Add MetricsAggregationMixin and AvgAggregation.

The Metrics Aggregation Mixin can be used as the base
for most metrics based aggregations.  The AvgAggregation
uses the metrics aggregation mixin for all methods.

dist/elastic.js

@@ -755,6 +755,115 @@
     };
   };
 
+  /**
+    @mixin
+    <p>The MetricsAggregationMixin provides support for common options used across
+    various metrics <code>Aggregation</code> implementations.  This object should
+    not be used directly.</p>
+
+    @name ejs.MetricsAggregationMixin
+    @ejs aggregation
+    @borrows ejs.AggregationMixin.aggregation as aggregation
+    @borrows ejs.AggregationMixin.agg as agg
+    @borrows ejs.AggregationMixin._type as _type
+    @borrows ejs.AggregationMixin.toJSON as toJSON
+
+    */
+  ejs.MetricsAggregationMixin = function (name, type) {
+
+    var
+      _common = ejs.AggregationMixin(name),
+      agg = _common.toJSON();
+
+    agg[name][type] = {};
+
+    return extend(_common, {
+
+      /**
+      <p>Sets the field to operate on.</p>
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} field a valid field name..
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      field: function (field) {
+        if (field == null) {
+          return agg[name][type].field;
+        }
+
+        agg[name][type].field = field;
+        return this;
+      },
+
+      /**
+      Allows you generate or modify the terms/values using a script.
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} scriptCode A valid script string to execute.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      script: function (scriptCode) {
+        if (scriptCode == null) {
+          return agg[name][type].script;
+        }
+
+        agg[name][type].script = scriptCode;
+        return this;
+      },
+
+      /**
+      The script language being used.
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} language The language of the script.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      lang: function (language) {
+        if (language == null) {
+          return agg[name][type].lang;
+        }
+
+        agg[name][type].lang = language;
+        return this;
+      },
+
+      /**
+      Set to true to assume script values are sorted.
+
+      @member ejs.MetricsAggregationMixin
+      @param {Boolean} trueFalse assume sorted values or not
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      scriptValuesSorted: function (trueFalse) {
+        if (trueFalse == null) {
+          return agg[name][type].script_values_sorted;
+        }
+
+        agg[name][type].script_values_sorted = trueFalse;
+        return this;
+      },
+
+      /**
+      Sets parameters that will be applied to the script.  Overwrites
+      any existing params.
+
+      @member ejs.MetricsAggregationMixin
+      @param {Object} p An object where the keys are the parameter name and
+        values are the parameter value.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      params: function (p) {
+        if (p == null) {
+          return agg[name][type].params;
+        }
+
+        agg[name][type].params = p;
+        return this;
+      }
+
+    });
+  };
+
   /**
     @mixin
     <p>The QueryMixin provides support for common options used across 
@@ -2887,6 +2996,41 @@
     });
   };
 
+  /**
+    @class
+    <p>A single-value metrics aggregation that computes the average of numeric
+    values that are extracted from the aggregated documents. These values can be
+    extracted either from specific numeric fields in the documents, or be
+    generated by a provided script.</p>
+
+    @name ejs.AvgAggregation
+    @ejs aggregation
+    @borrows ejs.MetricsAggregationMixin.field as field
+    @borrows ejs.MetricsAggregationMixin.script as script
+    @borrows ejs.MetricsAggregationMixin.lang as lang
+    @borrows ejs.MetricsAggregationMixin.scriptValuesSorted as scriptValuesSorted
+    @borrows ejs.MetricsAggregationMixin.params as params
+    @borrows ejs.MetricsAggregationMixin.aggregation as aggregation
+    @borrows ejs.MetricsAggregationMixin.agg as agg
+    @borrows ejs.MetricsAggregationMixin._type as _type
+    @borrows ejs.MetricsAggregationMixin.toJSON as toJSON
+
+    @desc
+    <p>Aggregation that computes the average of numeric values that are extracted
+    from the aggregated documents.</p>
+
+    @param {String} name The name which be used to refer to this aggregation.
+
+    */
+  ejs.AvgAggregation = function (name) {
+
+    var
+      _common = ejs.MetricsAggregationMixin(name, 'avg'),
+      agg = _common.toJSON();
+
+    return _common;
+  };
+
   /**
     @class
     <p>Defines a single bucket of all the documents in the current document set

src/aggregations/AvgAggregation.js

@@ -0,0 +1,34 @@
+  /**
+    @class
+    <p>A single-value metrics aggregation that computes the average of numeric
+    values that are extracted from the aggregated documents. These values can be
+    extracted either from specific numeric fields in the documents, or be
+    generated by a provided script.</p>
+
+    @name ejs.AvgAggregation
+    @ejs aggregation
+    @borrows ejs.MetricsAggregationMixin.field as field
+    @borrows ejs.MetricsAggregationMixin.script as script
+    @borrows ejs.MetricsAggregationMixin.lang as lang
+    @borrows ejs.MetricsAggregationMixin.scriptValuesSorted as scriptValuesSorted
+    @borrows ejs.MetricsAggregationMixin.params as params
+    @borrows ejs.MetricsAggregationMixin.aggregation as aggregation
+    @borrows ejs.MetricsAggregationMixin.agg as agg
+    @borrows ejs.MetricsAggregationMixin._type as _type
+    @borrows ejs.MetricsAggregationMixin.toJSON as toJSON
+
+    @desc
+    <p>Aggregation that computes the average of numeric values that are extracted
+    from the aggregated documents.</p>
+
+    @param {String} name The name which be used to refer to this aggregation.
+
+    */
+  ejs.AvgAggregation = function (name) {
+
+    var
+      _common = ejs.MetricsAggregationMixin(name, 'avg'),
+      agg = _common.toJSON();
+
+    return _common;
+  };

