import functools
import os
from collections import OrderedDict

from django.apps import apps
from django.conf import settings
from django.contrib.staticfiles import utils
from django.core.checks import Error
from django.core.exceptions import ImproperlyConfigured
from django.core.files.storage import (
    FileSystemStorage, Storage, default_storage,
)
from django.utils._os import safe_join
from django.utils.functional import LazyObject, empty
from django.utils.module_loading import import_string

# To keep track on which directories the finder has searched the static files.
searched_locations = []


class BaseFinder:
    """
    A base file finder to be used for custom staticfiles finder classes.
    """
    def check(self, **kwargs):
        raise NotImplementedError(
            'subclasses may provide a check() method to verify the finder is '
            'configured correctly.'
        )

    def find(self, path, all=False):
        """
        Given a relative file path, find an absolute file path.

        If the ``all`` parameter is False (default) return only the first found
        file path; if True, return a list of all found files paths.
        """
        raise NotImplementedError('subclasses of BaseFinder must provide a find() method')

    def list(self, ignore_patterns):
        """
        Given an optional list of paths to ignore, return a two item iterable
        consisting of the relative path and storage instance.
        """
        raise NotImplementedError('subclasses of BaseFinder must provide a list() method')


class FileSystemFinder(BaseFinder):
    """
    A static files finder that uses the ``STATICFILES_DIRS`` setting
    to locate files.
    """
    def __init__(self, app_names=None, *args, **kwargs):
        # List of locations with static files
        self.locations = []
        # Maps dir paths to an appropriate storage instance
        self.storages = OrderedDict()
        for root in settings.STATICFILES_DIRS:
            if isinstance(root, (list, tuple)):
                prefix, root = root
            else:
                prefix = ''
            if (prefix, root) not in self.locations:
                self.locations.append((prefix, root))
        for prefix, root in self.locations:
            filesystem_storage = FileSystemStorage(location=root)
            filesystem_storage.prefix = prefix
            self.storages[root] = filesystem_storage
        super().__init__(*args, **kwargs)

    def check(self, **kwargs):
        errors = []
        if not isinstance(settings.STATICFILES_DIRS, (list, tuple)):
            errors.append(Error(
                'The STATICFILES_DIRS setting is not a tuple or list.',
                hint='Perhaps you forgot a trailing comma?',
                id='staticfiles.E001',
            ))
        for root in settings.STATICFILES_DIRS:
            if isinstance(root, (list, tuple)):
                _, root = root
            if settings.STATIC_ROOT and os.path.abspath(settings.STATIC_ROOT) == os.path.abspath(root):
                errors.append(Error(
                    'The STATICFILES_DIRS setting should not contain the '
                    'STATIC_ROOT setting.',
                    id='staticfiles.E002',
                ))
        return errors

    def find(self, path, all=False):
        """
        Look for files in the extra locations as defined in STATICFILES_DIRS.
        """
        matches = []
        for prefix, root in self.locations:
            if root not in searched_locations:
                searched_locations.append(root)
            matched_path = self.find_location(root, path, prefix)
            if matched_path:
                if not all:
                    return matched_path
                matches.append(matched_path)
        return matches

    def find_location(self, root, path, prefix=None):
        """
        Find a requested static file in a location and return the found
        absolute path (or ``None`` if no match).
        """
        if prefix:
            prefix = '%s%s' % (prefix, os.sep)
            if not path.startswith(prefix):
                return None
            path = path[len(prefix):]
        path = safe_join(root, path)
        if os.path.exists(path):
            return path

    def list(self, ignore_patterns):
        """
        List all files in all locations.
        """
        for prefix, root in self.locations:
            storage = self.storages[root]
            for path in utils.get_files(storage, ignore_patterns):
                yield path, storage


class AppDirectoriesFinder(BaseFinder):
    """
    A static files finder that looks in the directory of each app as
    specified in the source_dir attribute.
    """
    storage_class = FileSystemStorage
    source_dir = 'static'

