feat: add thread detection helpers to reddit_comment strategy

app/services/platforms/reddit_comment.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+import re
 from datetime import date, timedelta
 
 import httpx
@@ -43,3 +44,39 @@ def parse_occurrence(occurrence: str | None) -> tuple[int, int] | None:
     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]
+
+
+def _extract_thread_id_from_url(url: str) -> str:
+    """Extract a Reddit post ID from a full Reddit URL.
+
+    Expects URLs of the form:
+        https://www.reddit.com/r/<sub>/comments/<id>/<title>/
+    Raises ValueError if the ID cannot be found.
+    """
+    match = re.search(r"/comments/([a-z0-9]+)/", url)
+    if not match:
+        raise ValueError(f"Cannot extract thread id from {url!r}")
+    return match.group(1)
+
+
+def _find_sticky(
+    sub: str,
+    title_pattern: str,
+    session_file: str | None = None,
+) -> str | None:
+    """Search the hot listing of a subreddit for a post matching title_pattern.
+
+    Uses the Reddit public JSON API (no auth required).
+    Returns the post ID (e.g. "abc123") of the first match, or None.
+    """
+    url = f"https://www.reddit.com/r/{sub}/hot.json?limit=10"
+    response = httpx.get(url, headers={"User-Agent": "magpie/1.0"})
+    payload = response.json()
+    children = payload.get("data", {}).get("children", [])
+    pattern_lower = title_pattern.lower()
+    for child in children:
+        post = child.get("data", {})
+        title = post.get("title", "")
+        if pattern_lower in title.lower():
+            return post.get("id")
+    return None

tests/services/platforms/test_reddit_comment.py

@@ -1,5 +1,12 @@
 from datetime import date
-from app.services.platforms.reddit_comment import is_nth_weekday, parse_occurrence
+from unittest.mock import MagicMock
+import pytest
+from app.services.platforms.reddit_comment import (
+    is_nth_weekday,
+    parse_occurrence,
+    _extract_thread_id_from_url,
+    _find_sticky,
+)
 
 
 # --- is_nth_weekday ---
@@ -49,3 +56,49 @@ def test_parse_occurrence_unknown_raises():
         assert False, "Expected ValueError"
     except ValueError:
         pass
+
+
+# --- _extract_thread_id_from_url ---
+
+def test_extract_thread_id_success():
+    url = "https://www.reddit.com/r/flipping/comments/abc123/weekly_thread/"
+    assert _extract_thread_id_from_url(url) == "abc123"
+
+
+def test_extract_thread_id_invalid():
+    with pytest.raises(ValueError):
+        _extract_thread_id_from_url("https://www.reddit.com/r/flipping/")
+
+
+# --- _find_sticky ---
+
+def _make_hot_json(posts: list[dict]) -> dict:
+    """Build a fake Reddit hot.json payload."""
+    return {"data": {"children": [{"data": p} for p in posts]}}
+
+
+def test_find_sticky_found(monkeypatch):
+    fake_response = MagicMock()
+    fake_response.json.return_value = _make_hot_json([
+        {"id": "abc123", "title": "Weekly Self-Promotion Thread"},
+        {"id": "xyz999", "title": "General Discussion"},
+    ])
+
+    import app.services.platforms.reddit_comment as rc_module
+    monkeypatch.setattr(rc_module.httpx, "get", lambda *a, **kw: fake_response)
+
+    result = _find_sticky("flipping", "Self-Promotion")
+    assert result == "abc123"
+
+
+def test_find_sticky_not_found(monkeypatch):
+    fake_response = MagicMock()
+    fake_response.json.return_value = _make_hot_json([
+        {"id": "xyz999", "title": "General Discussion"},
+    ])
+
+    import app.services.platforms.reddit_comment as rc_module
+    monkeypatch.setattr(rc_module.httpx, "get", lambda *a, **kw: fake_response)
+
+    result = _find_sticky("flipping", "Self-Promotion")
+    assert result is None