import parse
import sys
import os

EXIT_SUCCESS = 0
EXIT_FAILURE = 1

# Internal change-directory command.
def shell_cd (dir):
    os.chdir(dir)

# Internal exit/quit command.
def shell_exit(code):
    sys.exit(code)

# Execute simple command
def run_simple_command (simple_commands_list, father_command):
    cmd = simple_commands_list[0].word
    if cmd == 'exit' or cmd == 'quit':
        shell_exit(EXIT_SUCCESS)
    args = []
    for i in range(0, len(simple_commands_list)):
        args.append(simple_commands_list[i].word)
    if cmd == 'cd':
        shell_cd(args[1])
        return EXIT_SUCCESS
    try:
        pid = os.fork()
        if pid == -1:
	        # error forking
            return EXIT_FAILURE
        elif pid == 0:
	        # child process
                st = os.execvp("/bin/" + cmd, args)
	        #st = os.execvp(command, args)
	        # only if exec failed
	        # os._exit(st)
        else:
            os.waitpid(pid, 0)
            #only parent process gets here
            # status = os.waitpid(pid, 0)
            # if os.WIFEXITED(status):
            #    print("Child {} terminated normally, with code {}".format(pid, os.WEXITSTATUS(status)))
            #    return status
            return EXIT_SUCCESS
    except Exception as e:
        print("Error: {}".format (e))



    # TODO - extract command and arguments; ATTENTION! not all commands are simple_commands

    # TODO - extract redirects from father_command ???

    # TODO - fork parent process
    # TODO - execute child
    # TODO - wait for child
    # TODO - return exit status

# Process two commands in parallel, by creating two children.
def do_in_parallel (cmd1, cmd2, father_command):
    # TODO - execute cmd1 and cmd2 simultaneously
    pass

def do_on_pipe (cmd1, cmd2, father_command):
    # TODO - redirect the output of cmd1 to the input of cmd2
    pass

#Parse and execute a command.
def parse_command (command):
    if command.op == parse.OP_NONE:
        # TODO - run a simple command
        return run_simple_command (command.commands, command)
    elif command.op == parse.OP_SEQUENTIAL:
        # TODO - execute the commands one after the other
        pass
    elif command.op == parse.OP_PARALLEL:
        # TODO - execute the commands simultaneously
        pass
    elif command.op == parse.OP_CONDITIONAL_NZERO:
        # TODO - execute the second command only if the first one returns non zero
        pass
    elif command.op == parse.OP_CONDITIONAL_ZERO:
        # TODO - execute the second command only if the first one returns zero
        pass
    elif command.op == parse.OP_PIPE:
        # TODO - redirect the output of the first command to the input of the second
        return 0 # TODO - replace with actual exit code of command

fileName = sys.argv[1]
fileHandle = open(fileName, "r")
for line in fileHandle:
    command = parse.parse(line)
    #parse.dump(command) # TODO - delete the line before submitting the homework
    parse_command(command)
fileHandle.close()