Provide filter_results to refine a search

rspec-puppet-facts has a pattern where it does a lot of small searches
for every OS. By doing a single complex FacterDB.get_facts call to get
the only supported operating systems and then further refining that
result it can use the cache provided by FacterDB.get_facts.

This is quite hacky now because it duplicates internals from JGrep to
avoid serializing to JSON and parsing that again.

lib/facterdb.rb

@@ -123,4 +123,22 @@ def self.get_facts(filter = nil, cache = true, symbolize_keys: true)
     end
     result
   end
+
+  # @param results [Array[Hash]] The results from a get_facts call
+  # @param filter [Object] The filter to convert to jgrep string
+  # @return [Array[Hash[Symbol, Any]]]
+  #   Array of hashes of facts when symbolize_keys is true
+  # @return [Array[Hash[String, Any]]]
+  #   Array of hashes of facts when symbolize_keys is false
+  def self.filter_results(results, filter, symbolize_keys: true)
+    database = symbolize_keys ? results.map { |hash| hash.transform_keys(&:to_s) } : results
+
+    # TODO: This duplicates JGrep.jgrep to avoid JSON.parse(database.to_json)
+    # JGrep should provide an API for that
+    expression = generate_filter_str(filter)
+    call_stack = JGrep::Parser.new(expression).execution_stack
+    filtered = database.filter { |document| JGrep.eval_statement(document, call_stack) }
+
+    symbolize_keys ? filtered.map { |hash| hash.transform_keys(&:to_sym) } : filtered
+  end
 end

spec/facter_db_spec.rb

@@ -289,4 +289,22 @@
       end
     end
   end
+
+  describe '.filter_results' do
+    subject(:filtered) { FacterDB.filter_results(results, filter) }
+
+    let(:filters) { 'osfamily=Debian or osfamily=RedHat' }
+    let(:results) { FacterDB.get_facts(filters) }
+
+    # Just to make sure our results set contains what we want
+    it 'has both Debian and Red Hat in the unfiltered result' do
+      expect(results).to include(hash_including(osfamily: 'Debian')).and include(hash_including(osfamily: 'RedHat'))
+    end
+
+    context 'with filter for Debian' do
+      let(:filter) { 'osfamily=Debian' }
+
+      it { is_expected.to include(hash_including(osfamily: 'Debian')).and not_include(hash_including(osfamily: 'RedHat')) }
+    end
+  end
 end

spec/spec_helper.rb

@@ -14,6 +14,7 @@
 
 RSpec::Matchers.define_negated_matcher :not_be_nil, :be_nil
 RSpec::Matchers.define_negated_matcher :not_be_empty, :be_empty
+RSpec::Matchers.define_negated_matcher :not_include, :include
 
 def project_dir
   File.dirname File.dirname(File.expand_path(__FILE__))