import { appendFile, readFile, writeFile, mkdir } from "node:fs/promises";
import { dirname } from "node:path";
import { existsSync } from "node:fs";
import type { z } from "zod";

/**
 * Append a single record to a JSONL file. Creates parent dirs if needed.
 * Uses appendFile which is atomic on Linux for reasonable line sizes.
 */
export async function appendJsonl<T>(path: string, record: T): Promise<void> {
  const dir = dirname(path);
  if (!existsSync(dir)) await mkdir(dir, { recursive: true });
  await appendFile(path, JSON.stringify(record) + "\n");
}

/**
 * Read a JSONL file, parse each line with the given Zod schema.
 * Skips blank lines and lines that fail JSON.parse (truncated from crash).
 * Returns { records, skipped } so callers can log corruption.
 */
export async function readJsonl<S extends z.ZodType>(
  path: string,
  schema: S,
): Promise<{ records: z.infer<S>[]; skipped: number }> {
  if (!existsSync(path)) return { records: [], skipped: 0 };

  const text = await readFile(path, "utf-8");
  const lines = text.split("\n").filter((l) => l.trim().length > 0);
  const records: z.infer<S>[] = [];
  let skipped = 0;

  for (const line of lines) {
    try {
      const parsed = JSON.parse(line);
      const result = schema.safeParse(parsed);
      if (result.success) {
        records.push(result.data);
      } else {
        skipped++;
      }
    } catch {
      skipped++;
    }
  }

  return { records, skipped };
}

/**
 * Read raw JSON objects from JSONL without schema validation.
 * Useful for checkpoint recovery where we only need IDs.
 */
export async function readJsonlRaw(
  path: string,
): Promise<{ records: unknown[]; skipped: number }> {
  if (!existsSync(path)) return { records: [], skipped: 0 };

  const text = await readFile(path, "utf-8");
  const lines = text.split("\n").filter((l) => l.trim().length > 0);
  const records: unknown[] = [];
  let skipped = 0;

  for (const line of lines) {
    try {
      records.push(JSON.parse(line));
    } catch {
      skipped++;
    }
  }

  return { records, skipped };
}

/** Write an array of records as JSONL (overwrite). */
export async function writeJsonl<T>(path: string, records: T[]): Promise<void> {
  const dir = dirname(path);
  if (!existsSync(dir)) await mkdir(dir, { recursive: true });
  const content = records.map((r) => JSON.stringify(r)).join("\n") + "\n";
  await writeFile(path, content);
}