Add Rope::delete_at_char_index()

Just the beginnings of a rope implementation but I want to refactor
already so saving what I've got so far.

.gitignore

@@ -14,3 +14,5 @@ Cargo.lock
 # MSVC Windows builds of rustc generate these, which store debugging information
 *.pdb
 
+# Backup files
+*~

Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "ged"
+version = "0.1.0"
+edition = "2021"
+
+[dev-dependencies]
+ntest = "0.9.3"

src/core/fibbonacci.rs

@@ -0,0 +1,29 @@
+pub fn fibbonacci(index: usize) -> usize {
+    if index == 0 {
+        0
+    } else if index < 3 {
+        1
+    } else {
+        let mut values = vec![1;index+1];
+        for i in 3..index+1 {
+            values[i] = values[i - 1] + values[i - 2];
+        }
+        values[index]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_first_few_values() {
+        let expected_values = vec![
+            0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181,
+            6765, 10946,
+        ];
+        for (i, &n) in expected_values.iter().enumerate() {
+            assert_eq!(fibbonacci(i), n);
+        }
+    }
+}

src/core/mod.rs

@@ -0,0 +1,3 @@
+pub mod rope;
+
+mod fibbonacci;

src/core/rope.rs

@@ -0,0 +1,593 @@
+use {super::fibbonacci::fibbonacci, std::rc::Rc};
+
+/// [Rope](https://en.wikipedia.org/wiki/Rope_(data_structure)) data structure
+/// implementation.
+///
+/// This is the main data structure used to store text file contents while they
+/// are being edited.
+#[derive(Debug)]
+pub enum Rope {
+    Branch {
+        /// Total number of bytes in the string contained in the left subtree, or
+        /// the number of bytes in the string if this is a leaf.
+        bytes_weight: usize,
+
+        /// Total number of characters in the string contained in the left subtree,
+        /// or the number of characters in the string if this is a leaf.
+        chars_weight: usize,
+
+        /// Total number of line endings in the string contained in the left
+        /// subtree, or the number of line endings in the string if this is a leaf.
+        lines_weight: usize,
+
+        /// The root of the left subtree
+        left: Rc<Rope>,
+        /// The root of the right subtree
+        right: Option<Rc<Rope>>,
+    },
+    Leaf {
+        text: String,
+    },
+}
+
+impl Rope {
+    /// Create a new Rope containing the passed text in a single node.
+    pub fn new(contents: impl Into<String>) -> Rc<Self> {
+        let text = contents.into();
+        Rc::new(Rope::Leaf { text })
+    }
+
+    /// Create a new empty Rope
+    pub fn empty() -> Rc<Self> {
+        let text = "".into();
+        Rc::new(Rope::Leaf { text })
+    }
+
+    /// Return the total number of bytes in the text.
+    pub fn total_bytes(&self) -> usize {
+        match self {
+            Rope::Branch {
+                bytes_weight,
+                right: None,
+                ..
+            } => *bytes_weight,
+            Rope::Branch {
+                bytes_weight,
+                right: Some(right),
+                ..
+            } => bytes_weight + right.total_bytes(),
+            Rope::Leaf { text } => text.len(),
+        }
+    }
+
+    /// Return the total number of characters in the text.
+    pub fn total_chars(&self) -> usize {
+        match self {
+            Rope::Branch {
+                chars_weight,
+                right: None,
+                ..
+            } => *chars_weight,
+            Rope::Branch {
+                chars_weight,
+                right: Some(right),
+                ..
+            } => chars_weight + right.total_chars(),
+            Rope::Leaf { text } => text.chars().count(),
+        }
+    }
+
+    /// Return the total number of lines in the text
+    pub fn total_lines(&self) -> usize {
+        match self {
+            Rope::Branch {
+                lines_weight,
+                right: None,
+                ..
+            } => *lines_weight,
+            Rope::Branch {
+                lines_weight,
+                right: Some(right),
+                ..
+            } => lines_weight + right.total_lines(),
+            Rope::Leaf { text } => text.lines().count(),
+        }
+    }
+
+    /// 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.")
+        }
+    }
+
+    /// Return a new rope with `length` characters removed after `start`.
+    pub fn delete_at_char_index(self: &Rc<Rope>, start: usize, length: usize) -> Rc<Rope> {
+        let (beginning, rest) = self.split_at_char_index(start);
+        let (_, end) = rest.split_at_char_index(length);
