Adds fiat currency support for expenses

Extends expense entry functionality to support fiat currencies.

Users can now specify a currency (e.g., EUR, USD) when creating expense entries. The specified amount is converted to satoshis using exchange rates. The converted amount and currency information are stored in the journal entry metadata. Also adds an API endpoint to retrieve allowed currencies and updates the UI to allow currency selection when creating expense entries.

views_api.py

@@ -3,6 +3,7 @@ from http import HTTPStatus
 from fastapi import APIRouter, Depends, HTTPException
 from lnbits.core.models import WalletTypeInfo
 from lnbits.decorators import require_admin_key, require_invoice_key
+from lnbits.utils.exchange_rates import allowed_currencies, fiat_amount_as_satoshis
 
 from .crud import (
     create_account,
@@ -34,6 +35,15 @@ from .models import (
 castle_api_router = APIRouter(prefix="/api/v1", tags=["castle"])
 
 
+# ===== UTILITY ENDPOINTS =====
+
+
+@castle_api_router.get("/currencies")
+async def api_get_currencies() -> list[str]:
+    """Get list of allowed currencies for fiat conversion"""
+    return allowed_currencies()
+
+
 # ===== ACCOUNT ENDPOINTS =====
 
 
@@ -136,7 +146,32 @@ async def api_create_expense_entry(
     Create an expense entry for a user.
     If is_equity=True, records as equity contribution.
     If is_equity=False, records as liability (castle owes user).
+
+    If currency is provided, amount is converted from fiat to satoshis.
     """
+    # Handle currency conversion
+    amount_sats = int(data.amount)
+    metadata = {}
+
+    if data.currency:
+        # Validate currency
+        if data.currency.upper() not in allowed_currencies():
+            raise HTTPException(
+                status_code=HTTPStatus.BAD_REQUEST,
+                detail=f"Currency '{data.currency}' not allowed. Use one of: {', '.join(allowed_currencies())}",
+            )
+
+        # Convert fiat to satoshis
+        amount_sats = await fiat_amount_as_satoshis(data.amount, data.currency)
+
+        # Store currency metadata
+        metadata = {
+            "fiat_currency": data.currency.upper(),
+            "fiat_amount": round(data.amount, ndigits=3),
+            "fiat_rate": amount_sats / data.amount if data.amount > 0 else 0,
+            "btc_rate": (data.amount / amount_sats * 100_000_000) if amount_sats > 0 else 0,
+        }
+
     # Get or create expense account
     expense_account = await get_account_by_name(data.expense_account)
     if not expense_account:
@@ -162,21 +197,24 @@ async def api_create_expense_entry(
 
     # Create journal entry
     # DR Expense, CR User Account (Liability or Equity)
+    description_suffix = f" ({metadata['fiat_amount']} {metadata['fiat_currency']})" if metadata else ""
     entry_data = CreateJournalEntry(
-        description=data.description,
+        description=data.description + description_suffix,
         reference=data.reference,
         lines=[
             CreateEntryLine(
                 account_id=expense_account.id,
-                debit=data.amount,
+                debit=amount_sats,
                 credit=0,
                 description=f"Expense paid by user {data.user_wallet[:8]}",
+                metadata=metadata,
             ),
             CreateEntryLine(
                 account_id=user_account.id,
                 debit=0,
-                credit=data.amount,
+                credit=amount_sats,
                 description=f"{'Equity contribution' if data.is_equity else 'Amount owed to user'}",
+                metadata=metadata,
             ),
         ],
     )