Extract generic message count calculator

Progress toward #6

src/calculators/gender-message-count.js

@@ -1,28 +1,21 @@
+var trinaryGrouper = require('./trinary-grouper');
+
 class GenderMessageCountStatisticsGenerator{
   constructor(statistics, userIsMan) {
     this.statistics = statistics;
     this.userIsMan = userIsMan;
   }
 
   generate() {
-    var userIDs = Object.keys(this.statistics);
-
-    var counts = userIDs.reduce(function(counts, userID) {
-      var isMan = this.userIsMan[userID];
-      var count = this.statistics[userID];
-
-      if (isMan) {
-        counts.men += count;
-      } else if (isMan === false) {
-        counts.notMen += count;
-      } else {
-        counts.unknown += count;
+    return trinaryGrouper(
+      this.statistics,
+      this.userIsMan,
+      {
+        'true': 'men',
+        'false': 'notMen',
+        'else': 'unknown'
       }
-
-      return counts;
-    }.bind(this), {men: 0, notMen: 0, unknown: 0});
-
-    return counts;
+    );
   }
 }
 

src/calculators/race-message-count.js

@@ -1,4 +1,4 @@
-// FIXME extract a generalised solution from this and GenderMessageCount
+var trinaryGrouper = require('./trinary-grouper');
 
 class RaceMessageCount {
   constructor(statistics, userIsPersonOfColour) {
@@ -7,24 +7,15 @@ class RaceMessageCount {
   }
 
   generate() {
-    var userIDs = Object.keys(this.statistics);
-
-    var counts = userIDs.reduce(function(counts, userID) {
-      var isPersonOfColour = this.userIsPersonOfColour[userID];
-      var count = this.statistics[userID];
-
-      if (isPersonOfColour) {
-        counts.peopleOfColour += count;
-      } else if (isPersonOfColour === false) {
-        counts.whitePeople += count;
-      } else {
-        counts.unknown += count;
+    return trinaryGrouper(
+      this.statistics,
+      this.userIsPersonOfColour,
+      {
+        'true': 'peopleOfColour',
+        'false': 'whitePeople',
+        'else': 'unknown'
       }
-
-      return counts;
-    }.bind(this), {peopleOfColour: 0, whitePeople: 0, unknown: 0});
-
-    return counts;
+    );
   }
 }
 

src/calculators/trinary-grouper.js

@@ -0,0 +1,52 @@
+// TODO better name?
+
+// statistics = {
+//   a: 1,
+//   b: 2,
+//   c: 1
+// };
+//
+// mappings = {
+//   true: 'men',
+//   false: 'notMen',
+//   else: 'unknown'
+// };
+//
+// values = {
+//   a: true,
+//   b: false,
+// };
+//
+// =>
+//
+// {
+//   men: 1,
+//   notMen: 2,
+//   unknown: 1
+// }
+
+module.exports = function(statistics, values, mappings) {
+  var userIDs = Object.keys(statistics);
+
+  var emptyResult = {};
+  emptyResult[mappings.true] = 0;
+  emptyResult[mappings.false] = 0;
+  emptyResult[mappings.else] = 0;
+
+  var counts = userIDs.reduce(function(counts, userID) {
+    var value = values[userID];
+    var count = statistics[userID];
+
+    if (value) {
+      counts[mappings.true] += count;
+    } else if (value === false) {
+      counts[mappings.false] += count;
+    } else {
+      counts[mappings.else] += count;
+    }
+
+    return counts;
+  }, emptyResult);
+
+  return counts;
+};

test/calculators/trinary-grouper.js

@@ -0,0 +1,35 @@
+#!/usr/bin/env iojs --es_staging --use-strict
+
+var test = require('tape');
+
+var trinaryGrouper = require('../../src/calculators/trinary-grouper');
+
+test('trinaryGrouper groups counts by attribute value', function(t) {
+  var statistics = {
+    'Is tasty': 4,
+    'Is also tasty': 3,
+    'Not tasty': 2,
+    'Tastiness unknown': 1
+  };
+
+  var isTasty = {
+    'Is tasty': true,
+    'Is also tasty': true,
+    'Not tasty': false,
+    'Tastiness unknown': undefined
+  };
+
+  var mappings = {
+    'true': 'tasties',
+    'false': 'notTasties',
+    'else': 'mysterious'
+  };
+
+  var result = trinaryGrouper(statistics, isTasty, mappings);
+
+  t.equal(result.tasties, 7, 'counts 7 from tasties');
+  t.equal(result.notTasties, 2, 'counts 2 from non-tasties');
+  t.equal(result.mysterious, 1, 'counts 1 from mysterious');
+
+  t.end();
+});