#!/usr/bin/env python3

# -*- coding: utf-8 -*-

# Copyright (c) 2019 JDCR.
# Licensed under the GNU GPL v3. This program is provided with
# ABSOLUTELY NO WARRANTY, EXPRESS OR IMPLIED.

import subprocess
import sys
import pathlib

FILE_TO_RUN = "cam.py"
CACHE_FILE = "cache"

def do_shell_script(command, exit_to_shell=False):
    """Run input command in bash shell.
    Includes optional parameter exit_to_shell (default: False).
    If exit_to_shell is True, the function call returns the subprocess.Popen
    object used to run the command."""
    if exit_to_shell:
        return subprocess.Popen(["bash", "-c", command])
    subprocess.run(["bash", "-c", command])

def check_if_process_running():
    """Check if a process is currently running."""
    cache_file = pathlib.Path(CACHE_FILE)
    if cache_file.is_file():
        return True
    return False

def start():
    """Start the process for this program."""
    if not check_if_process_running():
        # Start the process
        process = do_shell_script("python3 {}".format(FILE_TO_RUN), True)
        
        # Save PID to enable stopping the process later
        cache = open(CACHE_FILE, "w")
        cache.write(str(process.pid))
        cache.close()
        
        # Log result to shell
        print("Started process with ID {}.".format(process.pid))
    else:
        print("Cannot start new process. A process is already running.")

def get_status():
    """Get the status of the process for this program."""
    if check_if_process_running():
        # Get the PID of the currently running process
        cache = open(CACHE_FILE, "r")
        pid = cache.read()
        cache.close()
        
        # Log result to shell
        print("Process running with ID {}.".format(pid))
    else:
        print("No process running.")

def stop():
    """Stop the process for this program."""
    if check_if_process_running():
        # Get the PID to stop the process and delete the cache file
        cache = open(CACHE_FILE, "r")
        pid = cache.read()
        cache.close()
        do_shell_script("rm {}".format(CACHE_FILE))
        
        # Stop the process
        do_shell_script("kill {}".format(pid))
        
        # Log result to shell
        print("Stopped process with ID {}.".format(pid))
    else:
        print("No process running.")

def show_help():
    """Show help documentation for this program."""
    help_doc = '''Usage: main [options]

Options:
  start    start the process for this program
  status   check if any process is running
  stop     stop the process for this program'''
    print(help_doc)

if __name__ == "__main__":
    if len(sys.argv) == 2:
        if sys.argv[1] == "start":
            start()
        elif sys.argv[1] == "status":
            get_status()
        elif sys.argv[1] == "stop":
            stop()
        else:
            show_help()
    else:
        show_help()