  })(0)
}

function getBlob(sbot, id, cb) {
  var blobs = sbot.blobs
  blobs.size(id, function (err, size) {
    if (err) return cb(err)
    if (typeof size === 'number') cb(null, blobs.get(id), size)
    else blobs.want(id, function (err, got) {
      if (err) cb(err)
      else if (!got) cb('missing blob ' + id)
      else blobs.size(id, function (err, size) {
        if (err) return cb(err)
        cb(null, blobs.get(id), size)
      })
    })
  })
}

SsbNpmRegistryServer.prototype.blobDist = function (id) {
  var m = /^&([^.]+)\.([a-z0-9]+)$/.exec(id)
  if (!m) throw new Error('bad blob id: ' + id)
  return {
    integrity: m[2] + '-' + m[1],
    tarball: this.wsLink + '/blobs/get/' + id
  }
}

function getMentions(links2, name) {
  return links2.read({
    query: [
      {$filter: {rel: ['mentions', name, {$gt: true}]}},
      {$filter: {dest: {$prefix: '&'}}},
      {$map: {
        name: ['rel', 1],
        size: ['rel', 2],
        link: 'dest',
        author: 'source',
        ts: 'ts'
      }}
    ]
  })
}

function mentionMatches(id, name, spec) {
  return function (mention) {
    var data = mention
      && (!id || id === mention.link)
      && mention.name
      && decodeName(mention.name)
    return data
      && data.name === name
      && (spec ? semver.satisfies(data.version, spec) : true)
  }
}

SsbNpmRegistryServer.prototype.getMentions = function (name) {
  if (!this.sbot.links2) return pull.empty()
  return getMentions(this.sbot.links2, name)
}

SsbNpmRegistryServer.prototype.getMsg = function (id, cb) {
  if (this.sbot.ooo) return this.sbot.ooo.get(id, cb)
  else this.sbot.get(id, function (err, value) {
    if (err) return cb(err)
    cb(null, {key: id, value: value})
  })
}

SsbNpmRegistryServer.prototype.streamTree = function (heads, prop) {
  var self = this
  var stack = heads.slice()
  var seen = {}
  return function (abort, cb) {
    if (abort) return cb(abort)
    for (var id; stack.length && seen[id = stack.pop()];);
    if (!id) return cb(true)
    seen[id] = true
    // TODO: use DFS
    self.getMsg(id, function (err, msg) {
      if (err) return cb(new Error(err.stack || err))
      var c = msg && msg.value && msg.value.content
      var links = c && c[prop]
      if (Array.isArray(links)) {
        stack.push.apply(stack, links)
      } else if (links) {
        stack.push(links)
      }
      cb(null, msg)
    })
  }
}

function Req(server, req, res) {
  this.server = server
  this.req = req
  this.res = res
  this.blobsToPush = []
  this.fetchAll = server.fetchAll != null ? server.fetchAll : true
  var ua = this.req.headers['user-agent']
  var m = /\bnpm\/([0-9]*)/.exec(ua)
  var npmVersion = m && m[1]
  this.needShasum = server.needShasum != null ? server.needShasum :
    (npmVersion && npmVersion < 5)
  this.wsLink = this.server.wsLink
}

Req.prototype.serve = function () {
  console.log(this.req.method, this.req.url, this.req.socket.remoteAddress.replace(/^::ffff:/, ''))
  this.res.setTimeout(0)
  var pathname = this.req.url.replace(/\?.*/, '')
  var m
  if ((m = /^\/(\^|%5[Ee])?(%25.*sha256)+(\/.*)$/.exec(pathname))) {
    try {
      this.headMsgIds = decodeURIComponent(m[2]).split(',')
      this.headMsgPlus = !!m[1]
      // ^ means also include packages published after the head message id
    } catch(e) {
      return this.respondError(400, e.stack || e)
    }
    pathname = m[3]
  }
  if (pathname === '/') return this.serveHome()
  if (pathname === '/robots.txt') return this.serveRobots()
  if (pathname === '/-/bootstrap') return this.serveBootstrap()
  if (pathname === '/-/whoami') return this.serveWhoami()
  if (pathname === '/-/ping') return this.respond(200, true)
  if (pathname === '/-/user/org.couchdb.user:1') return this.serveUser1()
  if (pathname.startsWith('/-/blobs/get/')) return this.serveBlob(pathname.substr(13))
  if (pathname.startsWith('/-/msg/')) return this.serveMsg(pathname.substr(7))
  if ((m = /^\/-\/prebuild\/(.*)$/.exec(pathname))) return this.servePrebuild(m[1])
  if (!/^\/-\//.test(pathname)) return this.servePkg(pathname.substr(1))
  return this.respond(404, {error: 'Not found'})
}

