# -*- coding:utf8 -*-
"""
Author : Myth
Date   : 18/1/11
Email  : email4myth at gmail.com
"""

import email
import email.header
import hashlib

import chardet


def choose_alternative_part(subparts):
    return sorted(subparts, key=lambda m: 1 if m.get_content_subtype() == 'html' else 0, reverse=True)[0]


def walk(mail):
    if mail.is_multipart():
        subparts = mail.get_payload()
        content_type = mail.get_content_type()
        if content_type and content_type.lower() == 'multipart/alternative':
            prefer_subpart = choose_alternative_part(subparts)
            for subpart in walk(prefer_subpart):
                yield subpart
        else:
            for subpart in subparts:
                for subsubpart in walk(subpart):
                    yield subsubpart
    else:
        yield mail


def decode_header(header):
    rmsg = ''
    header = header.replace('"', '')
    for ret in email.header.decode_header(header):
        msg, charset = ret
        msg = decode_str(msg, charset)
        if not rmsg:
            rmsg += msg
        else:
            rmsg += ' ' + msg
    return rmsg


def is_attachment(msg):
    return bool(msg.get_filename())


def split_letter_and_attach(msgs):
    letters = []
    attachments = []

    for msg in msgs:
        if is_attachment(msg):
            attachments.append(msg)
        elif msg.get_content_maintype().lower() == 'text':  # 非附件只取文本类内容
            letters.append(msg)
    return letters, attachments


def decode_str(s, charset, errors='ignore'):
    if not s:
        return s

    if isinstance(s, unicode):
        return s

    if not charset:
        ret = chardet.detect(s)
        # {'confidence': 0.99, 'encoding': 'GB2312'}
        if ret:
            charset = ret.get('encoding')

        if not charset:
            charset = 'utf-8'

    return s.decode(charset, errors=errors)


def merge_letters(letters):
    content = u''

    for letter in letters:
        payload = letter.get_payload(decode=True)
        if not payload:
            continue

        charset = letter.get_content_charset()
        payload = decode_str(payload, charset)

        content += payload
        content += '\r\n\r\n'

    return content


def content_md5(content):
    return hashlib.md5(content).hexdigest()


def save_attachment(attachment):
    content = attachment.get_payload(decode=True)
    filename = decode_header(attachment.get_filename())
    md5 = content_md5(content)
    return {
        'filename': filename,
        'md5': md5,
        'content': content
    }


def parse_raw_mail(raw_mail, truncated):
    try:
        mail = email.message_from_string(raw_mail.lstrip())
    except Exception as e:
        print "error happened when get message from str: %s" % e
        return {
            'content': '',
            'attachments': []
        }
    msgs = list(walk(mail))
    if not msgs:
        return {
            'content': '',
            'attachments': []
        }

    if truncated and is_attachment(msgs[-1]):  # ignore last truncated attachment
        msgs.pop()

    letters, attachments = split_letter_and_attach(msgs)

    letter_content = merge_letters(letters)

    attach_infos = []
    for attach in attachments:
        attach_info = save_attachment(attach)
        attach_infos.append(attach_info)

    mail_info = {
        'content': letter_content,
        'attachments': attach_infos
    }
    return mail_info