refactors

backend/auth.py

@@ -9,6 +9,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from database import get_db
 from models import Permission, User
+from repositories.user import UserRepository
 from schemas import UserResponse
 
 SECRET_KEY = os.environ["SECRET_KEY"]  # Required - see .env.example
@@ -45,8 +46,9 @@ def create_access_token(
 
 
 async def get_user_by_email(db: AsyncSession, email: str) -> User | None:
-    result = await db.execute(select(User).where(User.email == email))
-    return result.scalar_one_or_none()
+    """Get user by email (backwards compatibility wrapper)."""
+    repo = UserRepository(db)
+    return await repo.get_by_email(email)
 
 
 async def authenticate_user(db: AsyncSession, email: str, password: str) -> User | None:

backend/exceptions.py

@@ -0,0 +1,61 @@
+"""Standardized API exception classes for consistent error responses.
+
+Note: These exceptions use string detail for backward compatibility with existing tests.
+Future refactoring could standardize on structured error responses.
+"""
+
+from fastapi import HTTPException, status
+
+
+class APIError(HTTPException):
+    """Base API error with consistent structure.
+
+    Uses string detail for backward compatibility with existing tests.
+    """
+
+    def __init__(
+        self,
+        status_code: int,
+        message: str,
+    ):
+        super().__init__(status_code=status_code, detail=message)
+
+
+class NotFoundError(APIError):
+    """Resource not found error (404)."""
+
+    def __init__(self, resource: str):
+        super().__init__(
+            status_code=status.HTTP_404_NOT_FOUND,
+            message=f"{resource} not found",
+        )
+
+
+class ConflictError(APIError):
+    """Conflict error (409)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_409_CONFLICT,
+            message=message,
+        )
+
+
+class BadRequestError(APIError):
+    """Bad request error (400)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            message=message,
+        )
+
+
+class ServiceUnavailableError(APIError):
+    """Service unavailable error (503)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+            message=message,
+        )

backend/mappers.py

@@ -0,0 +1,91 @@
+"""Response mappers for converting models to API response schemas."""
+
+from models import Exchange, Invite
+from schemas import (
+    AdminExchangeResponse,
+    ExchangeResponse,
+    ExchangeUserContact,
+    InviteResponse,
+)
+
+
+class ExchangeMapper:
+    """Mapper for Exchange model to response schemas."""
+
+    @staticmethod
+    def to_response(
+        exchange: Exchange,
+        user_email: str | None = None,
+    ) -> ExchangeResponse:
+        """Convert an Exchange model to ExchangeResponse schema."""
+        email = user_email if user_email is not None else exchange.user.email
+        return ExchangeResponse(
+            id=exchange.id,
+            public_id=str(exchange.public_id),
+            user_id=exchange.user_id,
+            user_email=email,
+            slot_start=exchange.slot_start,
+            slot_end=exchange.slot_end,
+            direction=exchange.direction.value,
+            bitcoin_transfer_method=exchange.bitcoin_transfer_method.value,
+            eur_amount=exchange.eur_amount,
+            sats_amount=exchange.sats_amount,
+            market_price_eur=exchange.market_price_eur,
+            agreed_price_eur=exchange.agreed_price_eur,
+            premium_percentage=exchange.premium_percentage,
+            status=exchange.status.value,
+            created_at=exchange.created_at,
+            cancelled_at=exchange.cancelled_at,
+            completed_at=exchange.completed_at,
+        )
+
+    @staticmethod
+    def to_admin_response(exchange: Exchange) -> AdminExchangeResponse:
+        """Convert an Exchange model to AdminExchangeResponse with user contact."""
+        user = exchange.user
+        return AdminExchangeResponse(
+            id=exchange.id,
+            public_id=str(exchange.public_id),
+            user_id=exchange.user_id,
+            user_email=user.email,
+            user_contact=ExchangeUserContact(
+                email=user.email,
+                contact_email=user.contact_email,
+                telegram=user.telegram,
+                signal=user.signal,
+                nostr_npub=user.nostr_npub,
+            ),
+            slot_start=exchange.slot_start,
+            slot_end=exchange.slot_end,
+            direction=exchange.direction.value,
+            bitcoin_transfer_method=exchange.bitcoin_transfer_method.value,
+            eur_amount=exchange.eur_amount,
+            sats_amount=exchange.sats_amount,
+            market_price_eur=exchange.market_price_eur,
+            agreed_price_eur=exchange.agreed_price_eur,
+            premium_percentage=exchange.premium_percentage,
+            status=exchange.status.value,
+            created_at=exchange.created_at,
+            cancelled_at=exchange.cancelled_at,
+            completed_at=exchange.completed_at,
+        )
+
+
+class InviteMapper:
+    """Mapper for Invite model to response schemas."""
+
+    @staticmethod
+    def to_response(invite: Invite) -> InviteResponse:
+        """Build an InviteResponse from an Invite with loaded relationships."""
+        return InviteResponse(
+            id=invite.id,
+            identifier=invite.identifier,
+            godfather_id=invite.godfather_id,
+            godfather_email=invite.godfather.email,
+            status=invite.status.value,
+            used_by_id=invite.used_by_id,
+            used_by_email=invite.used_by.email if invite.used_by else None,
+            created_at=invite.created_at,
+            spent_at=invite.spent_at,
+            revoked_at=invite.revoked_at,
+        )

