"""Forms for the user_photos application."""
import hashlib
import os.path
import urlparse

from django import forms
from django.conf import settings

from core.download import download_file
from core.functions import remove_file, TemporaryFile
from core.images.upload import process_upload
from core.services import get_redis_connection
from user_photos.models import Photo


def rate_limit(key, limit, seconds):
    """Use Redis to do a rate limit check. Returns True if the limit is violated
    and False otherwise.

    key - the key to check in Redis
    limit - the rate limit maximum value
    seconds - the rate limit period in seconds

    """
    conn = get_redis_connection()
    val = conn.incr(key)
    if val == 1:
        conn.expire(key, seconds)
    return val > limit


def rate_limit_user(user):
    """Shared function to rate limit user uploads."""
    key = 'user_photos:counts:' + user.username
    limit = settings.USER_PHOTOS_RATE_LIMIT
    if rate_limit(key, *limit):
        raise forms.ValidationError("You've exceeded your upload quota. "
                "Please try again later.")


class UploadForm(forms.Form):
    image_file = forms.ImageField()

    def __init__(self, *args, **kwargs):
        self.user = kwargs.pop('user')
        super(UploadForm, self).__init__(*args, **kwargs)

    def clean(self):
        cleaned_data = super(UploadForm, self).clean()
        rate_limit_user(self.user)
        return cleaned_data

    def save(self):
        """Processes the image and creates a new Photo object, which is saved to
        the database. The new Photo instance is returned.

        Note that we do de-duplication. A signature is computed for the photo.
        If the user has already uploaded a file with the same signature, that
        photo object is returned instead.

        This function should only be called if is_valid() returns True.

        """
        # Check for duplicate uploads from this user
        signature = self._signature()
        try:
            return Photo.objects.get(user=self.user, signature=signature)
        except Photo.DoesNotExist:
            pass

        # Trying to use PIL (or Pillow) on a Django UploadedFile is often
        # problematic because the file is often an in-memory file if it is under
        # a certain size. This complicates matters and many of the operations we try
        # to perform on it fail if this is the case. To get around these issues,
        # we make a copy of the file on the file system and operate on the copy.

        fp = self.cleaned_data['image_file']
        ext = os.path.splitext(fp.name)[1]

        # Write the UploadedFile to a temporary file on disk
        with TemporaryFile(suffix=ext) as t:
            for chunk in fp.chunks():
                t.file.write(chunk)
            t.file.close()

            url, thumb_url = process_upload(self.user, t.filename)

        photo = Photo(user=self.user, url=url, thumb_url=thumb_url,
                signature=signature)
        photo.save()
        return photo

    def _signature(self):
        """Calculates and returns a signature for the image file as a hex digest
        string.

        This function should only be called if is_valid() is True.

        """
        fp = self.cleaned_data['image_file']
        md5 = hashlib.md5()
        for chunk in fp.chunks():
            md5.update(chunk)
        return md5.hexdigest()


class HotLinkImageForm(forms.Form):
    """Form for hot-linking images. If the supplied URL's host is on
    a white-list, return it as-is. Otherwise attempt to download the image at
    the given URL and upload it into our S3 storage. The URL to the new location
    is returned.
    """
    url = forms.URLField()

    def __init__(self, *args, **kwargs):
        self.user = kwargs.pop('user')
        super(HotLinkImageForm, self).__init__(*args, **kwargs)

    def clean_url(self):
        the_url = self.cleaned_data['url']
        self.url_parts = urlparse.urlsplit(the_url)
        if self.url_parts.scheme not in ['http', 'https']:
            raise forms.ValidationError("Invalid URL scheme")
        return the_url

    def clean(self):
        cleaned_data = super(HotLinkImageForm, self).clean()
        rate_limit_user(self.user)
        return cleaned_data

    def save(self):
        url = self.url_parts.geturl()
        if (self.url_parts.scheme == 'https' and
                self.url_parts.hostname in settings.USER_IMAGES_SOURCES):
            return url

        # Try to download the file
        with remove_file(download_file(url)) as path:
            url, _ = process_upload(self.user, path)

        return url