# Copyright (c) 2021 Ultimaker B.V.
# Uranium is released under the terms of the LGPLv3 or higher.

import imp
import json
import os
import shutil  # For deleting plugin directories;
import stat  # For setting file permissions correctly;
import time
import types
import zipfile
from typing import Any, Callable, Dict, List, Optional, Tuple, TYPE_CHECKING

from PyQt5.QtCore import QCoreApplication
from PyQt5.QtCore import QObject, pyqtSlot, QUrl, pyqtProperty, pyqtSignal

from UM.CentralFileStorage import CentralFileStorage
from UM.Logger import Logger
from UM.Message import Message
from UM.Platform import Platform
from UM.PluginError import PluginNotFoundError, InvalidMetaDataError
from UM.PluginObject import PluginObject  # For type hinting
from UM.Resources import Resources
from UM.Trust import Trust, TrustBasics, TrustException
from UM.Version import Version
from UM.i18n import i18nCatalog

i18n_catalog = i18nCatalog("uranium")

if TYPE_CHECKING:
    from UM.Application import Application


plugin_path_ignore_list = ["__pycache__", "tests", ".git"]


class PluginRegistry(QObject):
    """A central object to dynamically load modules as plugins.

    The PluginRegistry class can load modules dynamically and use
    them as plugins. Each plugin module is expected to be a directory with
    and `__init__` file defining a `getMetaData` and a `register` function.

    For more details, see the [plugins] file.

    [plugins]: docs/plugins.md
    """

    def __init__(self, application: "Application", parent: QObject = None) -> None:
        if PluginRegistry.__instance is not None:
            raise RuntimeError("Try to create singleton '%s' more than once" % self.__class__.__name__)
        PluginRegistry.__instance = self

        super().__init__(parent)
        self.preloaded_plugins = []  # type: List[str]  # List of plug-in names that must be loaded before the rest, if the plug-ins are available. They are loaded in this order too.

        self._application = application  # type: Application
        self._api_version = application.getAPIVersion()  # type: Version

        self._all_plugins = []        # type: List[str]
        self._metadata = {}           # type: Dict[str, Dict[str, Any]]

        self._plugins_installed = []  # type: List[str]

        # NOTE: The disabled_plugins and plugins_to_remove is explicitly set to None.
        # When actually loading the preferences, it's set to a list. This way we can see the
        # difference between no list and an empty one.
        self._disabled_plugins = []  # type: List[str]
        self._outdated_plugins = []  # type: List[str]
        self._plugins_to_install = dict()  # type: Dict[str, Dict[str, str]]
        self._plugins_to_remove = []  # type: List[str]

        self._plugins = {}            # type: Dict[str, types.ModuleType]
        self._found_plugins = {}      # type: Dict[str, types.ModuleType]  # Cache to speed up _findPlugin
        self._plugin_objects = {}     # type: Dict[str, PluginObject]

        self._plugin_locations = []  # type: List[str]
        self._plugin_folder_cache = {}  # type: Dict[str, List[Tuple[str, str]]]  # Cache to speed up _locatePlugin

        self._bundled_plugin_cache = {}  # type: Dict[str, bool]

        self._supported_file_types = {"umplugin": "Uranium Plugin"} # type: Dict[str, str]

        self._check_if_trusted = False  # type: bool
        self._clean_hierarchy_sent_messages = []  # type: List[str]
        self._debug_mode = False  # type: bool
        self._checked_plugin_ids = []     # type: List[str]
        self._distrusted_plugin_ids = []  # type: List[str]
        self._trust_checker = None  # type: Optional[Trust]

    pluginRemoved = pyqtSignal(str)

    def setCheckIfTrusted(self, check_if_trusted: bool, debug_mode: bool = False) -> None:
        self._check_if_trusted = check_if_trusted
        if self._check_if_trusted:
            self._trust_checker = Trust.getInstance()
            # 'Trust.getInstance()' will raise an exception if anything goes wrong (e.g.: 'unable to read public key').
            # Any such exception is explicitly _not_ caught here, as the application should quit with a crash.
            if self._trust_checker:
                self._trust_checker.setFollowSymlinks(debug_mode)

    def getCheckIfTrusted(self) -> bool:
        return self._check_if_trusted

    def initializeBeforePluginsAreLoaded(self) -> None:
        config_path = Resources.getConfigStoragePath()

        # File to store plugin info, such as which ones to install/remove and which ones are disabled.
        # At this point we can load this here because we already know the actual Application name, so the directory name
        self._plugin_config_filename = os.path.join(os.path.abspath(config_path), "plugins.json") # type: str

        from UM.Settings.ContainerRegistry import ContainerRegistry
        container_registry = ContainerRegistry.getInstance()

        try:
            with container_registry.lockFile():
                # Load the plugin info if exists
                if os.path.exists(self._plugin_config_filename):
                    Logger.log("i", "Loading plugin configuration file '%s'", self._plugin_config_filename)
                    with open(self._plugin_config_filename, "r", encoding = "utf-8") as f:
                        data = json.load(f)
                        self._disabled_plugins = data["disabled"]
                        self._plugins_to_install = data["to_install"]
                        self._plugins_to_remove = data["to_remove"]
        except:
            Logger.logException("e", "Failed to load plugin configuration file '%s'", self._plugin_config_filename)