Req.prototype.respond = function (status, message) {
  this.res.writeHead(status, {'content-type': 'application/json'})
  this.res.end(message && JSON.stringify(message, 0, 2))
}

Req.prototype.respondError = function (status, message) {
  this.respond(status, {error: message})
}

Req.prototype.respondErrorStr = function (status, err) {
  this.res.writeHead(status, {'content-type': 'text/plain'})
  this.res.end(err.stack || err)
}

Req.prototype.respondRaw = function (status, body) {
  this.res.writeHead(status)
  this.res.end(body)
}

Req.prototype.serveHome = function () {
  var self = this
  self.res.writeHead(200, {'content-type': 'text/html'})
  var port = 8044
  self.res.end('<!doctype html><html><head><meta charset=utf-8>' +
    '<title>' + escapeHTML(pkg.name) + '</title></head><body>' +
    '<h1>' + escapeHTML(pkg.name) + '</h1>\n' +
    '<p><a href="/-/bootstrap">Bootstrap</a></p>\n' +
    '</body></html>')
}

Req.prototype.getMsgIdForBlobMention = function (blobId, feedId, cb) {
  var self = this
  pull(
    self.server.sbot.links({
      source: feedId,
      dest: blobId,
      rel: 'mentions',
      values: true,
    }),
    pull.filter(function (msg) {
      var c = msg && msg.value && msg.value.content
      return c.type === 'npm-packages'
    }),
    pull.collect(function (err, msgs) {
      if (err) return cb(err)
      if (msgs.length === 0) return cb(new Error('Unable to find message id for mention ' + blobId + ' ' + feedId))
      if (msgs.length > 1) console.warn('Warning: multiple messages mentioning blob id ' + blobId + ' ' + feedId)
      // TODO: make a smarter decision about which message id to use
      cb(null, msgs.pop().key)
    })
  )
}

Req.prototype.resolvePkg = function (pkgSpec, cb) {
  var m = /(.[^@]*)(?:@(.*))?/.exec(pkgSpec)
  if (!m) return cb(new Error('unable to parse spec: \'' + pkgSpec + '\''))
  var self = this
  var pkgName = m[1]
  var spec = m[2] || '*'
  var versions = {}
  var distTags = {}
  pull(
    self.getMentions({$prefix: 'npm:' + pkgName + ':'}),
    pull.drain(function (mention) {
      var data = decodeName(mention.name)
      if (!data.version) return
      if (data.distTag) {
        distTags[data.distTag] = data.version
      }
      versions[data.version] = {
        author: mention.author,
        name: pkgName,
        version: data.version,
        blobId: mention.link
      }
    }, function (err) {
      if (err) return cb(err)
      var version = distTags[spec]
        || semver.maxSatisfying(Object.keys(versions), spec)
      var item = versions[version]
      if (!item) return cb(new Error('Version not found: ' + pkgName + '@' + spec))
      self.getMsgIdForBlobMention(item.blobId, item.author, function (err, id) {
        if (err) return cb(err)
        item.msgId = id
        cb(null, item)
      })
    })
  )
}

Req.prototype.resolvePkgs = function (specs, cb) {
  var done = multicb({pluck: 1})
  var self = this
  specs.forEach(function (spec) {
    self.resolvePkg(spec, done())
  })
  done(cb)
}

