Get appending at the end of the rope to work

editor-challenge/src/doc_rope.rs

@@ -2,7 +2,7 @@ use std::{mem, ops::Deref};
 
 const CHUNK_SIZE: usize = 10;
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 struct NodeId(usize);
 
 impl Deref for NodeId {
@@ -12,14 +12,15 @@ impl Deref for NodeId {
     }
 }
 
+#[derive(Debug)]
 enum Node {
     Interior {
         // the number of characters to the left of this node
         // the number of lines to the left of this node
         char_count: usize,
 
-        left: NodeId,
+        left: Option<NodeId>,
-        right: NodeId,
+        right: Option<NodeId>,
     },
     Leaf(LeafNode),
 }
@@ -33,6 +34,7 @@ impl Node {
     }
 }
 
+#[derive(Debug)]
 struct LeafNode(String);
 
 impl LeafNode {
@@ -56,97 +58,55 @@ impl From<String> for LeafNode {
     }
 }
 
-// a Rope is a regular tree which adds on some extra behavior for dealing with a continuous data
+/// A Rope is a regular tree which adds on some extra behavior for dealing with a continuous data
-// structure.
+/// structure. In this case, the nodes all contain strings, and the rope is arranged such that a
+/// depth-first traversal will yield the entire contents of the rope in proper order.
+#[derive(Debug)]
 pub struct Rope {
     node_count: usize,
     contents: Vec<Option<Node>>,
 }
 
 impl Rope {
+    /// Insert text at an index within the document. loc is the number of characters from the
+    /// beginning.
     pub fn insert_at(&mut self, loc: usize, text: String) {
-        unimplemented!();
+        match self.find_insertion_node_id(loc) {
-    }
+            None => {
-
+                let node = Node::Leaf(LeafNode::from(text));
-    pub fn append(&mut self, text: String) {
+                self.node_count += 1;
-        if self.node_count == 0 {
+                self.contents.push(Some(node));
-            let node = Node::Leaf(LeafNode::from(text));
-            self.node_count += 1;
-            self.contents.push(Some(node));
-        } else {
-            // Let's grab a node. If it's a leaf node, we need to convert it into a interior node.
-            // In doing so, we need to move the current leaf node into a left-hand child and create
-            // the right-hand child.
-            //
-            // If it's an interior node, we'll dig deeper. Not doing any tree rebalancing at the
-            // moment.
-            //
-            // First thing we need to know is what mode of node we have. That's going to determine
-            // which branch of operations we go into. We want to do this without borrowing the data
-            // for anything more than the match.
-            // let mut node = mem::replace(&mut self.contents[0], None);
-            match self.contents[0] {
-                Some(Node::Interior { ref left, ref right, .. }) => {
-
-                }
-                Some(Node::Leaf(_)) => {
-                    let Some(Node::Leaf(mut ln)) = mem::replace(&mut self.contents[0], None) else {
-                        panic!("Should never leave an empty space in the node list")
-                    };
-                    let contents = ln.take();
-
-                    let lnode = Node::Leaf(LeafNode::from(contents));
-                    let rnode = Node::Leaf(LeafNode::from(text));
-
-                    let lnode_id = self.node_count;
-                    let rnode_id = self.node_count + 1;
-
-                    let interior_node = Node::Interior {
-                        char_count: lnode.len(),
-                        left: NodeId(lnode_id),
-                        right: NodeId(rnode_id),
-                    };
-
-                    let _ = mem::replace(&mut self.contents[0], Some(interior_node));
-
-                    self.node_count += 2;
-                    self.contents.push(Some(lnode));
-                    self.contents.push(Some(rnode));
-                }
-                None => panic!("Should never leave an empty space in the node list"),
             }
-            /*
+            Some(id) => {
-            let mut node = &mut self.contents[0];
+                self.insert_at_node(id, text);
-            if let Node::Leaf(s) = node {
-                let contents = s.take();
-
-                let lnode = Node::Leaf(LeafNode::from(contents));
-                let rnode = Node::Leaf(LeafNode::from(text));
-                self.contents.push(lnode);
-                self.contents.push(rnode);
-                let lnode_id = self.node_count;
-                let rnode_id = self.node_count + 1;
-                self.node_count += 2;
-                *node = Node::Interior{
-                    char_count: 0,
-                    left: NodeId(lnode_id),
-                    right: NodeId(rnode_id),
-                };
             }
-            */
         }
     }
 
+    /// Append text to the end of the document.
+    pub fn append(&mut self, text: String) {
+        self.insert_at(self.len(), text);
+    }
+
+    /// Convert the entire rope back to a continuous String.
     pub fn to_string(&self) -> String {
+        if self.contents.is_empty() {
+            return "".to_owned();
+        }
+
         let mut r = String::new();
         let mut stack = vec![NodeId(0)];
 
         while let Some(current_id) = stack.pop() {
             let node = &self.contents[*current_id];
             match node {
-                Some(Node::Interior{ left, right, .. }) => {
+                Some(Node::Interior { left, right, .. }) => {
-                    stack.push(*right);
+                    if let Some(right_id) = *right {
-                    stack.push(*left);
+                        stack.push(right_id);
+                    }
+                    if let Some(left_id) = *left {
+                        stack.push(left_id);
+                    }
                 }
                 Some(Node::Leaf(ln)) => r.push_str(ln.as_str()),
                 None => panic!("Should never leave an empty space in the node list"),
@@ -156,6 +116,7 @@ impl Rope {
         r
     }
 
