[gnome-software] ords: Use the Wilson algorithm to set priority when not sent

[Richard Hughes <rhughes src gnome org>]

commit 19d9b4949741323a1ed3164786ab7bbb38e51914
Author: Richard Hughes <richard hughsie com>
Date:   Thu Jul 28 09:47:08 2016 +0100

    ords: Use the Wilson algorithm to set priority when not sent
    
    If the user is not sending the local data for privacy reasons we can't
    calculate this server side.

 src/plugins/gs-plugin-odrs.c |   18 +++++++++++++++++-
 1 files changed, 17 insertions(+), 1 deletions(-)
---
diff --git a/src/plugins/gs-plugin-odrs.c b/src/plugins/gs-plugin-odrs.c
index f231bdc..ddd066b 100644
--- a/src/plugins/gs-plugin-odrs.c
+++ b/src/plugins/gs-plugin-odrs.c
@@ -24,6 +24,7 @@
 #include <gnome-software.h>
 #include <json-glib/json-glib.h>
 #include <string.h>
+#include <math.h>
 
 /*
  * SECTION:
@@ -239,8 +240,23 @@ gs_plugin_odrs_parse_review_object (GsPlugin *plugin, JsonObject *item)
        /* assemble review */
        if (json_object_has_member (item, "rating"))
                as_review_set_rating (rev, (gint) json_object_get_int_member (item, "rating"));
-       if (json_object_has_member (item, "score"))
+       if (json_object_has_member (item, "score")) {
                as_review_set_priority (rev, (gint) json_object_get_int_member (item, "score"));
+       } else if (json_object_has_member (item, "karma_up") &&
+                  json_object_has_member (item, "karma_down")) {
+               gdouble ku = (gdouble) json_object_get_int_member (item, "karma_up");
+               gdouble kd = (gdouble) json_object_get_int_member (item, "karma_down");
+               gdouble wilson = 0.f;
+
+               /* from http://www.evanmiller.org/how-not-to-sort-by-average-rating.html */
+               if (ku > 0 || kd > 0) {
+                       wilson = ((ku + 1.9208) / (ku + kd) -
+                                 1.96 * sqrt ((ku * kd) / (ku + kd) + 0.9604) /
+                                 (ku + kd)) / (1 + 3.8416 / (ku + kd));
+                       wilson *= 100.f;
+               }
+               as_review_set_priority (rev, (gint) wilson);
+       }
        if (json_object_has_member (item, "user_hash"))
                as_review_set_reviewer_id (rev, json_object_get_string_member (item, "user_hash"));
        if (json_object_has_member (item, "user_display"))