From e5de86ec30cecacf6469845248e0d7191549259a Mon Sep 17 00:00:00 2001
From: Teck Wan <36706647+teckwan@users.noreply.github.com>
Date: Thu, 16 Sep 2021 11:21:42 +0200
Subject: [PATCH] Add conversion methods to ease usage (#56)

---
 History.md                               |  1 +
 lib/rgeo/geo_json.rb                     |  1 +
 lib/rgeo/geo_json/conversion_methods.rb  | 50 ++++++++++++++++++++++++
 lib/rgeo/geo_json/entities.rb            |  3 ++
 test/basic_test.rb                       | 45 +++++++++++++++++++++
 test/common/conversion_test.rb           | 29 ++++++++++++++
 test/geos_capi/conversion_test.rb        | 13 ++++++
 test/geos_ffi/conversion_test.rb         | 13 ++++++
 test/simple_cartesian/conversion_test.rb | 13 ++++++
 test/simple_mercator/conversion_test.rb  | 13 ++++++
 10 files changed, 181 insertions(+)
 create mode 100644 lib/rgeo/geo_json/conversion_methods.rb
 create mode 100644 test/common/conversion_test.rb
 create mode 100644 test/geos_capi/conversion_test.rb
 create mode 100644 test/geos_ffi/conversion_test.rb
 create mode 100644 test/simple_cartesian/conversion_test.rb
 create mode 100644 test/simple_mercator/conversion_test.rb

diff --git a/History.md b/History.md
index 3aa8a6c..5a947ad 100644
--- a/History.md
+++ b/History.md
@@ -2,6 +2,7 @@
 
 * Delegation to inner geometry for a feature (#53)
 * MultiJson rather than JSON (#46)
+* Conversion methods for better integration with core (#56)
 
 ### 2.1.1 / 2018-11-27
 
diff --git a/lib/rgeo/geo_json.rb b/lib/rgeo/geo_json.rb
index aca6a12..5c398ad 100644
--- a/lib/rgeo/geo_json.rb
+++ b/lib/rgeo/geo_json.rb
@@ -2,6 +2,7 @@
 
 require "rgeo"
 require_relative "geo_json/version"
+require_relative "geo_json/conversion_methods"
 require_relative "geo_json/entities"
 require_relative "geo_json/coder"
 require_relative "geo_json/interface"
diff --git a/lib/rgeo/geo_json/conversion_methods.rb b/lib/rgeo/geo_json/conversion_methods.rb
new file mode 100644
index 0000000..d669774
--- /dev/null
+++ b/lib/rgeo/geo_json/conversion_methods.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module RGeo
+  # This module serves to provide handy methods when using GeoJSON. The methods
+  # provided eases the passage between entities and GeoJSON String/Hash.
+  module GeoJSON::ConversionMethods
+    # Convert a geometry to a GeoJSON Hash
+    def as_geojson
+      GeoJSON.encode(self)
+    end
+    alias as_json as_geojson
+
+    # Convert a geometry to a GeoJSON String
+    def to_geojson
+      ::MultiJson.dump(as_geojson)
+    end
+    alias to_json to_geojson
+  end
+
+  # These convenience methods are added directly into the module rather than
+  # including the module above into the Feature::Instance module which is in
+  # every geometry implementation. This is due to a behavior in ruby versions
+  # <3.0.2 where dynamically included modules will not be included automatically
+  # in the ancestor tree.
+  # See https://bugs.ruby-lang.org/issues/9573 for more information.
+  module Feature
+    module Instance
+      # Convert a geometry to a GeoJSON Hash
+      def as_geojson
+        GeoJSON.encode(self)
+      end
+      alias as_json as_geojson
+
+      # Convert a geometry to a GeoJSON String
+      def to_geojson
+        ::MultiJson.dump(as_geojson)
+      end
+      alias to_json to_geojson
+    end
+
+    module Factory::Instance
+      # Parses a GeoJSON String/Hash, or an IO object from which
+      # the JSON string is read and returns the corresponding
+      # feature. Returns nil if unable to parse.
+      def parse_geojson(input)
+        GeoJSON.decode(input, geo_factory: self)
+      end
+    end
+  end
+end
diff --git a/lib/rgeo/geo_json/entities.rb b/lib/rgeo/geo_json/entities.rb
index 6e17292..9a2e1f4 100644
--- a/lib/rgeo/geo_json/entities.rb
+++ b/lib/rgeo/geo_json/entities.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative "collection_methods"
+require_relative "conversion_methods"
 
 module RGeo
   module CastOverlay
@@ -45,6 +46,7 @@ module DelegateToGeometry
     # engine and features.
     class Feature
       include DelegateToGeometry
+      include ConversionMethods
 
       # Create a feature wrapping the given geometry, with the given ID
       # and properties.
@@ -123,6 +125,7 @@ def keys
     class FeatureCollection
       include Enumerable
       include CollectionMethods
+      include ConversionMethods
 
