package agent

import (
	"os"
	"os/exec"

	"github.com/creack/pty"
)

// PTY is a pseudo-terminal running an interactive login shell.
type PTY struct {
	cmd *exec.Cmd
	f   *os.File
}

// StartPTY launches the shell attached to a new PTY. The agent runs as root
// (systemd User=root), so this is a root shell by design.
func StartPTY() (*PTY, error) {
	shell := "/bin/bash"
	if _, err := os.Stat(shell); err != nil {
		shell = "/bin/sh"
	}
	cmd := exec.Command(shell, "-l")
	cmd.Env = append(os.Environ(), "TERM=xterm-256color")
	f, err := pty.Start(cmd)
	if err != nil {
		return nil, err
	}
	return &PTY{cmd: cmd, f: f}, nil
}

// Read reads terminal output.
func (p *PTY) Read(b []byte) (int, error) { return p.f.Read(b) }

// Write writes keystrokes to the terminal.
func (p *PTY) Write(b []byte) (int, error) { return p.f.Write(b) }

// Resize changes the terminal window size.
func (p *PTY) Resize(cols, rows uint16) {
	if cols == 0 || rows == 0 {
		return
	}
	_ = pty.Setsize(p.f, &pty.Winsize{Rows: rows, Cols: cols})
}

// Close terminates the shell and releases the PTY.
func (p *PTY) Close() error {
	err := p.f.Close()
	if p.cmd.Process != nil {
		_ = p.cmd.Process.Kill()
	}
	_ = p.cmd.Wait()
	return err
}