import base64
import email
import json
import logging
import os
import sys

from apiclient import errors
from pathlib import Path
from pytz import timezone
from send_email import get_gmail_service
from email.message import EmailMessage
from email.utils import parsedate_to_datetime


def ListMessagesWithLabels(service, user_id, label_ids=[]):
    """List all Messages of the user's mailbox with label_ids applied.

    Args:
     service: Authorized Gmail API service instance.
     user_id: User's email address. The special value "me"
     can be used to indicate the authenticated user.
     label_ids: Only return Messages with these labelIds applied.

    Returns:
     List of Messages that have all required Labels applied. Note that the
     returned list contains Message IDs, you must use get with the
     appropriate id to get the details of a Message.
    """
    try:
        response = service.users().messages().list(userId=user_id,
                                                   labelIds=label_ids).execute()
        if 'messages' in response:
            yield from response['messages']
        while 'nextPageToken' in response:
            page_token = response['nextPageToken']
            response = service.users().messages().list(userId=user_id,
                                                       labelIds=label_ids,
                                                       pageToken=page_token).execute()
            yield from response['messages']

    except errors.HttpError as error:
        print(json.loads(error.content.decode('utf-8'))['error']['message'])


def ListHistory(service, user_id, label_id=None, start_history_id=10000):
    """List History of all changes to the user's mailbox.

    Args:
    service: Authorized Gmail API service instance.
    user_id: User's email address. The special value "me"
    can be used to indicate the authenticated user.
    start_history_id: Only return Histories at or after start_history_id.

    Returns:
    A list of mailbox changes that occurred after the start_history_id.
    """
    history = (service.users().history().list(userId=user_id,
                                              startHistoryId=start_history_id,
                                              historyTypes="messageAdded",
                                              labelId=label_id)
               .execute())
    changes = history['history'] if 'history' in history else []
    for change in changes:
        if 'messagesAdded' in change:
            for c in change['messagesAdded']:
                yield c['message']

    while 'nextPageToken' in history:
        page_token = history['nextPageToken']
        history = (service.users().history().list(userId=user_id,
                                                  startHistoryId=start_history_id,
                                                  pageToken=page_token).execute())
        for change in history['history']:
            if 'messagesAdded' in change:
                for c in change['messagesAdded']:
                    yield c['message']

def labels_dict(service, user_id):
    """Returns a dictionary mapping labels to labelids.

    Args:
     service: Authorized Gmail API service instance.
     user_id: User's email address. The special value "me"

    Returns:
     dictionary mapping labels to labelids.
    """
    try:
        response = service.users().labels().list(userId=user_id).execute()
        labels = response['labels']
        return {label['name']: label['id'] for label in labels}
    except errors.HttpError as error:
        print(json.loads(error.content.decode('utf-8'))['error']['message'])

class GmailMessage(EmailMessage):
    _labels = labels_dict(EmailMessage._service, 'me')

    def msgdict(self):
        return {'raw': base64.urlsafe_b64encode(self.as_bytes()).decode()}

    def send(self):
        try:
            message = (self._service.users().messages().
                       send(userId='me',body=self.msgdict())
                       .execute())
            print('Message Id: %s' % message['id'])
        except errors.HttpError as error:
            print('An error occurred: %s' % error)

    @staticmethod
    def list_msg_ids(label, start_history_id=None):
        if start_history_id is not None:
            return ListHistory(EmailMessage._service,
                               'me',
                               label_id=GmailMessage._labels[label],
                               start_history_id=start_history_id)
        else:
            return ListMessagesWithLabels(EmailMessage._service,
                                          'me',
                                          label_ids=[GmailMessage._labels[label]])

    @classmethod
    def from_id(cls, msg_id, user_id='me'):
        try:
            message = (cls._service.users().messages().
                       get(userId=user_id, id=msg_id, format='raw').execute())
            instance = email.message_from_bytes(
                base64.urlsafe_b64decode(message['raw']),
                policy=email.policy.EmailPolicy())
            instance.history_id = message['historyId']
            return instance
        except errors.HttpError as error:
            print(json.loads(error.content.decode('utf-8'))['error']['message'])

def save_emails(update=True):
    """Download new emails that were labeled swaptions."""
    DATA_DIR = Path(os.getenv("DATA_DIR"))

    if update:
        try:
            last_history_id = int((DATA_DIR / ".lastHistoryId").read_text())
        except FileNotFoundError:
            logging.error("can't find .lastHistoryId file")
            sys.exit()
        existing_msgs = []
    else:
        p = DATA_DIR / "swaptions"
        existing_msgs = set(str(x).split("_")[1] for x in p.iterdir() if x.is_file())
        last_history_id = None

    for msg in GmailMessage.list_msg_ids('swaptions', last_history_id):
        if msg['id'] in existing_msgs:
            continue
        try:
            message = GmailMessage.from_id(msg['id'])
            logging.info(message.history_id)
            subject = message['subject']
            date = parsedate_to_datetime(message['date'])
            if date.tzinfo is None:
                date = date.replace(tzinfo=timezone('utc'))
            date = date.astimezone(timezone('America/New_York'))
            body = message.get_body('plain')
            content = body.get_content()
        except (KeyError, UnicodeDecodeError, AttributeError) as e:
            logging.error("error decoding " + msg['id'])
            continue
        else:
            email = (DATA_DIR / "swaptions" /
                     f"{date:%Y-%m-%d %H-%M-%S}_{msg['id']}")
            with email.open("w") as fh:
                fh.write(subject + "\r\n")
                fh.write(content)
    try:
        new_history_id = message.history_id
        (DATA_DIR / ".lastHistoryId").write_text(message.history_id)
    except UnboundLocalError:
        pass

if __name__ == '__main__':
    try:
        save_emails()
    except errors.HttpError as e:
        logging.error(e)
        save_emails(update=False)