backend/repositories/__init__.py

@@ -0,0 +1,6 @@
+"""Repository layer for database queries."""
+
+from repositories.price import PriceRepository
+from repositories.user import UserRepository
+
+__all__ = ["PriceRepository", "UserRepository"]

backend/repositories/price.py

@@ -0,0 +1,27 @@
+"""Price repository for database queries."""
+
+from sqlalchemy import desc, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models import PriceHistory
+from price_fetcher import PAIR_BTC_EUR, SOURCE_BITFINEX
+
+
+class PriceRepository:
+    """Repository for price-related database queries."""
+
+    def __init__(self, db: AsyncSession):
+        self.db = db
+
+    async def get_latest(
+        self, source: str = SOURCE_BITFINEX, pair: str = PAIR_BTC_EUR
+    ) -> PriceHistory | None:
+        """Get the most recent price from the database."""
+        query = (
+            select(PriceHistory)
+            .where(PriceHistory.source == source, PriceHistory.pair == pair)
+            .order_by(desc(PriceHistory.timestamp))
+            .limit(1)
+        )
+        result = await self.db.execute(query)
+        return result.scalar_one_or_none()

backend/repositories/user.py

@@ -0,0 +1,23 @@
+"""User repository for database queries."""
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models import User
+
+
+class UserRepository:
+    """Repository for user-related database queries."""
+
+    def __init__(self, db: AsyncSession):
+        self.db = db
+
+    async def get_by_email(self, email: str) -> User | None:
+        """Get a user by email."""
+        result = await self.db.execute(select(User).where(User.email == email))
+        return result.scalar_one_or_none()
+
+    async def get_by_id(self, user_id: int) -> User | None:
+        """Get a user by ID."""
+        result = await self.db.execute(select(User).where(User.id == user_id))
+        return result.scalar_one_or_none()

backend/routes/exchange.py

@@ -3,16 +3,16 @@
 import uuid
 from datetime import UTC, date, datetime, time, timedelta
 
-from fastapi import APIRouter, Depends, HTTPException, Query
-from pydantic import BaseModel
-from sqlalchemy import and_, desc, select
-from sqlalchemy.exc import IntegrityError
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from sqlalchemy import and_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import joinedload
 
 from auth import require_permission
 from database import get_db
 from date_validation import validate_date_in_range
+from exceptions import BadRequestError
+from mappers import ExchangeMapper
 from models import (
     Availability,
     BitcoinTransferMethod,
@@ -24,169 +24,35 @@ from models import (
     User,
 )
 from price_fetcher import PAIR_BTC_EUR, SOURCE_BITFINEX, fetch_btc_eur_price
+from repositories.price import PriceRepository
 from schemas import (
     AdminExchangeResponse,
+    AvailableSlotsResponse,
+    BookableSlot,
+    ExchangeConfigResponse,
+    ExchangePriceResponse,
     ExchangeRequest,
     ExchangeResponse,
-    ExchangeUserContact,
+    PriceResponse,
+    UserSearchResult,
 )
+from services.exchange import ExchangeService
 from shared_constants import (
     EUR_TRADE_INCREMENT,
     EUR_TRADE_MAX,
     EUR_TRADE_MIN,
-    LIGHTNING_MAX_EUR,
     PREMIUM_PERCENTAGE,
-    PRICE_STALENESS_SECONDS,
     SLOT_DURATION_MINUTES,
 )
 
 router = APIRouter(prefix="/api/exchange", tags=["exchange"])
 
