From 042a13c033d8c81404463cd036f6d9ebf6f16bf6 Mon Sep 17 00:00:00 2001
From: Zixuan Chen <remch183@outlook.com>
Date: Mon, 30 Oct 2023 21:55:35 +0800
Subject: [PATCH] perf: make id span easier to merge

---
 crates/loro-common/src/span.rs                | 87 ++++++++++++++++++-
 .../src/container/list/list_op.rs             |  2 +
 .../src/container/richtext/tracker.rs         |  2 +-
 3 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/crates/loro-common/src/span.rs b/crates/loro-common/src/span.rs
index 50c8f23e1..75711ce11 100644
--- a/crates/loro-common/src/span.rs
+++ b/crates/loro-common/src/span.rs
@@ -67,6 +67,11 @@ impl CounterSpan {
         }
     }
 
+    #[inline(always)]
+    pub fn bidirectional(&self) -> bool {
+        (self.end - self.start).abs() == 1
+    }
+
     #[inline(always)]
     pub fn direction(&self) -> i32 {
         if self.start < self.end {
@@ -141,6 +146,20 @@ impl CounterSpan {
             self.end = new_end.min(self.start);
         }
     }
+
+    /// if we can merge element on the left, this method return the last atom of it
+    fn prev_pos(&self) -> i32 {
+        if self.start < self.end {
+            self.start - 1
+        } else {
+            self.start + 1
+        }
+    }
+
+    /// if we can merge element on the right, this method return the first atom of it
+    fn next_pos(&self) -> i32 {
+        self.end
+    }
 }
 
 impl HasLength for CounterSpan {
@@ -176,13 +195,32 @@ impl Sliceable for CounterSpan {
 impl Mergable for CounterSpan {
     #[inline]
     fn is_mergable(&self, other: &Self, _: &()) -> bool {
-        // TODO: can use the similar logic as [DeleteSpan] to merge
-        self.end == other.start && self.direction() == other.direction()
+        match (self.bidirectional(), other.bidirectional()) {
+            (true, true) => self.start + 1 == other.start || self.start == other.start + 1,
+            (true, false) => self.start == other.prev_pos(),
+            (false, true) => self.next_pos() == other.start,
+            (false, false) => {
+                self.next_pos() == other.start && self.direction() == other.direction()
+            }
+        }
     }
 
     #[inline]
     fn merge(&mut self, other: &Self, _: &()) {
-        self.end = other.end;
+        match (self.bidirectional(), other.bidirectional()) {
+            (true, true) => {
+                if self.start + 1 == other.start {
+                    self.end = self.start + 2;
+                } else if self.start - 1 == other.start {
+                    self.end = self.start - 2;
+                }
+            }
+            (true, false) => self.end = other.end,
+            (false, true) => self.end = self.end + self.direction(),
+            (false, false) => {
+                self.end = other.end;
+            }
+        }
     }
 }
 
@@ -444,4 +482,47 @@ mod test_id_span {
         let slice: Vec<IdSpan> = id_span_vec.slice_iter(5, 14).map(|x| x.into()).collect();
         assert_eq!(slice, id_spans!([0, 95, 90], [2, 2, 4], [2, 8, 6]).to_vec());
     }
+
+    #[test]
+    fn merge() {
+        let mut a = CounterSpan::new(0, 2);
+        let b = CounterSpan::new(2, 1);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(0, 3));
+
+        let mut a = CounterSpan::new(3, 2);
+        let b = CounterSpan::new(2, 1);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(3, 1));
+
+        let mut a = CounterSpan::new(4, 2);
+        let b = CounterSpan::new(2, 3);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(4, 1));
+
+        let mut a = CounterSpan::new(8, 9);
+        let b = CounterSpan::new(9, 8);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(8, 10));
+
+        let mut a = CounterSpan::new(8, 9);
+        let b = CounterSpan::new(10, 11);
+        assert!(!a.is_mergable(&b, &()));
+
+        let mut a = CounterSpan::new(0, 2);
+        let b = CounterSpan::new(2, 4);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(0, 4));
+
+        let mut a = CounterSpan::new(4, 2);
+        let b = CounterSpan::new(2, 0);
+        assert!(a.is_mergable(&b, &()));
+        a.merge(&b, &());
+        assert_eq!(a, CounterSpan::new(4, 0));
+    }
 }
diff --git a/crates/loro-internal/src/container/list/list_op.rs b/crates/loro-internal/src/container/list/list_op.rs
index fe34e4fd9..8baa1290f 100644
--- a/crates/loro-internal/src/container/list/list_op.rs
+++ b/crates/loro-internal/src/container/list/list_op.rs
@@ -190,6 +190,8 @@ impl Mergable for DeleteSpan {
     where
         Self: Sized,
     {
+        // merge continuous deletions:
+        // note that the previous deletions will affect the position of the later deletions
         match (self.bidirectional(), other.bidirectional()) {
             (true, true) => self.pos == other.pos || self.pos == other.pos + 1,
             (true, false) => self.pos == other.prev_pos(),
diff --git a/crates/loro-internal/src/container/richtext/tracker.rs b/crates/loro-internal/src/container/richtext/tracker.rs
index 08a18e6f4..4ddaf7cc6 100644
--- a/crates/loro-internal/src/container/richtext/tracker.rs
+++ b/crates/loro-internal/src/container/richtext/tracker.rs
@@ -228,7 +228,7 @@ impl Tracker {
         self._checkout(from, false);
         self._checkout(to, true);
         // debug_log::debug_dbg!(from, to, &self);
-        self.id_to_cursor.diagnose();
+        // self.id_to_cursor.diagnose();
         self.rope.get_diff()
     }
 }