+    /// Calculate the length of the stored string.
     pub fn len(&self) -> usize {
         // This can be optimized later. Do a traversal of each right node. We already have
         // character counts of each left tree. Only count the length of the final right leaf.
@@ -177,6 +138,74 @@ impl Rope {
     fn node_count(&self) -> usize {
         self.node_count
     }
+
+    // Find the node ID of the insertion point. This is not fully implemented, in that this
+    // function ignores the offset from the beginning. Because of that, it is also always inserting
+    // onto the right side, and never traversing down the left.
+    fn find_insertion_node_id(&self, _loc: usize) -> Option<NodeId> {
+        let mut current_id = NodeId(0);
+        loop {
+            match self.contents.get(*current_id) {
+                Some(Some(Node::Interior { ref right, .. })) => match right {
+                    Some(id) => current_id = *id,
+                    None => return Some(current_id),
+                },
+                Some(Some(Node::Leaf(_))) => return Some(current_id),
+                Some(None) => panic!("There should never be an empty node in the tree"),
+                // This only happens when the list is empty. Otherwise, we're detecting the None in
+                // advance.
+                None => return None,
+            }
+        }
+    }
+
+    // Insert text at a particular node location.
+    //
+    // This is not a self-balancing operation (yet). Once we know where text needs to be inserted,
+    // based on the offset from the beginning, we can grab that node and either replace it (if it
+    // is a Leaf node) or update it (if it is an Interior node).
+    //
+    // This function is currently naive, in that it will always assume that text needs to be added
+    // to the right side, which may not be correct.
+    fn insert_at_node(&mut self, id: NodeId, text: String) {
+        match self.contents[*id] {
+            Some(Node::Interior { ref mut right, .. }) => {
+                let new_node = Node::Leaf(LeafNode::from(text));
+                let new_node_id = NodeId(self.node_count + 1);
+
+                *right = Some(new_node_id);
+                self.contents.push(Some(new_node));
+
+                self.node_count += 1;
+            }
+            Some(Node::Leaf(_)) => {
+                let Some(Node::Leaf(mut ln)) = mem::replace(&mut self.contents[*id], None) else {
+                    panic!("Should never leave an empty space in the node list")
+                };
+                let contents = ln.take();
+
+                let lnode = Node::Leaf(LeafNode::from(contents));
+                let rnode = Node::Leaf(LeafNode::from(text));
+
+                let lnode_id = self.node_count;
+                let rnode_id = self.node_count + 1;
+
+                let interior_node = Node::Interior {
+                    char_count: lnode.len(),
+                    left: Some(NodeId(lnode_id)),
+                    right: Some(NodeId(rnode_id)),
+                };
+
+                let _ = mem::replace(&mut self.contents[*id], Some(interior_node));
+
+                self.node_count += 2;
+                self.contents.push(Some(lnode));
+                self.contents.push(Some(rnode));
+
+            }
+            None => panic!("Should never leave an empty space in the node list"),
+        }
+    }
 }
 
 impl Default for Rope {
@@ -199,9 +228,9 @@ impl From<String> for Rope {
 
         while lst.len() > CHUNK_SIZE {
             (first, lst) = lst.split_at(CHUNK_SIZE);
-            println!("[{}] [{}]", first, lst);
             rope.append(first.to_owned());
         }
+        rope.append(lst.to_owned());
         rope
     }
 }
@@ -210,15 +239,31 @@ impl From<String> for Rope {
 mod test {
     use super::*;
 
+    struct TestCase {
+        content: String,
+    }
+
     #[test]
     fn it_creates_a_rope_from_a_string() {
-        let content =
+        let test_cases = vec![
+            TestCase{ content: "".to_owned() },
+            TestCase{ content: "This".to_owned() },
+            TestCase{ content: "This is some basic".to_owned() },
+            TestCase{ content: "This is some basic context which is much smaller".to_owned() },
+            TestCase{ content:
             "This is some basic context which is much smaller than the rope is designed for."
-                .to_owned();
+                .to_owned()
+            },
+        ];
 
-        let rope = Rope::from(content.clone());
+        for case in test_cases {
+            let rope = Rope::from(case.content.clone());
 
-        assert_eq!(rope.to_string(), content);
+            for (idx, node) in rope.contents.iter().enumerate() {
-        assert_eq!(rope.len(), content.len());
+            }
+
+            assert_eq!(rope.len(), case.content.len(), "{}", case.content);
+            assert_eq!(rope.to_string(), case.content, "{:?}", case.content);
+        }
     }
 }