import type { ThreadMessageLike } from "@assistant-ui/react";

/**
 * When a streamed message is persisted, the backend returns the durable
 * turn_id; merge it into assistant-ui metadata for turn-scoped actions.
 */
export function mergeChatTurnIdIntoMessage(
	msg: ThreadMessageLike,
	turnId: string | null | undefined
): ThreadMessageLike {
	if (!turnId) return msg;
	const existingMeta = (msg.metadata ?? {}) as { custom?: Record<string, unknown> };
	const existingCustom = existingMeta.custom ?? {};
	if ((existingCustom as { chatTurnId?: string }).chatTurnId === turnId) return msg;
	return {
		...msg,
		metadata: {
			...existingMeta,
			custom: { ...existingCustom, chatTurnId: turnId },
		},
	};
}

export function readStreamedChatTurnId(data: unknown): string | null {
	if (typeof data !== "object" || data === null) return null;
	const value = (data as { chat_turn_id?: unknown }).chat_turn_id;
	return typeof value === "string" && value.length > 0 ? value : null;
}

/**
 * Parse the payload of `data-user-message-id` / `data-assistant-message-id`
 * SSE events emitted by `stream_new_chat` and `stream_resume_chat` after
 * `persist_user_turn` / `persist_assistant_shell` resolve a canonical
 * `new_chat_messages.id`. Mirrors {@link readStreamedChatTurnId}.
 *
 * Returns `null` when the payload is malformed (missing or non-numeric
 * `message_id`); callers should treat this as "ignore the event" so a
 * malformed BE payload never overwrites the optimistic id with a bogus
 * value.
 */
export function readStreamedMessageId(
	data: unknown
): { messageId: number; turnId: string | null } | null {
	if (typeof data !== "object" || data === null) return null;
	const obj = data as { message_id?: unknown; turn_id?: unknown };
	if (typeof obj.message_id !== "number" || !Number.isFinite(obj.message_id)) {
		return null;
	}
	const turnId = typeof obj.turn_id === "string" && obj.turn_id.length > 0 ? obj.turn_id : null;
	return { messageId: obj.message_id, turnId };
}

export function applyTurnIdToAssistantMessageList(
	messages: ThreadMessageLike[],
	assistantMsgId: string,
	turnId: string
): ThreadMessageLike[] {
	return messages.map((m) => (m.id === assistantMsgId ? mergeChatTurnIdIntoMessage(m, turnId) : m));
}