Req.prototype.serveBootstrap = function () {
  var self = this
  var pkgs = self.server.npmConfig.defaultPkgs || ['scuttlebot', 'ssb-npm', 'git-ssb']
  var ssbNpmRegistryName = require('./package.json').name
  var ssbNpmRegistryVersion = require('./package.json').version
  var ssbNpmRegistryNameVersion = ssbNpmRegistryName + '-' + ssbNpmRegistryVersion
  var ssbNpmRegistrySpec = ssbNpmRegistryName + '@^' + ssbNpmRegistryVersion
  var done = multicb({pluck: 1, spread: true})
  self.resolvePkg(ssbNpmRegistrySpec, done())
  self.resolvePkgs(pkgs, done())
  done(function (err, ssbNpmRegistryPkgInfo, pkgsInfo) {
    if (err) return self.respondErrorStr(500, err.stack || err)
    if (!ssbNpmRegistryPkgInfo) return self.respondErrorStr(500, 'Missing ssb-npm-registry package')
    var ssbNpmRegistryBlobId = ssbNpmRegistryPkgInfo.blobId
    var ssbNpmRegistryBlobHex = idToHex(ssbNpmRegistryBlobId)
    var pkgMsgs = pkgsInfo.map(function (info) { return info.msgId })
    var globalPkgs = pkgsInfo.map(function (info) {
      return info.name + '@' + info.version
    }).join(' ')
    var npmCmd = 'install -g ' + globalPkgs
    var tmpDir = '/tmp/' + encodeURIComponent(ssbNpmRegistryNameVersion)
    var tarballLink = self.wsLink + '/blobs/get/' + ssbNpmRegistryBlobId

    var script =
      'mkdir -p ' + tmpDir + ' && cd ' + tmpDir + ' &&\n' +
      'wget -q \'' + tarballLink + '\' -O package.tgz &&\n' +
      'echo \'' + ssbNpmRegistryBlobHex + '  package.tgz\' | sha256sum -c &&\n' +
      'tar xzf package.tgz &&\n' +
      './*/bootstrap/bin.js --ws-url ' + self.wsLink + ' \\\n' +
        pkgMsgs.map(function (id) {
          return '  --branch ' + id + ' \\\n'
        }).join('') +
        '  -- ' + npmCmd + ' &&\n' +
      'sbot server'

    self.res.writeHead(200, {'Content-type': 'text/plain'})
    self.res.end(script)
  })
}

Req.prototype.serveRobots = function () {
  this.res.writeHead(200, {'Content-type': 'text/plain'})
  this.res.end('User-agent: *\nDisallow: /\n')
}

Req.prototype.serveWhoami = function () {
  var self = this
  self.server.sbot.whoami(function (err, feed) {
    if (err) return self.respondError(500, err.stack || err)
    self.respond(200, {username: feed.id})
  })
}

Req.prototype.serveUser1 = function () {
  this.respond(this.req.method === 'PUT' ? 201 : 200, {token: '1'})
}

Req.prototype.serveBlob = function (id) {
  var self = this
  if (self.req.headers['if-none-match'] === id) return self.respondRaw(304)
  getBlob(self.server.sbot, id, function (err, readBlob, size) {
    if (err) {
      if (/^invalid/.test(err.message)) return self.respondErrorStr(400, err.message)
      else return self.respondErrorStr(500, err.message || err)
    }
    self.res.writeHead(200, {
      'Cache-Control': 'public, max-age=315360000',
      'Content-Length': size,
      'etag': id
    })
    pull(
      readBlob,
      toPull(self.res, function (err) {
        if (err) console.error('[npm-registry]', err)
      })
    )
  })
}

Req.prototype.serveMsg = function (id) {
  var self = this
  try { id = decodeURIComponent(id) }
  catch (e) {}
  if (self.req.headers['if-none-match'] === id) return self.respondRaw(304)
  self.server.sbot.get(id, function (err, value) {
    if (err) return self.respondError(500, err.message || err)
    var out = new Buffer(JSON.stringify({key: id, value: value}, null, 2), 'utf8')
    self.res.writeHead(200, {
      'Content-Type': 'application/json',
      'Cache-Control': 'public, max-age=315360000',
      'Content-Length': out.length,
      'etag': id
    })
    self.res.end(out)
  })
}

function decodeName(name) {
  var parts = String(name).replace(/\.tgz$/, '').split(':')
  return {
    name: parts[1],
    version: parts[2],
    distTag: parts[3],
  }
}

