import type { CommandOptions } from '../types';

/**
 * Shared helpers for `head`/`tail`: resolve the line count from the usual flag forms and gather
 * inputs (named files, or stdin when none). Kept separate so both commands stay DRY.
 */

/** Resolve a line count from `-n N`, `-n=N`, or `-N` flags. Returns the count + remaining file args. */
export function resolveCount(
  flags: Record<string, boolean | string> | undefined,
  args: string[],
  def = 10,
): { count: number; files: string[] } {
  let count = def;
  let files = [...args];
  for (const k of Object.keys(flags ?? {})) if (/^\d+$/.test(k)) count = parseInt(k, 10); // -50
  if (typeof flags?.n === 'string' && /^\d+$/.test(flags.n)) {
    count = parseInt(flags.n, 10); // -n=50
  } else if (flags?.n === true && files.length && /^\d+$/.test(files[0])) {
    count = parseInt(files[0], 10); // -n 50
    files = files.slice(1);
  }
  return { count: Math.max(0, count), files };
}

/** Read each file's content (or stdin when no files). Throws a CLI-style message on a bad path. */
export async function gatherInputs(
  files: string[],
  options: CommandOptions,
): Promise<Array<{ name: string; content: string }>> {
  const { fs, cwd, stdin } = options;
  if (files.length === 0) return [{ name: '', content: await stdin.readAll() }];
  const out: Array<{ name: string; content: string }> = [];
  for (const file of files) {
    const p = fs.resolvePath(file, cwd);
    if (!(await fs.exists(p))) throw new Error(`${file}: No such file or directory`);
    if (!(await fs.isFile(p))) throw new Error(`${file}: Is a directory`);
    out.push({ name: file, content: await fs.readFile(p) });
  }
  return out;
}

/** Split into lines, dropping the single empty element a trailing newline produces (so counts match coreutils). */
export function toLines(content: string): string[] {
  const lines = content.split('\n');
  if (lines.length && lines[lines.length - 1] === '') lines.pop();
  return lines;
}