import tempfile
import types

from django.db.models.loading import cache
from django.utils.functional import wraps

from imagekit.lib import Image, ImageFile


def img_to_fobj(img, format, **kwargs):
    tmp = tempfile.TemporaryFile()
    try:
        img.save(tmp, format, **kwargs)
    except IOError:
        # PIL can have problems saving large JPEGs if MAXBLOCK isn't big enough,
        # So if we have a problem saving, we temporarily increase it. See
        # http://github.com/jdriscoll/django-imagekit/issues/50
        old_maxblock = ImageFile.MAXBLOCK
        ImageFile.MAXBLOCK = img.size[0] * img.size[1]
        try:
            img.save(tmp, format, **kwargs)
        finally:
            ImageFile.MAXBLOCK = old_maxblock
    tmp.seek(0)
    return tmp


def get_spec_files(instance):
    try:
        return instance._ik.spec_files
    except AttributeError:
        return []


def open_image(target):
    target.seek(0)
    img = Image.open(target)
    img.copy = types.MethodType(_wrap_copy(img.copy), img, img.__class__)
    return img


def _wrap_copy(f):
    @wraps(f)
    def copy(self):
        img = f()
        try:
            img.app = self.app
        except AttributeError:
            pass
        try:
            img._getexif = self._getexif
        except AttributeError:
            pass
        return img
    return copy


class UnknownExtensionError(Exception):
    pass


class UnknownFormatError(Exception):
    pass


_pil_init = 0


def _preinit_pil():
    """Loads the standard PIL file format drivers. Returns True if ``preinit()``
    was called (and there's a potential that more drivers were loaded) or False
    if there is no possibility that new drivers were loaded.

    """
    global _pil_init
    if _pil_init < 1:
        Image.preinit()
        _pil_init = 1
        return True
    return False


def _init_pil():
    """Loads all PIL file format drivers. Returns True if ``init()`` was called
    (and there's a potential that more drivers were loaded) or False if there is
    no possibility that new drivers were loaded.

    """
    global _pil_init
    _preinit_pil()
    if _pil_init < 2:
        Image.init()
        _pil_init = 2
        return True
    return False


def _extension_to_format(extension):
    return Image.EXTENSION.get(extension.lower())


def _format_to_extension(format):
    if format:
        for k, v in Image.EXTENSION.iteritems():
            if v == format.upper():
                return k
    return None


def extension_to_format(extension):
    """Returns the format that corresponds to the provided extension.

    """
    format = _extension_to_format(extension)
    if not format and _preinit_pil():
        format = _extension_to_format(extension)
    if not format and _init_pil():
        format = _extension_to_format(extension)
    if not format:
        raise UnknownExtensionError(extension)
    return format


def format_to_extension(format):
    """Returns the first extension that matches the provided format.

    """
    extension = None
    if format:
        extension = _format_to_extension(format)
        if not extension and _preinit_pil():
            extension = _format_to_extension(format)
        if not extension and _init_pil():
            extension = _format_to_extension(format)
    if not extension:
        raise UnknownFormatError(format)
    return extension


def _get_models(apps):
    models = []
    for app_label in apps or []:
        app = cache.get_app(app_label)
        models += [m for m in cache.get_models(app)]
    return models


def invalidate_app_cache(apps):
    for model in _get_models(apps):
        print 'Invalidating cache for "%s.%s"' % (model._meta.app_label, model.__name__)
        for obj in model._default_manager.order_by('-pk'):
            for f in get_spec_files(obj):
                f.invalidate()


def validate_app_cache(apps, force_revalidation=False):
    for model in _get_models(apps):
        for obj in model._default_manager.order_by('-pk'):
            model_name = '%s.%s' % (model._meta.app_label, model.__name__)
            if force_revalidation:
                print 'Invalidating & validating cache for "%s"' % model_name
            else:
                print 'Validating cache for "%s"' % model_name
            for f in get_spec_files(obj):
                if force_revalidation:
                    f.invalidate()
                f.validate()