Merge pull request #26209 from overleaf/em-multiple-edit-ops

Support multiple ops in the history OT ShareJS type

GitOrigin-RevId: fad1e9081ed1978de414c5130692d3b23fcd13d8

services/web/frontend/js/features/ide-react/editor/share-js-history-ot-type.ts

@@ -30,18 +30,49 @@ export const historyOTType = {
   api,
 
   transformX(ops1: EditOperation[], ops2: EditOperation[]) {
-    const [a, b] = EditOperationTransformer.transform(ops1[0], ops2[0])
-    return [[a], [b]]
+    // Dynamic programming algorithm: gradually transform both sides in a nested
+    // loop.
+    const left = [...ops1]
+    const right = [...ops2]
+    for (let i = 0; i < left.length; i++) {
+      for (let j = 0; j < right.length; j++) {
+        // At this point:
+        // left[0..i] is ops1[0..i] rebased over ops2[0..j-1]
+        // right[0..j] is ops2[0..j] rebased over ops1[0..i-1]
+        const [a, b] = EditOperationTransformer.transform(left[i], right[j])
+        left[i] = a
+        right[j] = b
+      }
+    }
+    return [left, right]
   },
 
   apply(snapshot: StringFileData, ops: EditOperation[]) {
     const afterFile = StringFileData.fromRaw(snapshot.toRaw())
-    afterFile.edit(ops[0])
+    for (const op of ops) {
+      afterFile.edit(op)
+    }
     return afterFile
   },
 
   compose(ops1: EditOperation[], ops2: EditOperation[]) {
-    return [ops1[0].compose(ops2[0])]
+    const ops = [...ops1, ...ops2]
+    let currentOp = ops.shift()
+    if (currentOp === undefined) {
+      // No ops to process
+      return []
+    }
+    const result = []
+    for (const op of ops) {
+      if (currentOp.canBeComposedWith(op)) {
+        currentOp = currentOp.compose(op)
+      } else {
+        result.push(currentOp)
+        currentOp = op
+      }
+    }
+    result.push(currentOp)
+    return result
   },
 
   // Do not provide normalize, used by submitOp to fixup bad input.