From 7f4b8eaebc0676648d789f21be013c991377dd42 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lauren=C8=9Biu=20Nicola?= <lnicola@dend.ro>
Date: Mon, 4 Dec 2023 20:47:23 +0200
Subject: [PATCH] Add Geometry::difference

---
 CHANGES.md            |  6 +++-
 src/vector/ops/set.rs | 72 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index bfb4f8e2..7d2758ee 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,9 +2,13 @@
 
 ## Unreleased
 
+- Added `Geometry::difference`.
+
+   - <https://github.com/georust/gdal/pull/487>
+
 - Added support for digital elevation model raster processing: `aspect`, `color_relief`, `hillshade`, `roughness`, `slope`, `terrain_ruggedness_index`, `topographic_position_index`.
 
-   - <https://github.com/georust/gdal/pull/456> 
+   - <https://github.com/georust/gdal/pull/456>
 
 - Added pre-built bindings for GDAL 3.8
 
diff --git a/src/vector/ops/set.rs b/src/vector/ops/set.rs
index b920772b..9a81ab6a 100644
--- a/src/vector/ops/set.rs
+++ b/src/vector/ops/set.rs
@@ -74,6 +74,41 @@ impl Geometry {
             Some(Geometry::with_c_geometry(ogr_geom, true))
         }
     }
+
+    /// Computes the [geometric difference][difference] of `self` and `other`.
+    ///
+    /// Generates a new geometry which is the difference of the two geometries operated on.
+    ///
+    /// # Notes
+    /// * Geometry validity is not checked, and invalid geometry will generate unpredictable results.
+    /// Use [`Geometry::is_valid`] if validity might be in question.
+    /// * If GEOS is *not* enabled, this function will always return `None`.
+    /// You may check for GEOS support with [`VersionInfo::has_geos`][has_geos].
+    ///
+    /// # Returns
+    /// * `Some(geometry)`: a new `Geometry` representing the computed difference
+    /// * `None`: when the union could not be computed
+    ///
+    /// See: [`OGR_G_Difference`][OGR_G_Difference]
+    ///
+    /// [OGR_G_Difference]: https://gdal.org/api/vector_c_api.html#_CPPv416OGR_G_Difference12OGRGeometryH12OGRGeometryH
+    /// [difference]: https://en.wikipedia.org/wiki/Constructive_solid_geometry#Workings
+    /// [has_geos]: crate::version::VersionInfo::has_geos
+    pub fn difference(&self, other: &Self) -> Option<Self> {
+        if !self.has_gdal_ptr() {
+            return None;
+        }
+        if !other.has_gdal_ptr() {
+            return None;
+        }
+        unsafe {
+            let ogr_geom = gdal_sys::OGR_G_Difference(self.c_geometry(), other.c_geometry());
+            if ogr_geom.is_null() {
+                return None;
+            }
+            Some(Geometry::with_c_geometry(ogr_geom, true))
+        }
+    }
 }
 
 #[cfg(test)]
@@ -172,4 +207,41 @@ mod tests {
 
         assert_eq!(res.unwrap().area(), 50.0);
     }
+
+    #[test]
+    #[allow(clippy::float_cmp)]
+    fn test_difference_success() {
+        let geom =
+            Geometry::from_wkt("POLYGON ((0.0 10.0, 0.0 0.0, 10.0 0.0, 10.0 10.0, 0.0 10.0))")
+                .unwrap();
+        let other = Geometry::from_wkt("POLYGON ((1 -5, 1 1, -5 1, -5 -5, 1 -5))").unwrap();
+
+        let res = geom.difference(&other).unwrap();
+        assert_eq!(res.area(), 99.0);
+    }
+
+    #[test]
+    fn test_difference_no_gdal_ptr() {
+        let geom =
+            Geometry::from_wkt("POLYGON ((0.0 10.0, 0.0 0.0, 10.0 0.0, 10.0 10.0, 0.0 10.0))")
+                .unwrap();
+        let other = unsafe { Geometry::lazy_feature_geometry() };
+
+        let res = geom.difference(&other);
+        assert!(res.is_none());
+    }
+
+    #[test]
+    #[allow(clippy::float_cmp)]
+    fn test_difference_no_intersects() {
+        let geom =
+            Geometry::from_wkt("POLYGON ((0.0 5.0, 0.0 0.0, 5.0 0.0, 5.0 5.0, 0.0 5.0))").unwrap();
+
+        let other =
+            Geometry::from_wkt("POLYGON ((15.0 15.0, 15.0 20.0, 20.0 20.0, 20.0 15.0, 15.0 15.0))")
+                .unwrap();
+
+        let res = geom.difference(&other);
+        assert_eq!(res.unwrap().area(), 25.0);
+    }
 }