        # Also load data from preferences, where the plugin info used to be saved
        preferences = self._application.getPreferences()
        disabled_plugins = preferences.getValue("general/disabled_plugins")
        disabled_plugins = disabled_plugins.split(",") if disabled_plugins else []
        disabled_plugins = [plugin for plugin in disabled_plugins if len(plugin.strip()) > 0]
        for plugin_id in disabled_plugins:
            if plugin_id not in self._disabled_plugins:
                self._disabled_plugins.append(plugin_id)

        plugins_to_remove = preferences.getValue("general/plugins_to_remove")
        plugins_to_remove = plugins_to_remove.split(",") if plugins_to_remove else []
        for plugin_id in plugins_to_remove:
            if plugin_id not in self._plugins_to_remove:
                self._plugins_to_remove.append(plugin_id)

        # Remove plugins that need to be removed
        for plugin_id in self._plugins_to_remove:
            self._removePlugin(plugin_id)
        self._plugins_to_remove = []
        if plugins_to_remove is not None:
            preferences.setValue("general/plugins_to_remove", "")
        self._savePluginData()

        # Install the plugins that need to be installed (overwrite existing)
        for plugin_id, plugin_info in self._plugins_to_install.items():
            self._installPlugin(plugin_id, plugin_info["filename"])
        self._plugins_to_install = {}
        self._savePluginData()

    def initializeAfterPluginsAreLoaded(self) -> None:
        preferences = self._application.getPreferences()

        # Remove the old preferences settings from preferences
        preferences.resetPreference("general/disabled_plugins")
        preferences.resetPreference("general/plugins_to_remove")

    def _savePluginData(self) -> None:
        from UM.Settings.ContainerRegistry import ContainerRegistry
        container_registry = ContainerRegistry.getInstance()
        try:
            with container_registry.lockFile():
                with open(self._plugin_config_filename, "w", encoding = "utf-8") as f:
                    data = json.dumps({"disabled": self._disabled_plugins,
                                       "to_install": self._plugins_to_install,
                                       "to_remove": self._plugins_to_remove,
                                       })
                    f.write(data)
        except:
            # Since we're writing to file (and waiting for a lock), there are a few things that can go wrong.
            # There is no need to crash the application for this, but it is a failure that we want to log.
            Logger.logException("e", "Unable to save the plugin data.")

    # TODO:
    # - [ ] Improve how metadata is stored. It should not be in the 'plugin' prop
    #       of the dictionary item.
    # - [ ] Remove usage of "active" in favor of "enabled".
    # - [ ] Switch self._disabled_plugins to self._plugins_disabled
    # - [ ] External plugins only appear in installed after restart
    #
    # NOMENCLATURE:
    # Enabled (active):  A plugin which is installed and currently enabled.
    # Disabled: A plugin which is installed but not currently enabled.
    # Available: A plugin which is not installed but could be.
    # Installed: A plugin which is installed locally in Cura.

    #===============================================================================
    # PUBLIC METHODS
    #===============================================================================

    #   Add a plugin location to the list of locations to search:
    def addPluginLocation(self, location: str) -> None:
        if not os.path.isdir(location):
            Logger.warning("Plugin location {0} must be a folder.".format(location))
            return

        self._plugin_locations.append(location)

    #   Check if all required plugins are loaded:
    def checkRequiredPlugins(self, required_plugins: List[str]) -> bool:
        plugins = self._findInstalledPlugins()
        for plugin_id in required_plugins:
            if plugin_id not in plugins:
                Logger.log("e", "Plugin %s is required, but not added or loaded", plugin_id)
                return False
        return True

    #   Remove plugin from the list of enabled plugins and save to preferences:
    def disablePlugin(self, plugin_id: str) -> None:
        if plugin_id not in self._disabled_plugins:
            self._disabled_plugins.append(plugin_id)
        self._savePluginData()

    #   Add plugin to the list of enabled plugins and save to preferences:
    def enablePlugin(self, plugin_id: str) -> None:
        if plugin_id in self._disabled_plugins:
            self._disabled_plugins.remove(plugin_id)
        self._savePluginData()

    #   Get a list of enabled plugins:
    def getActivePlugins(self) -> List[str]:
        plugin_list = []
        for plugin_id in self._all_plugins:
            if self.isActivePlugin(plugin_id):
                plugin_list.append(plugin_id)
        return plugin_list

    #   Get a list of all metadata matching a certain subset of metadata:
    #   \param kwargs Keyword arguments.
    #       Possible keywords:
    #       - filter: \type{dict} The subset of metadata that should be matched.
    #       - active_only: Boolean, True when only active plugin metadata should
    #         be returned.
    def getAllMetaData(self, **kwargs: Any):
        data_filter = kwargs.get("filter", {})
        active_only = kwargs.get("active_only", False)
        metadata_list = []
        for plugin_id in self._all_plugins:
            if active_only and (plugin_id in self._disabled_plugins or plugin_id in self._outdated_plugins):
                continue
            plugin_metadata = self.getMetaData(plugin_id)
            if self._subsetInDict(plugin_metadata, data_filter):
                metadata_list.append(plugin_metadata)
        return metadata_list

