import concurrent.futures
import email
import hashlib
import imaplib
import logging
import sys
import time
from email.header import decode_header
from email.utils import parsedate_to_datetime
from json import JSONEncoder
from pathlib import Path
from typing import List

import chardet

from iarchiver.email import extract_emails, normalize_for_imap_folder


def md5_chunked(data: bytes, size: int = 1024):
    m = hashlib.md5()
    for i in range(0, len(data), size):
        m.update(data[i:i + size])
    return m.hexdigest()


class FileAttachment:
    def __init__(self, file_name: str, file_hash: str):
        self.filename = file_name
        self.hash = file_hash

    def to_dict(self):
        return {'filename': self.filename, 'hash': self.hash}


class FileAttachmentEncoder(JSONEncoder):
    def default(self, o):
        if isinstance(o, FileAttachment):
            return o.to_dict()
        return super().default(o)


class MailConnection:
    def __init__(self, host: str, username: str, password: str, attachments_dir: Path):
        self.mail = imaplib.IMAP4_SSL(host)
        self.mail.login(username, password)
        self.attachments_dir = attachments_dir.expanduser().absolute().resolve()
        self.folder_structure = {}
        self.logger = logging.getLogger('iarchiver.mail_conn')
        self.logger.setLevel(logging.INFO)

    def load_folders(self):
        self.folder_structure = [f.decode().split(' "/" ')[1].replace('"', '').replace("\\'", "'") for f in self.mail.list()[1]]
        return self.folder_structure

    def __fetch_email(self, i):
        result, data = self.mail.uid('fetch', str(i), '(BODY[])')  # fetch the raw email
        if data[0] is None:
            return
        raw_email_bytes = data[0][1]
        try:
            detected = chardet.detect(raw_email_bytes)
        except TypeError as e:
            self.logger.critical(f'Failed to decode an email. Timeout? - {e}')
            sys.exit(1)
        encoding = detected['encoding']
        if not encoding:
            encoding = 'utf-8'
        raw_email = raw_email_bytes.decode(encoding, errors='replace')
        email_message = email.message_from_string(raw_email)
        date_header = email_message['Date']
        if not date_header:
            date_header = 0
        date = parsedate_to_datetime(date_header)
        unix_timestamp = int(time.mktime(date.timetuple()))

        from_addr = email_message['From']
        to_addr = email_message['To']
        if not from_addr and not to_addr:
            return
        if not from_addr:
            from_addr = ''
        if not to_addr:
            to_addr = ''

        from_header = ', '.join(extract_emails(from_addr))
        to_header = ', '.join(extract_emails(to_addr))
        if '@' not in from_header:
            from_header = from_addr
        if '@' not in to_header:
            to_header = to_addr

        subject_header = email_message['Subject']
        if subject_header:
            subject = decode_header(subject_header)[0][0]
            if isinstance(subject, bytes):
                try:
                    detected = chardet.detect(subject)
                    encoding = detected['encoding']
                    if not encoding:
                        encoding = 'utf-8'
                    subject = subject.decode(encoding, errors='replace')
                except UnicodeDecodeError:
                    subject = subject.decode('utf-8')
        else:
            return

        attachments = []
        if email_message.is_multipart():
            for part in email_message.walk():
                # content_type = part.get_content_type()
                content_disposition = str(part.get("Content-Disposition"))
                if "attachment" in content_disposition:
                    filename = part.get_filename()
                    if filename:
                        # The filename of the file is the hash of its content, which should de-duplicate files.
                        filecontents = part.get_payload(decode=True)
                        if not filecontents:
                            continue
                        filehash = md5_chunked(filecontents)
                        part.set_payload(f'MD5:{filehash}')  # replace the attachment with its hash
                        filepath = self.attachments_dir / filehash
                        file_obj = FileAttachment(filename, filehash)
                        if not filepath.is_file():
                            with open(filepath, 'wb') as f:
                                f.write(filecontents)
                        attachments.append(file_obj)
        raw_email_clean = email_message.as_string()
        return unix_timestamp, to_header, from_header, subject, raw_email_clean, attachments

    def fetch_folder(self, folder: str, search_criterion: List[str] = None, max_threads: int = 1):
        """
        Don't use multiple threads because most mail servers don't allow the client to multiplex.
        """
        if not search_criterion:
            search_criterion = ['ALL']
        self.mail.select(normalize_for_imap_folder(folder))
        for search_item in search_criterion:
            result, data = self.mail.uid('search', search_item)
            mail_ids = data[0]
            id_list = mail_ids.split()
            if not len(id_list):
                # Empty folder
                return
            first_email_id = int(id_list[0])
            latest_email_id = int(id_list[-1])

            with concurrent.futures.ThreadPoolExecutor(max_workers=max_threads) as executor:
                futures = {executor.submit(self.__fetch_email, i) for i in range(latest_email_id, first_email_id, -1)}
                for future in concurrent.futures.as_completed(futures):
                    result = future.result()
                    if result is not None:
                        yield result