-# =============================================================================
-# Constants for satoshi calculations
-# =============================================================================
-
-SATS_PER_BTC = 100_000_000
-
-
-# =============================================================================
-# Pydantic models for price endpoint
-# =============================================================================
-
-
-class ExchangeConfigResponse(BaseModel):
-    """Exchange configuration for the frontend."""
-
-    eur_min: int
-    eur_max: int
-    eur_increment: int
-    premium_percentage: int
-
-
-class PriceResponse(BaseModel):
-    """Current BTC/EUR price for trading.
-
-    Note: The actual agreed price depends on trade direction (buy/sell)
-    and is calculated by the frontend using market_price and premium_percentage.
-    """
-
-    market_price: float  # Raw price from exchange
-    premium_percentage: int
-    timestamp: datetime
-    is_stale: bool
-
-
-class ExchangePriceResponse(BaseModel):
-    """Combined price and configuration response."""
-
-    price: PriceResponse | None  # None if price fetch failed
-    config: ExchangeConfigResponse
-    error: str | None = None
-
-
-class BookableSlot(BaseModel):
-    """A single bookable time slot."""
-
-    start_time: datetime
-    end_time: datetime
-
-
-class AvailableSlotsResponse(BaseModel):
-    """Response containing available slots for a date."""
-
-    date: date
-    slots: list[BookableSlot]
-
 
 # =============================================================================
 # Helper functions
 # =============================================================================
 
 
-def apply_premium_for_direction(
-    market_price: float,
-    premium_percentage: int,
-    direction: TradeDirection,
-) -> float:
-    """
-    Apply premium to market price based on trade direction.
-
-    The premium is always favorable to the admin:
-    - When user BUYS BTC: user pays MORE (market * (1 + premium/100))
-    - When user SELLS BTC: user receives LESS (market * (1 - premium/100))
-    """
-    if direction == TradeDirection.BUY:
-        return market_price * (1 + premium_percentage / 100)
-    else:  # SELL
-        return market_price * (1 - premium_percentage / 100)
-
-
-def calculate_sats_amount(
-    eur_cents: int,
-    price_eur_per_btc: float,
-) -> int:
-    """
-    Calculate satoshi amount from EUR cents and price.
-
-    Args:
-        eur_cents: Amount in EUR cents (e.g., 10000 = €100)
-        price_eur_per_btc: Price in EUR per BTC
-
-    Returns:
-        Amount in satoshis
-    """
-    eur_amount = eur_cents / 100
-    btc_amount = eur_amount / price_eur_per_btc
-    return int(btc_amount * SATS_PER_BTC)
-
-
-async def get_latest_price(db: AsyncSession) -> PriceHistory | None:
-    """Get the most recent price from the database."""
-    query = (
-        select(PriceHistory)
-        .where(
-            PriceHistory.source == SOURCE_BITFINEX, PriceHistory.pair == PAIR_BTC_EUR
-        )
-        .order_by(desc(PriceHistory.timestamp))
-        .limit(1)
-    )
-    result = await db.execute(query)
-    return result.scalar_one_or_none()
-
-
-def is_price_stale(price_timestamp: datetime) -> bool:
-    """Check if a price is older than the staleness threshold."""
-    age_seconds = (datetime.now(UTC) - price_timestamp).total_seconds()
-    return age_seconds > PRICE_STALENESS_SECONDS
-
-
-def _to_exchange_response(
-    exchange: Exchange,
-    user_email: str | None = None,
-) -> ExchangeResponse:
-    """Convert an Exchange model to ExchangeResponse schema."""
-    email = user_email if user_email is not None else exchange.user.email
-    return ExchangeResponse(
-        id=exchange.id,
-        public_id=str(exchange.public_id),
-        user_id=exchange.user_id,
-        user_email=email,
-        slot_start=exchange.slot_start,
-        slot_end=exchange.slot_end,
-        direction=exchange.direction.value,
-        bitcoin_transfer_method=exchange.bitcoin_transfer_method.value,
-        eur_amount=exchange.eur_amount,
-        sats_amount=exchange.sats_amount,
-        market_price_eur=exchange.market_price_eur,
-        agreed_price_eur=exchange.agreed_price_eur,
-        premium_percentage=exchange.premium_percentage,
-        status=exchange.status.value,
-        created_at=exchange.created_at,
-        cancelled_at=exchange.cancelled_at,
-        completed_at=exchange.completed_at,
-    )
-
-
 # =============================================================================
 # Price Endpoint
 # =============================================================================
@@ -216,11 +82,14 @@ async def get_exchange_price(
         premium_percentage=PREMIUM_PERCENTAGE,
     )
 
