#!/usr/bin/env python3
"""shellmcp: an MCP server with one tool, `run`, that runs a bash command. Stdlib only, stdio.

--mode readonly (default) runs every command in a bubblewrap sandbox: the filesystem is
read-only except a private /tmp, there is no network, no other process is visible, and the
--hide paths (always ~/.ssh and ~/.gnupg) look empty. --mode all runs commands with the
user's full permissions; let the MCP client ask before each call.
"""

import argparse
import getpass
import json
import os
import shutil
import signal
import socket
import subprocess
import sys

ENV = {"PAGER": "cat", "GIT_PAGER": "cat", "NO_COLOR": "1", "TERM": "dumb"}


def cut(text, limit):
    """text, or its head and tail around a note when it is longer than limit."""
    if len(text) <= limit:
        return text
    half = limit // 2
    return f"{text[:half]}\n[... {len(text) - 2 * half} characters cut ...]\n{text[-half:]}"


def run(command, cwd, timeout=60, limit=8000, prefix=()):
    """The exit code and combined stdout and stderr of `bash -c command`, as one text."""
    proc = subprocess.Popen([*prefix, "bash", "-c", command], cwd=cwd, stdin=subprocess.DEVNULL,
                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
                            env={**os.environ, **ENV}, start_new_session=True)
    try:
        out, _ = proc.communicate(timeout=timeout)
        head = f"exit code {proc.returncode}"
    except subprocess.TimeoutExpired:
        os.killpg(proc.pid, signal.SIGKILL)
        try:
            out, _ = proc.communicate(timeout=5)
        except subprocess.TimeoutExpired:  # a process left the group and holds the pipe
            out = b""
        head = f"timed out after {timeout} s, killed"
    return f"{head}\n{cut(out.decode(errors='replace'), limit)}"

def sandbox(cwd, hide=()):
    """The bwrap argv prefix of --mode readonly."""
    argv = ["bwrap", "--ro-bind", "/", "/", "--dev", "/dev", "--proc", "/proc",
            "--tmpfs", "/tmp", "--tmpfs", "/run", "--unshare-net", "--unshare-ipc",
            "--unshare-pid", "--die-with-parent", "--new-session"]
    for path in hide:
        if os.path.isdir(path):
            argv += ["--tmpfs", path]
        elif os.path.exists(path):
            argv += ["--ro-bind", "/dev/null", path]
    return argv + ["--chdir", cwd]

PREFERRED = {  # named in the tool description when installed, in this order
    "rg": "search file contents (instead of grep)", "fd": "find files (instead of find)",
    "eza": "list files (instead of ls)", "sd": "find and replace (instead of sed)",
    "dust": "disk usage (instead of du)", "procs": "processes (instead of ps)",
    "jq": "query JSON", "ast-grep": "search code by syntax", "tokei": "count lines of code"}


def describe(mode, cwd, timeout, limit):
    """The tool description: where commands run, the limits, and the modern tools installed."""
    text = (f"Run a bash command on {socket.gethostname()} as {getpass.getuser()} in {cwd}. "
            f"Returns its exit code and combined stdout and stderr (at most {limit} characters; "
            f"the middle of longer output is cut). Commands are killed after {timeout} s. "
            "There is no terminal: interactive programs, pagers and prompts fail.")
    if mode == "readonly":
        text += (" Read-only sandbox: nothing can be written except /tmp, which is emptied "
                 "after every command; no network; other processes are not visible. To change "
                 "something, give the user the command to run instead.")
    else:
        text += (" Commands run with the user's full permissions: they can change files, "
                 "processes and the network.")
    tools = [f"{name}: {what}" for name, what in PREFERRED.items() if shutil.which(name)]
    if tools:
        text += " Installed, prefer these: " + "; ".join(tools) + "."
    return text