common/rust: add Line type

common/rust/src/vec2.rs

@@ -6,8 +6,8 @@ use std::{
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Vec2 {
-    x: i32, // increases toward right
-    y: i32, // increases toward top
+    pub x: i32, // increases toward right
+    pub y: i32, // increases toward top
 }
 
 impl Vec2 {
@@ -140,3 +140,57 @@ impl FromStr for Direction {
         }
     }
 }
+
+/// A line from one point to another.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Line {
+    pub start: Vec2,
+    pub end: Vec2,
+}
+
+impl Line {
+    /// Returns an iterator over the line's points represented as [`Vec2`], including the start and
+    /// end points.
+    ///
+    /// Only works for orthogonal lines.
+    #[must_use]
+    pub fn points(self) -> Option<LinePoints> {
+        LinePoints::try_from(self).ok()
+    }
+}
+
+/// An iterator over a line's points. See [`Line::points()`] for details.
+pub struct LinePoints {
+    line: Option<Line>,
+}
+
+impl TryFrom<Line> for LinePoints {
+    type Error = ();
+
+    fn try_from(line: Line) -> Result<Self, Self::Error> {
+        if line.start.x == line.end.x || line.start.y == line.end.y {
+            Ok(Self { line: Some(line) })
+        } else {
+            Err(())
+        }
+    }
+}
+
+impl Iterator for LinePoints {
+    type Item = Vec2;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let Some(line) = self.line.as_mut() else { return None };
+
+        let delta = (line.end - line.start).map(i32::signum);
+
+        let p = line.start;
+        line.start += delta;
+
+        if delta == Vec2::new(0, 0) {
+            self.line = None;
+        }
+
+        Some(p)
+    }
+}