Add common user code problems to campaign editor

In level view, showing data from last 30 days, with top 20 issues by
count.

app/templates/editor/campaign/campaign-level-view.jade

@@ -39,7 +39,29 @@
   else
     div Loading...
 
-                
+  h4 Common Problems
+  if commonProblems
+    if commonProblems.startDay
+      if commonProblems.endDay
+        div(style='font-size:10pt') #{commonProblems.startDay} to #{commonProblems.endDay}
+      else
+        div(style='font-size:10pt') #{commonProblems.startDay} to today
+    table.table.table-bordered.table-condensed.table-hover(style='font-size:10pt')
+      thead
+        tr
+          td Language
+          td Error Message
+          td Error Hint
+          td Count
+      tbody
+        - for (var i = 0; i < commonProblems.length && i < 20; i++)
+          tr
+            td= commonProblems[i].language
+            td= commonProblems[i].message
+            td= commonProblems[i].hint
+            td= commonProblems[i].count
+  else
+    div Loading...
 
 if level.get('tasks')
   .tasks

app/views/editor/campaign/CampaignLevelView.coffee

@@ -15,12 +15,14 @@ module.exports = class CampaignLevelView extends CocoView
     @listenToOnce @fullLevel, 'sync', => @render?()
 
     @levelSlug = @level.get('slug')
+    @getCommonLevelProblems()
     @getLevelCompletions()
     @getLevelPlaytimes()
 
   getRenderData: ->
     c = super()
     c.level = if @fullLevel.loaded then @fullLevel else @level
+    c.commonProblems = @commonProblems
     c.levelCompletions = @levelCompletions
     c.levelPlaytimes = @levelPlaytimes
     c
@@ -29,6 +31,27 @@ module.exports = class CampaignLevelView extends CocoView
     @$el.addClass('hidden')
     @trigger 'hidden'
 
+  getCommonLevelProblems: ->
+    # Fetch last 30 days of common level problems
+    startDay = new Date()
+    startDay.setDate(startDay.getUTCDate() - 29)
+    startDay = startDay.getUTCFullYear() + '-' + (startDay.getUTCMonth() + 1) + '-' + startDay.getUTCDate()
+
+    success = (data) =>
+      return if @destroyed
+      @commonProblems = data
+      @commonProblems.startDay = startDay
+      @render()
+
+    # TODO: Why do we need this url dash?
+    request = @supermodel.addRequestResource 'common_problems', {
+      url: '/db/user_code_problem/-/common_problems'
+      data: {startDay: startDay, slug: @levelSlug}
+      method: 'POST'
+      success: success
+    }, 0
+    request.load()
+
   getLevelCompletions: ->
     # Fetch last 7 days of level completion counts
     success = (data) =>

server/user_code_problems/user_code_problem_handler.coffee

@@ -23,4 +23,62 @@ class UserCodeProblemHandler extends Handler
     ucp.set('creator', req.user._id)
     ucp
 
+  getByRelationship: (req, res, args...) ->
+    return @getCommonLevelProblemsBySlug(req, res) if args[1] is 'common_problems'
+    super(arguments...)
+
+  getCommonLevelProblemsBySlug: (req, res) ->
+    # Returns an ordered array of common user code problems with: language, message, hint, count
+    # Parameters:
+    # slug - level slug
+    # startDay - Inclusive, optional, e.g. '2014-12-14'
+    # endDay - Exclusive, optional, e.g. '2014-12-16'
+
+    levelSlug = req.query.slug or req.body.slug
+    startDay = req.query.startDay or req.body.startDay
+    endDay = req.query.endDay or req.body.endDay
+
+    return @sendSuccess res, [] unless levelSlug?
+
+    # Cache results for 1 day
+    @commonLevelProblemsCache ?= {}
+    @commonLevelProblemsCachedSince ?= new Date()
+    if (new Date()) - @commonLevelProblemsCachedSince > 86400 * 1000  # Dumb cache expiration
+      @commonLevelProblemsCache = {}
+      @commonLevelProblemsCachedSince = new Date()
+    cacheKey = levelSlug
+    cacheKey += 's' + startDay if startDay?
+    cacheKey += 'e' + endDay if endDay?
+    return @sendSuccess res, commonProblems if commonProblems = @commonLevelProblemsCache[cacheKey]
+
+    # Build query
+    match = if startDay? or endDay? then {$match: {$and: []}} else {$match: {}}
+    match["$match"]["$and"].push created: {$gte: new Date(startDay + "T00:00:00.000Z")} if startDay?
+    match["$match"]["$and"].push created: {$lt: new Date(endDay + "T00:00:00.000Z")} if endDay?
+    group = {"$group": {"_id": {"errMessage": "$errMessageNoLineInfo", "errHint": "$errHint", "language": "$language", "levelID": "$levelID"}, "count": {"$sum": 1}}}
+    sort = { $sort : { "_id.levelID": 1, count : -1, "_id.language": 1 } }
+    query = UserCodeProblem.aggregate match, group, sort
+
+    query.exec (err, data) =>
+      if err? then return @sendDatabaseError res, err
+
+      # Build per-level common problem lists
+      commonProblems = {}
+      for item in data
+        levelID = item._id.levelID
+        commonProblems[levelID] ?= []
+        commonProblems[levelID].push
+          language: item._id.language
+          message: item._id.errMessage
+          hint: item._id.errHint
+          count: item.count
+
+      # Cache all the levels
+      for levelID of commonProblems
+        cacheKey = levelID
+        cacheKey += 's' + startDay if startDay?
+        cacheKey += 'e' + endDay if endDay?
+        @commonLevelProblemsCache[cacheKey] = commonProblems[levelID]
+      @sendSuccess res, commonProblems[levelSlug]
+
 module.exports = new UserCodeProblemHandler()