Refactor coordinate system

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/classes/coordinate_2d.dart

@@ -0,0 +1,54 @@
+import 'dart:math' as math;
+
+/// A robust, immutable 2D coordinate.
+class Coordinate2D implements Comparable<Coordinate2D> {
+  final double x;
+  final double y;
+
+  const Coordinate2D(this.x, this.y);
+
+  /// Factory for a (0,0) coordinate.
+  static const Coordinate2D zero = Coordinate2D(0.0, 0.0);
+
+  // --- Core Logic ---
+
+  /// Returns the Euclidean distance between this and [other].
+  /// Uses the formula: $$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$$
+  double distanceTo(Coordinate2D other) {
+    final dx = x - other.x;
+    final dy = y - other.y;
+    return math.sqrt(dx * dx + dy * dy);
+  }
+
+  /// True if both ordinates are finite (not NaN or Infinity).
+  bool get isValid => x.isFinite && y.isFinite;
+
+  Coordinate2D operator +(Coordinate2D other) =>
+      Coordinate2D(x + other.x, y + other.y);
+  Coordinate2D operator -(Coordinate2D other) =>
+      Coordinate2D(x - other.x, y - other.y);
+  Coordinate2D operator *(double factor) =>
+      Coordinate2D(x * factor, y * factor);
+  Coordinate2D operator /(double divisor) =>
+      Coordinate2D(x / divisor, y / divisor);
+
+  @override
+  bool operator ==(Object other) =>
+      identical(this, other) ||
+      other is Coordinate2D &&
+          runtimeType == other.runtimeType &&
+          x == other.x &&
+          y == other.y;
+
+  @override
+  int get hashCode => Object.hash(x, y);
+
+  @override
+  int compareTo(Coordinate2D other) {
+    if (x != other.x) return x.compareTo(other.x);
+    return y.compareTo(other.y);
+  }
+
+  @override
+  String toString() => 'Coordinate($x, $y)';
+}