import datetime

from .. import db
from .exceptions import *

class BaseStorage:
    def __init__(self, app):
        self.app = app

    def verify_file(self, file):
        user = file.user_id is not None
        size_limit = self.app.config.get('USER_FILE_SIZE_LIMIT' if user else 'ANONYMOUS_FILE_SIZE_LIMIT')
        if size_limit is not None and file.size > size_limit:
            raise FileSizeError('The file size is too large (max {})'.format(db.File.pretty_size(size_limit)))

    def add_file(self, file_hash, filename, size, user=None, ip=None, verify=True):
        '''Adds the file to the database.

        Call from store_file after the file is successfully stored.'''
        with db.session_scope() as sess:
            f = db.File(file_hash, filename, size, datetime.datetime.utcnow(), user.id if user else None, ip)
            # Raises on invalid files
            self.verify_file(f)
            sess.add(f)
            sess.commit()
            sess.refresh(f)
        return f

    def store_file(self, uploaded_file, file_hash, filename, user, ip):
        '''Store uploaded_file.'''
        raise NotImplementedError()

    def get_file(self, f):
        '''Return a file object for the specified file.

        Subclasses can also return a flask.Response instance if required.'''
        raise NotImplementedError()

    def delete_file(self, f):
        '''Delete the specified file.'''
        raise NotImplementedError()

    def temp_file(self, f):
        '''Context manager which returns a temporary file for reading.

        This is used internally for eg. thumbnails.'''
        raise NotImplementedError()

    def get_thumbnail(self, f):
        '''Return a file object for the specified file's thumbnail.

        Subclasses can also return a flask.Response instance if required.'''
        raise NotImplementedError()

    def store_thumbnail(self, f, stream):
        '''Store thumbnail for the specified file.'''
        raise NotImplementedError()