Req.prototype.getMsgMentions = function (name) {
  return pull(
    this.server.streamTree(this.headMsgIds, 'dependencyBranch'),
    // decryption could be done here
    pull.map(function (msg) {
      var c = msg.value && msg.value.content
      if (!c.mentions || !Array.isArray(c.mentions)) return []
      return c.mentions.map(function (mention) {
        return {
          name: mention.name,
          size: mention.size,
          link: mention.link,
          author: msg.value.author,
          ts: msg.value.timestamp,
        }
      })
    }),
    pull.flatten(),
    pull.filter(typeof name === 'string' ? function (link) {
      return link.name === name
    } : name && name.$prefix ? function (link) {
      return link.name.substr(0, name.$prefix.length) === name.$prefix
    } : function () {
      throw new TypeError('unsupported name filter')
    })
  )
}

Req.prototype.getMentions = function (name) {
  var useMsgMentions = this.headMsgIds
  var useServerMentions = !this.headMsgIds || this.headMsgPlus
  if (useServerMentions && !this.server.sbot.links2) {
    return this.headMsgPlus
      ? pull.error(new Error('ssb-links scuttlebot plugin is needed for ^msgid queries'))
      : pull.error(new Error('ssb-links scuttlebot plugin is needed for non-msgid queries'))
  }
  return cat([
    useMsgMentions ? this.getMsgMentions(name) : pull.empty(),
    useServerMentions ? this.server.getMentions(name) : pull.empty()
  ])
}

Req.prototype.getMentionLinks = function (blobId) {
  return pull(
    this.headMsgIds
      ? this.server.streamTree(this.headMsgIds, 'dependencyBranch')
      : this.server.sbot.links({
        dest: blobId,
        rel: 'mentions',
        values: true,
      }),
    // decryption could be done here
    pull.map(function (msg) {
      var c = msg.value && msg.value.content
      return c && Array.isArray(c.mentions) && c.mentions || []
    }),
    pull.flatten(),
    pull.filter(function (link) {
      return link && link.link === blobId
    })
  )
}

Req.prototype.servePkg = function (pathname) {
  var self = this
  var parts = pathname.split('/')
  var pkgName = parts.shift().replace(/%2f/i, '/')
  if (parts[0] === '-rev') return this.respondError(501, 'Unpublish is not supported')
  var spec = parts.shift()
  if (spec) try { spec = decodeURIComponent(spec) } finally {}
  if (parts.length > 0) return this.respondError(404)
  if (self.req.method === 'PUT') return self.publishPkg(pkgName)
  var obj = {
    _id: pkgName,
    name: pkgName,
    'dist-tags': {},
    versions: {}
  }
  var distTags = {/* <tag>: {version, ts}*/}
  pull(
    self.getMentions({$prefix: 'npm:' + pkgName + ':'}),
    pull.drain(function (mention) {
      var data = decodeName(mention.name)
      if (!data.version) return
      if (data.distTag) {
        var tag = distTags[data.distTag]
        if (!tag || mention.ts > tag.ts) {
          /* TODO: sort by causal order instead of only by timestamps */
          distTags[data.distTag] = {ts: mention.ts, version: data.version}
        }
      }
      obj.versions[data.version] = {
        author: {
          url: mention.author
        },
        name: pkgName,
        version: data.version,
        dist: self.server.blobDist(mention.link)
      }
    }, function (err) {
      if (err) return self.respondError(500, err.stack || err)
      for (var tag in distTags) {
        obj['dist-tags'][tag] = distTags[tag].version
      }
      if (spec) resolveSpec()
      else if (self.fetchAll) resolveAll()
      else resolved()
    })
  )
  function resolveSpec() {
    var version = obj['dist-tags'][spec]
      || semver.maxSatisfying(Object.keys(obj.versions), spec)
    obj = obj.versions[version]
    if (!obj) return self.respondError(404, 'version not found: ' + spec)
    self.populatePackageJson(obj, function (err, pkg) {
      if (err) return resolved(err)
      obj = pkg || obj
      resolved()
    })
  }
  function resolveVersion(version, cb) {
    self.populatePackageJson(obj.versions[version], function (err, pkg) {
      if (err) return cb(err)
      if (pkg) obj.versions[version] = pkg
      cb()
    })
  }
  function resolveAll() {
    var done = multicb()
    for (var version in obj.versions) {
      resolveVersion(version, done())
    }
    done(resolved)
  }
  function resolved(err) {
    if (err) return self.respondError(500, err.stack || err)
    self.respond(200, obj)
  }
}

