From 95194149291fd138cc0fe14001bb4d068de73cde Mon Sep 17 00:00:00 2001
From: Rahix <rahix@rahix.de>
Date: Mon, 28 Jul 2025 15:38:36 +0200
Subject: [PATCH] Push all ultimate elements to the bottom of the graph

In dot rendering, put all ultimate elements (those that nothing further
depends on) on the same rank, meaning the very bottom.

This helps to visualize our ultimate goals more easily and also shows
elements that are probably a requisite to something else that has not
yet been modelled.
---
 techtree-manager/src/tree.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/techtree-manager/src/tree.rs b/techtree-manager/src/tree.rs
index 0574f73..f87873c 100644
--- a/techtree-manager/src/tree.rs
+++ b/techtree-manager/src/tree.rs
@@ -160,6 +160,16 @@ impl Tree {
         Subtree::new_for_element(self, element)
     }
 
+    pub fn iter_ultimate_elements<'a>(&'a self) -> impl Iterator<Item = ElementIndex> + 'a {
+        self.graph.node_indices().filter(|index| {
+            // If there are no incoming edges, then this is an ultimate element!
+            self.graph
+                .neighbors_directed(*index, petgraph::Direction::Incoming)
+                .next()
+                .is_none()
+        })
+    }
+
     pub fn to_dot(&self) -> String {
         let dot = petgraph::dot::Dot::with_attr_getters(
             &self.graph,
@@ -173,9 +183,16 @@ impl Tree {
             &|_g, (_, element)| element.to_dot_node_attributes(None),
         );
 
+        let ultimate_elements: Vec<_> = self
+            .iter_ultimate_elements()
+            .map(|idx| idx.index().to_string())
+            .collect();
+        let ultimate_element_list = ultimate_elements.join("; ");
+
         format!(
             r#"digraph {{
     ranksep=1.2
+    {{ rank=same; {ultimate_element_list}; }}
 {:?}
 }}
 "#,