# app/api/v1/endpoints/costs.py import logging from fastapi import APIRouter, Depends, HTTPException, status from sqlalchemy import select from sqlalchemy.ext.asyncio import AsyncSession from sqlalchemy.orm import Session, selectinload from decimal import Decimal, ROUND_HALF_UP from app.database import get_db from app.api.dependencies import get_current_user from app.models import ( User as UserModel, Group as GroupModel, List as ListModel, Expense as ExpenseModel, Item as ItemModel, UserGroup as UserGroupModel, SplitTypeEnum, ExpenseSplit as ExpenseSplitModel, Settlement as SettlementModel ) from app.schemas.cost import ListCostSummary, GroupBalanceSummary from app.schemas.expense import ExpenseCreate from app.crud import list as crud_list from app.crud import expense as crud_expense from app.core.exceptions import ListNotFoundError, ListPermissionError, UserNotFoundError, GroupNotFoundError logger = logging.getLogger(__name__) router = APIRouter() @router.get( "/lists/{list_id}/cost-summary", response_model=ListCostSummary, summary="Get Cost Summary for a List", tags=["Costs"], responses={ status.HTTP_403_FORBIDDEN: {"description": "User does not have permission to access this list"}, status.HTTP_404_NOT_FOUND: {"description": "List or associated user not found"} } ) async def get_list_cost_summary( list_id: int, db: AsyncSession = Depends(get_db), current_user: UserModel = Depends(get_current_user), ): """ Retrieves a calculated cost summary for a specific list, detailing total costs, equal shares per user, and individual user balances based on their contributions. The user must have access to the list to view its cost summary. Costs are split among group members if the list belongs to a group, or just for the creator if it's a personal list. All users who added items with prices are included in the calculation. """ logger.info(f"User {current_user.email} requesting cost summary for list {list_id}") # 1. Verify user has access to the target list try: await crud_list.check_list_permission(db=db, list_id=list_id, user_id=current_user.id) except ListPermissionError as e: logger.warning(f"Permission denied for user {current_user.email} on list {list_id}: {str(e)}") raise except ListNotFoundError as e: logger.warning(f"List {list_id} not found when checking permissions for cost summary: {str(e)}") raise # 2. Get the list with its items and users list_result = await db.execute( select(ListModel) .options( selectinload(ListModel.items).options(selectinload(ItemModel.added_by_user)), selectinload(ListModel.group).options(selectinload(GroupModel.user_associations).options(selectinload(UserGroupModel.user))), selectinload(ListModel.creator) ) .where(ListModel.id == list_id) ) db_list = list_result.scalars().first() if not db_list: raise ListNotFoundError(list_id) # 3. Get or create an expense for this list expense_result = await db.execute( select(ExpenseModel) .where(ExpenseModel.list_id == list_id) .options(selectinload(ExpenseModel.splits)) ) db_expense = expense_result.scalars().first() if not db_expense: # Create a new expense for this list total_amount = sum(item.price for item in db_list.items if item.price is not None and item.price > Decimal("0")) if total_amount == Decimal("0"): return ListCostSummary( list_id=db_list.id, list_name=db_list.name, total_list_cost=Decimal("0.00"), num_participating_users=0, equal_share_per_user=Decimal("0.00"), user_balances=[] ) # Create expense with ITEM_BASED split type expense_in = ExpenseCreate( description=f"Cost summary for list {db_list.name}", total_amount=total_amount, list_id=list_id, split_type=SplitTypeEnum.ITEM_BASED, paid_by_user_id=current_user.id # Use current user as payer for now ) db_expense = await crud_expense.create_expense(db=db, expense_in=expense_in) # 4. Calculate cost summary from expense splits participating_users = set() user_items_added_value = {} total_list_cost = Decimal("0.00") # Get all users who added items for item in db_list.items: if item.price is not None and item.price > Decimal("0") and item.added_by_user: participating_users.add(item.added_by_user) user_items_added_value[item.added_by_user.id] = user_items_added_value.get(item.added_by_user.id, Decimal("0.00")) + item.price total_list_cost += item.price # Get all users from expense splits for split in db_expense.splits: if split.user: participating_users.add(split.user) num_participating_users = len(participating_users) if num_participating_users == 0: return ListCostSummary( list_id=db_list.id, list_name=db_list.name, total_list_cost=Decimal("0.00"), num_participating_users=0, equal_share_per_user=Decimal("0.00"), user_balances=[] ) equal_share_per_user = (total_list_cost / Decimal(num_participating_users)).quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) remainder = total_list_cost - (equal_share_per_user * num_participating_users) user_balances = [] first_user_processed = False for user in participating_users: items_added = user_items_added_value.get(user.id, Decimal("0.00")) current_user_share = equal_share_per_user if not first_user_processed and remainder != Decimal("0"): current_user_share += remainder first_user_processed = True balance = items_added - current_user_share user_identifier = user.name if user.name else user.email user_balances.append( UserCostShare( user_id=user.id, user_identifier=user_identifier, items_added_value=items_added.