feat(Firestore): SUM / AVG aggregation feature

Firestore/src/Aggregate.php

@@ -37,6 +37,16 @@ class Aggregate
      */
     private const TYPE_COUNT = 'count';
 
+    /**
+     * Default placeholder for all sum aggregate props.
+     */
+    private const TYPE_SUM = 'sum';
+
+    /**
+     * Default placeholder for all average aggregate props.
+     */
+    private const TYPE_AVG = 'avg';
+
     /**
      * @var array Aggregation properties for an AggregateQuery.
      */
@@ -63,9 +73,64 @@ private function __construct($aggregationType)
      */
     public static function count()
     {
-        $count = new Aggregate(self::TYPE_COUNT);
-        $count->props[$count->aggregationType] = [];
-        return $count;
+        return self::createAggregate(self::TYPE_COUNT);
+    }
+
+    /**
+     * Creates sum aggregation properties.
+     *
+     * Example:
+     * ```
+     * $sum = Aggregate::sum('field_to_aggregate_upon');
+     * ```
+     * Result of SUM aggregation can be a integer or a float.
+     * Sum of integers which exceed maxinum integer value returns a float.
+     * Sum of numbers exceeding max float value returns `INF`.
+     * Sum of data which contains `NaN` returns `NaN`.
+     * Non numeric values are ignored.
+     *
+     * @param string $field The relative path of the field to aggregate upon.
+     * @return Aggregate
+     */
+    public static function sum($field)
+    {
+        return self::createAggregate(self::TYPE_SUM, $field);
+    }
+
+    /**
+     * Creates average aggregation properties.
+     *
+     * Example:
+     * ```
+     * $avg = Aggregate::avg('field_to_aggregate_upon');
+     * ```
+     *
+     * Result of AVG aggregation can be a float or a null.
+     * Average of empty valid data set return `null`.
+     * Average of numbers exceeding max float value returns `INF`.
+     * Average of data which contains `NaN` returns `NaN`.
+     * Non numeric values are ignored.
+     *
+     * @param string|null $field The relative path of the field to aggregate upon.
+     * @return Aggregate
+     */
+    public static function avg($field)
+    {
+        return self::createAggregate(self::TYPE_AVG, $field);
+    }
+
+    private static function createAggregate(string $type, $field = null)
+    {
+        $aggregate = new Aggregate($type);
+        $aggregate->props[$aggregate->aggregationType] = [];
+        if (!is_null($field)) {
+            $aggregate->props[$aggregate->aggregationType] = [
+                'field' => [
+                    'fieldPath' => $field
+                ]
+            ];
+        }
+        return $aggregate;
     }
 
     /**

Firestore/src/AggregateQuerySnapshot.php

@@ -96,7 +96,7 @@ public function getReadTime()
      * Get the Query Aggregation value.
      *
      * @param string $alias The aggregation alias.
-     * @return int
+     * @return mixed
      * @throws \InvalidArgumentException If provided alias does not exist in result.
      */
     public function get($alias)
@@ -106,7 +106,13 @@ public function get($alias)
         }
         $result = $this->aggregateFields[$alias];
         if (is_array($result)) {
-            return $result['integerValue'];
+            $key = array_key_first($result);
+            if ($key == 'nullValue') {
+                return null;
+            }
+            // `$result` would contain only one of
+            // (@see https://cloud.google.com/firestore/docs/reference/rest/v1/Value)
+            return $result[$key];
         }
         return $result;
     }

Firestore/src/Query.php

@@ -195,6 +195,64 @@ public function count(array $options = [])
         return $aggregationResult->get('count');
     }
 
+    /**
+     * Gets the sum of all documents matching the provided query filters.
+     *
+     * Example:
+     * ```
+     * $sum = $query->sum();
+     * ```
+     *
+     * Sum of integers which exceed maximum integer value returns a float.
+     * Sum of numbers exceeding max float value returns `INF`.
+     * Sum of data which contains `NaN` returns `NaN`.
+     * Non numeric values are ignored.
+     *
+     * @param string $field The relative path of the field to aggregate upon.
+     * @param array $options [optional] {
+     *     Configuration options is an array.
+     *
+     *     @type Timestamp $readTime Reads entities as they were at the given timestamp.
+     * }
+     * @return int|float
+     */
+    public function sum(string $field, array $options = [])
+    {
+        $aggregateQuery = $this->addAggregation(Aggregate::sum($field)->alias('sum'));
+
+        $aggregationResult = $aggregateQuery->getSnapshot($options);
+        return $aggregationResult->get('sum');
+    }
+
+    /**
+     * Gets the average of all documents matching the provided query filters.
+     *
+     * Example:
+     * ```
+     * $avg = $query->avg();
+     * ```
+     *
+     * Average of empty valid data set return `null`.
+     * Average of numbers exceeding max float value returns `INF`.
+     * Average of data which contains `NaN` returns `NaN`.
+     * Non numeric values are ignored.
+     *
+     * @param string $field The relative path of the field to aggregate upon.
+     * @param array $options [optional] {
+     *     Configuration options is an array.
+     *
+     *     @type Timestamp $readTime Reads entities as they were at the given timestamp.
+     * }
+     * @return float|null
+     */
+    public function avg(string $field, array $options = [])
+    {
+        $aggregateQuery = $this->addAggregation(Aggregate::avg($field)->alias('avg'));
+
+        $aggregationResult = $aggregateQuery->getSnapshot($options);
+        return $aggregationResult->get('avg');
+    }
+
     /**
      * Returns an aggregate query provided an aggregation with existing query filters.
      *