Break out PathMap from RbxSession

server/src/path_map.rs

@@ -0,0 +1,73 @@
+use std::{
+    path::{Path, PathBuf},
+    collections::{HashMap, HashSet},
+};
+
+#[derive(Debug)]
+struct PathMapNode<T> {
+    value: T,
+    children: HashSet<PathBuf>,
+}
+
+/// A map from paths to instance IDs, with a bit of additional data that enables
+/// removing a path and all of its child paths from the tree in constant time.
+#[derive(Debug)]
+pub struct PathMap<T> {
+    nodes: HashMap<PathBuf, PathMapNode<T>>,
+}
+
+impl<T> PathMap<T> {
+    pub fn new() -> PathMap<T> {
+        PathMap {
+            nodes: HashMap::new(),
+        }
+    }
+
+    pub fn get(&self, path: &Path) -> Option<&T> {
+        self.nodes.get(path).map(|v| &v.value)
+    }
+
+    pub fn insert(&mut self, path: PathBuf, value: T) {
+        if let Some(parent_path) = path.parent() {
+            if let Some(parent) = self.nodes.get_mut(parent_path) {
+                parent.children.insert(path.to_path_buf());
+            }
+        }
+
+        self.nodes.insert(path, PathMapNode {
+            value,
+            children: HashSet::new(),
+        });
+    }
+
+    pub fn remove(&mut self, root_path: &Path) -> Option<T> {
+        if let Some(parent_path) = root_path.parent() {
+            if let Some(parent) = self.nodes.get_mut(parent_path) {
+                parent.children.remove(root_path);
+            }
+        }
+
+        let mut root_node = match self.nodes.remove(root_path) {
+            Some(node) => node,
+            None => return None,
+        };
+
+        let root_value = root_node.value;
+        let mut to_visit: Vec<PathBuf> = root_node.children.drain().collect();
+
+        while let Some(path) = to_visit.pop() {
+            match self.nodes.remove(&path) {
+                Some(mut node) => {
+                    for child in node.children.drain() {
+                        to_visit.push(child);
+                    }
+                },
+                None => {
+                    warn!("Consistency issue; tried to remove {} but it was already removed", path.display());
+                },
+            }
+        }
+
+        Some(root_value)
+    }
+}