+        beginning.concat(end)
+    }
+
+    /// 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_at_char_index(self: &Rc<Self>, index: usize) -> (Rc<Self>, Rc<Self>) {
+        match *self.as_ref() {
+            Rope::Branch {
+                chars_weight,
+                ref left,
+                ref right,
+                ..
+            } => {
+                if index < chars_weight {
+                    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_at_char_index(index - chars_weight);
+                        (
+                            Rope::join(left.clone(), Some(first)).rebalance(),
+                            second.rebalance(),
+                        )
+                    } else {
+                        (left.clone(), right.clone())
+                    }
+                } else {
+                    (left.clone(), Rope::empty())
+                }
+            }
+            Rope::Leaf { ref text } => {
+                if let Some((byte_index, _)) = text.char_indices().nth(index) {
+                    let (first, second) = text.split_at(byte_index);
+                    (Rope::new(first), Rope::new(second))
+                } else {
+                    (self.clone(), Rope::empty())
+                }
+            }
+        }
+    }
+
+    pub fn is_balanced(&self) -> bool {
+        match self {
+            Rope::Branch { bytes_weight, .. } => fibbonacci(self.depth() + 2) <= *bytes_weight,
+            Rope::Leaf { .. } => true,
+        }
+    }
+
+    pub fn rebalance(self: Rc<Rope>) -> Rc<Rope> {
+        if self.is_balanced() {
+            return self;
+        }
+        let leaf_nodes: Vec<_> = self.iter_nodes().collect();
+        merge(&leaf_nodes)
+    }
+
+    /// Number of steps between this node and its most distance descendant
+    ///
+    /// Leaf nodes have a depth of 0 and each branch node has a depth one
+    /// greater than the depth of deepest child.
+    pub fn depth(&self) -> usize {
+        match self {
+            Rope::Branch { left, right, .. } => {
+                left.depth()
+                    .max(right.as_ref().map(|r| r.depth()).unwrap_or(0))
+                    + 1
+            }
+            Rope::Leaf { .. } => 0,
+        }
+    }
+
+    /// Returns true if this node is a leaf node, false otherwise
+    pub fn is_leaf(&self) -> bool {
+        match &self {
+            Rope::Branch { .. } => false,
+            Rope::Leaf { .. } => true,
+        }
+    }
+
+    /// Returns an iterator over the chars of the text
+    pub fn iter_chars(self: &Rc<Self>) -> CharIterator {
+        CharIterator::new(self)
+    }
+
+    /// Concatenate two Ropes without rebalancing.
+    ///
+    /// Combines to ropes by creating a new parent node and adding `left` and
+    /// `right` as children. If `right` is [None] then the resulting node will
+    /// only have one child.
+    fn join(left: Rc<Rope>, right: Option<Rc<Rope>>) -> Rc<Self> {
+        Rc::new(Rope::Branch {
+            bytes_weight: left.total_bytes(),
+            chars_weight: left.total_chars(),
+            lines_weight: left.total_lines(),
+            left,
+            right,
+        })
+    }
+
+    /// Returns an iterater over the leaf nodes
+    fn iter_nodes(self: Rc<Self>) -> NodeIterator {
+        NodeIterator::new(self)
+    }
+}
+
+fn merge(leaf_nodes: &[Rc<Rope>]) -> Rc<Rope> {
+    match leaf_nodes.len() {
+        0 => panic!("Attempt to merge empty list"),
+        1 => leaf_nodes[0].clone(),
+        2 => Rope::join(leaf_nodes[0].clone(), Some(leaf_nodes[1].clone())),
+        3.. => {
+            let mid = leaf_nodes.len() / 2;
+            Rope::join(merge(&leaf_nodes[..mid]), Some(merge(&leaf_nodes[mid..])))
+        }
+    }
+}
+
+struct NodeIterator {
+    stack: Vec<Rc<Rope>>,
+}
+
+impl NodeIterator {
+    fn new(rope: Rc<Rope>) -> Self {
+        let mut result = NodeIterator { stack: vec![] };
+        result.push_tree(rope);
+        result
+    }
+
+    fn push_tree(&mut self, node: Rc<Rope>) {
+        let mut curr = node;
+        self.stack.push(curr.clone());
+        while let Rope::Branch { left, .. } = curr.as_ref() {
+            self.stack.push(left.clone());
+            curr = left.clone();
+        }
+    }
+}
+
+impl Iterator for NodeIterator {
+    type Item = Rc<Rope>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let curr = self.stack.pop()?;
+        if let Rope::Branch { right, .. } = curr.as_ref() {
+            if let Some(right) = right {
+                self.push_tree(right.clone());