    #   Get a list of disabled plugins:
    def getDisabledPlugins(self) -> List[str]:
        return self._disabled_plugins

    #   Get a list of installed plugins:
    #   NOTE: These are plugins which have already been registered. This list is
    #         actually populated by the private _findInstalledPlugins() method.
    def getInstalledPlugins(self) -> List[str]:
        plugins = self._plugins_installed.copy()
        for plugin_id in self._plugins_to_remove:
            if plugin_id in plugins:
                plugins.remove(plugin_id)
        for plugin_id in self._plugins_to_install:
            if plugin_id not in plugins:
                plugins.append(plugin_id)
        return sorted(plugins)

    #   Get the metadata for a certain plugin:
    #   NOTE: InvalidMetaDataError is raised when no metadata can be found or
    #         the metadata misses the right keys.
    def getMetaData(self, plugin_id: str) -> Dict[str, Any]:
        if plugin_id not in self._metadata:
            try:
                if not self._populateMetaData(plugin_id):
                    return {}
            except InvalidMetaDataError:
                return {}

        return self._metadata[plugin_id]

    @pyqtSlot(str, result = "QVariantMap")
    def installPlugin(self, plugin_path: str) -> Optional[Dict[str, str]]:
        plugin_path = QUrl(plugin_path).toLocalFile()

        plugin_id = self._getPluginIdFromFile(plugin_path)
        if plugin_id is None: #Failed to load.
            return None

        # Remove it from the to-be-removed list if it's there
        if plugin_id in self._plugins_to_remove:
            self._plugins_to_remove.remove(plugin_id)
            self._savePluginData()

        # Copy the plugin file to the cache directory so it can later be used for installation
        cache_dir = os.path.join(Resources.getCacheStoragePath(), "plugins")
        if not os.path.exists(cache_dir):
            os.makedirs(cache_dir, exist_ok = True)
        cache_plugin_filename = os.path.join(cache_dir, plugin_id + ".plugin")
        if os.path.exists(cache_plugin_filename):
            os.remove(cache_plugin_filename)
        shutil.copy2(plugin_path, cache_plugin_filename)

        # Add new install data
        install_info = {"plugin_id": plugin_id,
                        "filename": cache_plugin_filename}
        self._plugins_to_install[plugin_id] = install_info
        self._savePluginData()
        Logger.log("i", "Plugin '%s' has been scheduled for installation.", plugin_id)

        result = {"status": "ok",
                  "id": "",
                  "message": i18n_catalog.i18nc("@info:status", "The plugin has been installed.\nPlease re-start the application to activate the plugin."),
                  }
        return result

    #   Check by ID if a plugin is active (enabled):
    def isActivePlugin(self, plugin_id: str) -> bool:
        if plugin_id not in self._disabled_plugins and plugin_id not in self._outdated_plugins and plugin_id in self._all_plugins:
            return True

        return False

    def isBundledPlugin(self, plugin_id: str) -> bool:
        if plugin_id in self._bundled_plugin_cache:
            return self._bundled_plugin_cache[plugin_id]
        install_prefix = os.path.abspath(self._application.getInstallPrefix())

        # Go through all plugin locations and check if the given plugin is located in the installation path.
        is_bundled = False
        for plugin_dir in self._plugin_locations:
            if not TrustBasics.isPathInLocation(install_prefix, plugin_dir):
                # To prevent the situation in a 'trusted' env. that the user-folder has a supposedly 'bundled' plugin:
                if self._check_if_trusted:
                    result = self._locatePlugin(plugin_id, plugin_dir)
                    if result:
                        is_bundled = False
                        break
                else:
                    continue

            result = self._locatePlugin(plugin_id, plugin_dir)
            if result:
                is_bundled = True
                break
        self._bundled_plugin_cache[plugin_id] = is_bundled
        return is_bundled

    # Indicates that a specific plugin is currently being loaded. If the plugin_id is empty, it means that no plugin
    # is currently being loaded.
    pluginLoadStarted = pyqtSignal(str, arguments = ["plugin_id"])

    def loadPlugins(self, metadata: Optional[Dict[str, Any]] = None) -> None:
        """Load all plugins matching a certain set of metadata

        :param metadata: The meta data that needs to be matched.
        NOTE: This is the method which kicks everything off at app launch.
        """

        start_time = time.time()

        # First load all of the pre-loaded plug-ins.
        for preloaded_plugin in self.preloaded_plugins:
            self.loadPlugin(preloaded_plugin)

        # Get a list of all installed plugins:
        plugin_ids = self._findInstalledPlugins()
        for plugin_id in plugin_ids:
            if plugin_id in self.preloaded_plugins:
                continue  # Already loaded this before.

