Rename buffer crate to text and name its entrypoint after the crate

Co-Authored-By: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/text/src/operation_queue.rs

@@ -0,0 +1,127 @@
+use super::Operation;
+use std::{fmt::Debug, ops::Add};
+use sum_tree::{Cursor, Dimension, Edit, Item, KeyedItem, SumTree, Summary};
+
+#[derive(Clone, Debug)]
+pub struct OperationQueue(SumTree<Operation>);
+
+#[derive(Clone, Copy, Debug, Default, Eq, Ord, PartialEq, PartialOrd)]
+pub struct OperationKey(clock::Lamport);
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub struct OperationSummary {
+    pub key: OperationKey,
+    pub len: usize,
+}
+
+impl OperationKey {
+    pub fn new(timestamp: clock::Lamport) -> Self {
+        Self(timestamp)
+    }
+}
+
+impl OperationQueue {
+    pub fn new() -> Self {
+        OperationQueue(SumTree::new())
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.summary().len
+    }
+
+    pub fn insert(&mut self, mut ops: Vec<Operation>) {
+        ops.sort_by_key(|op| op.lamport_timestamp());
+        ops.dedup_by_key(|op| op.lamport_timestamp());
+        self.0
+            .edit(ops.into_iter().map(Edit::Insert).collect(), &());
+    }
+
+    pub fn drain(&mut self) -> Self {
+        let clone = self.clone();
+        self.0 = SumTree::new();
+        clone
+    }
+
+    pub fn cursor(&self) -> Cursor<Operation, ()> {
+        self.0.cursor()
+    }
+}
+
+impl Summary for OperationSummary {
+    type Context = ();
+
+    fn add_summary(&mut self, other: &Self, _: &()) {
+        assert!(self.key < other.key);
+        self.key = other.key;
+        self.len += other.len;
+    }
+}
+
+impl<'a> Add<&'a Self> for OperationSummary {
+    type Output = Self;
+
+    fn add(self, other: &Self) -> Self {
+        assert!(self.key < other.key);
+        OperationSummary {
+            key: other.key,
+            len: self.len + other.len,
+        }
+    }
+}
+
+impl<'a> Dimension<'a, OperationSummary> for OperationKey {
+    fn add_summary(&mut self, summary: &OperationSummary, _: &()) {
+        assert!(*self <= summary.key);
+        *self = summary.key;
+    }
+}
+
+impl Item for Operation {
+    type Summary = OperationSummary;
+
+    fn summary(&self) -> Self::Summary {
+        OperationSummary {
+            key: OperationKey::new(self.lamport_timestamp()),
+            len: 1,
+        }
+    }
+}
+
+impl KeyedItem for Operation {
+    type Key = OperationKey;
+
+    fn key(&self) -> Self::Key {
+        OperationKey::new(self.lamport_timestamp())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_len() {
+        let mut clock = clock::Lamport::new(0);
+
+        let mut queue = OperationQueue::new();
+        assert_eq!(queue.len(), 0);
+
+        queue.insert(vec![
+            Operation::Test(clock.tick()),
+            Operation::Test(clock.tick()),
+        ]);
+        assert_eq!(queue.len(), 2);
+
+        queue.insert(vec![Operation::Test(clock.tick())]);
+        assert_eq!(queue.len(), 3);
+
+        drop(queue.drain());
+        assert_eq!(queue.len(), 0);
+
+        queue.insert(vec![Operation::Test(clock.tick())]);
+        assert_eq!(queue.len(), 1);
+    }
+
+    #[derive(Clone, Debug, Eq, PartialEq)]
+    struct TestOperation(clock::Lamport);
+}