import { promises as fs } from 'node:fs';
import { dirname, isAbsolute, join, resolve } from 'node:path';

/** Resolve an ACP path against the agent worktree and read a slice of lines. */
export async function readWorktreeTextFile(
  worktreePath: string,
  filePath: string,
  line?: number | null,
  limit?: number | null,
): Promise<string> {
  const absolute = isAbsolute(filePath) ? filePath : resolve(worktreePath, filePath);
  if (!absolute.startsWith(resolve(worktreePath))) {
    throw new Error(`path escapes worktree: ${filePath}`);
  }
  const raw = await fs.readFile(absolute, 'utf8');
  if (!line && !limit) return raw;
  const lines = raw.split(/\r?\n/);
  const start = Math.max((line ?? 1) - 1, 0);
  const end = limit ? start + limit : undefined;
  return lines.slice(start, end).join('\n');
}

/** Write a file inside the worktree (creates parent dirs). */
export async function writeWorktreeTextFile(
  worktreePath: string,
  filePath: string,
  content: string,
): Promise<void> {
  const absolute = isAbsolute(filePath) ? filePath : resolve(worktreePath, filePath);
  if (!absolute.startsWith(resolve(worktreePath))) {
    throw new Error(`path escapes worktree: ${filePath}`);
  }
  await fs.mkdir(dirname(absolute), { recursive: true });
  await fs.writeFile(absolute, content, 'utf8');
}