From c3ebef8fc1feab0db3870e299c26eaf7ea7d71a6 Mon Sep 17 00:00:00 2001
From: Matthew Gordon <mgordon@sparkgeo.com>
Date: Sat, 19 Oct 2024 21:47:30 -0300
Subject: [PATCH] Add Rope::insert_char_at_index()

---
 src/core/rope.rs | 47 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 40 insertions(+), 7 deletions(-)

diff --git a/src/core/rope.rs b/src/core/rope.rs
index 1b313f9..5286a16 100644
--- a/src/core/rope.rs
+++ b/src/core/rope.rs
@@ -94,15 +94,33 @@ impl Rope {
         }
     }
 
-    pub fn concat(first: Rc<Rope>, second: Rc<Rope>) -> Rc<Rope> {
-        Rope::join(first, Some(second)).rebalance()
+    /// Returns a new rope created from concatenating `other` onto the end of
+    /// this one.
+    pub fn concat(self: Rc<Rope>, other: Rc<Rope>) -> Rc<Rope> {
+        Rope::join(self, Some(other)).rebalance()
+    }
+
+    /// Insert new text into the rope at a given character index.
+    pub fn insert_at_char_index(self: &Rc<Rope>, index: usize, text: impl Into<String>) -> Rc<Rope> {
+        let new_node = Rope::new(text);
+        let total_chars = self.total_chars();
+        if index == 0 {
+            new_node.concat(self.clone())
+        } else if index < total_chars {
+            let (before, after) = self.split_at_char_index(index);
+            before.concat(new_node).concat(after)
+        } else if index == total_chars {
+            self.clone().concat(new_node)
+        } else {
+            panic!("Attempt to insert past end of rope.")
+        }
     }
 
     /// Split the rope in two at character `index`.
     ///
     /// The result is two Ropes—one containing the first 'i' characters of the
     /// text and the other containing the rest of the text.
-    pub fn split(self: &Rc<Self>, index: usize) -> (Rc<Self>, Rc<Self>) {
+    pub fn split_at_char_index(self: &Rc<Self>, index: usize) -> (Rc<Self>, Rc<Self>) {
         match *self.as_ref() {
             Rope::Branch {
                 chars_weight,
@@ -111,14 +129,14 @@ impl Rope {
                 ..
             } => {
                 if index < chars_weight {
-                    let (first, second) = left.split(index);
+                    let (first, second) = left.split_at_char_index(index);
                     (
                         first.rebalance(),
                         Rope::join(second, right.as_ref().map(|r| r.clone())).rebalance(),
                     )
                 } else if let Some(right) = right {
                     if index > chars_weight {
-                        let (first, second) = right.split(index - chars_weight);
+                        let (first, second) = right.split_at_char_index(index - chars_weight);
                         (
                             Rope::join(left.clone(), Some(first)).rebalance(),
                             second.rebalance(),
@@ -430,7 +448,7 @@ mod tests {
         let target = small_test_rope();
         let full_string = small_test_rope_full_string();
         for i in 0..(full_string.chars().count()) {
-            let (first, second) = target.split(i);
+            let (first, second) = target.split_at_char_index(i);
             let first_string: String = first.iter_chars().collect();
             let second_string: String = second.iter_chars().collect();
             assert_eq!(first_string, full_string[0..i]);
@@ -446,7 +464,7 @@ mod tests {
             .chars()
             .collect();
         for i in 0..(expected_chars.len()) {
-            let (first, second) = target.split(i);
+            let (first, second) = target.split_at_char_index(i);
             let string: String = first.iter_chars().collect();
             let expected: String = expected_chars[0..i].iter().collect();
             assert_eq!(string, expected);
@@ -525,4 +543,19 @@ mod tests {
             1
         );
     }
+
+    #[test]
+    fn insert_at_char_index() {
+        let target = Rope::new("The brown dog");
+        assert_eq!(target.iter_chars().collect::<String>(), "The brown dog");
+        let rope1 = target.insert_at_char_index(4, "quick");
+        assert_eq!(target.iter_chars().collect::<String>(), "The brown dog");
+        assert_eq!(rope1.iter_chars().collect::<String>(), "The quickbrown dog");
+        let rope2 = rope1.insert_at_char_index(9, " ");
+        assert_eq!(target.iter_chars().collect::<String>(), "The brown dog");
+        assert_eq!(rope1.iter_chars().collect::<String>(), "The quickbrown dog");
+        assert_eq!(rope2.iter_chars().collect::<String>(), "The quick brown dog");
+        let rope3 = rope2.insert_at_char_index("The quick brown dog".len(), " jumps over the lazy fox.");
+        assert_eq!(rope3.iter_chars().collect::<String>(), "The quick brown dog jumps over the lazy fox.");
+    }
 }