Req.prototype.servePrebuild = function (name) {
  var self = this
  var getMention = self.getMentions('prebuild:' + name)
  var blobsByAuthor = {/* <author>: BlobId */}
  pull(getMention, pull.drain(function (link) {
    blobsByAuthor[link.author] = link.link
  }, function (err) {
    if (err) return self.respondError(500, err.stack || err)
    var authorsByLink = {/* <BlobId>: [FeedId...] */}
    var blobId
    for (var feed in blobsByAuthor) {
      var blob = blobId = blobsByAuthor[feed]
      var feeds = authorsByLink[blob] || (authorsByLink[blob] = [])
      feeds.push(feed)
    }
    switch (Object.keys(authorsByLink).length) {
      case 0:
        return self.respondError(404, 'Not Found')
      case 1:
        self.res.writeHead(303, {Location: self.wsLink + '/blobs/get/' + blobId})
        return self.res.end()
      default:
        return self.respond(300, {choices: authorsByLink})
    }
  }))
}

var localhosts = {
  '::1': true,
  '127.0.0.1': true,
  '::ffff:127.0.0.1': true,
}

Req.prototype.publishPkg = function (pkgName) {
  var self = this
  var remoteAddress = self.req.socket.remoteAddress
  if (!(remoteAddress in localhosts)) {
    return self.respondError(403, 'You may not publish as this user.')
  }

  var chunks = []
  self.req.on('data', function (data) {
    chunks.push(data)
  })
  self.req.on('end', function () {
    var data
    try {
      data = JSON.parse(Buffer.concat(chunks))
    } catch(e) {
      return self.respondError(400, e.stack)
    }
    return self.publishPkg2(pkgName, data || {})
  })
}

Req.prototype.publishPkg2 = function (name, data) {
  var self = this
  if (data.users) console.trace('[npm-registry] users property is not supported')
  var attachments = data._attachments || {}
  var links = {/* <name>-<version>.tgz: {link: <BlobId>, size: number} */}
  var done = multicb()
  function addAttachmentAsBlob(filename, cb) {
    var data = attachments[filename].data
    var tarball = new Buffer(data, 'base64')
    var length = attachments[filename].length
    if (length && length !== tarball.length) return self.respondError(400,
      'Length mismatch for attachment \'' + filename + '\'')
    self.server.sbot.blobs.add(function (err, id) {
      if (err) return cb(err)
      self.blobsToPush.push(id)
      var shasum = crypto.createHash('sha1').update(tarball).digest('hex')
      links[filename] = {link: id, size: tarball.length, shasum: shasum}
      cb()
    })(pull.once(tarball))
  }
  for (var filename in attachments) {
    addAttachmentAsBlob(filename, done())
  }
  done(function (err) {
    if (err) return self.respondError(500, err.stack || err)
    try {
      self.publishPkg3(name, data, links)
    } catch(e) {
      self.respondError(500, e.stack || e)
    }
  })
}

Req.prototype.publishPkg3 = function (name, data, links) {
  var self = this
  var versions = data.versions || {}
  var linksByVersion = {/* <version>: link */}

  // associate tarball blobs with versions
  for (var version in versions) {
    var pkg = versions[version]
    if (!pkg) return self.respondError(400, 'Bad package object')
    if (!pkg.dist) return self.respondError(400, 'Missing package dist property')
    if (!pkg.dist.tarball) return self.respondError(400, 'Missing dist.tarball property')
    if (pkg.deprecated) return self.respondError(501, 'Deprecation is not supported')
    var m = /\/-\/([^\/]+)$/.exec(pkg.dist.tarball)
    if (!m) return self.respondError(400, 'Bad tarball URL \'' + pkg.dist.tarball + '\'')
    var filename = m[1]
    var link = links[filename]
    if (!link) return self.respondError(501, 'Unable to find attachment \'' + filename + '\'')
    // TODO?: try to find missing tarball mentioned in other messages
    if (pkg.version && pkg.version !== version)
      return self.respondError(400, 'Mismatched package version: ' + [pkg.version, version])
    linksByVersion[version] = link
    link.version = version
    link.dependencies = pkg.dependencies || {}
    link.bundledDependencies = pkg.bundledDependencies || pkg.bundleDependencies
  }

