''' Boilerplate for constructing an email with the Python SendGrid v3 API.

Example Usage:

mail = SendGridEmail(
    subject='Test Email',
    to_email='customer@email.com',
    from_email='test@superdupertest.com',
    html_template='test.html'
)

mail.apply_subs([
    ('-name-', 'jimmy'),
    ('-company-', 'JimbosJellyBeans'),
])

mail.attach_item(
    file='test_file.txt',
    type_='text/plain',
    filename='Test File.txt',
    disposition='attachment',
    cid='TestFile'
)

response = mail.send()
print(response)
'''
import base64

import sendgrid
from sendgrid.helpers.mail import \
    Email, Content, Mail, Substitution, Attachment

from secrets import SENDGRID_API_KEY


class SendGridEmail:
    ''' A basic SendGrid email object constructor.

    Parameters:
        subject (str): email title.
        from_email (str): address to use as the sender.
        to_email (str): address to send the email to.
        html_template (str): path to the HTML to use as the email body.

    Attributes:
        mail (Mail): a SendGrid Mail object.
    '''

    def __init__(self, subject, from_email, to_email, html_template):
        self.subject = subject
        self.to_email = Email(to_email)
        self.from_email = Email(from_email)
        self.html_template = html_template
        self.mail = self._create_mail()

    def _create_mail(self):
        ''' Creates basic SendGrid Mail object.'''
        html = open(self.html_template, 'r').read()
        content = Content(type_='text/html', value=html)
        return Mail(self.from_email, self.subject, self.to_email, content)

    def _encode_file(self, file):
        ''' Return file contents as base64 encoded.'''
        with open(file, 'rb') as f:
            data = f.read()
            f.close()
        encoded = base64.b64encode(data).decode()
        return encoded

    def attach_item(self, file, type_, filename, disposition, cid):
        ''' Attach an item to the Mail object.'''
        attachment = Attachment()
        endoded_report = self._encode_file(file)
        attachment.content = endoded_report
        attachment.type = type_
        attachment.filename = filename
        attachment.disposition = disposition
        attachment.content_id = cid
        self.mail.add_attachment(attachment)

    def apply_subs(self, subs):
        ''' Substitute template tags in the HTML with variables.'''
        for sub in subs:
            tag, value = sub
            self.mail.personalizations[0].add_substitution(
                Substitution(tag, value)
            )

    def send(self):
        sg = sendgrid.SendGridAPIClient(apikey=SENDGRID_API_KEY)
        response = sg.client.mail.send.post(request_body=self.mail.get())
        status = response._status_code
        if not 200 <= status < 300:
            raise IOError('SendGrid response is {}'.format(status))
        return status