Extract generic participant count calculator

Progress toward #6

src/calculators/gender-participant-count.js

@@ -1,27 +1,21 @@
+var trinaryCounter = require('./trinary-counter');
+
 class GenderParticipantCountReportGenerator {
   constructor(userMessages, userIsMan) {
     this.userMessages = userMessages;
     this.userIsMan = userIsMan;
   }
 
   generate() {
-    var userIDs = Object.keys(this.userMessages);
-
-    var counts = userIDs.reduce(function(counts, userID) {
-      var isMan = this.userIsMan[userID];
-
-      if (isMan) {
-        counts.men += 1;
-      } else if (isMan === false) {
-        counts.notMen += 1;
-      } else {
-        counts.unknown += 1;
+    return trinaryCounter(
+      this.userMessages,
+      this.userIsMan,
+      {
+        'true': 'men',
+        'false': 'notMen',
+        'else': 'unknown'
       }
-
-      return counts;
-    }.bind(this), {men: 0, notMen: 0, unknown: 0});
-
-    return counts;
+    );
   }
 }
 

src/calculators/trinary-counter.js

@@ -0,0 +1,24 @@
+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];
+
+    if (value) {
+      counts[mappings.true] += 1;
+    } else if (value === false) {
+      counts[mappings.false] += 1;
+    } else {
+      counts[mappings.else] += 1;
+    }
+
+    return counts;
+  }, emptyResult);
+
+  return counts;
+};

test/calculators/trinary-counter.js

@@ -0,0 +1,35 @@
+#!/usr/bin/env iojs --es_staging --use-strict
+
+var test = require('tape');
+
+var trinaryCounter = require('../../src/calculators/trinary-counter');
+
+test('trinaryCounter counts by attribute value', function(t) {
+  var statistics = {
+    'Is Purple': 4,
+    'Is Also Purple': 3,
+    'Is Yellow': 2,
+    'Colour unknown': 1
+  };
+
+  var isPurple = {
+    'Is Purple': true,
+    'Is Also Purple': true,
+    'Is Yellow': false,
+    'Colour unknown': undefined
+  };
+
+  var mappings = {
+    'true': 'purples',
+    'false': 'notPurples',
+    'else': 'hmm'
+  };
+
+  var result = trinaryCounter(statistics, isPurple, mappings);
+
+  t.equal(result.purples, 2, 'counts 2 purples');
+  t.equal(result.notPurples, 1, 'counts 1 not-purple');
+  t.equal(result.hmm, 1, 'counts 1 unknown');
+
+  t.end();
+});