1 files changed, 46 insertions, 0 deletions
diff --git a/frontend/src/lib/draftGuard.ts b/frontend/src/lib/draftGuard.ts
new file mode 100644
index 0000000..d6a5222
--- /dev/null
+++ b/frontend/src/lib/draftGuard.ts
@@ -0,0 +1,46 @@
+import { diffLines, diffWordsWithSpace } from 'diff';
+
+export interface DiffStats {
+  added: number;
+  removed: number;
+}
+
+export function unifiedDiffStats(before: string, after: string): DiffStats {
+  const parts = diffLines(before, after);
+  let added = 0;
+  let removed = 0;
+  for (const p of parts) {
+    if (p.added) added += p.value.replace(/\n$/, '').split('\n').length;
+    else if (p.removed) removed += p.value.replace(/\n$/, '').split('\n').length;
+  }
+  return { added, removed };
+}
+
+export interface ServerDraft {
+  generation: number;
+  code: string;
+}
+
+export interface ConflictVerdict {
+  stale: boolean;
+  serverEqualsLocal: boolean;
+  localDirty: boolean;
+}
+
+export class ConflictResolver {
+  constructor(private local: { generation: number; code: string }) {}
+
+  onServerState(server: ServerDraft, lastKnownGeneration: number): ConflictVerdict {
+    const stale = server.generation !== lastKnownGeneration && lastKnownGeneration !== null;
+    const serverEqualsLocal = server.generation === this.local.generation && server.code === this.local.code;
+    return { stale, serverEqualsLocal, localDirty: true };
+  }
+
+  retryPlan(server: ServerDraft): { generation: number; code: string } {
+    return { generation: server.generation, code: this.local.code };
+  }
+}
+
+export function wordDiff(before: string, after: string) {
+  return diffWordsWithSpace(before, after);
+}