[DSL] Added the pipeline aggregations

This patch adds the support for pipeline aggregations to the Ruby DSL.

See https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline.html

Closes #312

Author: send

Diff for: lib/elasticsearch/dsl/search/aggregations/avg_bucket.rb

@@ -0,0 +1,34 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A sibling pipeline aggregation which calculates the (mean) average value of a specified metric in a sibling aggregation.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :avg_monthly_sales do
+        #       avg_bucket buckets_path: 'sales_per_month>sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :avg_monthly_sales do
+        #       avg_bucket do
+        #         buckets_path 'sales_per_month>sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-avg-bucket-aggregation.html
+        #
+        class AvgBucket
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/bucket_script.rb

@@ -0,0 +1,36 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A parent pipeline aggregation which executes a script which can perform per bucket computations on specified metrics in the parent multi-bucket aggregation.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :t-shirt-percentage do
+        #       bucket_script buckets_path: { tShirtSales: 't-shirts>sales', totalSales: 'total_sales' }, script: 'tShirtSales / totalSales * 100'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :t-shirt-percentage do
+        #       bucket_script do
+        #         buckets_path tShirtSales: 't-shirts>sales', totalSales: 'total_sales'
+        #         script 'tShirtSales / totalSales * 100'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-bucket-script-aggregation.html
+        #
+        class BucketScript
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :script
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/bucket_selector.rb

@@ -0,0 +1,35 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A parent pipeline aggregation which executes a script which determines whether the current bucket will be retained in the parent multi-bucket aggregation.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :sales_bucket_filter do
+        #       bucket_selector buckets_path: { totalSales: 'total_sales' }, script: 'totalSales <= 50'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :sales_bucket_filter do
+        #       bucket_selector do
+        #         buckets_path totalSales: 'total_sales'
+        #         script 'totalSales <= 50'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-bucket-selector-aggregation.html
+        #
+        class BucketSelector
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :script
+          option_method :gap_policy
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/cumulative_sum.rb

@@ -0,0 +1,33 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A parent pipeline aggregation which calculates the cumulative sum of a specified metric in a parent histogram (or date_histogram) aggregation. 
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :cumulative_sales do
+        #       cumulative_sum buckets_path: 'sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :cumulative_sales do
+        #       cumulative_sum do
+        #         buckets_path 'sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-cumulative-sum-aggregation.html
+        #
+        class CumulativeSum
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/derivative.rb

@@ -0,0 +1,34 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A parent pipeline aggregation which calculates the derivative of a specified metric in a parent histogram (or date_histogram) aggregation.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :sales_deriv do
+        #       derivative buckets_path: 'sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :sales_deriv do
+        #       derivative do
+        #         buckets_path 'sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-derivative-aggregation.html
+        #
+        class Derivative
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/extended_stats_bucket.rb

@@ -0,0 +1,34 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A sibling pipeline aggregation which calculates a variety of stats across all bucket of a specified metric in a sibling aggregation. The specified metric must be numeric and the sibling aggregation must be a multi-bucket aggregation.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :stats_monthly_sales do
+        #       extended_stats_bucket buckets_path: 'sales_per_month>sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :stats_monthly_sales do
+        #       extended_stats_bucket do
+        #         buckets_path 'sales_per_month>sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-extended-stats-bucket-aggregation.html
+        #
+        class ExtendedStatsBucket
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/max_bucket.rb

@@ -0,0 +1,34 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A sibling pipeline aggregation which identifies the bucket(s) with the maximum value of a specified metric in a sibling aggregation and outputs both the value and the key(s) of the bucket(s).
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :max_monthly_sales do
+        #       max_bucket buckets_path: 'sales_per_month>sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :max_monthly_sales do
+        #       max_bucket do
+        #         buckets_path 'sales_per_month>sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-max-bucket-aggregation.html
+        #
+        class MaxBucket
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/min_bucket.rb

@@ -0,0 +1,34 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A sibling pipeline aggregation which identifies the bucket(s) with the minimum value of a specified metric in a sibling aggregation and outputs both the value and the key(s) of the bucket(s).
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :min_monthly_sales do
+        #       min_bucket buckets_path: 'sales_per_month>sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :min_monthly_sales do
+        #       min_bucket do
+        #         buckets_path 'sales_per_month>sales'
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-min-bucket-aggregation.html
+        #
+        class MinBucket
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/moving_avg.rb

@@ -0,0 +1,42 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # Given an ordered series of data, the Moving Average aggregation will slide a window across the data and emit the average value of that window. 
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :the_movavg do
+        #       moving_avg buckets_path: 'the_sum'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :the_movavg do
+        #       moving_avg do
+        #         buckets_path 'the_sum'
+        #         model 'holt'
+        #         window 5
+        #         gap_policy 'insert_zero'
+        #         settings({ alpha: 0.5 })
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-movavg-aggregation.html
+        #
+        class MovingAvg
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :model
+          option_method :gap_policy
+          option_method :window
+          option_method :format
+          option_method :minimize
+          option_method :settings
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/percentiles_bucket.rb

@@ -0,0 +1,36 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # A sibling pipeline aggregation which calculates percentiles across all bucket of a specified metric in a sibling aggregation. 
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :sum_monthly_sales do
+        #       percentiles_bucket buckets_path: 'sales_per_month>sales'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :sum_monthly_sales do
+        #       percentiles_bucket do
+        #         buckets_path 'sales_per_month>sales'
+        #         percents [25.0 50.0 75.0]
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-percentiles-bucket-aggregation.html
+        #
+        class PercentilesBucket
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :gap_policy
+          option_method :format
+          option_method :percents
+        end
+      end
+    end
+  end
+end

Diff for: lib/elasticsearch/dsl/search/aggregations/serial_diff.rb

@@ -0,0 +1,36 @@
+module Elasticsearch
+  module DSL
+    module Search
+      module Aggregations
+
+        # Serial differencing is a technique where values in a time series are subtracted from itself at different time lags or periods.
+        #
+        # @example Passing the options as a Hash
+        #
+        #     aggregation :thirtieth_difference do
+        #       serial_diff buckets_path: 'the_sum'
+        #     end
+        #
+        # @example Passing the options as a block
+        #
+        #     aggregation :thirtieth_difference do
+        #       serial_diff do
+        #         buckets_path 'the_sum'
+        #         lag 30
+        #       end
+        #     end
+        #
+        # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-serialdiff-aggregation.html
+        #
+        class SerialDiff
+          include BaseAggregationComponent
+
+          option_method :buckets_path
+          option_method :lag
+          option_method :gap_policy
+          option_method :format
+        end
+      end
+    end
+  end
+end