            self.pluginLoadStarted.emit(plugin_id)

            # Get the plugin metadata:
            try:
                plugin_metadata = self.getMetaData(plugin_id)
            except TrustException:
                Logger.error("Plugin {} was not loaded because it could not be verified.", plugin_id)
                message_text = i18n_catalog.i18nc("@error:untrusted",
                                                  "Plugin {} was not loaded because it could not be verified.", plugin_id)
                Message(text = message_text, message_type = Message.MessageType.ERROR).show()
                continue

            # Save all metadata to the metadata dictionary:
            self._metadata[plugin_id] = plugin_metadata
            if metadata is None or self._subsetInDict(self._metadata[plugin_id], metadata):
                #
                try:
                    self.loadPlugin(plugin_id)
                    QCoreApplication.processEvents()  # Ensure that the GUI does not freeze.
                    # Add the plugin to the list after actually load the plugin:
                    self._all_plugins.append(plugin_id)
                    self._plugins_installed.append(plugin_id)
                except PluginNotFoundError:
                    pass

        self.pluginLoadStarted.emit("")
        Logger.log("d", "Loading all plugins took %s seconds", time.time() - start_time)

    # Checks if the given plugin API version is compatible with the current version.
    def isPluginApiVersionCompatible(self, plugin_api_version: "Version") -> bool:
        return plugin_api_version.getMajor() == self._api_version.getMajor() \
               and plugin_api_version.getMinor() <= self._api_version.getMinor()

    #   Load a single plugin by ID:
    def loadPlugin(self, plugin_id: str) -> None:
        # If plugin has already been loaded, do not load it again:
        if plugin_id in self._plugins:
            Logger.log("w", "Plugin %s was already loaded", plugin_id)
            return

        # Find the actual plugin on drive, do security checks if necessary:
        plugin = self._findPlugin(plugin_id)

        # If not found, raise error:
        if not plugin:
            self.removeCorruptedPluginMessage(plugin_id)
            raise PluginNotFoundError(plugin_id)

        # If found, but isn't in the metadata dictionary, add it:
        if plugin_id not in self._metadata:
            try:
                self._populateMetaData(plugin_id)
            except InvalidMetaDataError:
                return

        # Do not load plugin that has been disabled
        if plugin_id in self._disabled_plugins:
            Logger.log("i", "Plugin [%s] has been disabled. Skip loading it.", plugin_id)
            return

        # If API version is incompatible, don't load it.
        supported_sdk_versions = self._metadata[plugin_id].get("plugin", {}).get("supported_sdk_versions", [Version("0")])
        is_plugin_supported = False
        for supported_sdk_version in supported_sdk_versions:
            is_plugin_supported |= self.isPluginApiVersionCompatible(supported_sdk_version)
            if is_plugin_supported:
                break

        if not is_plugin_supported:
            Logger.log("w", "Plugin [%s] with supported sdk versions [%s] is incompatible with the current sdk version [%s].",
                       plugin_id, [str(version) for version in supported_sdk_versions], self._api_version)
            self._outdated_plugins.append(plugin_id)
            return

        try:
            to_register = plugin.register(self._application)  # type: ignore  # We catch AttributeError on this in case register() doesn't exist.
            if not to_register:
                Logger.log("w", "Plugin %s did not return any objects to register", plugin_id)
                self.removeCorruptedPluginMessage(plugin_id)
                return
            for plugin_type, plugin_object in to_register.items():
                if type(plugin_object) == list:
                    for metadata_index, nested_plugin_object in enumerate(plugin_object):
                        nested_plugin_object.setVersion(self._metadata[plugin_id].get("plugin", {}).get("version"))
                        all_metadata = self._metadata[plugin_id].get(plugin_type, [])
                        try:
                            nested_plugin_object.setMetaData(all_metadata[metadata_index])
                        except IndexError:
                            nested_plugin_object.setMetaData({})
                        self._addPluginObject(nested_plugin_object, plugin_id, plugin_type)
                else:
                    plugin_object.setVersion(self._metadata[plugin_id].get("plugin", {}).get("version"))
                    metadata = self._metadata[plugin_id].get(plugin_type, {})
                    if type(metadata) == list:
                        try:
                            metadata = metadata[0]
                        except IndexError:
                            metadata = {}
                    plugin_object.setMetaData(metadata)
                    self._addPluginObject(plugin_object, plugin_id, plugin_type)

            self._plugins[plugin_id] = plugin
            self.enablePlugin(plugin_id)
            Logger.info("Loaded plugin %s", plugin_id)

        except Exception:
            self.removeCorruptedPluginMessage(plugin_id)

    def _acceptedRemoveCorruptedPluginMessage(self, plugin_id: str, original_message: Message):
        message_data = self.uninstallPlugin(plugin_id)
        original_message.hide()
        message = Message(text = message_data["message"], message_type = Message.MessageType.NEUTRAL, lifetime = 0)
        message.addAction("dismiss",
                           name = i18n_catalog.i18nc("@action:button", "Dismiss"),
                           icon = "",
                           description = "Dismiss this message",
                           button_align = Message.ActionButtonAlignment.ALIGN_RIGHT)
        message.pyQtActionTriggered.connect(lambda message, action: message.hide())
        message.show()

