feat(chat): add local-first conversation workspace

chat/lib/message-graph.ts

@@ -0,0 +1,62 @@
+import type {StoredChatMessage} from "./conversation-types";
+
+export function mergeMessageGraph(...groups: StoredChatMessage[][]) {
+  return new Map(groups.flat().map((message) => [message.id, message]));
+}
+
+export function messagePathInGraph(messages: Map<string, StoredChatMessage>, headMessageId: string | null) {
+  const reversed: StoredChatMessage[] = [];
+  const seen = new Set<string>();
+  let cursor = headMessageId;
+  while (cursor) {
+    if (seen.has(cursor) || reversed.length >= 500) return [];
+    seen.add(cursor);
+    const message = messages.get(cursor);
+    if (!message) return [];
+    reversed.push(message);
+    cursor = message.parentMessageId;
+  }
+  return reversed.reverse();
+}
+
+export function messageChildrenInGraph(messages: Map<string, StoredChatMessage>, parentMessageId: string | null) {
+  return [...messages.values()]
+    .filter((message) => message.parentMessageId === parentMessageId)
+    .sort((left, right) => left.createdAt.localeCompare(right.createdAt) || left.id.localeCompare(right.id));
+}
+
+export function rootEditAlternativesInGraph(messages: Map<string, StoredChatMessage>, messageId: string) {
+  const roots = [...messages.values()].filter((message) => message.parentMessageId === null);
+  const related = new Set([messageId]);
+  let changed = true;
+  while (changed) {
+    changed = false;
+    for (const message of roots) {
+      const sourceMessageId = "sourceMessageId" in message.origin ? message.origin.sourceMessageId : undefined;
+      if (!related.has(message.id) && (!sourceMessageId || !related.has(sourceMessageId))) continue;
+      if (!related.has(message.id)) { related.add(message.id); changed = true; }
+      if (sourceMessageId && !related.has(sourceMessageId)) { related.add(sourceMessageId); changed = true; }
+    }
+  }
+  return roots
+    .filter((message) => related.has(message.id))
+    .sort((left, right) => left.createdAt.localeCompare(right.createdAt) || left.id.localeCompare(right.id));
+}
+
+export function newestBranchTipInGraph(
+  messages: Map<string, StoredChatMessage>,
+  startId: string,
+  currentPathIds: Set<string>,
+  currentHeadMessageId: string | null
+) {
+  if (currentPathIds.has(startId)) return currentHeadMessageId || startId;
+  let cursor = startId;
+  const seen = new Set<string>();
+  while (!seen.has(cursor)) {
+    seen.add(cursor);
+    const children = messageChildrenInGraph(messages, cursor);
+    if (!children.length) return cursor;
+    cursor = children.at(-1)!.id;
+  }
+  return startId;
+}