/** Stable across database Dates, JSON SSE payloads, and Nuxt hydration. */
export const serializeTopicSnapshot = (topic: unknown): string => JSON.stringify(topic, (_key, value) => {
    if (value === null || typeof value !== 'object' || Array.isArray(value)) {
        return value;
    }

    return Object.fromEntries(Object.keys(value).sort().map(key => [key, value[key]]));
});

/** Absolute offsets make replay across a snapshot boundary idempotent. */
export const appendTextDelta = (current: string, content: string, offset?: number): string => {
    if (offset === undefined) {
        return current + content;
    }
    if (offset > current.length) {
        // A gap requires reconciliation, not silently concatenating corrupt text.
        return current;
    }
    const overlap = current.length - offset;
    return overlap >= content.length ? current : current + content.slice(overlap);
};