1 files changed, 117 insertions, 0 deletions
diff --git a/src/main/otTransform.ts b/src/main/otTransform.ts
new file mode 100644
index 0000000..0d05450
--- /dev/null
+++ b/src/main/otTransform.ts
@@ -0,0 +1,117 @@
+// OT transform functions for main process (mirror of renderer transform)
+import type { OtOp } from './otTypes'
+import { isInsert, isDelete, isComment } from './otTypes'
+
+export function transformOps(
+  ops1: OtOp[],
+  ops2: OtOp[]
+): { left: OtOp[]; right: OtOp[] } {
+  let right = ops2
+
+  const newLeft: OtOp[] = []
+  for (const op1 of ops1) {
+    let transformed = op1
+    const newRight: OtOp[] = []
+    for (const op2 of right) {
+      const { left: tl, right: tr } = transformOp(transformed, op2)
+      transformed = tl
+      newRight.push(tr)
+    }
+    newLeft.push(transformed)
+    right = newRight
+  }
+
+  return { left: newLeft, right }
+}
+
+function transformOp(op1: OtOp, op2: OtOp): { left: OtOp; right: OtOp } {
+  if (isInsert(op1) && isInsert(op2)) {
+    if (op1.p <= op2.p) {
+      return { left: op1, right: { ...op2, p: op2.p + op1.i.length } }
+    } else {
+      return { left: { ...op1, p: op1.p + op2.i.length }, right: op2 }
+    }
+  }
+
+  if (isInsert(op1) && isDelete(op2)) {
+    if (op1.p <= op2.p) {
+      return { left: op1, right: { ...op2, p: op2.p + op1.i.length } }
+    } else if (op1.p >= op2.p + op2.d.length) {
+      return { left: { ...op1, p: op1.p - op2.d.length }, right: op2 }
+    } else {
+      return { left: { ...op1, p: op2.p }, right: op2 }
+    }
+  }
+
+  if (isDelete(op1) && isInsert(op2)) {
+    if (op2.p <= op1.p) {
+      return { left: { ...op1, p: op1.p + op2.i.length }, right: op2 }
+    } else if (op2.p >= op1.p + op1.d.length) {
+      return { left: op1, right: { ...op2, p: op2.p - op1.d.length } }
+    } else {
+      return { left: op1, right: { ...op2, p: op2.p - op1.d.length } }
+    }
+  }
+
+  if (isDelete(op1) && isDelete(op2)) {
+    if (op1.p >= op2.p + op2.d.length) {
+      return {
+        left: { ...op1, p: op1.p - op2.d.length },
+        right: { ...op2, p: op2.p }
+      }
+    } else if (op2.p >= op1.p + op1.d.length) {
+      return {
+        left: op1,
+        right: { ...op2, p: op2.p - op1.d.length }
+      }
+    } else {
+      const overlapStart = Math.max(0, op2.p - op1.p)
+      const overlapEnd = Math.min(op1.d.length, op2.p + op2.d.length - op1.p)
+      let newOp1Text = op1.d
+      if (overlapEnd > overlapStart) {
+        newOp1Text = op1.d.slice(0, overlapStart) + op1.d.slice(overlapEnd)
+      }
+
+      const overlapStart2 = Math.max(0, op1.p - op2.p)
+      const overlapEnd2 = Math.min(op2.d.length, op1.p + op1.d.length - op2.p)
+      let newOp2Text = op2.d
+      if (overlapEnd2 > overlapStart2) {
+        newOp2Text = op2.d.slice(0, overlapStart2) + op2.d.slice(overlapEnd2)
+      }
+
+      const newP1 = op1.p <= op2.p ? op1.p : op1.p - (overlapEnd2 - overlapStart2)
+      const newP2 = op2.p <= op1.p ? op2.p : op2.p - (overlapEnd - overlapStart)
+
+      return {
+        left: newOp1Text ? { d: newOp1Text, p: Math.max(0, newP1) } : { d: '', p: 0 },
+        right: newOp2Text ? { d: newOp2Text, p: Math.max(0, newP2) } : { d: '', p: 0 }
+      }
+    }
+  }
+
+  if (isComment(op1) || isComment(op2)) {
+    if (isComment(op1)) {
+      if (isInsert(op2) && op2.p <= op1.p) {
+        return { left: { ...op1, p: op1.p + op2.i.length }, right: op2 }
+      }
+      if (isDelete(op2) && op2.p < op1.p) {
+        const shift = Math.min(op2.d.length, op1.p - op2.p)
+        return { left: { ...op1, p: op1.p - shift }, right: op2 }
+      }
+    }
+
+    if (isComment(op2)) {
+      if (isInsert(op1) && op1.p <= op2.p) {
+        return { left: op1, right: { ...op2, p: op2.p + op1.i.length } }
+      }
+      if (isDelete(op1) && op1.p < op2.p) {
+        const shift = Math.min(op1.d.length, op2.p - op1.p)
+        return { left: op1, right: { ...op2, p: op2.p - shift } }
+      }
+    }
+
+    return { left: op1, right: op2 }
+  }
+
+  return { left: op1, right: op2 }
+}