+            }
+            self.next()
+        } else {
+            Some(curr)
+        }
+    }
+}
+
+pub struct CharIterator {
+    node_iterator: NodeIterator,
+    current_text: Option<String>,
+    str_index: usize,
+}
+
+impl CharIterator {
+    fn new(rope: &Rc<Rope>) -> Self {
+        let mut node_iterator = NodeIterator::new(rope.clone());
+        let current_text = Self::next_string(&mut node_iterator);
+        CharIterator {
+            node_iterator,
+            current_text,
+            str_index: 0,
+        }
+    }
+
+    fn next_string(node_iterator: &mut NodeIterator) -> Option<String> {
+        node_iterator.next().map(|rope| {
+            if let Rope::Leaf { text } = rope.as_ref() {
+                text.clone()
+            } else {
+                panic!("Rope NodeIterator yielded non-leaf node.")
+            }
+        })
+    }
+}
+
+impl Iterator for CharIterator {
+    type Item = char;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.current_text
+            .as_ref()
+            .and_then(|text| {
+                let c = text.chars().nth(self.str_index);
+                self.str_index += 1;
+                c
+            })
+            .or_else(|| {
+                self.current_text = Self::next_string(&mut self.node_iterator);
+                if self.current_text.is_some() {
+                    self.str_index = 0;
+                    self.next()
+                } else {
+                    None
+                }
+            })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ntest::timeout;
+
+    fn small_test_rope() -> Rc<Rope> {
+        Rope::join(
+            Rope::join(
+                Rope::join(Rope::new("abc"), Some(Rope::new("def"))),
+                Some(Rope::join(Rope::new("g"), Some(Rope::new("hi")))),
+            ),
+            Some(Rope::join(
+                Rope::join(
+                    Rope::join(Rope::new("jklm"), Some(Rope::new("n"))),
+                    Some(Rope::join(Rope::new("op"), Some(Rope::new("qr")))),
+                ),
+                Some(Rope::join(Rope::new("stuv"), Some(Rope::new("wxyz")))),
+            )),
+        )
+    }
+
+    fn small_test_rope_leaf_strings() -> Vec<&'static str> {
+        vec![
+            "abc", "def", "g", "hi", "jklm", "n", "op", "qr", "stuv", "wxyz",
+        ]
+    }
+
+    fn small_test_rope_full_string() -> &'static str {
+        "abcdefghijklmnopqrstuvwxyz"
+    }
+
+    fn small_test_rope_with_multibyte_chars() -> Rc<Rope> {
+        Rope::join(
+            Rope::join(
+                Rope::join(Rope::new("aあbc"), Some(Rope::new("deえf"))),
+                Some(Rope::join(Rope::new("g"), Some(Rope::new("hiい")))),
+            ),
+            Some(Rope::join(
+                Rope::join(
+                    Rope::join(Rope::new("jklm"), Some(Rope::new("n"))),
+                    Some(Rope::join(Rope::new("おop"), Some(Rope::new("qr")))),
+                ),
+                Some(Rope::join(Rope::new("stuうv"), Some(Rope::new("wxyz")))),
+            )),
+        )
+    }
+
+    fn small_test_rope_with_multibyte_chars_leaf_strings() -> Vec<&'static str> {
+        vec![
+            "aあbc", "deえf", "g", "hiい", "jklm", "n", "おop", "qr", "stuうv", "wxyz",
+        ]
+    }
+
+    fn small_test_rope_with_multibyte_chars_full_string() -> &'static str {
+        "aあbcdeえfghiいjklmnおopqrstuうvwxyz"
+    }
+
+    impl Rope {
+        fn unwrap_branch_left(&self) -> &Rc<Rope> {
+            match self {
+                Rope::Branch { left, .. } => left,
+                Rope::Leaf { .. } => panic!("Expected branch node but found leaf"),
+            }
+        }
+
+        fn unwrap_branch_right(&self) -> Option<&Rc<Rope>> {
+            match self {
+                Rope::Branch { right, .. } => right.as_ref(),
+                Rope::Leaf { .. } => panic!("Expected branch node but found leaf"),
+            }
+        }
+    }
+
+    #[test]
+    #[timeout(100)]
+    fn node_iterator_for_single_node_returns_node_and_only_node() {
+        let target = Rope::new("The");
+
+        let result: Vec<_> = target.iter_nodes().collect();
+        assert_eq!(result.len(), 1);
+        assert_eq!(result[0].total_bytes(), 3);
+        assert_eq!(result[0].total_chars(), 3);
+        assert_eq!(result[0].total_lines(), 1);
+        match result[0].as_ref() {
+            Rope::Leaf { text, .. } => assert_eq!(text, "The"),
+            _ => panic!(),
+        }
+    }
+
+    #[test]
+    #[timeout(100)]
+    fn node_iterator_returns_nodes_in_correct_order() {
