import sys
import uuid
import pkgutil
import importlib
from hashlib import md5
from types import ModuleType
from collections import Counter
from importlib.abc import MetaPathFinder
from importlib.machinery import PathFinder
from typing import Set, List, Optional, Iterable

_internal_space = ModuleType(__name__ + "._internal")
_internal_space.__path__ = []  # type: ignore
sys.modules[_internal_space.__name__] = _internal_space

_manager_stack: List["PluginManager"] = []


class _NamespaceModule(ModuleType):
    """Simple namespace module to store plugins."""

    @property
    def __path__(self):
        return []

    def __getattr__(self, name: str):
        try:
            return super().__getattr__(name)  # type: ignore
        except AttributeError:
            if name.startswith("__"):
                raise
            raise RuntimeError("Plugin manager not activated!")


class _InternalModule(ModuleType):
    """Internal module for each plugin manager."""

    def __init__(self, plugin_manager: "PluginManager"):
        super().__init__(
            f"{_internal_space.__name__}.{plugin_manager.internal_id}")
        self.__plugin_manager__ = plugin_manager

    @property
    def __path__(self) -> List[str]:
        return list(self.__plugin_manager__.search_path)


class PluginManager:

    def __init__(self,
                 namespace: Optional[str] = None,
                 plugins: Optional[Iterable[str]] = None,
                 search_path: Optional[Iterable[str]] = None,
                 *,
                 id: Optional[str] = None):
        self.namespace: Optional[str] = namespace
        self.namespace_module: Optional[ModuleType] = self._setup_namespace(
            namespace)

        self.id: str = id or str(uuid.uuid4())
        self.internal_id: str = md5(
            ((self.namespace or "") + self.id).encode()).hexdigest()
        self.internal_module = self._setup_internal_module(self.internal_id)

        # simple plugin not in search path
        self.plugins: Set[str] = set(plugins or [])
        self.search_path: Set[str] = set(search_path or [])
        # ensure can be loaded
        self.list_plugins()

    def _setup_namespace(self,
                         namespace: Optional[str] = None
                        ) -> Optional[ModuleType]:
        if not namespace:
            return None

        try:
            module = importlib.import_module(namespace)
        except ImportError:
            module = _NamespaceModule(namespace)
            if "." in namespace:
                parent = importlib.import_module(namespace.rsplit(".", 1)[0])
                setattr(parent, namespace.rsplit(".", 1)[1], module)

        sys.modules[namespace] = module
        return module

    def _setup_internal_module(self, internal_id: str) -> ModuleType:
        if hasattr(_internal_space, internal_id):
            raise RuntimeError("Plugin manager already exists!")
        module = _InternalModule(self)
        sys.modules[module.__name__] = module
        setattr(_internal_space, internal_id, module)
        return module

    def __enter__(self):
        if self in _manager_stack:
            raise RuntimeError("Plugin manager already activated!")
        _manager_stack.append(self)
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        try:
            _manager_stack.pop()
        except IndexError:
            pass

    def search_plugins(self) -> List[str]:
        return [
            module_info.name
            for module_info in pkgutil.iter_modules(self.search_path)
        ]

    def list_plugins(self) -> Set[str]:
        _pre_managers: List[PluginManager]
        if self in _manager_stack:
            _pre_managers = _manager_stack[:_manager_stack.index(self)]
        else:
            _pre_managers = _manager_stack[:]

        _search_path: Set[str] = set()
        for manager in _pre_managers:
            _search_path |= manager.search_path
        if _search_path & self.search_path:
            raise RuntimeError("Duplicate plugin search path!")

        _search_plugins = self.search_plugins()
        c = Counter([*_search_plugins, *self.plugins])
        conflict = [name for name, num in c.items() if num > 1]
        if conflict:
            raise RuntimeError(
                f"More than one plugin named {' / '.join(conflict)}!")
        return set(_search_plugins) | self.plugins

    def load_plugin(self, name) -> ModuleType:
        if name in self.plugins:
            return importlib.import_module(name)

        if "." in name:
            raise ValueError("Plugin name cannot contain '.'")
        with self:
            return importlib.import_module(f"{self.namespace}.{name}")

    def load_all_plugins(self) -> List[ModuleType]:
        return [self.load_plugin(name) for name in self.list_plugins()]

    def _rewrite_module_name(self, module_name) -> Optional[str]:
        if module_name == self.namespace:
            return self.internal_module.__name__
        elif module_name.startswith(self.namespace + "."):
            path = module_name.split(".")
            length = self.namespace.count(".") + 1
            return f"{self.internal_module.__name__}.{'.'.join(path[length:])}"
        elif module_name in self.search_plugins():
            return f"{self.internal_module.__name__}.{module_name}"
        return None


class PluginFinder(MetaPathFinder):

    def find_spec(self, fullname: str, path, target):
        if _manager_stack:
            index = -1
            while -index <= len(_manager_stack):
                manager = _manager_stack[index]
                newname = manager._rewrite_module_name(fullname)
                if newname:
                    spec = PathFinder.find_spec(newname,
                                                list(manager.search_path),
                                                target)
                    if spec:
                        return spec
                index -= 1
        return None


sys.meta_path.insert(0, PluginFinder())