+    price_repo = PriceRepository(db)
+    service = ExchangeService(db)
+
     # Try to get the latest cached price
-    cached_price = await get_latest_price(db)
+    cached_price = await price_repo.get_latest()
 
     # If no cached price or it's stale, try to fetch a new one
-    if cached_price is None or is_price_stale(cached_price.timestamp):
+    if cached_price is None or service.is_price_stale(cached_price.timestamp):
         try:
             price_value, timestamp = await fetch_btc_eur_price()
 
@@ -270,7 +139,7 @@ async def get_exchange_price(
             market_price=cached_price.price,
             premium_percentage=PREMIUM_PERCENTAGE,
             timestamp=cached_price.timestamp,
-            is_stale=is_price_stale(cached_price.timestamp),
+            is_stale=service.is_price_stale(cached_price.timestamp),
         ),
         config=config,
     )
@@ -377,194 +246,34 @@ async def create_exchange(
     - Price is not stale
     - EUR amount is within configured limits
     """
-    slot_date = request.slot_start.date()
-    validate_date_in_range(slot_date, context="book")
-
-    # Check if user already has a trade on this date
-    existing_trade_query = select(Exchange).where(
-        and_(
-            Exchange.user_id == current_user.id,
-            Exchange.slot_start >= datetime.combine(slot_date, time.min, tzinfo=UTC),
-            Exchange.slot_start
-            < datetime.combine(slot_date, time.max, tzinfo=UTC) + timedelta(days=1),
-            Exchange.status == ExchangeStatus.BOOKED,
-        )
-    )
-    existing_trade_result = await db.execute(existing_trade_query)
-    existing_trade = existing_trade_result.scalar_one_or_none()
-
-    if existing_trade:
-        raise HTTPException(
-            status_code=400,
-            detail=(
-                f"You already have a trade booked on {slot_date.strftime('%Y-%m-%d')}. "
-                f"Only one trade per day is allowed. "
-                f"Trade ID: {existing_trade.public_id}"
-            ),
-        )
-
     # Validate direction
     try:
         direction = TradeDirection(request.direction)
     except ValueError:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Invalid direction: {request.direction}. Must be 'buy' or 'sell'.",
+        raise BadRequestError(
+            f"Invalid direction: {request.direction}. Must be 'buy' or 'sell'."
         ) from None
 
     # Validate bitcoin transfer method
     try:
         bitcoin_transfer_method = BitcoinTransferMethod(request.bitcoin_transfer_method)
     except ValueError:
-        raise HTTPException(
-            status_code=400,
-            detail=(
-                f"Invalid bitcoin_transfer_method: {request.bitcoin_transfer_method}. "
-                "Must be 'onchain' or 'lightning'."
-            ),
+        raise BadRequestError(
+            f"Invalid bitcoin_transfer_method: {request.bitcoin_transfer_method}. "
+            "Must be 'onchain' or 'lightning'."
         ) from None
 