    def removeCorruptedPluginMessage(self, plugin_id: str) -> None:
        """Shows a message to the user remove the corrupted plugin"""
        message_text = i18n_catalog.i18nc("@error",
                                          "The plugin {} could not be loaded. Re-installing the plugin might solve "
                                          "the issue", plugin_id)
        unable_to_load_plugin_message = Message(text = message_text, message_type = Message.MessageType.ERROR, lifetime = 0)
        unable_to_load_plugin_message.addAction("remove",
                               name = i18n_catalog.i18nc("@action:button", "Remove plugin"),
                               icon = "",
                               description = "Remove the plugin",
                               button_align = Message.ActionButtonAlignment.ALIGN_RIGHT)

        # Listen for the pyqt signal, since that one does support lambda's
        unable_to_load_plugin_message.pyQtActionTriggered.connect(lambda message, action: self._acceptedRemoveCorruptedPluginMessage(plugin_id, message))

        unable_to_load_plugin_message.show()
        Logger.logException("e", "Error loading plugin %s:", plugin_id)

    #   Uninstall a plugin with a given ID:
    @pyqtSlot(str, result = "QVariantMap")
    def uninstallPlugin(self, plugin_id: str) -> Dict[str, str]:
        if plugin_id in self._plugins_to_install:
            del self._plugins_to_install[plugin_id]
            self._savePluginData()
            message_text = i18n_catalog.i18nc("@info:status", "Plugin no longer scheduled to be installed.")
            Logger.log("i", "Plugin '%s' removed from to-be-installed list.", plugin_id)
        elif plugin_id not in self._plugins_to_remove:
            self._plugins_to_remove.append(plugin_id)
            self._savePluginData()
            message_text = i18n_catalog.i18nc("@info:status",
                "The plugin has been removed.\nPlease restart {0} to finish uninstall.",
                self._application.getApplicationName())
            Logger.log("i", "Plugin '%s' has been scheduled for later removal.", plugin_id)

        # Remove the plugin object from the Plugin Registry:
        if plugin_id in self._plugins:
            del self._plugins[plugin_id]

        if plugin_id in self._plugins_installed:
            self._plugins_installed.remove(plugin_id)

        self.pluginRemoved.emit(plugin_id)

        result = {
            "status": "ok",
            "message": message_text,
            "id": plugin_id
        }
        return result

    # Installs the given plugin file. It will overwrite the existing plugin if present.
    def _installPlugin(self, plugin_id: str, plugin_path: str) -> None:
        Logger.log("i", "Attempting to install a new plugin %s from file '%s'", plugin_id, plugin_path)

        local_plugin_path = os.path.join(Resources.getStoragePath(Resources.Resources), "plugins")

        if plugin_id in self._bundled_plugin_cache:
            del self._bundled_plugin_cache[plugin_id]

        try:
            with zipfile.ZipFile(plugin_path, "r") as zip_ref:
                plugin_folder = os.path.join(local_plugin_path, plugin_id)

                # Overwrite the existing plugin if already installed
                if os.path.isdir(plugin_folder):
                    shutil.rmtree(plugin_folder, ignore_errors = True)
                os.makedirs(plugin_folder, exist_ok = True)

                # Extract all files
                for info in zip_ref.infolist():
                    extracted_path = zip_ref.extract(info.filename, path = plugin_folder)
                    permissions = os.stat(extracted_path).st_mode
                    os.chmod(extracted_path, permissions | stat.S_IEXEC) # Make these files executable.
        except: # Installing a new plugin should never crash the application.
            Logger.logException("e", "An exception occurred while installing plugin {path}".format(path = plugin_path))

        if plugin_id in self._disabled_plugins:
            self._disabled_plugins.remove(plugin_id)

    # Removes the given plugin.
    def _removePlugin(self, plugin_id: str) -> None:
        plugin_folder = os.path.join(Resources.getStoragePath(Resources.Resources), "plugins")
        plugin_path = os.path.join(plugin_folder, plugin_id)

        if plugin_id in self._bundled_plugin_cache:
            del self.bundled_plugin_cache[plugin_id]

        Logger.log("i", "Attempting to remove plugin '%s' from directory '%s'", plugin_id, plugin_path)
        try:
            shutil.rmtree(plugin_path)
        except EnvironmentError as e:
            Logger.error("Unable to remove plug-in {plugin_id}: {err}".format(plugin_id = plugin_id, err = str(e)))

#===============================================================================
# PRIVATE METHODS
#===============================================================================

    def _getPluginIdFromFile(self, filename: str) -> Optional[str]:
        plugin_id = None
        try:
            with zipfile.ZipFile(filename, "r") as zip_ref:
                for file_info in zip_ref.infolist():
                    if file_info.filename.endswith("/"):
                        plugin_id = file_info.filename.strip("/")
                        break
        except zipfile.BadZipFile:
            Logger.logException("e", "Failed to load plug-in file. The zip archive seems to be corrupt.")
            return None  # Signals that loading this failed.
        except FileNotFoundError:
            Logger.logException("e", "Failed to load plug-in file as we were unable to find it.")
            return None  # Signals that loading this failed.
        return plugin_id

