chore(billing): add backfill script for amount_usd on old purchase transactions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/scripts/backfill_amount_usd.py

@@ -0,0 +1,90 @@
+"""
+One-time migration: backfill amount_usd on purchase credit_transactions.
+
+Matches pack by:
+  1. pack_id extracted from description "Purchased <pack_id> pack (...)"
+  2. Fallback: closest credits count match from app_settings packs
+  3. Fallback: test pack = $1.00
+"""
+import asyncio
+import re
+import sys
+import os
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
+
+PACK_PRICES = {
+    "starter": 49.0,
+    "pro":     199.0,
+    "scale":   499.0,
+    "test":    1.0,
+}
+
+CREDITS_TO_PACK = {
+    50:  ("starter", 49.0),
+    220: ("pro",     199.0),
+    600: ("scale",   499.0),
+}
+
+
+def _resolve_price(description: str, credits: int) -> float | None:
+    """Return USD price for a transaction, or None if can't determine."""
+    # Try to extract pack_id from description
+    m = re.match(r"Purchased\s+(\S+)\s+pack", description or "", re.IGNORECASE)
+    if m:
+        pack_id = m.group(1).lower()
+        if pack_id in PACK_PRICES:
+            return PACK_PRICES[pack_id]
+
+    # Fallback: exact credits match
+    if credits in CREDITS_TO_PACK:
+        return CREDITS_TO_PACK[credits][1]
+
+    # Fallback: closest credits match within 10%
+    for c, (_, price) in CREDITS_TO_PACK.items():
+        if abs(c - credits) / max(c, 1) < 0.1:
+            return price
+
+    return None
+
+
+async def main():
+    from motor.motor_asyncio import AsyncIOMotorClient
+    from app.config import Config
+
+    mongo_uri = os.environ.get("MONGO_URI", Config.MONGO_URI)
+    db_name = mongo_uri.rstrip("/").split("/")[-1].split("?")[0] or "cohorta_db"
+    client = AsyncIOMotorClient(mongo_uri)
+    db = client[db_name]
+
+    cursor = db.credit_transactions.find({
+        "type": "purchase",
+        "amount_usd": {"$exists": False},
+    })
+
+    updated = 0
+    skipped = 0
+
+    async for tx in cursor:
+        description = tx.get("description", "")
+        credits = tx.get("amount", 0)
+        price = _resolve_price(description, credits)
+
+        if price is None:
+            print(f"  SKIP  id={tx['_id']}  desc='{description}'  credits={credits}  — cannot determine price")
+            skipped += 1
+            continue
+
+        await db.credit_transactions.update_one(
+            {"_id": tx["_id"]},
+            {"$set": {"amount_usd": price}},
+        )
+        print(f"  SET   id={tx['_id']}  desc='{description}'  credits={credits}  → ${price}")
+        updated += 1
+
+    print(f"\nDone: {updated} updated, {skipped} skipped.")
+    client.close()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())