Epicure/apps/web/lib/messaging.ts

import { db, conversations, eq, and } from "@epicure/db";
import { randomUUID } from "crypto";

/** Normalizes a pair so (userAId, userBId) is order-independent. */
function orderPair(idA: string, idB: string): [string, string] {
  return idA < idB ? [idA, idB] : [idB, idA];
}

export async function findOrCreateConversation(userId1: string, userId2: string) {
  const [userAId, userBId] = orderPair(userId1, userId2);

  const existing = await db.query.conversations.findFirst({
    where: and(eq(conversations.userAId, userAId), eq(conversations.userBId, userBId)),
  });
  if (existing) return existing;

  const [created] = await db
    .insert(conversations)
    .values({ id: randomUUID(), userAId, userBId })
    .onConflictDoNothing()
    .returning();

  if (created) return created;

  // Lost a race with a concurrent insert — fetch what the winner created.
  const row = await db.query.conversations.findFirst({
    where: and(eq(conversations.userAId, userAId), eq(conversations.userBId, userBId)),
  });
  if (!row) throw new Error("Failed to create conversation");
  return row;
}

export function isParticipant(
  conversation: { userAId: string; userBId: string },
  userId: string
): boolean {
  return conversation.userAId === userId || conversation.userBId === userId;
}

export function otherParticipantId(
  conversation: { userAId: string; userBId: string },
  userId: string
): string {
  return conversation.userAId === userId ? conversation.userBId : conversation.userAId;
}