const MIN_BUN_VERSION = '1.3.14';
const MIN_SVELTE_VERSION = '5.55.1';

export function compareVersions(actual: string, required: string): boolean {
  // Strip any prerelease/build suffix (e.g. `1.3.14-canary.5`) before parsing —
  // otherwise `Number('14-canary')` is NaN, `NaN !== 0` is true, and `NaN > 0`
  // is false, which would reject an otherwise-valid canary runtime.
  const parse = (v: string): number[] => v.split('.').map((seg) => parseInt(seg, 10) || 0);
  const a = parse(actual);
  const r = parse(required);
  for (let i = 0; i < 3; i++) {
    const diff = (a[i] ?? 0) - (r[i] ?? 0);
    if (diff !== 0) {
      return diff > 0;
    }
  }
  return true;
}

let cached: Promise<{ svelteVersion: string }> | undefined;

export function checkEnvironment(): Promise<{ svelteVersion: string }> {
  return (cached ??= runCheck().catch((err) => {
    cached = undefined;
    throw err;
  }));
}

async function runCheck(): Promise<{ svelteVersion: string }> {
  if (typeof Bun === 'undefined') {
    throw new Error('Mochi requires the Bun runtime.');
  }

  if (!compareVersions(Bun.version, MIN_BUN_VERSION)) {
    throw new Error(`Mochi requires Bun ${MIN_BUN_VERSION} or higher (found ${Bun.version}).`);
  }

  let svelteVersion: string;
  try {
    // Resolve svelte from the framework's own location first — that's the exact
    // copy ComponentRegistry imports for compilation, and unlike process.cwd() it
    // doesn't depend on where the process was launched (cwd breaks the resolve in
    // monorepos or whenever the app is started from a non-root directory).
    let pkgPath: string;
    try {
      pkgPath = Bun.resolveSync('svelte/package.json', import.meta.dir);
    } catch {
      pkgPath = Bun.resolveSync('svelte/package.json', process.cwd());
    }
    const pkg = (await Bun.file(pkgPath).json()) as { version: string };
    svelteVersion = pkg.version;
  } catch {
    throw new Error(`Mochi requires Svelte ${MIN_SVELTE_VERSION} or higher. Is svelte installed in your project?`);
  }

  if (!compareVersions(svelteVersion, MIN_SVELTE_VERSION)) {
    throw new Error(`Mochi requires Svelte ${MIN_SVELTE_VERSION} or higher (found ${svelteVersion}).`);
  }

  return { svelteVersion };
}