contrib/nitrpg: enable statistics collection from GithubEvent

This shows how to implement GameReactors.
Statistics will also be used latter in the web display.

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --git a/contrib/nitrpg/src/statistics.nit b/contrib/nitrpg/src/statistics.nit
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+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Copyright 2014-2015 Alexandre Terrasa <alexandre@moz-code.org>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Statistics about the Game.
+#
+# This module uses `GameReactor` to extract statistics about the game from
+# triggered `Github::Event`.
+module statistics
+
+import game
+import github::hooks
+
+redef class Game
+
+       # Statistics for this game instance.
+       var stats = new GameStats
+
+       redef fun from_json(json) do
+               super
+               if json.has_key("statistics") then
+                       stats.from_json(json["statistics"].as(JsonObject))
+               end
+       end
+
+       redef fun to_json do
+               var obj = super
+               obj["statistics"] = stats.to_json
+               return obj
+       end
+
+       redef fun pretty do
+               var res = new FlatBuffer
+               res.append super
+               res.append "# stats:\n"
+               res.append stats.pretty
+               return res.write_to_string
+       end
+
+       redef fun clear do
+               super
+               stats.clear
+       end
+end
+
+# Game statistics structure that can be saved as a `GameEntity`.
+class GameStats
+       super GameEntity
+
+       redef var key = "statistics"
+
+       # Used internally to stats values.
+       private var stats = new HashMap[String, Int]
+
+       init do clear
+
+       # Load `self` from saved data
+       private fun from_json(json: JsonObject) do
+               for k, v in json do stats[k] = v.as(Int)
+       end
+
+       redef fun to_json do
+               var obj = new JsonObject
+               for k, v in stats do obj[k] = v
+               return obj
+       end
+
+       # Retrieves the current value of `key` statistic entry.
+       fun [](key: String): Int do return stats[key]
+
+       # Increments the value of `key` statistic entry by 1.
+       fun incr(key: String) do stats[key] += 1
+
+       # Decrements the value of `key` statistic entry by 1.
+       fun decr(key: String) do stats[key] -= 1
+
+       # Reset game stats.
+       fun clear do
+               stats["issues"] = 0
+               stats["issues_open"] = 0
+               stats["pulls"] = 0
+               stats["pulls_open"] = 0
+       end
+
+       redef fun pretty do
+               var res = new FlatBuffer
+               for k, v in stats do
+                       res.append "# {v} {k}\n"
+               end
+               return res.write_to_string
+       end
+end
+
+# `GameReactor` that computes statistics about the game.
+class StatisticsReactor
+       super GameReactor
+
+       redef fun react_event(game, e) do
+               super # log events
+               e.react_stats_event(game)
+               game.save
+       end
+end
+
+redef class GithubEvent
+       # Reacts to a statistics related event.
+       #
+       # Called by `StatisticsReactor::react_event`.
+       # No-op by default.
+       private fun react_stats_event(game: Game) do end
+end
+
+redef class IssuesEvent
+
+       # Count opened and closed issues.
+       redef fun react_stats_event(game) do
+               if action == "opened" then
+                       game.stats.incr("issues")
+                       game.stats.incr("issues_open")
+               else if action == "reopened" then
+                       game.stats.incr("issues_open")
+               else if action == "closed" then
+                       game.stats.decr("issues_open")
+               end
+       end
+end
+
+redef class PullRequestEvent
+
+       # Count opened and closed pull requests.
+       redef fun react_stats_event(game) do
+               if action == "opened" then
+                       game.stats.incr("pulls")
+                       game.stats.incr("pulls_open")
+               else if action == "reopened" then
+                       game.stats.incr("pulls_open")
+               else if action == "closed" then
+                       game.stats.decr("pulls_open")
+               end
+       end
+end