    #   Returns a list of all possible plugin ids in the plugin locations:
    def _findInstalledPlugins(self, paths = None) -> List[str]:
        plugin_ids = []

        if not paths:
            paths = self._plugin_locations

        for folder in paths:
            try:
                if not os.path.isdir(folder):
                    continue

                for file in os.listdir(folder):
                    filepath = os.path.join(folder, file)
                    if os.path.isdir(filepath):
                        if os.path.isfile(os.path.join(filepath, "__init__.py")):
                            plugin_ids.append(file)
                        else:
                            plugin_ids += self._findInstalledPlugins([filepath])
            except EnvironmentError as err:
                Logger.warning("Unable to read folder {folder}: {err}".format(folder = folder, err = err))
                continue

        return plugin_ids

    def _findPlugin(self, plugin_id: str) -> Optional[types.ModuleType]:
        """Try to find a module implementing a plugin

        :param plugin_id: The name of the plugin to find
        :returns: module if it was found (and, if 'self._check_if_trusted' is set, also secure), None otherwise
        """

        if plugin_id in self._found_plugins:
            return self._found_plugins[plugin_id]
        locations = []
        for folder in self._plugin_locations:
            location = self._locatePlugin(plugin_id, folder)
            if location:
                locations.append(location)

        if not locations:
            return None
        final_location = locations[0]

        if len(locations) > 1:
            # We found multiple versions of the plugin. Let's find out which one to load!
            highest_version = Version(0)

            for loc in locations:
                meta_data = {}  # type: Dict[str, Any]
                plugin_location = os.path.join(loc, plugin_id)
                metadata_file = os.path.join(plugin_location, "plugin.json")
                try:
                    with open(metadata_file, "r", encoding="utf-8") as file_stream:
                        self._parsePluginInfo(plugin_id, file_stream.read(), meta_data)
                    current_version = Version(meta_data["plugin"]["version"])
                except InvalidMetaDataError:
                    current_version = Version("0.0.0")
                    Logger.log("e", f"The plugin.json in '{plugin_location}' is invalid. Assuming that the version of '{plugin_id}' is {current_version}.")
                if current_version > highest_version:
                    highest_version = current_version
                    final_location = loc

        # Move data (if any) to central storage
        central_storage_file = os.path.join(final_location, plugin_id, TrustBasics.getCentralStorageFilename())
        if os.path.exists(central_storage_file):
            plugin_final_path = os.path.join(final_location, plugin_id)

            if self._check_if_trusted and plugin_id not in self._checked_plugin_ids and not self.isBundledPlugin(plugin_id):
                # Do a quick check if the central-storage file itself hasn't been tampered with (and such).
                # This is necessary, as we move to central storage first, and only _then_ properly check the manifest.
                if self._trust_checker and not self._trust_checker.signedFolderPreStorageCheck(plugin_final_path):
                    self._distrusted_plugin_ids.append(plugin_id)
                    return None

            try:
                with open(central_storage_file, "r", encoding = "utf-8") as file_stream:
                    if not self._handleCentralStorage(file_stream.read(), plugin_final_path, is_bundled_plugin = self.isBundledPlugin(plugin_id)):
                        return None
            except:
                pass
        try:
            file, path, desc = imp.find_module(plugin_id, [final_location])
        except Exception:
            Logger.logException("e", "Import error when importing %s", plugin_id)
            return None

        # Define a trusted plugin as either: already checked, correctly signed, or bundled with the application.
        if self._check_if_trusted and plugin_id not in self._checked_plugin_ids and not self.isBundledPlugin(plugin_id):

            # NOTE: '__pychache__'s (+ subfolders) are deleted on startup _before_ load module:
            if not TrustBasics.removeCached(path):
                self._distrusted_plugin_ids.append(plugin_id)
                return None

            # Do the actual check:
            if self._trust_checker is not None and self._trust_checker.signedFolderCheck(path):
                self._checked_plugin_ids.append(plugin_id)
            else:
                self._distrusted_plugin_ids.append(plugin_id)
                return None

        try:
            module = imp.load_module(plugin_id, file, path, desc) #type: ignore #MyPy gets the wrong output type from imp.find_module for some reason.
        except Exception:
            Logger.logException("e", "Import error loading module %s", plugin_id)
            return None
        finally:
            if file:
                os.close(file) #type: ignore #MyPy gets the wrong output type from imp.find_module for some reason.
        self._found_plugins[plugin_id] = module
        return module

    def _locatePlugin(self, plugin_id: str, folder: str) -> Optional[str]:
        if not os.path.isdir(folder):
            return None

