import { existsSync, readFileSync, readdirSync } from "node:fs";
import { dirname, extname, join, relative, resolve } from "node:path";

export interface ReachabilityIssue {
  code: "WRN-REACH-MIDDLEWARE" | "WRN-REACH-QUEUE" | "WRN-REACH-WORKER";
  file: string;
  message: string;
}

function sourceFiles(directory: string): string[] {
  if (!existsSync(directory)) return [];
  const output: string[] = [];
  for (const entry of readdirSync(directory, { withFileTypes: true })) {
    const path = join(directory, entry.name);
    if (entry.isDirectory()) output.push(...sourceFiles(path));
    else if ([".ts", ".js", ".mts", ".mjs"].includes(extname(entry.name))) output.push(path);
  }
  return output;
}

/** Static registration audit for convention-discovered application modules. */
export function checkReachability(appRoot: string): ReachabilityIssue[] {
  const root = resolve(appRoot);
  const app = join(root, "app");
  const all = sourceFiles(app).map((file) => ({ file, source: readFileSync(file, "utf8") }));
  const issues: ReachabilityIssue[] = [];

  for (const entry of all) {
    const path = relative(root, entry.file).replace(/\\/g, "/");
    if (path.startsWith("app/middleware/") && !/\bexport\s+default\b/.test(entry.source)) {
      issues.push({
        code: "WRN-REACH-MIDDLEWARE",
        file: path,
        message: "Middleware discovery requires a default export.",
      });
    }
    if (
      path.startsWith("app/queues/") &&
      /\bdefineQueue\s*\(/.test(entry.source) &&
      !/\bexport\s+default\b/.test(entry.source)
    ) {
      issues.push({
        code: "WRN-REACH-QUEUE",
        file: path,
        message: "Queue discovery requires the defined queue to be exported as default.",
      });
    }
    if (
      /\bdefineWorker\s*(?:<[^>]+>)?\s*\(/.test(entry.source) &&
      !/\brunWorker\s*\(/.test(entry.source)
    ) {
      const stem = entry.file.replace(/\.[^.]+$/, "");
      const imported = all.some(
        (candidate) =>
          candidate.file !== entry.file &&
          candidate.source
            .replace(/\\/g, "/")
            .includes(relative(dirname(candidate.file), stem).replace(/\\/g, "/")),
      );
      if (!imported) {
        issues.push({
          code: "WRN-REACH-WORKER",
          file: path,
          message: "Worker is defined but no application module imports it or calls runWorker().",
        });
      }
    }
  }
  return issues;
}

export function assertReachability(appRoot: string): void {
  const issues = checkReachability(appRoot);
  if (!issues.length) return;
  throw new Error(
    `WRN-REACHABILITY: unreachable application exports\n${issues
      .map((issue) => `- ${issue.code} ${issue.file}: ${issue.message}`)
      .join("\n")}`,
  );
}