feat: add is_nth_weekday() and parse_occurrence() for scheduled comment gating

app/services/platforms/reddit_comment.py

@@ -0,0 +1,45 @@
+from __future__ import annotations
+
+import logging
+from datetime import date, timedelta
+
+import httpx
+
+from app.services.platforms.base import PostingStrategy, PostResult
+
+logger = logging.getLogger(__name__)
+
+# Weekday names → int (0=Mon, 6=Sun)
+_WEEKDAY_MAP = {
+    "monday": 0, "tuesday": 1, "wednesday": 2, "thursday": 3,
+    "friday": 4, "saturday": 5, "sunday": 6,
+}
+# Ordinal names → n
+_ORDINAL_MAP = {"first": 1, "second": 2, "third": 3}
+
+
+def is_nth_weekday(dt: date, weekday: int, n: int) -> bool:
+    """True if dt is the nth occurrence of weekday (0=Mon, 6=Sun) in its month."""
+    first_of_month = dt.replace(day=1)
+    days_until = (weekday - first_of_month.weekday()) % 7
+    first_occurrence = first_of_month + timedelta(days=days_until)
+    nth_occurrence = first_occurrence + timedelta(weeks=n - 1)
+    return dt == nth_occurrence
+
+
+def parse_occurrence(occurrence: str | None) -> tuple[int, int] | None:
+    """Parse an occurrence string into (weekday, n) or None for 'every'.
+
+    Supported: "first_sunday", "second_monday", "third_friday", etc.
+    Returns None for "every" or None input.
+    Raises ValueError for unrecognised patterns.
+    """
+    if occurrence is None or occurrence == "every":
+        return None
+    parts = occurrence.lower().split("_", 1)
+    if len(parts) != 2:
+        raise ValueError(f"Unrecognised occurrence format: {occurrence!r}")
+    ordinal, weekday_name = parts
+    if ordinal not in _ORDINAL_MAP or weekday_name not in _WEEKDAY_MAP:
+        raise ValueError(f"Unrecognised occurrence: {occurrence!r}")
+    return _WEEKDAY_MAP[weekday_name], _ORDINAL_MAP[ordinal]

tests/services/platforms/test_reddit_comment.py

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+from datetime import date
+from app.services.platforms.reddit_comment import is_nth_weekday, parse_occurrence
+
+
+# --- is_nth_weekday ---
+
+def test_first_sunday_of_april_2026():
+    # 2026-04-05 is the first Sunday of April 2026
+    assert is_nth_weekday(date(2026, 4, 5), weekday=6, n=1) is True
+
+
+def test_second_sunday_of_april_2026_is_not_first():
+    assert is_nth_weekday(date(2026, 4, 12), weekday=6, n=1) is False
+
+
+def test_first_sunday_of_may_2026():
+    # 2026-05-03 is the first Sunday of May 2026
+    assert is_nth_weekday(date(2026, 5, 3), weekday=6, n=1) is True
+
+
+def test_last_friday_not_matched_by_first():
+    # 2026-04-24 is the last Friday of April — not the first
+    assert is_nth_weekday(date(2026, 4, 24), weekday=4, n=1) is False
+
+
+def test_first_friday_of_april_2026():
+    # 2026-04-03 is the first Friday
+    assert is_nth_weekday(date(2026, 4, 3), weekday=4, n=1) is True
+
+
+# --- parse_occurrence ---
+
+def test_parse_occurrence_every_returns_none():
+    assert parse_occurrence("every") is None
+
+
+def test_parse_occurrence_none_returns_none():
+    assert parse_occurrence(None) is None
+
+
+def test_parse_occurrence_first_sunday():
+    weekday, n = parse_occurrence("first_sunday")
+    assert weekday == 6 and n == 1
+
+
+def test_parse_occurrence_unknown_raises():
+    try:
+        parse_occurrence("fourth_wednesday")
+        assert False, "Expected ValueError"
+    except ValueError:
+        pass