import json, os, errno

# self-explanatory
default_config = {}

# This will contain the current configuration after loading the file and
# combining it with the default configuration. All changes will be done here
config = None

# The file to work with
config_file_path = None

################################################################################
# file interaction
################################################################################

# set the config file to use
def set_file_path(file_path):
    global config_file_path
    # error handling
    if os.path.exists(file_path):
        if os.path.isdir(file_path):
            raise IOError(errno.EISDIR, "Is a directory", file_path)
        if os.access(file_path, os.R_OK) and os.access(file_path, os.W_OK):
            pass
        else:
            raise IOError(errno.EACCES, "Read AND write permissions required", file_path)
    else:
        config_file = open(file_path, "w")
        config_file.write("{}")
        config_file.close()
    # actually setting the file path
    config_file_path = file_path

# loads the json file at file_path and updates the default configuration with it
# overwrites any existing configuration adjustments
# TODO: handle None as file name (raise an exception)
def load():
    global config_file_path
    global config
    global default_config
    # read the config file
    config_file = open(config_file_path,"r")
    config_string = config_file.read()
    config_file.close()
    # combine with default config
    config = default_config.copy()
    config.update(json.loads(config_string))


# stores the current configuration to the file at file_path
# TODO: handle None (raise an exception)
def store():
    global config
    global config_file_path
    if not config is None:
        config_file = open(config_file_path, "w")
        config_file.write(json.dumps(config))
        config_file.close()

################################################################################
# default config / config setup
# These functions should be used BEFORE loading the config file
################################################################################

#defines a new option group in the default config
# TODO: handle existing groups (raise an exception)
def define_group(group):
    global default_config
    default_config.update({group : {}})

# defines a new option in the default config
# TODO: handle existing options (raise an exception)
def define_option(group, name, default_value):
    global default_config
    default_config[group].update({name : default_value})

# self-explanatory
def clear_definitions():
    global default_config
    default_config = {}

################################################################################
# adjust an existing configuration for new needs
################################################################################

# remove the given option from the configuration and return the value to allow
# for conversion if desired
# TODO: implement
def remove_option(group, name):
    pass

# move the value of an option to another place
# TODO: implement
def rename_option(old_group, old_name, new_group, new_name):
    pass

# remove an entire group from the configuration, never to be seen again
# TODO: implement
def remove_group(group):
    pass

# self-explanatory
# TODO: implement
def rename_group(old_group, new_group):
    pass

################################################################################
# config interaction
################################################################################

# get the value of the given option
def fetch(group, name):
    global config
    if config is None:
        load()
    return config[group][name]

# set the value of a config option
def set(group, name, value):
    global config
    if config is None:
        load()
    config[group][name] = value