Add page to create new letter branding

This has a form with 3 fields - the file upload field, logo name, and an
optional logo domain. Logos need to be uploaded in `.svg` format and we
then convert this to `.png` format and upload both file types to S3 as
well as saving the letter branding details in the database.

app/main/__init__.py

@@ -29,6 +29,7 @@ from app.main.views import (  # noqa
     find_users,
     platform_admin,
     email_branding,
+    letter_branding,
     conversation,
     organisations,
     notifications,

app/main/forms.py

@@ -851,6 +851,21 @@ class ServiceUpdateEmailBranding(StripWhitespaceForm):
             raise ValidationError('This field is required')
 
 
+class SVGFileUpload(StripWhitespaceForm):
+    file = FileField_wtf(
+        'Upload an SVG logo',
+        validators=[
+            FileAllowed(['svg'], 'SVG Images only!'),
+            DataRequired(message="You need to upload a file to submit")
+        ]
+    )
+
+
+class ServiceLetterBrandingDetails(StripWhitespaceForm):
+    name = StringField('Name of brand', validators=[DataRequired()])
+    domain = GovernmentDomainField('Domain')
+
+
 class PDFUploadForm(StripWhitespaceForm):
     file = FileField_wtf(
         'Upload a letter in PDF format to check if it fits in the printable area',

app/main/views/letter_branding.py

@@ -0,0 +1,103 @@
+from flask import (
+    current_app,
+    redirect,
+    render_template,
+    request,
+    session,
+    url_for,
+)
+from flask_login import login_required
+from requests import get as requests_get
+
+from app import letter_branding_client
+from app.main import main
+from app.main.forms import ServiceLetterBrandingDetails, SVGFileUpload
+from app.s3_client.s3_logo_client import (
+    LETTER_TEMP_TAG,
+    delete_letter_temp_file,
+    delete_letter_temp_files_created_by,
+    get_letter_filename_with_no_path_or_extension,
+    letter_filename_for_db,
+    permanent_letter_logo_name,
+    persist_logo,
+    upload_letter_png_logo,
+    upload_letter_temp_logo,
+)
+from app.utils import get_logo_cdn_domain, user_is_platform_admin
+
+
+@main.route("/letter-branding/create", methods=['GET', 'POST'])
+@main.route("/letter-branding/create/<path:logo>", methods=['GET', 'POST'])
+@login_required
+@user_is_platform_admin
+def create_letter_branding(logo=None):
+    file_upload_form = SVGFileUpload()
+    letter_branding_details_form = ServiceLetterBrandingDetails()
+
+    file_upload_form_submitted = file_upload_form.file.data
+    details_form_submitted = request.form.get('operation') == 'branding-details'
+
+    if file_upload_form_submitted and file_upload_form.validate_on_submit():
+        upload_filename = upload_letter_temp_logo(
+            file_upload_form.file.data.filename,
+            file_upload_form.file.data,
+            current_app.config['AWS_REGION'],
+            user_id=session["user_id"]
+        )
+
+        if logo and logo.startswith(LETTER_TEMP_TAG.format(user_id=session['user_id'])):
+            delete_letter_temp_file(logo)
+
+        return redirect(url_for('.create_letter_branding', logo=upload_filename))
+
+    if details_form_submitted and letter_branding_details_form.validate_on_submit():
+        if logo:
+            db_filename = letter_filename_for_db(logo, session['user_id'])
+
+            letter_branding_client.create_letter_branding(
+                filename=db_filename,
+                name=letter_branding_details_form.name.data,
+                domain=letter_branding_details_form.domain.data,
+            )
+
+            png_file = get_png_file_from_svg(logo)
+
+            persist_logo(logo, permanent_letter_logo_name(db_filename, 'svg'))
+
+            upload_letter_png_logo(
+                permanent_letter_logo_name(db_filename, 'png'),
+                png_file,
+                current_app.config['AWS_REGION'],
+            )
+
+            delete_letter_temp_files_created_by(session['user_id'])
+
+            # TODO: redirect to all letter branding page once it exists
+            return redirect(url_for('main.platform_admin'))
+
+        # Show error on upload form if trying to submit with no logo
+        file_upload_form.validate()
+
+    return render_template(
+        'views/letter-branding/manage-letter-branding.html',
+        file_upload_form=file_upload_form,
+        letter_branding_details_form=letter_branding_details_form,
+        cdn_url=get_logo_cdn_domain(),
+        logo=logo
+    )
+
+
+def get_png_file_from_svg(filename):
+    filename_for_template_preview = get_letter_filename_with_no_path_or_extension(filename)
+
+    template_preview_svg_endpoint = '{}/{}.svg.png'.format(
+        current_app.config['TEMPLATE_PREVIEW_API_HOST'],
+        filename_for_template_preview
+    )
+
+    response = requests_get(
+        template_preview_svg_endpoint,
+        headers={'Authorization': 'Token {}'.format(current_app.config['TEMPLATE_PREVIEW_API_KEY'])}
+    )
+
+    return response.content