import json
import os
import pkg_resources

from django.conf import settings
from django.urls import re_path, include

DJANGO_MAIN_MODULE = 'main'
MODULE_CONFIG_FILE_NAME = 'module_config.json'


class ModuleConfigError(Exception):
    pass


class ModuleMeta:
    _json_file = 'module.json'
    _root_url_name = 'root'

    def __init__(self, package_name):
        self._package_name = package_name
        self._app_config = None
        self._additional_apps = []
        self._url_prefix = None
        self._load_from_package()

    def __str__(self):
        t = '- {}'.format(self._package_name)
        return t

    @property
    def package(self):
        return self._package_name

    @property
    def app(self):
        if self._app_config:
            app = self._app_config
            if app.startswith('.'):
                app = self._package_name + app
        else:
            app = self._package_name
        return app

    @property
    def additional_apps(self):
        return self._additional_apps

    @property
    def url_prefix(self):
        if self._url_prefix is None:
            return self._package_name
        else:
            return self._url_prefix

    @property
    def url_namespace(self):
        return self._package_name.replace('.', '_')

    @property
    def url_conf_pattern(self):
        url_pattern = '^{}/'.format(self.url_prefix)
        url_conf = self._package_name + '.urls'
        return re_path(url_pattern, include(url_conf, self.url_namespace))

    def _load_from_package(self):
        package_name = self._package_name
        json_text = pkg_resources.resource_string(package_name, self._json_file)
        meta_dict = json.loads(json_text)
        meta_dict['package'] = package_name
        self.load_from_dict(meta_dict)

    def load_from_dict(self, meta_dict):
        self._package_name = meta_dict.get('package', None)
        self._app_config = meta_dict.get('app_config', None)
        self._additional_apps = meta_dict.get('additional_apps', [])
        self._url_prefix = meta_dict.get('url_prefix', None)

    def dump_as_dict(self):
        d = {
            'package': self._package_name,
        }
        if self._app_config:
            d['app_config'] = self._app_config
        if self._additional_apps:
            d['additional_apps'] = self._additional_apps
        if self._url_prefix:
            d['url_prefix'] = self._url_prefix
        return d


class ModuleConfig:
    _lazy_load = True

    def __init__(self, config_file_path=None, django_base_dir=None):
        if config_file_path is None:
            if django_base_dir is None:
                django_base_dir = settings.BASE_DIR
            config_file_path = os.path.join(django_base_dir, DJANGO_MAIN_MODULE, MODULE_CONFIG_FILE_NAME)
        self._config_file_path = config_file_path

        self._modules = {}

        self._loaded = False
        if not self._lazy_load:
            self._load()

    def _lazy_init(self):
        if not self._loaded:
            self._load()

    def _load(self):
        path = self._config_file_path

        self._modules = {}

        if os.path.exists(path):
            with open(path, 'r', encoding='ascii') as f:
                data = json.load(f)
        else:
            data = {}

        if 'modules' in data:
            for meta_dict in data['modules']:
                module_name = meta_dict['package']
                self._modules[module_name] = ModuleMeta(module_name)
                self._modules[module_name].load_from_dict(meta_dict)

        self._loaded = True

    @property
    def modules(self):
        self._lazy_init()
        return self._modules

    def save(self):
        path = self._config_file_path

        if os.path.exists(path):
            self._lazy_init()
        else:
            self._loaded = True

        data = {
            'modules': [],
        }
        for meta_obj in self._modules.values():
            data['modules'].append(meta_obj.dump_as_dict())

        with open(path, 'w', encoding='ascii') as f:
            json.dump(data, f, indent=4)