Extracts body of gmail mail

extract_body_from_gmail_mail.py

'''
Example of usage:
from googleapiclient.discovery import build
from httplib2 import Http
from oauth2client import file

# Create google client first, for example
storage = file.Storage('path_to_google_oauth_credentials')
creds = storage.get()
http = creds.authorize(Http())
gmail_client = build('gmail', 'v1', http=http)

# then retrieve mail data by API call
gmail_message_id = 12345
gmail_mail = gmail_client.users().messages().get(userId='me', id=gmail_message_id).execute()

# finally, extract mail body
mail_body = get_mail_body(gmail_mail['payload'])
'''

import base64
from typing import List

def get_mail_body(payload: dict) -> str:
    if payload['mimeType'] in ('text/html', 'text/plain'):
        data = payload['body'].get('data')
        if data:
            return encode_decode_body(data)

    for part in sort_parts_by_mime_type(payload.get('parts', [])):
        return get_mail_body(part)

    return payload.get('snippet', 'Can not read gmail body')

def encode_decode_body(body: str) -> str:
    return base64.urlsafe_b64decode(body.encode('ASCII')).decode()

def sort_parts_by_mime_type(parts: List) -> List:
    res = []
    for mime_type in ('text/html', 'text/plain'):  # try to extract HTML first, then plain text
        for p in parts:
            if p['mimeType'] == mime_type:
                res.append(p)
    for p in parts:
        if p['mimeType'].startswith('multipart'):
            res.append(p)
    return res