From f98436f46d187ff997f5960ebc5354155f78a9d0 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Fri, 29 Sep 2023 10:22:37 +0200
Subject: [PATCH] Add `CurveBoundary::subset`

---
 .../src/algorithms/approx/curve/segment.rs    | 12 ++----------
 crates/fj-core/src/geometry/boundary.rs       | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/crates/fj-core/src/algorithms/approx/curve/segment.rs b/crates/fj-core/src/algorithms/approx/curve/segment.rs
index 5dc30242e..0047e712f 100644
--- a/crates/fj-core/src/algorithms/approx/curve/segment.rs
+++ b/crates/fj-core/src/algorithms/approx/curve/segment.rs
@@ -78,17 +78,9 @@ impl CurveApproxSegment {
             "Expected subset to be defined by normalized boundary."
         );
 
-        let [min, max] = boundary.inner;
-
-        self.boundary.inner = {
-            let [self_min, self_max] = self.boundary.inner;
-
-            let min = cmp::max(self_min, min);
-            let max = cmp::min(self_max, max);
-
-            [min, max]
-        };
+        self.boundary = self.boundary.subset(boundary);
 
+        let [min, max] = self.boundary.inner;
         self.points
             .retain(|point| point.local_form > min && point.local_form < max);
     }
diff --git a/crates/fj-core/src/geometry/boundary.rs b/crates/fj-core/src/geometry/boundary.rs
index 0f68432e0..a7d2dea5b 100644
--- a/crates/fj-core/src/geometry/boundary.rs
+++ b/crates/fj-core/src/geometry/boundary.rs
@@ -1,5 +1,5 @@
 use std::{
-    cmp::Ordering,
+    cmp::{self, Ordering},
     hash::{Hash, Hasher},
 };
 
@@ -75,6 +75,23 @@ impl CurveBoundary<Point<1>> {
 
         a_low <= b_high && a_high >= b_low
     }
+
+    /// Create the subset of this boundary and another
+    ///
+    /// The result will be normalized.
+    #[must_use]
+    pub fn subset(self, other: Self) -> Self {
+        let self_ = self.normalize();
+        let other = other.normalize();
+
+        let [self_min, self_max] = self_.inner;
+        let [other_min, other_max] = other.inner;
+
+        let min = cmp::max(self_min, other_min);
+        let max = cmp::min(self_max, other_max);
+
+        Self { inner: [min, max] }
+    }
 }
 
 impl<S, T: CurveBoundaryElement> From<[S; 2]> for CurveBoundary<T>