radial sugiyama positioning integration

radial_sugiyama/src/error.rs

@@ -0,0 +1,70 @@
+use std::error::Error;
+use std::fmt::{Display, Formatter};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum LayoutError {
+    InvalidNodeIndex {
+        edge_index: usize,
+        node_index: usize,
+        node_count: usize,
+    },
+    SelfLoop {
+        edge_index: usize,
+        node: usize,
+    },
+    DuplicateEdge {
+        edge_index: usize,
+        source: usize,
+        target: usize,
+    },
+    CycleDetected,
+    InvalidHierarchyEdge {
+        edge_index: usize,
+        source: usize,
+        target: usize,
+        source_level: usize,
+        target_level: usize,
+    },
+}
+
+impl Display for LayoutError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            LayoutError::InvalidNodeIndex {
+                edge_index,
+                node_index,
+                node_count,
+            } => write!(
+                f,
+                "edge {} references node {} but graph only has {} nodes",
+                edge_index, node_index, node_count
+            ),
+            LayoutError::SelfLoop { edge_index, node } => {
+                write!(f, "edge {} is a self-loop on node {}", edge_index, node)
+            }
+            LayoutError::DuplicateEdge {
+                edge_index,
+                source,
+                target,
+            } => write!(
+                f,
+                "edge {} duplicates existing directed edge {} -> {}",
+                edge_index, source, target
+            ),
+            LayoutError::CycleDetected => write!(f, "graph must be a directed acyclic graph"),
+            LayoutError::InvalidHierarchyEdge {
+                edge_index,
+                source,
+                target,
+                source_level,
+                target_level,
+            } => write!(
+                f,
+                "edge {} ({} -> {}) violates hierarchy levels {} -> {}",
+                edge_index, source, target, source_level, target_level
+            ),
+        }
+    }
+}
+
+impl Error for LayoutError {}