       # Create a new FeatureCollection with the given features, which must
       # be provided as an Enumerable.
diff --git a/test/basic_test.rb b/test/basic_test.rb
index c9ce1b8..da78bf6 100644
--- a/test/basic_test.rb
+++ b/test/basic_test.rb
@@ -283,4 +283,49 @@ def test_feature_cast
     point_feature = RGeo::GeoJSON::Feature.new(factory.point(1, 1))
     assert poly.contains?(point_feature)
   end
+
+  def test_feature_to_geojson
+    json = {
+      "type" => "Feature",
+      "geometry" => {
+        "type" => "Polygon",
+        "coordinates" => [[[10.0, 20.0], [12.0, 22.0], [-3.0, 24.0], [10.0, 20.0]]]
+      },
+      "properties" => {}
+    }
+    feature = RGeo::GeoJSON.decode(json)
+    assert_equal(
+      json,
+      feature.as_geojson
+    )
+    assert_equal(
+      '{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[10.0,20.0],[12.0,22.0],[-3.0,24.0],[10.0,20.0]]]},"properties":{}}',
+      feature.to_geojson
+    )
+  end
+
+  def test_feature_collection_to_geojson
+    json = {
+      "type" => "FeatureCollection",
+      "features" => [
+        {
+          "type" => "Feature",
+          "geometry" => {
+            "type" => "Point",
+            "coordinates" => [10.0, 20.0],
+          },
+          "properties" => {}
+        }
+      ]
+    }
+    feature_collection = RGeo::GeoJSON.decode(json)
+    assert_equal(
+      json,
+      feature_collection.as_geojson
+    )
+    assert_equal(
+      '{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Point","coordinates":[10.0,20.0]},"properties":{}}]}',
+      feature_collection.to_geojson
+    )
+  end
 end
diff --git a/test/common/conversion_test.rb b/test/common/conversion_test.rb
new file mode 100644
index 0000000..928edac
--- /dev/null
+++ b/test/common/conversion_test.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module RGeo
+  module GeoJSON # :nodoc:
+    module Tests # :nodoc:
+      module Common # :nodoc:
+        module ConversionTests # :nodoc:
+          def test_geometry_to_geojson
+            pt = @factory.point(1, 2)
+            assert_equal(
+              { "type" => "Point", "coordinates" => [1.0, 2.0] },
+              pt.as_geojson
+            )
+            assert_equal(
+              '{"type":"Point","coordinates":[1.0,2.0]}',
+              pt.to_geojson
+            )
+          end
+
+          def test_parse_geojson
+            pt = @factory.point(1, 2)
+            assert_equal(pt, @factory.parse_geojson(pt.as_geojson))
+            assert_equal(pt, @factory.parse_geojson(pt.to_geojson))
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/geos_capi/conversion_test.rb b/test/geos_capi/conversion_test.rb
new file mode 100644
index 0000000..0ae076e
--- /dev/null
+++ b/test/geos_capi/conversion_test.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require_relative "../../lib/rgeo-geojson"
+require_relative "../common/conversion_test"
+
+class GeosConversionTest < Minitest::Test # :nodoc:
+  include RGeo::GeoJSON::Tests::Common::ConversionTests
+
+  def setup
+    @factory = RGeo::Geos.factory
+  end
+end
diff --git a/test/geos_ffi/conversion_test.rb b/test/geos_ffi/conversion_test.rb
new file mode 100644
index 0000000..8e88a18
--- /dev/null
+++ b/test/geos_ffi/conversion_test.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require_relative "../../lib/rgeo-geojson"
+require_relative "../common/conversion_test"
+
+class GeosFFIConversionTest < Minitest::Test # :nodoc:
+  include RGeo::GeoJSON::Tests::Common::ConversionTests
+
+  def setup
+    @factory = RGeo::Geos.factory(native_interface: :ffi)
+  end
+end
diff --git a/test/simple_cartesian/conversion_test.rb b/test/simple_cartesian/conversion_test.rb
new file mode 100644
index 0000000..9c45e08
--- /dev/null
+++ b/test/simple_cartesian/conversion_test.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require_relative "../../lib/rgeo-geojson"
+require_relative "../common/conversion_test"
+
+class CartesianConversionTest < Minitest::Test # :nodoc:
+  include RGeo::GeoJSON::Tests::Common::ConversionTests
+
+  def setup
+    @factory = RGeo::Cartesian.simple_factory
+  end
+end
diff --git a/test/simple_mercator/conversion_test.rb b/test/simple_mercator/conversion_test.rb
new file mode 100644
index 0000000..1fd5592
--- /dev/null
+++ b/test/simple_mercator/conversion_test.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require_relative "../../lib/rgeo-geojson"
+require_relative "../common/conversion_test"
+
+class MercatorConversionTest < Minitest::Test # :nodoc:
+  include RGeo::GeoJSON::Tests::Common::ConversionTests
+
+  def setup
+    @factory = RGeo::Geographic.simple_mercator_factory
+  end
+end