  // associate blobs with dist-tags
  var tags = data['dist-tags'] || {}
  for (var tag in tags) {
    var version = tags[tag]
    var link = linksByVersion[version]
    if (!link) return self.respondError(501, 'Setting a dist-tag for a version not being published is not supported.')
    // TODO?: support setting dist-tag without version,
    // by looking up a tarball blob for the version
    link.tag = tag
  }

  // compute blob links to publish
  var mentions = []
  for (var filename in links) {
    var link = links[filename] || {}
    if (!link.version) return self.respondError(400, 'Attachment ' + filename + ' was not linked to in the package metadata')
    mentions.push({
      name: 'npm:' + name + ':' + link.version + (link.tag ? ':' + link.tag : ''),
      link: link.link,
      size: link.size,
      shasum: link.shasum,
      dependencies: link.dependencies,
      bundledDependencies: link.bundledDependencies,
    })
  }
  return self.publishPkgs(mentions)
}

Req.prototype.publishPkgs = function (mentions) {
  var self = this
  exports.publishPkgMentions(self.server.sbot, mentions, function (err, msgs) {
    if (err) return self.respondError(500, err.stack || err)
    self.server.pushBlobs(self.blobsToPush, function (err) {
      if (err) console.error('[npm-registry] Failed to push blob ' + id + ': ' + (err.stack || err))
      self.respond(201)
      console.log(msgs.map(function (msg) { return msg.key }).join('\n'))
    })
  })
}

Req.prototype.populatePackageJson = function (obj, cb) {
  var self = this
  var blobId = obj.dist.tarball.replace(/.*\/blobs\/get\//, '')
  var deps, bundledDeps, shasum

  // look for dependencies in links.
  // then fallback to getting it from the tarball blob

  pull(
    self.getMentionLinks(blobId),
    pull.drain(function (link) {
      if (link.dependencies) deps = link.dependencies
      if (link.shasum) shasum = link.shasum
      bundledDeps = link.bundledDependencies || link.bundleDependencies || bundledDeps
      // how to handle multiple assignments of dependencies to a package?
    }, function (err) {
      if (err) return cb(new Error(err.stack || err))
      if (deps && (shasum || !self.needShasum)) {
        // assume that the dependencies in the links to the blob are
        // correct.
        obj.dependencies = deps
        obj.bundledDependencies = bundledDeps
        if (shasum) obj.dist.shasum = obj._shasum = shasum
        cb(null, obj)
      } else {
        // get dependencies from the tarball
        getPackageJsonFromTarballBlob(self.server.sbot, blobId, function (err, pkg) {
          if (err) return cb(err)
          pkg.dist = obj.dist
          pkg.dist.shasum = pkg._shasum
          pkg.author = pkg.author || obj.author
          pkg.version = pkg.version || obj.version
          pkg.name = pkg.name || obj.name
          cb(null, pkg)
        })
      }
    })
  )
}

function getPackageJsonFromTarballBlob(sbot, id, cb) {
  var self = this
  getBlob(sbot, id, function (err, readBlob) {
    if (err) return cb(err)
    cb = once(cb)
    var extract = tar.extract()
    var pkg, shasum
    extract.on('entry', function (header, stream, next) {
      if (/^[^\/]*\/package\.json$/.test(header.name)) {
        pull(toPull.source(stream), pull.collect(function (err, bufs) {
          if (err) return cb(err)
          try { pkg = JSON.parse(Buffer.concat(bufs)) }
          catch(e) { return cb(e) }
          next()
        }))
      } else {
        stream.on('end', next)
        stream.resume()
      }
    })
    extract.on('finish', function () {
      pkg._shasum = shasum
      cb(null, pkg)
    })
    pull(
      readBlob,
      hash('sha1', 'hex', function (err, sum) {
        if (err) return cb(err)
        shasum = sum
      }),
      toPull(zlib.createGunzip()),
      toPull(extract)
    )
  })
}