import logging
from dataclasses import dataclass
from typing import List

from django.contrib.auth.models import User
from django.utils import timezone

from bookmarks.models import Bookmark, Tag
from bookmarks.services import tasks
from bookmarks.services.parser import parse, NetscapeBookmark
from bookmarks.utils import parse_timestamp

logger = logging.getLogger(__name__)


@dataclass
class ImportResult:
    total: int = 0
    success: int = 0
    failed: int = 0


@dataclass
class ImportOptions:
    map_private_flag: bool = False


class TagCache:
    def __init__(self, user: User):
        self.user = user
        self.cache = dict()
        # Init cache with all existing tags for that user
        tags = Tag.objects.filter(owner=user)
        for tag in tags:
            self.put(tag)

    def get(self, tag_name: str):
        tag_name_lowercase = tag_name.lower()
        if tag_name_lowercase in self.cache:
            return self.cache[tag_name_lowercase]
        else:
            return None

    def get_all(self, tag_names: List[str]):
        result = []
        for tag_name in tag_names:
            tag = self.get(tag_name)
            # Prevent returning duplicates
            if not (tag in result):
                result.append(tag)

        return result

    def put(self, tag: Tag):
        self.cache[tag.name.lower()] = tag


def import_netscape_html(html: str, user: User, options: ImportOptions = ImportOptions()) -> ImportResult:
    result = ImportResult()
    import_start = timezone.now()

    try:
        netscape_bookmarks = parse(html)
    except:
        logging.exception('Could not read bookmarks file.')
        raise

    parse_end = timezone.now()
    logger.debug(f'Parse duration: {parse_end - import_start}')

    # Create and cache all tags beforehand
    _create_missing_tags(netscape_bookmarks, user)
    tag_cache = TagCache(user)

    # Split bookmarks to import into batches, to keep memory usage for bulk operations manageable
    batches = _get_batches(netscape_bookmarks, 200)
    for batch in batches:
        _import_batch(batch, user, options, tag_cache, result)

    # Create snapshots for newly imported bookmarks
    tasks.schedule_bookmarks_without_snapshots(user)
    # Load favicons for newly imported bookmarks
    tasks.schedule_bookmarks_without_favicons(user)

    end = timezone.now()
    logger.debug(f'Import duration: {end - import_start}')

    return result


def _create_missing_tags(netscape_bookmarks: List[NetscapeBookmark], user: User):
    tag_cache = TagCache(user)
    tags_to_create = []

    for netscape_bookmark in netscape_bookmarks:
        for tag_name in netscape_bookmark.tag_names:
            tag = tag_cache.get(tag_name)
            if not tag:
                tag = Tag(name=tag_name, owner=user)
                tag.date_added = timezone.now()
                tags_to_create.append(tag)
                tag_cache.put(tag)

    Tag.objects.bulk_create(tags_to_create)


def _get_batches(items: List, batch_size: int):
    batches = []
    offset = 0
    num_items = len(items)

    while offset < num_items:
        batch = items[offset:min(offset + batch_size, num_items)]
        if len(batch) > 0:
            batches.append(batch)
        offset = offset + batch_size

    return batches


def _import_batch(netscape_bookmarks: List[NetscapeBookmark],
                  user: User,
                  options: ImportOptions,
                  tag_cache: TagCache,
                  result: ImportResult):
    # Query existing bookmarks
    batch_urls = [bookmark.href for bookmark in netscape_bookmarks]
    existing_bookmarks = Bookmark.objects.filter(owner=user, url__in=batch_urls)

    # Create or update bookmarks from parsed Netscape bookmarks
    bookmarks_to_create = []
    bookmarks_to_update = []

    for netscape_bookmark in netscape_bookmarks:
        result.total = result.total + 1
        try:
            # Lookup existing bookmark by URL, or create new bookmark if there is no bookmark for that URL yet
            bookmark = next(
                (bookmark for bookmark in existing_bookmarks if bookmark.url == netscape_bookmark.href), None)
            if not bookmark:
                bookmark = Bookmark(owner=user)
                is_update = False
            else:
                is_update = True
            # Copy data from parsed bookmark
            _copy_bookmark_data(netscape_bookmark, bookmark, options)
            # Validate bookmark fields, exclude owner to prevent n+1 database query,
            # also there is no specific validation on owner
            bookmark.clean_fields(exclude=['owner'])
            # Schedule for update or insert
            if is_update:
                bookmarks_to_update.append(bookmark)
            else:
                bookmarks_to_create.append(bookmark)

            result.success = result.success + 1
        except:
            shortened_bookmark_tag_str = str(netscape_bookmark)[:100] + '...'
            logging.exception('Error importing bookmark: ' + shortened_bookmark_tag_str)
            result.failed = result.failed + 1

    # Bulk update bookmarks in DB
    Bookmark.objects.bulk_update(bookmarks_to_update, ['url',
                                                       'date_added',
                                                       'date_modified',
                                                       'unread',
                                                       'shared',
                                                       'title',
                                                       'description',
                                                       'notes',
                                                       'owner'])
    # Bulk insert new bookmarks into DB
    Bookmark.objects.bulk_create(bookmarks_to_create)

    # Bulk assign tags
    # In Django 3, bulk_create does not return the auto-generated IDs when bulk inserting,
    # so we have to reload the inserted bookmarks, and match them to the parsed bookmarks by URL
    existing_bookmarks = Bookmark.objects.filter(owner=user, url__in=batch_urls)

    BookmarkToTagRelationShip = Bookmark.tags.through
    relationships = []

    for netscape_bookmark in netscape_bookmarks:
        # Lookup bookmark by URL again
        bookmark = next(
            (bookmark for bookmark in existing_bookmarks if bookmark.url == netscape_bookmark.href), None)

        if not bookmark:
            # Something is wrong, we should have just created this bookmark
            shortened_bookmark_tag_str = str(netscape_bookmark)[:100] + '...'
            logging.warning(
                f'Failed to assign tags to the bookmark: {shortened_bookmark_tag_str}. Could not find bookmark by URL.')
            continue

        # Get tag models by string, schedule inserts for bookmark -> tag associations
        tags = tag_cache.get_all(netscape_bookmark.tag_names)
        for tag in tags:
            relationships.append(BookmarkToTagRelationShip(bookmark=bookmark, tag=tag))

    # Insert all bookmark -> tag associations at once, should ignore errors if association already exists
    BookmarkToTagRelationShip.objects.bulk_create(relationships, ignore_conflicts=True)


def _copy_bookmark_data(netscape_bookmark: NetscapeBookmark, bookmark: Bookmark, options: ImportOptions):
    bookmark.url = netscape_bookmark.href
    if netscape_bookmark.date_added:
        bookmark.date_added = parse_timestamp(netscape_bookmark.date_added)
    else:
        bookmark.date_added = timezone.now()
    bookmark.date_modified = bookmark.date_added
    bookmark.unread = netscape_bookmark.to_read
    if netscape_bookmark.title:
        bookmark.title = netscape_bookmark.title
    if netscape_bookmark.description:
        bookmark.description = netscape_bookmark.description
    if netscape_bookmark.notes:
        bookmark.notes = netscape_bookmark.notes
    if options.map_private_flag and not netscape_bookmark.private:
        bookmark.shared = True
    if netscape_bookmark.archived:
        bookmark.is_archived = True