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP), amount_due=current_user_share.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP), balance=balance.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) ) ) user_balances.sort(key=lambda x: x.user_identifier) return ListCostSummary( list_id=db_list.id, list_name=db_list.name, total_list_cost=total_list_cost.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP), num_participating_users=num_participating_users, equal_share_per_user=equal_share_per_user.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP), user_balances=user_balances ) @router.get( "/groups/{group_id}/balance-summary", response_model=GroupBalanceSummary, summary="Get Detailed Balance Summary for a Group", tags=["Costs", "Groups"], responses={ status.HTTP_403_FORBIDDEN: {"description": "User does not have permission to access this group"}, status.HTTP_404_NOT_FOUND: {"description": "Group not found"} } ) async def get_group_balance_summary( group_id: int, db: AsyncSession = Depends(get_db), current_user: UserModel = Depends(get_current_user), ): """ Retrieves a detailed financial balance summary for all users within a specific group. It considers all expenses, their splits, and all settlements recorded for the group. The user must be a member of the group to view its balance summary. """ logger.info(f"User {current_user.email} requesting balance summary for group {group_id}") # 1. Verify user is a member of the target group group_check = await db.execute( select(GroupModel) .options(selectinload(GroupModel.member_associations)) .where(GroupModel.id == group_id) ) db_group_for_check = group_check.scalars().first() if not db_group_for_check: raise GroupNotFoundError(group_id) user_is_member = any(assoc.user_id == current_user.id for assoc in db_group_for_check.member_associations) if not user_is_member: raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=f"User not a member of group {group_id}") # 2. Get all expenses and settlements for the group expenses_result = await db.execute( select(ExpenseModel) .where(ExpenseModel.group_id == group_id) .options(selectinload(ExpenseModel.splits).selectinload(ExpenseSplitModel.user)) ) expenses = expenses_result.scalars().all() settlements_result = await db.execute( select(SettlementModel) .where(SettlementModel.group_id == group_id) .options( selectinload(SettlementModel.paid_by_user), selectinload(SettlementModel.paid_to_user) ) ) settlements = settlements_result.scalars().all() # 3. Calculate user balances user_balances_data = {} for assoc in db_group_for_check.member_associations: if assoc.user: user_balances_data[assoc.user.id] = UserBalanceDetail( user_id=assoc.user.id, user_identifier=assoc.user.name if assoc.user.name else assoc.user.email ) # Process expenses for expense in expenses: if expense.paid_by_user_id in user_balances_data: user_balances_data[expense.paid_by_user_id].total_paid_for_expenses += expense.total_amount for split in expense.splits: if split.user_id in user_balances_data: user_balances_data[split.user_id].total_share_of_expenses += split.owed_amount # Process settlements for settlement in settlements: if settlement.paid_by_user_id in user_balances_data: user_balances_data[settlement.paid_by_user_id].total_settlements_paid += settlement.amount if settlement.paid_to_user_id in user_balances_data: user_balances_data[settlement.paid_to_user_id].total_settlements_received += settlement.amount # Calculate net balances final_user_balances = [] for user_id, data in user_balances_data.items(): data.net_balance = ( data.total_paid_for_expenses + data.total_settlements_received ) - (data.total_share_of_expenses + data.total_settlements_paid) data.total_paid_for_expenses = data.total_paid_for_expenses.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) data.total_share_of_expenses = data.total_share_of_expenses.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) data.total_settlements_paid = data.total_settlements_paid.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) data.total_settlements_received = data.total_settlements_received.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) data.net_balance = data.net_balance.quantize(Decimal("0.01"), rounding=ROUND_HALF_UP) final_user_balances.append(data) # Sort by user identifier final_user_balances.sort(key=lambda x: x.user_identifier) # Calculate suggested settlements suggested_settlements = calculate_suggested_settlements(final_user_balances) return GroupBalanceSummary( group_id=db_group_for_check.id, group_name=db_group_for_check.name, user_balances=final_user_balances, suggested_settlements=suggested_settlements )