From 72be193fa1db221ecdc0c5e697643236f70d2f3d Mon Sep 17 00:00:00 2001
From: Josh Kingsley <josh@joshkingsley.me>
Date: Sat, 15 Nov 2025 22:04:16 +0200
Subject: feat(crdt): add Doc::merge method

---
 crdt/src/lib.rs | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 4 deletions(-)

(limited to 'crdt')

diff --git a/crdt/src/lib.rs b/crdt/src/lib.rs
index 39c5f0e..3983692 100644
--- a/crdt/src/lib.rs
+++ b/crdt/src/lib.rs
@@ -1,6 +1,6 @@
 mod vector_clock;
 
-use std::fmt::Display;
+use std::{collections::BTreeSet, fmt::Display};
 
 use uuid::Uuid;
 
@@ -14,12 +14,32 @@ pub enum Error {
     NotFound(DerivedId),
 }
 
-#[derive(Default)]
+#[derive(Default, Clone)]
 pub struct Doc {
     ops: Vec<Op>,
 }
 
 impl Doc {
+    pub fn from_ops(actor_id: &Uuid, payloads: &[OpPayload]) -> Self {
+        let mut clock = VectorClock::new();
+
+        let ops = payloads
+            .iter()
+            .cloned()
+            .map(|payload| {
+                clock = clock.inc(&actor_id);
+
+                Op {
+                    id: Uuid::now_v7(),
+                    clock: clock.clone(),
+                    payload,
+                }
+            })
+            .collect();
+
+        Doc { ops }
+    }
+
     pub fn append_op(&mut self, actor_id: &Uuid, payload: OpPayload) {
         // Increment the last clock for the provided actor
         let clock = self
@@ -36,6 +56,18 @@ impl Doc {
         });
     }
 
+    pub fn merge(&mut self, other: &Doc) {
+        let op_ids: BTreeSet<Uuid> = self.ops.iter().map(|op| op.id).collect();
+
+        for op in &other.ops {
+            if !op_ids.contains(&op.id) {
+                self.ops.push(op.clone());
+            }
+        }
+
+        self.ops.sort_by(|op1, op2| op1.clock.cmp(&op2.clock));
+    }
+
     pub fn realize(&self) -> Result<RealizedDoc, Error> {
         let mut realized = RealizedDoc::default();
 
@@ -47,7 +79,7 @@ impl Doc {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Op {
     id: Uuid,
     payload: OpPayload,
@@ -132,7 +164,7 @@ impl Op {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum OpPayload {
     CreateGrid {
         rows: usize,
@@ -202,6 +234,51 @@ impl DerivableId for Uuid {
 mod tests {
     use super::*;
 
+    #[test]
+    fn merge() {
+        let actor1 = Uuid::now_v7();
+        let actor2 = Uuid::now_v7();
+
+        let mut doc1 = Doc::from_ops(
+            &actor1,
+            &[OpPayload::CreateGrid {
+                rows: 4,
+                base_cells_per_row: 16,
+            }],
+        );
+
+        let mut doc2 = Doc::from_ops(
+            &actor2,
+            &[OpPayload::CreateGrid {
+                rows: 4,
+                base_cells_per_row: 16,
+            }],
+        );
+
+        doc1.merge(&doc2);
+
+        assert_eq!(doc1.ops.len(), 2);
+        assert_eq!(doc1.ops.last().unwrap(), doc2.ops.last().unwrap());
+
+        doc2.merge(&doc1);
+
+        assert_eq!(doc2.ops.len(), 2);
+    }
+
+    #[test]
+    fn concurrent_ops() {
+        let actor1 = Uuid::now_v7();
+        let actor2 = Uuid::now_v7();
+
+        let doc = Doc::from_ops(
+            &actor1,
+            &[OpPayload::CreateGrid {
+                rows: 4,
+                base_cells_per_row: 16,
+            }],
+        );
+    }
+
     #[test]
     fn realize_doc() {
         let actor_id = Uuid::now_v7();
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