        # self._plugin_folder_cache is a per-plugin-location list of all subfolders that contain a __init__.py file
        if folder not in self._plugin_folder_cache:
            plugin_folders = []
            for root, dirs, files in os.walk(folder, topdown = True, followlinks = True):
                # modify dirs in place to ignore .git, pycache and test folders completely
                dirs[:] = [d for d in dirs if d not in plugin_path_ignore_list]

                if "plugin.json" in files:
                    plugin_folders.append((root, os.path.basename(root)))

            self._plugin_folder_cache[folder] = plugin_folders

        for folder_path, folder_name in self._plugin_folder_cache[folder]:
            if folder_name == plugin_id:
                return os.path.abspath(os.path.join(folder_path, ".."))

        return None

    def _handleCentralStorage(self, file_data: str, plugin_path: str, is_bundled_plugin: bool = False) -> bool:
        """
        Plugins can indicate that they want certain things to be stored in a central location.
        In the case of a signed plugin you *must* do this by means of the central_storage.json file.
        :param file_data: The data as loaded from the file
        :param plugin_path: The location of the plugin on the file system
        :return: False if there is a security suspicion, True otherwise (even if the method otherwise fails).
        """
        try:
            file_manifest = json.loads(file_data)
        except (json.decoder.JSONDecodeError, UnicodeDecodeError):
            Logger.logException("e", f"Failed to parse the central storage file for '{plugin_path}'.")
            return True

        for file_to_move in file_manifest:
            full_path = os.path.join(plugin_path, file_to_move[0])
            try:
                CentralFileStorage.store(full_path, file_to_move[1], Version(file_to_move[2]), move_file = not is_bundled_plugin)
            except (FileExistsError, TypeError, IndexError, OSError):
                Logger.logException("w", f"Can't move file {file_to_move[0]} to central storage for '{plugin_path}'.")
        return True

    #   Load the plugin data from the stream and in-place update the metadata.
    def _parsePluginInfo(self, plugin_id, file_data, meta_data):
        try:
            meta_data["plugin"] = json.loads(file_data)
        except json.decoder.JSONDecodeError:
            Logger.logException("e", "Failed to parse plugin.json for plugin %s", plugin_id)
            raise InvalidMetaDataError(plugin_id)

        # Check if metadata is valid;
        if "version" not in meta_data["plugin"]:
            Logger.log("e", "Version must be set!")
            raise InvalidMetaDataError(plugin_id)

        # Check if the plugin states what API version it needs.
        if "api" not in meta_data["plugin"] and "supported_sdk_versions" not in meta_data["plugin"]:
            Logger.log("e", "The API or the supported_sdk_versions must be set!")
            raise InvalidMetaDataError(plugin_id)
        else:
            # Store the api_version as a Version object.
            all_supported_sdk_versions = []  # type: List[Version]
            if "supported_sdk_versions" in meta_data["plugin"]:
                all_supported_sdk_versions += [Version(supported_version) for supported_version in
                                               meta_data["plugin"]["supported_sdk_versions"]]
            if "api" in meta_data["plugin"]:
                all_supported_sdk_versions += [Version(meta_data["plugin"]["api"])]
            meta_data["plugin"]["supported_sdk_versions"] = all_supported_sdk_versions

        if "i18n-catalog" in meta_data["plugin"]:
            # A catalog was set, try to translate a few strings
            i18n_catalog = i18nCatalog(meta_data["plugin"]["i18n-catalog"])
            if "name" in meta_data["plugin"]:
                meta_data["plugin"]["name"] = i18n_catalog.i18n(meta_data["plugin"]["name"])
            if "description" in meta_data["plugin"]:
                meta_data["plugin"]["description"] = i18n_catalog.i18n(meta_data["plugin"]["description"])

    def _populateMetaData(self, plugin_id: str) -> bool:
        """Populate the list of metadata"""

        plugin = self._findPlugin(plugin_id)
        if not plugin:
            Logger.log("w", "Could not find plugin %s", plugin_id)
            return False

        location = None
        for folder in self._plugin_locations:
            location = self._locatePlugin(plugin_id, folder)
            if location:
                break

        if not location:
            Logger.log("w", "Could not find plugin %s", plugin_id)
            return False
        location = os.path.join(location, plugin_id)

        try:
            meta_data = plugin.getMetaData() #type: ignore #We catch the AttributeError that this would raise if the module has no getMetaData function.
            metadata_file = os.path.join(location, "plugin.json")
            try:
                with open(metadata_file, "r", encoding = "utf-8") as file_stream:
                    self._parsePluginInfo(plugin_id, file_stream.read(), meta_data)
            except FileNotFoundError:
                Logger.logException("e", "Unable to find the required plugin.json file for plugin %s", plugin_id)
                raise InvalidMetaDataError(plugin_id)
            except UnicodeDecodeError:
                Logger.logException("e", "The plug-in metadata file for plug-in {plugin_id} is corrupt.".format(plugin_id = plugin_id))
                raise InvalidMetaDataError(plugin_id)
            except EnvironmentError as e:
                Logger.logException("e", "Can't open the metadata file for plug-in {plugin_id}: {err}".format(plugin_id = plugin_id, err = str(e)))
                raise InvalidMetaDataError(plugin_id)

