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. The conversions to
symbols and back to strings is also inefficient.

lib/facterdb.rb

@@ -149,4 +149,20 @@ def self.get_facts(filter = nil, cache = 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
+  def self.filter_results(results, filter)
+    # TODO: it's really inefficient to do to_s and to_sym all the time
+    database = results.map { |hash| hash.to_h { |k, v| [k.to_s, v] } }
+
+    # 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) }
+
+    filtered.map { |hash| hash.to_h { |k, v| [k.to_sym, v] } }
+  end
 end

spec/facterdb_spec.rb

@@ -353,4 +353,22 @@
       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__))