feat: provide logos via jinja method (#59) (#61)

Co-authored-by: Raffael Meyer <14891507+barredterra@users.noreply.github.com>

README.md

@@ -153,6 +153,22 @@ The following fields of the **Sales Invoice** are currently considered for the e
 
 Document-level discounts are currently not supported, because the e invoice standard requires much more information than just the discount amount (e.g. the reason and applicable VAT rate).
 
+#### Embedding the Factur-X logo
+
+If you like, you can embed one of the official Factur-X logos in your invoice PDF. This way, a human can easily identify the invoice as a Factur-X eInvoice.
+
+To do this, use the `get_einvoice_logo` method in your jinja **Print Format**. This method returns a base64-encoded data URL, which can be used in an `<img>` tag.
+
+```jinja
+<img src="{{ get_einvoice_logo(doc.einvoice_profile) }}" alt="{{ doc.einvoice_profile }} e-invoice logo" />
+```
+
+The following logos are available:
+
+BASIC | EN 16931 | EXTENDED
+--- | --- | ---
+![BASIC](eu_einvoice/public/img/fx-basic.png) | ![EN 16931](eu_einvoice/public/img/fx-en16931.png) | ![EXTENDED](eu_einvoice/public/img/fx-extended.png)
+
 ### Purchase Invoice
 
 To import a new eInvoice, create a new **E Invoice Import** and upload the XML or PDF file.

eu_einvoice/hooks.py

@@ -77,10 +77,11 @@
 # ----------
 
 # add methods and filters to jinja environment
-# jinja = {
-# 	"methods": "eu_einvoice.utils.jinja_methods",
-# 	"filters": "eu_einvoice.utils.jinja_filters"
-# }
+jinja = {
+	"methods": [
+		"eu_einvoice.jinja.get_einvoice_logo",
+	],
+}
 
 # Installation
 # ------------

eu_einvoice/jinja.py

@@ -0,0 +1,21 @@
+import base64
+from pathlib import Path
+from typing import Literal
+
+PROFILE_TO_LOGO = {
+	"BASIC": "public/img/fx-basic.png",
+	"EN 16931": "public/img/fx-en16931.png",
+	"EXTENDED": "public/img/fx-extended.png",
+}
+
+
+def get_einvoice_logo(profile: Literal["BASIC", "EN 16931", "EXTENDED"]) -> str | None:
+	"""Return the logo for the given profile, as a base64 encoded data URL."""
+	if profile not in PROFILE_TO_LOGO:
+		return None
+
+	logo_path = Path(__file__).parent / PROFILE_TO_LOGO.get(profile)
+	logo_bytes = logo_path.read_bytes()
+	logo_base64 = base64.b64encode(logo_bytes).decode("utf-8")
+
+	return f"data:image/png;base64,{logo_base64}"