-    # Validate EUR amount
-    if request.eur_amount < EUR_TRADE_MIN * 100:
-        raise HTTPException(
-            status_code=400,
-            detail=f"EUR amount must be at least €{EUR_TRADE_MIN}",
-        )
-    if request.eur_amount > EUR_TRADE_MAX * 100:
-        raise HTTPException(
-            status_code=400,
-            detail=f"EUR amount must be at most €{EUR_TRADE_MAX}",
-        )
-    if request.eur_amount % (EUR_TRADE_INCREMENT * 100) != 0:
-        raise HTTPException(
-            status_code=400,
-            detail=f"EUR amount must be a multiple of €{EUR_TRADE_INCREMENT}",
-        )
-
-    # Validate Lightning threshold
-    if (
-        bitcoin_transfer_method == BitcoinTransferMethod.LIGHTNING
-        and request.eur_amount > LIGHTNING_MAX_EUR * 100
-    ):
-        raise HTTPException(
-            status_code=400,
-            detail=(
-                f"Lightning payments are only allowed for amounts up to "
-                f"€{LIGHTNING_MAX_EUR}. For amounts above €{LIGHTNING_MAX_EUR}, "
-                "please use onchain transactions."
-            ),
-        )
-
-    # Validate slot timing - compute valid boundaries from slot duration
-    valid_minutes = tuple(range(0, 60, SLOT_DURATION_MINUTES))
-    if request.slot_start.minute not in valid_minutes:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Slot must be on {SLOT_DURATION_MINUTES}-minute boundary",
-        )
-    if request.slot_start.second != 0 or request.slot_start.microsecond != 0:
-        raise HTTPException(
-            status_code=400,
-            detail="Slot start time must not have seconds or microseconds",
-        )
-
-    # Verify slot falls within availability
-    slot_start_time = request.slot_start.time()
-    slot_end_dt = request.slot_start + timedelta(minutes=SLOT_DURATION_MINUTES)
-    slot_end_time = slot_end_dt.time()
-
-    result = await db.execute(
-        select(Availability).where(
-            and_(
-                Availability.date == slot_date,
-                Availability.start_time <= slot_start_time,
-                Availability.end_time >= slot_end_time,
-            )
-        )
-    )
-    matching_availability = result.scalar_one_or_none()
-
-    if not matching_availability:
-        slot_str = request.slot_start.strftime("%Y-%m-%d %H:%M")
-        raise HTTPException(
-            status_code=400,
-            detail=f"Selected slot at {slot_str} UTC is not available",
-        )
-
-    # Get and validate price
-    cached_price = await get_latest_price(db)
-
-    if cached_price is None:
-        raise HTTPException(
-            status_code=503,
-            detail="Price data unavailable. Please try again later.",
-        )
-
-    if is_price_stale(cached_price.timestamp):
-        raise HTTPException(
-            status_code=503,
-            detail="Price is stale. Please refresh and try again.",
-        )
-
-    # Calculate agreed price based on direction
-    market_price = cached_price.price
-    agreed_price = apply_premium_for_direction(
-        market_price, PREMIUM_PERCENTAGE, direction
-    )
-
-    # Calculate sats amount based on agreed price
-    sats_amount = calculate_sats_amount(request.eur_amount, agreed_price)
-
-    # Check if slot is already booked (only consider BOOKED status, not cancelled)
-    slot_booked_query = select(Exchange).where(
-        and_(
-            Exchange.slot_start == request.slot_start,
-            Exchange.status == ExchangeStatus.BOOKED,
-        )
-    )
-    slot_booked_result = await db.execute(slot_booked_query)
-    slot_booked = slot_booked_result.scalar_one_or_none()
-
-    if slot_booked:
-        slot_str = request.slot_start.strftime("%Y-%m-%d %H:%M")
-        raise HTTPException(
-            status_code=409,
-            detail=(
-                f"This slot at {slot_str} UTC has already been booked. "
-                "Select another slot."
-            ),
-        )
-
-    # Create the exchange
-    exchange = Exchange(
-        user_id=current_user.id,
+    # Use service to create exchange (handles all validation)
+    service = ExchangeService(db)
+    exchange = await service.create_exchange(
+        user=current_user,
         slot_start=request.slot_start,
-        slot_end=slot_end_dt,
         direction=direction,
         bitcoin_transfer_method=bitcoin_transfer_method,
         eur_amount=request.eur_amount,
-        sats_amount=sats_amount,
-        market_price_eur=market_price,
-        agreed_price_eur=agreed_price,
-        premium_percentage=PREMIUM_PERCENTAGE,
-        status=ExchangeStatus.BOOKED,
     )
 