        except AttributeError as e:
            Logger.log("e", "Plug-in {plugin_id} has no getMetaData function to get metadata of the plug-in: {err}".format(plugin_id = plugin_id, err = str(e)))
            raise InvalidMetaDataError(plugin_id)
        except TypeError as e:
            Logger.log("e", "Plug-in {plugin_id} has a getMetaData function with the wrong signature: {err}".format(plugin_id = plugin_id, err = str(e)))
            raise InvalidMetaDataError(plugin_id)

        if not meta_data:
            raise InvalidMetaDataError(plugin_id)

        meta_data["id"] = plugin_id
        meta_data["location"] = location

        # Application-specific overrides
        appname = self._application.getApplicationName()
        if appname in meta_data:
            meta_data.update(meta_data[appname])
            del meta_data[appname]

        self._metadata[plugin_id] = meta_data
        return True

    #   Check if a certain dictionary contains a certain subset of key/value pairs
    #   \param dictionary \type{dict} The dictionary to search
    #   \param subset \type{dict} The subset to search for
    def _subsetInDict(self, dictionary: Dict[Any, Any], subset: Dict[Any, Any]) -> bool:
        for key in subset:
            if key not in dictionary:
                return False
            if subset[key] != {} and dictionary[key] != subset[key]:
                return False
        return True

    def getPluginObject(self, plugin_id: str) -> PluginObject:
        """Get a specific plugin object given an ID. If not loaded, load it.

        :param plugin_id: The ID of the plugin object to get.
        """

        if plugin_id not in self._plugins:
            self.loadPlugin(plugin_id)
        if plugin_id not in self._plugin_objects:
            raise PluginNotFoundError(plugin_id)
        return self._plugin_objects[plugin_id]

    def _addPluginObject(self, plugin_object: PluginObject, plugin_id: str, plugin_type: str) -> None:
        plugin_object.setPluginId(plugin_id)
        self._plugin_objects[plugin_id] = plugin_object
        try:
            self._type_register_map[plugin_type](plugin_object)
        except Exception as e:
            Logger.logException("e", "Unable to add plugin %s", plugin_id)

    def addSupportedPluginExtension(self, extension: str, description: str) -> None:
        if extension not in self._supported_file_types:
            self._supported_file_types[extension] = description
            self.supportedPluginExtensionsChanged.emit()

    supportedPluginExtensionsChanged = pyqtSignal()

    @pyqtProperty("QStringList", notify=supportedPluginExtensionsChanged)
    def supportedPluginExtensions(self) -> List[str]:
        file_types = []
        all_types = []

        if Platform.isLinux():
            for ext, desc in self._supported_file_types.items():
                file_types.append("{0} (*.{1} *.{2})".format(desc, ext.lower(), ext.upper()))
                all_types.append("*.{0} *.{1}".format(ext.lower(), ext.upper()))
        else:
            for ext, desc in self._supported_file_types.items():
                file_types.append("{0} (*.{1})".format(desc, ext))
                all_types.append("*.{0}".format(ext))

        file_types.sort()
        file_types.insert(0, i18n_catalog.i18nc("@item:inlistbox", "All Supported Types ({0})", " ".join(all_types)))
        file_types.append(i18n_catalog.i18nc("@item:inlistbox", "All Files (*)"))
        return file_types

    def getPluginPath(self, plugin_id: str) -> Optional[str]:
        """Get the path to a plugin.

        :param plugin_id: The PluginObject.getPluginId() of the plugin.
        :return: The absolute path to the plugin or an empty string if the plugin could not be found.
        """

        if plugin_id in self._plugins:
            plugin = self._plugins.get(plugin_id)
        else:
            plugin = self._findPlugin(plugin_id)

        if not plugin:
            return None

        path = os.path.dirname(self._plugins[plugin_id].__file__)
        if os.path.isdir(path):
            return path

        return None

    @classmethod
    def addType(cls, plugin_type: str, register_function: Callable[[Any], None]) -> None:
        """Add a new plugin type.

        This function is used to add new plugin types. Plugin types are simple
        string identifiers that match a certain plugin to a registration function.

        The callable `register_function` is responsible for handling the object.
        Usually it will add the object to a list of objects in the relevant class.
        For example, the plugin type 'tool' has Controller::addTool as register
        function.

        `register_function` will be called every time a plugin of `type` is loaded.

        :param plugin_type: The name of the plugin type to add.
        :param register_function: A callable that takes an object as parameter.
        """

        cls._type_register_map[plugin_type] = register_function

    @classmethod
    def removeType(cls, plugin_type: str) -> None:
        """Remove a plugin type.

        :param plugin_type: The plugin type to remove.
        """

        if plugin_type in cls._type_register_map:
            del cls._type_register_map[plugin_type]

    _type_register_map = {}  # type: Dict[str, Callable[[Any], None]]
    __instance = None    # type: PluginRegistry

    @classmethod
    def getInstance(cls, *args, **kwargs) -> "PluginRegistry":
        return cls.__instance
