import type { Command, CommandOptions, CommandResult } from '../types';
import { resolveCount, gatherInputs, toLines } from './_textlines';

export const tailCommand: Command = {
  name: 'tail',
  description: 'Output the last N lines of each file (default 10)',
  usage: 'tail [-n N | -N] [file...]',

  async execute(args: string[], options: CommandOptions): Promise<CommandResult> {
    const { stdout } = options;
    const { count, files } = resolveCount(options.flags, args);
    try {
      const inputs = await gatherInputs(files, options);
      const multi = inputs.length > 1;
      for (let i = 0; i < inputs.length; i++) {
        const lines = toLines(inputs[i].content);
        const picked = count <= 0 ? [] : lines.slice(-count); // slice(-0) would return everything
        if (multi) await stdout.write(`${i ? '\n' : ''}==> ${inputs[i].name} <==\n`);
        if (picked.length) await stdout.write(picked.join('\n') + '\n');
      }
      return { exitCode: 0 };
    } catch (error) {
      await stdout.write(`tail: ${error instanceof Error ? error.message : String(error)}\n`);
      return { exitCode: 1 };
    }
  },
};