/**
 * Per-page performance budget enforcement. Kept as pure helpers so unit tests
 * don't need a running browser — the crawler calls `checkPerformanceBudget`
 * after metrics are collected and appends the resulting PageErrors.
 */

import type { PageError, PerformanceBudget, PerformanceMetrics } from "./types.js";
import { PERF_BUDGET_KEYS } from "./types.js";

/**
 * Compare measured metrics against a budget and return one invariant-violation
 * per breach. Returns an empty array when budget is undefined or empty,
 * or when every measured metric is within its limit.
 */
export function checkPerformanceBudget(
  metrics: PerformanceMetrics,
  budget: PerformanceBudget | undefined,
  url: string,
  now: number = Date.now()
): PageError[] {
  if (!budget) return [];
  const errors: PageError[] = [];
  for (const key of PERF_BUDGET_KEYS) {
    const limit = budget[key];
    const measured = metrics[key];
    if (typeof limit !== "number" || typeof measured !== "number") continue;
    if (measured <= limit) continue;
    const name = `perf-budget.${key}`;
    errors.push({
      type: "invariant-violation",
      message: `[${name}] ${key}=${Math.round(measured)}ms > budget ${limit}ms`,
      invariantName: name,
      url,
      timestamp: now,
    });
  }
  return errors;
}