src/mixins/MetricsAggregationMixin.js

@@ -0,0 +1,108 @@
+  /**
+    @mixin
+    <p>The MetricsAggregationMixin provides support for common options used across
+    various metrics <code>Aggregation</code> implementations.  This object should
+    not be used directly.</p>
+
+    @name ejs.MetricsAggregationMixin
+    @ejs aggregation
+    @borrows ejs.AggregationMixin.aggregation as aggregation
+    @borrows ejs.AggregationMixin.agg as agg
+    @borrows ejs.AggregationMixin._type as _type
+    @borrows ejs.AggregationMixin.toJSON as toJSON
+
+    */
+  ejs.MetricsAggregationMixin = function (name, type) {
+
+    var
+      _common = ejs.AggregationMixin(name),
+      agg = _common.toJSON();
+
+    agg[name][type] = {};
+
+    return extend(_common, {
+
+      /**
+      <p>Sets the field to operate on.</p>
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} field a valid field name..
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      field: function (field) {
+        if (field == null) {
+          return agg[name][type].field;
+        }
+
+        agg[name][type].field = field;
+        return this;
+      },
+
+      /**
+      Allows you generate or modify the terms/values using a script.
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} scriptCode A valid script string to execute.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      script: function (scriptCode) {
+        if (scriptCode == null) {
+          return agg[name][type].script;
+        }
+
+        agg[name][type].script = scriptCode;
+        return this;
+      },
+
+      /**
+      The script language being used.
+
+      @member ejs.MetricsAggregationMixin
+      @param {String} language The language of the script.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      lang: function (language) {
+        if (language == null) {
+          return agg[name][type].lang;
+        }
+
+        agg[name][type].lang = language;
+        return this;
+      },
+
+      /**
+      Set to true to assume script values are sorted.
+
+      @member ejs.MetricsAggregationMixin
+      @param {Boolean} trueFalse assume sorted values or not
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      scriptValuesSorted: function (trueFalse) {
+        if (trueFalse == null) {
+          return agg[name][type].script_values_sorted;
+        }
+
+        agg[name][type].script_values_sorted = trueFalse;
+        return this;
+      },
+
+      /**
+      Sets parameters that will be applied to the script.  Overwrites
+      any existing params.
+
+      @member ejs.MetricsAggregationMixin
+      @param {Object} p An object where the keys are the parameter name and
+        values are the parameter value.
+      @returns {Object} returns <code>this</code> so that calls can be chained.
+      */
+      params: function (p) {
+        if (p == null) {
+          return agg[name][type].params;
+        }
+
+        agg[name][type].params = p;
+        return this;
+      }
+
+    });
+  };

tests/aggregation_test.js

@@ -28,7 +28,7 @@ exports.aggregations = {
     done();
   },
   exists: function (test) {
-    test.expect(9);
+    test.expect(10);
 
     test.ok(ejs.GlobalAggregation, 'GlobalAggregation');
     test.ok(ejs.FilterAggregation, 'FilterAggregation');
@@ -39,6 +39,57 @@ exports.aggregations = {
     test.ok(ejs.NestedAggregation, 'NestedAggregation');
     test.ok(ejs.RangeAggregation, 'RangeAggregation');
     test.ok(ejs.SignificantTermsAggregation, 'SignificantTermsAggregation');
+    test.ok(ejs.AvgAggregation, 'AvgAggregation');
+
+    test.done();
+  },
+  AvgAggregation: function (test) {
+    test.expect(11);
+
+    var agg = ejs.AvgAggregation('myagg'),
+      ta1 = ejs.TermsAggregation('ta1').field('f1'),
+      expected,
+      doTest = function () {
+        test.deepEqual(agg.toJSON(), expected);
+      };
+
+    expected = {
+      myagg: {avg: {}}
+    };
+
+    test.ok(agg, 'AvgAggregation exists');
+    test.ok(agg.toJSON(), 'toJSON() works');
+    doTest();
+
+    agg.field('f1');
+    expected.myagg.avg.field = 'f1';
+    doTest();
+
+    agg.script('s1');
+    expected.myagg.avg.script = 's1';
+    doTest();
+
+    agg.lang('mvel');
+    expected.myagg.avg.lang = 'mvel';
+    doTest();
+
+    agg.scriptValuesSorted(false);
+    expected.myagg.avg.script_values_sorted = false;
+    doTest();
+
+    agg.params({p1: 'v1'});
+    expected.myagg.avg.params = {p1: 'v1'};
+    doTest();
+
+    agg.agg(ta1);
+    expected.myagg.aggs = ta1.toJSON();
+    doTest();
+
+    test.strictEqual(agg._type(), 'aggregation');
+
+    test.throws(function () {
+      agg.agggregation('invalid');
+    }, TypeError);
 
     test.done();
   },