Add 'include' to metadata to include other files. (#11)

Problem statement: I have a directory of files, and want
calendars for each (e.g. internal team events, public events).  And
then I want an "all.ics" that combines all others (or some subset of
others).

I could modify my Makefile to combile it different ways.  But I
would rather some way to not mix instructions and definitions.

Proposed solution: an `include` field.

  ```
  include:
    - other.yaml
    - third.yaml
  ```

  When the file is being loaded, all the events from these other files
  will be read and inserted into this calendar.  This also works
  recursively.  Paths are interpreted relatively

Author: rkdarst

tests/test_include.py

@@ -0,0 +1,59 @@
+import io
+import textwrap
+
+from yaml2ics import files_to_calendar
+
+
+def _read(f, mode=None):
+    if f == "a.yaml":
+        return io.StringIO(
+            textwrap.dedent(
+                """
+            name: NAME123
+            include:
+             - b.yaml
+             - c.yaml
+            events:
+              - summary: AAAAA
+                begin: 2021-04-22
+            """
+            )
+        )
+    if f == "b.yaml":
+        return io.StringIO(
+            textwrap.dedent(
+                """
+            include:
+             - d.yaml
+            events:
+              - summary: BBBBB
+                begin: 2021-04-22
+            """
+            )
+        )
+    else:
+        # Return template with summary of the letters
+        return io.StringIO(
+            textwrap.dedent(
+                """
+            events:
+              - summary: %s
+                begin: 2021-04-22
+            """
+                % (f[0].upper() * 5)
+            )
+        )
+
+
+def test_include_calendars(monkeypatch):
+    """Calendar that includes other calendars"""
+    monkeypatch.setitem(__builtins__, "open", _read)
+    cal = files_to_calendar(["a.yaml"])
+    cal_str = cal.serialize()
+    assert cal_str.startswith("BEGIN:VCALENDAR")
+    assert "AAAAA" in cal_str
+    assert "BBBBB" in cal_str
+    assert "CCCCC" in cal_str
+    assert "DDDDD" in cal_str
+    assert "NAME:NAME123" in cal_str
+    assert cal_str.endswith("END:VCALENDAR")

yaml2ics.py

@@ -95,8 +95,8 @@ def events_to_calendar(events: list) -> str:
     return cal
 
 
-def files_to_calendar(files: list) -> ics.Calendar:
-    """'main' function: list of files to our result"""
+def files_to_events(files: list) -> (ics.Calendar, str):
+    """Process files to a list of events"""
     all_events = []
     name = None
 
@@ -108,13 +108,26 @@ def files_to_calendar(files: list) -> ics.Calendar:
         tz = calendar_yaml.get("timezone", None)
         if tz is not None:
             tz = gettz(tz)
+        if "include" in calendar_yaml:
+            included_events, _name = files_to_events(
+                os.path.join(os.path.dirname(f), newfile)
+                for newfile in calendar_yaml["include"]
+            )
+            all_events.extend(included_events)
         for event in calendar_yaml.get("events", []):
             all_events.append(event_from_yaml(event, tz=tz))
 
         # We can only provide one calendar name, so we'll
         # keep the last one we find
         name = calendar_yaml.get("name", name)
 
+    return all_events, name
+
+
+def files_to_calendar(files: list) -> ics.Calendar:
+    """'main function: list of files to our result"""
+    all_events, name = files_to_events(files)
+
     calendar = events_to_calendar(all_events)
     if name is not None:
         calendar.extra.append(ics.ContentLine(name="NAME", value=name))