import fs from "node:fs";
import path from "node:path";
import JSON5 from "json5";
import { expandHomePrefix } from "../infra/home-dir.js";
import { CONFIG_DIR } from "../utils.js";
import type { CronStoreFile } from "./types.js";

export const DEFAULT_CRON_DIR = path.join(CONFIG_DIR, "cron");
export const DEFAULT_CRON_STORE_PATH = path.join(DEFAULT_CRON_DIR, "jobs.json");

export function resolveCronStorePath(storePath?: string) {
  if (storePath?.trim()) {
    const raw = storePath.trim();
    if (raw.startsWith("~")) {
      return path.resolve(expandHomePrefix(raw));
    }
    return path.resolve(raw);
  }
  return DEFAULT_CRON_STORE_PATH;
}

export async function loadCronStore(storePath: string): Promise<CronStoreFile> {
  try {
    const raw = await fs.promises.readFile(storePath, "utf-8");
    let parsed: unknown;
    try {
      parsed = JSON5.parse(raw);
    } catch (err) {
      throw new Error(`Failed to parse cron store at ${storePath}: ${String(err)}`, {
        cause: err,
      });
    }
    const parsedRecord =
      parsed && typeof parsed === "object" && !Array.isArray(parsed)
        ? (parsed as Record<string, unknown>)
        : {};
    const jobs = Array.isArray(parsedRecord.jobs) ? (parsedRecord.jobs as never[]) : [];
    return {
      version: 1,
      jobs: jobs.filter(Boolean) as never as CronStoreFile["jobs"],
    };
  } catch (err) {
    if ((err as { code?: unknown })?.code === "ENOENT") {
      return { version: 1, jobs: [] };
    }
    throw err;
  }
}

export async function saveCronStore(storePath: string, store: CronStoreFile) {
  await fs.promises.mkdir(path.dirname(storePath), { recursive: true });
  const { randomBytes } = await import("node:crypto");
  const json = JSON.stringify(store, null, 2);
  let previous: string | null = null;
  try {
    previous = await fs.promises.readFile(storePath, "utf-8");
  } catch (err) {
    if ((err as { code?: unknown }).code !== "ENOENT") {
      throw err;
    }
  }
  if (previous === json) {
    return;
  }
  const tmp = `${storePath}.${process.pid}.${randomBytes(8).toString("hex")}.tmp`;
  await fs.promises.writeFile(tmp, json, "utf-8");
  if (previous !== null) {
    try {
      await fs.promises.copyFile(storePath, `${storePath}.bak`);
    } catch {
      // best-effort
    }
  }
  await renameWithRetry(tmp, storePath);
}

const RENAME_MAX_RETRIES = 3;
const RENAME_BASE_DELAY_MS = 50;

async function renameWithRetry(src: string, dest: string): Promise<void> {
  for (let attempt = 0; attempt <= RENAME_MAX_RETRIES; attempt++) {
    try {
      await fs.promises.rename(src, dest);
      return;
    } catch (err) {
      const code = (err as { code?: string }).code;
      if (code === "EBUSY" && attempt < RENAME_MAX_RETRIES) {
        await new Promise((resolve) => setTimeout(resolve, RENAME_BASE_DELAY_MS * 2 ** attempt));
        continue;
      }
      // Windows doesn't reliably support atomic replace via rename when dest exists.
      if (code === "EPERM" || code === "EEXIST") {
        await fs.promises.copyFile(src, dest);
        await fs.promises.unlink(src).catch(() => {});
        return;
      }
      throw err;
    }
  }
}
