JI-1139 Add xAPI extension for statement when there exists alternatives

This is needed to reduce the solution space that grows exponentially
when there are alternatives in the crp, since crp requires
and exhaustive list of all possible solution combinations.
@see https://github.com/adlnet/xAPI-Spec/blob/master/xAPI-Data.md#correct-responses-pattern

.h5pignore

@@ -0,0 +1,2 @@
+crowdin.yml
+.gitignore

js/blanks.js

@@ -9,6 +9,10 @@ H5P.Blanks = (function ($, Question) {
   var STATE_SHOWING_SOLUTION = 'showing-solution';
   var STATE_FINISHED = 'finished';
 
+  const XAPI_ALTERNATIVE_EXTENSION = 'https://h5p.org/x-api/alternatives';
+  const XAPI_CASE_SENSITIVITY = 'https://h5p.org/x-api/case-sensitivity';
+  const XAPI_REPORTING_VERSION_EXTENSION = 'https://h5p.org/x-api/h5p-reporting-version';
+
   /**
    * @typedef {Object} Params
    *  Parameters/configuration object for Blanks
@@ -624,39 +628,48 @@ H5P.Blanks = (function ($, Question) {
     };
     definition.type = 'http://adlnet.gov/expapi/activities/cmi.interaction';
     definition.interactionType = 'fill-in';
-    definition.correctResponsesPattern = ['{case_matters=' + this.params.behaviour.caseSensitive + '}'];
-    var firstCorrectResponse = true;
+    const crpPrefix = '{case_matters=' + this.params.behaviour.caseSensitive + '}';
+    const clozeSolutions = [];
     // xAPI forces us to create solution patterns for all possible solution combinations
     for (var i = 0; i < this.params.questions.length; i++) {
       var question = this.handleBlanks(this.params.questions[i], function (solution) {
-        // Store new patterns for each extra alternative answer
-        var newPatterns = [];
-        for (var j = 0; j < definition.correctResponsesPattern.length; j++) {
-          if (!firstCorrectResponse) {
-            definition.correctResponsesPattern[j] += '[,]';
-          }
-          var prefix = definition.correctResponsesPattern[j];
-          for (var k = 0; k < solution.solutions.length; k++) {
-            if (k === 0) {
-              // This is the first possible answr, just add it to the pattern
-              definition.correctResponsesPattern[j] += solution.solutions[k];
-            }
-            else {
-              // This is an alternative possible answer, we need to create a new permutation
-              newPatterns.push(prefix + solution.solutions[k]);
-            }
-          }
-        }
-        // Add any new permutations to the list of response patterns
-        definition.correctResponsesPattern = definition.correctResponsesPattern.concat(newPatterns);
-
-        firstCorrectResponse = false;
+        // Collect solutions
+        clozeSolutions.push(solution.solutions);
 
         // We replace the solutions in the question with a "blank"
         return '__________';
       });
       definition.description['en-US'] += question;
     }
+
+    const hasAlternatives = clozeSolutions.some(function (cloze) {
+      return cloze.length > 1;
+    });
+
+    /**
+     * Note:
+     * If alternatives are used we don't provide a correct responses pattern
+     * since the solution space grows exponentially. We instead provide an
+     * extension for allowing reports to be generated.
+     * This is the recommended approach ref:
+     * @see(https://github.com/adlnet/xAPI-Spec/blob/master/xAPI-Data.md#correct-responses-pattern)
+     */
+    if (hasAlternatives) {
+      // Use extension to avoid exponentially growing solution space
+      definition.extensions = definition.extensions || {};
+      definition.extensions[XAPI_CASE_SENSITIVITY] = this.params.behaviour.caseSensitive;
+      definition.extensions[XAPI_ALTERNATIVE_EXTENSION] = clozeSolutions;
+    }
+    else {
+      // Use correct responses pattern
+      const singleAnswer = clozeSolutions.join('[,]');
+
+      definition.correctResponsesPattern = [
+        crpPrefix + singleAnswer,
+      ];
+    }
+
+
     return definition;
   };
 
@@ -665,7 +678,14 @@ H5P.Blanks = (function ($, Question) {
    */
   Blanks.prototype.addQuestionToXAPI = function (xAPIEvent) {
     var definition = xAPIEvent.getVerifiedStatementValue(['object', 'definition']);
-    $.extend(definition, this.getxAPIDefinition());
+    $.extend(true, definition, this.getxAPIDefinition());
+
+    // Set reporting module version if alternative extension is used
+    if (definition.extensions && definition.extensions[XAPI_ALTERNATIVE_EXTENSION]) {
+      const context = xAPIEvent.getVerifiedStatementValue(['context']);
+      context.extensions = context.extensions || {};
+      context.extensions[XAPI_REPORTING_VERSION_EXTENSION] = '1.1.0';
+    }
   };
 
   /**