+        let strings = small_test_rope_leaf_strings();
+        let target = small_test_rope();
+
+        let result: Vec<_> = target.iter_nodes().take(26).collect();
+        assert_eq!(result.len(), 10);
+        for (node, string) in result.iter().zip(strings) {
+            match &node.as_ref() {
+                Rope::Leaf { text } => assert_eq!(text, string),
+                _ => panic!(),
+            }
+        }
+    }
+
+    #[test]
+    #[timeout(100)]
+    fn char_iterator_returns_chars_in_correct_order() {
+        let target = small_test_rope();
+
+        let result: Vec<_> = target.iter_chars().collect();
+        assert_eq!(result.len(), 26);
+        for (&target_char, expected_char) in
+            result.iter().zip(small_test_rope_full_string().chars())
+        {
+            assert_eq!(target_char, expected_char);
+        }
+    }
+
+    #[test]
+    #[timeout(100)]
+    fn split_splits_at_correct_location() {
+        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_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]);
+            assert_eq!(second_string, full_string[i..]);
+        }
+    }
+
+    #[test]
+    #[timeout(100)]
+    fn split_splits_at_correct_location_with_multibyte_chars() {
+        let target = small_test_rope_with_multibyte_chars();
+        let expected_chars: Vec<_> = small_test_rope_with_multibyte_chars_full_string()
+            .chars()
+            .collect();
+        for i in 0..(expected_chars.len()) {
+            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);
+            let string: String = second.iter_chars().collect();
+            let expected: String = expected_chars[i..].iter().collect();
+            assert_eq!(string, expected);
+        }
+    }
+
+    #[test]
+    fn depths_have_correct_values() {
+        let target = small_test_rope_with_multibyte_chars();
+        assert_eq!(target.depth(), 4);
+        assert_eq!(target.unwrap_branch_left().depth(), 2);
+        assert_eq!(target.unwrap_branch_left().unwrap_branch_left().depth(), 1);
+        assert_eq!(
+            target
+                .unwrap_branch_left()
+                .unwrap_branch_left()
+                .unwrap_branch_left()
+                .depth(),
+            0
+        );
+        assert_eq!(
+            target
+                .unwrap_branch_left()
+                .unwrap_branch_left()
+                .unwrap_branch_right()
+                .unwrap()
+                .depth(),
+            0
+        );
+        assert_eq!(
+            target
+                .unwrap_branch_left()
+                .unwrap_branch_right()
+                .unwrap()
+                .depth(),
+            1
+        );
+        assert_eq!(
+            target
+                .unwrap_branch_left()
+                .unwrap_branch_right()
+                .unwrap()
+                .unwrap_branch_left()
+                .depth(),
+            0
+        );
+        assert_eq!(
+            target
+                .unwrap_branch_left()
+                .unwrap_branch_right()
+                .unwrap()
+                .unwrap_branch_right()
+                .unwrap()
+                .depth(),
+            0
+        );
+        assert_eq!(target.unwrap_branch_right().unwrap().depth(), 3);
+        assert_eq!(
+            target
+                .unwrap_branch_right()
+                .unwrap()
+                .unwrap_branch_left()
+                .depth(),
+            2
+        );
+        assert_eq!(
+            target
+                .unwrap_branch_right()
+                .unwrap()
+                .unwrap_branch_right()
+                .unwrap()
+                .depth(),
+            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."
+        );
+    }
+
+    #[test]
+    fn delete_at_char_index() {
+        let target = Rope::new("The quick brown fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index(10, 6);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "The quick fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index(0, 4);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "quick brown fox jumps over the lazy dog.");
+        let test = target.delete_at_char_index("The quick brown fox jumps over the lazy dog.".len()-5, 5);
+        assert_eq!(target.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy dog.");
+        assert_eq!(test.iter_chars().collect::<String>(), "The quick brown fox jumps over the lazy");
+    }
+}

src/main.rs

@@ -0,0 +1,5 @@
+mod core;
+
+fn main() {
+    println!("Hello, world!");
+}