    def __init__(self, app_names=None, *args, **kwargs):
        # The list of apps that are handled
        self.apps = []
        # Mapping of app names to storage instances
        self.storages = OrderedDict()
        app_configs = apps.get_app_configs()
        if app_names:
            app_names = set(app_names)
            app_configs = [ac for ac in app_configs if ac.name in app_names]
        for app_config in app_configs:
            app_storage = self.storage_class(
                os.path.join(app_config.path, self.source_dir))
            if os.path.isdir(app_storage.location):
                self.storages[app_config.name] = app_storage
                if app_config.name not in self.apps:
                    self.apps.append(app_config.name)
        super().__init__(*args, **kwargs)

    def list(self, ignore_patterns):
        """
        List all files in all app storages.
        """
        for storage in self.storages.values():
            if storage.exists(''):  # check if storage location exists
                for path in utils.get_files(storage, ignore_patterns):
                    yield path, storage

    def find(self, path, all=False):
        """
        Look for files in the app directories.
        """
        matches = []
        for app in self.apps:
            app_location = self.storages[app].location
            if app_location not in searched_locations:
                searched_locations.append(app_location)
            match = self.find_in_app(app, path)
            if match:
                if not all:
                    return match
                matches.append(match)
        return matches

    def find_in_app(self, app, path):
        """
        Find a requested static file in an app's static locations.
        """
        storage = self.storages.get(app)
        if storage:
            # only try to find a file if the source dir actually exists
            if storage.exists(path):
                matched_path = storage.path(path)
                if matched_path:
                    return matched_path


class BaseStorageFinder(BaseFinder):
    """
    A base static files finder to be used to extended
    with an own storage class.
    """
    storage = None

    def __init__(self, storage=None, *args, **kwargs):
        if storage is not None:
            self.storage = storage
        if self.storage is None:
            raise ImproperlyConfigured("The staticfiles storage finder %r "
                                       "doesn't have a storage class "
                                       "assigned." % self.__class__)
        # Make sure we have a storage instance here.
        if not isinstance(self.storage, (Storage, LazyObject)):
            self.storage = self.storage()
        super().__init__(*args, **kwargs)

    def find(self, path, all=False):
        """
        Look for files in the default file storage, if it's local.
        """
        try:
            self.storage.path('')
        except NotImplementedError:
            pass
        else:
            if self.storage.location not in searched_locations:
                searched_locations.append(self.storage.location)
            if self.storage.exists(path):
                match = self.storage.path(path)
                if all:
                    match = [match]
                return match
        return []

    def list(self, ignore_patterns):
        """
        List all files of the storage.
        """
        for path in utils.get_files(self.storage, ignore_patterns):
            yield path, self.storage


class DefaultStorageFinder(BaseStorageFinder):
    """
    A static files finder that uses the default storage backend.
    """
    storage = default_storage

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        base_location = getattr(self.storage, 'base_location', empty)
        if not base_location:
            raise ImproperlyConfigured("The storage backend of the "
                                       "staticfiles finder %r doesn't have "
                                       "a valid location." % self.__class__)


def find(path, all=False):
    """
    Find a static file with the given path using all enabled finders.

    If ``all`` is ``False`` (default), return the first matching
    absolute path (or ``None`` if no match). Otherwise return a list.
    """
    searched_locations[:] = []
    matches = []
    for finder in get_finders():
        result = finder.find(path, all=all)
        if not all and result:
            return result
        if not isinstance(result, (list, tuple)):
            result = [result]
        matches.extend(result)
    if matches:
        return matches
    # No match.
    return [] if all else None


def get_finders():
    for finder_path in settings.STATICFILES_FINDERS:
        yield get_finder(finder_path)


@functools.lru_cache(maxsize=None)
def get_finder(import_path):
    """
    Import the staticfiles finder class described by import_path, where
    import_path is the full Python path to the class.
    """
    Finder = import_string(import_path)
    if not issubclass(Finder, BaseFinder):
        raise ImproperlyConfigured('Finder "%s" is not a subclass of "%s"' %
                                   (Finder, BaseFinder))
    return Finder()
