Add get_reverse_subject_map()

This was sparked by an issue in which STSS 2520 appears as a prerequisite for some other course in Fall 2025, but STSS no longer exists. However, we still want to convert the subject name into its respective code, so a function that could create a "master" subject reverse lookup map across multiple terms was needed.

Author: ramonechen

app/scrapers/sis_scraper.py

@@ -2,6 +2,7 @@
 import json
 import re
 import time
+from datetime import datetime
 from enum import Enum
 from pathlib import Path
 from typing import Any
@@ -28,6 +29,32 @@ class ClassColumn(str, Enum):
     TERM = "term"
 
 
+async def get_reverse_subject_map(
+    session: aiohttp.ClientSession,
+    start_year: int = 1998,
+    end_year: int = datetime.now().year,
+    seasons: list[str] = None,
+) -> dict[str, str]:
+    """
+    Fetches the list of subjects from the specific range of years and seasons, and
+    returns a mapping of subject names to subject codes.
+
+    Defaults to a range from 1998 to the current year, and Spring, Summer, and Fall
+    seasons. SIS data begins in Summer 1998.
+    """
+    subject_name_code_map = {}
+    if seasons is None:
+        seasons = ["spring", "summer", "fall"]
+    async with aiohttp.ClientSession() as session:
+        for year in range(start_year, end_year + 1):
+            for season in seasons:
+                term = get_term_code(year, season)
+                subjects = await get_term_subjects(session, term)
+                for subject in subjects:
+                    subject_name_code_map[subject["description"]] = subject["code"]
+    return subject_name_code_map
+
+
 async def get_term_subjects(
     session: aiohttp.ClientSession, term: str
 ) -> list[dict[str, str]]: