const SCRIPT_SRC_PATTERN = /<script\b([^>]*)\bsrc\s*=\s*(['"])([^'"]+)\2([^>]*)>/gi;

export const KNOWN_PLATFORM_SCRIPT_ALIASES = [
  {
    id: 'chart.js',
    target: '/assets/chart.umd.min.js',
    patterns: [
      /cdn\.jsdelivr\.net\/npm\/chart\.js(?:@[^/]+)?\/dist\/chart\.(?:umd\.)?min\.js/i,
      /cdnjs\.cloudflare\.com\/ajax\/libs\/Chart\.js\/[^/]+\/chart\.(?:umd\.)?min\.js/i,
      /unpkg\.com\/chart\.js(?:@[^/]+)?\/dist\/chart\.(?:umd\.)?min\.js/i,
    ],
  },
];

function normalizeScriptUrl(value) {
  return String(value ?? '').trim().replace(/&amp;/g, '&');
}

export function isExternalScriptSrc(src) {
  const normalized = normalizeScriptUrl(src);
  if (!normalized) return false;
  if (/^https?:\/\//i.test(normalized)) return true;
  if (/^\/\//.test(normalized)) return true;
  return false;
}

function resolveKnownPlatformScriptTarget(src) {
  const normalized = normalizeScriptUrl(src);
  if (!isExternalScriptSrc(normalized)) return null;
  const probe = normalized.startsWith('//') ? `https:${normalized}` : normalized;
  for (const alias of KNOWN_PLATFORM_SCRIPT_ALIASES) {
    if (alias.patterns.some((pattern) => pattern.test(probe))) {
      return alias.target;
    }
  }
  return null;
}

export function findExternalScriptSources(html) {
  const sources = [];
  const seen = new Set();
  for (const match of String(html ?? '').matchAll(SCRIPT_SRC_PATTERN)) {
    const src = normalizeScriptUrl(match[3]);
    if (!isExternalScriptSrc(src) || seen.has(src)) continue;
    seen.add(src);
    sources.push(src);
  }
  return sources;
}

export function rewriteKnownCdnScriptSources(html) {
  const rewrites = [];
  const next = String(html ?? '').replace(
    SCRIPT_SRC_PATTERN,
    (full, before, quote, src, after) => {
      const normalized = normalizeScriptUrl(src);
      const target = resolveKnownPlatformScriptTarget(normalized);
      if (!target) return full;
      rewrites.push({ from: normalized, to: target });
      return `<script${before}src=${quote}${target}${quote}${after}>`;
    },
  );
  return {
    html: next,
    rewrittenCount: rewrites.length,
    rewrites,
  };
}