#!/usr/bin/python

import errno
import os
import subprocess
import sys

progname = 'attachandrun'

def extract(args):
    if len(args) < 1:
        raise Exception('Missing arguments')
    return (args[0], args[1:])

def usage():
    print >>sys.stderr, 'Usage: %s [--check|-c] locker program program_name [args...]' % (progname,)
    sys.exit(1)

def invoke(args):
    try:
        process = subprocess.Popen(args,
                                   stdout=subprocess.PIPE)
        result, _ = process.communicate()
        if process.returncode != 0:
            raise Exception("Non-zero return code from '%s'" % (args[0],))
        return result.strip()
    except subprocess.CalledProcessError as e:
        print >>sys.stderr, "Unable to invoke '%s'." % (args[0],)
        sys.exit(1)

def attach(locker):
    try:
        return invoke(['attach', '-p', locker])
    except Exception as e:
        raise Exception("Could not find locker '%s'" % (locker,))

def athdir(path):
    try:
        return invoke(['athdir', '-t', 'bin', '-p', path])
    except Exception as e:
        raise Exception("Could not find binary directory in '%s'" % (path,))

def execute(path, args):
    try:
        os.execv(path, args)
    except OSError as e:
        return e.errno

def main():
    # First, figure out our name, in the strange case it isn't
    # 'attachandrun'. After we process each argument, consume it.
    global progname
    potential, argv = extract(sys.argv)
    progname = os.path.basename(potential)

    if len(argv) < 1:
        raise Exception('Missing arguments')
    
    check = False
    if argv[0] == '--check' or argv[0] == '-c':
        check = True
        _, argv = extract(argv)
    locker, argv = extract(argv)
    program, argv = extract(argv)

    # Use attach and athdir to figure out where the program we want to
    # execute lives
    locker_path = attach(locker)
    program_location = os.path.join(athdir(locker_path), program)

    # If we're in check (aka dry-run), see if we can execute this
    # program
    if check:
        if os.access(program_location, os.X_OK):
            sys.exit(0)
        sys.exit(1)

    # Actually execute the program, 
    error = execute(program_location, argv)
    print >>sys.stderr, "%s: %s" % (progname, os.strerror(error))
    
if __name__ == '__main__':
    try:
        main()
    except Exception as e:
        print >>sys.stderr, "%s: %s" % (progname, e)
        usage()