Add filter script for ics files.

This is a python script for python 3 using the vobject library to show
details about an ics file (text/calendar attachment).

Signed-off-by: Jens Grassel <jens@wegtam.com>
Tested-by: Moritz Poldrack <moritz@poldrack.dev>

Makefile

@@ -105,6 +105,7 @@ install: $(DOCS) aerc
 	install -m755 filters/hldiff $(DESTDIR)$(SHAREDIR)/filters/hldiff
 	install -m755 filters/html $(DESTDIR)$(SHAREDIR)/filters/html
 	install -m755 filters/plaintext $(DESTDIR)$(SHAREDIR)/filters/plaintext
+	install -m755 filters/show-ics-details.py $(DESTDIR)$(SHAREDIR)/filters/show-ics-details.py
 	install -m644 templates/new_message $(DESTDIR)$(SHAREDIR)/templates/new_message
 	install -m644 templates/quoted_reply $(DESTDIR)$(SHAREDIR)/templates/quoted_reply
 	install -m644 templates/forward_as_body $(DESTDIR)$(SHAREDIR)/templates/forward_as_body

filters/show-ics-details.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+
+"""Parse a vcard file given via stdin and output some details.
+Currently the following details are displayed if present:
+
+- start date and time
+- the summary information of the event
+- a list of attendees
+- the description of the event
+
+Please note: if multiple events are included in the data then only the
+first one will be parsed and displayed!
+
+REQUIREMENTS:
+- Python 3
+- Python 3 - vobject library
+
+To use as a filter in aerc, add the following line to your aerc.config:
+text/calendar=show-ics-details.py
+"""
+
+import re
+import sys
+
+import vobject
+
+
+def remove_mailto(message: str) -> str:
+    """Remove a possible existing 'mailto:' from the given message.
+
+    Keyword arguments:
+    message -- A message string.
+    """
+    return re.sub(r'^mailto:', '', message, flags=re.IGNORECASE)
+
+def extract_field(cal: vobject.icalendar.VCalendar2_0, name: str) -> str:
+    """Extract the desired field from the given calendar object.
+
+    Keyword arguments:
+    cal -- A VCalendar 2.0 object.
+    name -- The field name.
+    """
+    try:
+        match name.strip():
+            case 'attendees':
+                attendees = []
+                for attendee in cal.vevent.attendee_list:
+                    attendees.append(remove_mailto(attendee.valueRepr()).strip())
+                return ', '.join(attendees)
+            case 'description':
+                return cal.vevent.description.valueRepr().strip()
+            case 'dtstart':
+                return str(cal.vevent.dtstart.valueRepr()).strip()
+            case 'organizer':
+                return remove_mailto(cal.vevent.organizer.valueRepr()).strip()
+            case 'summary':
+                return cal.vevent.summary.valueRepr().strip()
+            case _:
+                return ''
+    except AttributeError:
+        return ''
+
+attendees   = ''
+description = ''
+dtstart     = ''
+error       = ''
+organizer   = ''
+summary     = ''
+
+try:
+    cal         = vobject.readOne(sys.stdin)
+    attendees   = extract_field(cal, 'attendees')
+    description = extract_field(cal, 'description')
+    dtstart     = extract_field(cal, 'dtstart')
+    organizer   = extract_field(cal, 'organizer')
+    summary     = extract_field(cal, 'summary')
+except vobject.base.ParseError:
+    error = '**Sorry, but we could not parse the calendar!**'
+
+if error:
+    print(error)
+    print("")
+
+print(f"Date/Time : {dtstart}")
+print(f"Summary   : {summary}")
+print(f"Organizer : {organizer}")
+print(f"Attendees : {attendees}")
+print("")
+print(description)