import path from "path";
import fs from "fs-extra";

export interface RuleModule {
  runScanner: () => Promise<{
    deprecatedItems: string[];
    autoFixTargets: string[];
  }>;
}

function getFallbackRule(fromVersion: number, toVersion: number): RuleModule {
  return {
    async runScanner() {
      return {
        deprecatedItems: [
          `⚠ No rule defined for migration ${fromVersion} → ${toVersion}.`,
          `⚠ No scanning performed.`
        ],
        autoFixTargets: []
      };
    }
  };
}

export async function getRulesForVersion(
  fromVersion: number,
  toVersion: number
): Promise<RuleModule> {
  const rulesDir = path.join(
    process.cwd(),
    "src",
    "frameworks",
    "angular",
    "rules"
  );

  const ruleFileName = `${fromVersion}-to-${toVersion}.js`; // When compiled to dist
  const ruleFileTs = `${fromVersion}-to-${toVersion}.ts`;  // Dev mode fallback

  const ruleJsPath = path.join(rulesDir, ruleFileName);
  const ruleTsPath = path.join(rulesDir, ruleFileTs);

  // JS build file takes priority (dist)
  if (fs.existsSync(ruleJsPath)) {
    const mod = await import(ruleJsPath);
    return mod.default as RuleModule;
  }

  // TS file fallback for dev mode
  if (fs.existsSync(ruleTsPath)) {
    const mod = await import(ruleTsPath);
    return mod.default as RuleModule;
  }

  // Fallback if no rule exists
  return getFallbackRule(fromVersion, toVersion);
}