-    db.add(exchange)
-
-    try:
-        await db.commit()
-        await db.refresh(exchange)
-    except IntegrityError as e:
-        await db.rollback()
-        # This should rarely happen now since we check explicitly above,
-        # but keep it for other potential integrity violations
-        raise HTTPException(
-            status_code=409,
-            detail="Database constraint violation. Please try again.",
-        ) from e
-
-    return _to_exchange_response(exchange, current_user.email)
+    return ExchangeMapper.to_response(exchange, current_user.email)
 
 
 # =============================================================================
@@ -587,7 +296,7 @@ async def get_my_trades(
     )
     exchanges = result.scalars().all()
 
-    return [_to_exchange_response(ex, current_user.email) for ex in exchanges]
+    return [ExchangeMapper.to_response(ex, current_user.email) for ex in exchanges]
 
 
 @trades_router.get("/{public_id}", response_model=ExchangeResponse)
@@ -597,20 +306,10 @@ async def get_my_trade(
     current_user: User = Depends(require_permission(Permission.VIEW_OWN_EXCHANGES)),
 ) -> ExchangeResponse:
     """Get a specific trade by public ID. User can only access their own trades."""
-    result = await db.execute(
-        select(Exchange).where(
-            and_(Exchange.public_id == public_id, Exchange.user_id == current_user.id)
-        )
-    )
-    exchange = result.scalar_one_or_none()
+    service = ExchangeService(db)
+    exchange = await service.get_exchange_by_public_id(public_id, user=current_user)
 
-    if not exchange:
-        raise HTTPException(
-            status_code=404,
-            detail="Trade not found or you don't have permission to view it.",
-        )
-
-    return _to_exchange_response(exchange, current_user.email)
+    return ExchangeMapper.to_response(exchange, current_user.email)
 
 
 @trades_router.post("/{public_id}/cancel", response_model=ExchangeResponse)
@@ -620,48 +319,20 @@ async def cancel_my_trade(
     current_user: User = Depends(require_permission(Permission.CANCEL_OWN_EXCHANGE)),
 ) -> ExchangeResponse:
     """Cancel one of the current user's exchanges."""
-    # Get the exchange with eager loading of user relationship
-    result = await db.execute(
-        select(Exchange)
-        .options(joinedload(Exchange.user))
-        .where(Exchange.public_id == public_id)
-    )
-    exchange = result.scalar_one_or_none()
+    service = ExchangeService(db)
+    # Get exchange without user filter first to check ownership separately
+    exchange = await service.get_exchange_by_public_id(public_id)
 
-    if not exchange:
-        raise HTTPException(
-            status_code=404,
-            detail="Trade not found",
-        )
-
-    # Verify ownership
+    # Check ownership - return 403 if user doesn't own it
     if exchange.user_id != current_user.id:
         raise HTTPException(
-            status_code=403,
+            status_code=status.HTTP_403_FORBIDDEN,
             detail="Cannot cancel another user's trade",
         )
 
-    # Check if already in a final state
-    if exchange.status != ExchangeStatus.BOOKED:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Cannot cancel: status is '{exchange.status.value}'",
-        )
+    exchange = await service.cancel_exchange(exchange, current_user, is_admin=False)
 
-    # Check if slot time has already passed
-    if exchange.slot_start <= datetime.now(UTC):
-        raise HTTPException(
-            status_code=400,
-            detail="Cannot cancel: trade slot time has already passed",
-        )
-
-    exchange.status = ExchangeStatus.CANCELLED_BY_USER
-    exchange.cancelled_at = datetime.now(UTC)
-
-    await db.commit()
-    await db.refresh(exchange)
-
-    return _to_exchange_response(exchange, current_user.email)
+    return ExchangeMapper.to_response(exchange, current_user.email)
 
 
 # =============================================================================
@@ -671,37 +342,6 @@ async def cancel_my_trade(
 admin_trades_router = APIRouter(prefix="/api/admin/trades", tags=["admin-trades"])
 
 
-def _to_admin_exchange_response(exchange: Exchange) -> AdminExchangeResponse:
-    """Convert an Exchange model to AdminExchangeResponse with user contact."""
-    user = exchange.user
-    return AdminExchangeResponse(
-        id=exchange.id,
-        public_id=str(exchange.public_id),
-        user_id=exchange.user_id,
-        user_email=user.email,
-        user_contact=ExchangeUserContact(
-            email=user.email,
-            contact_email=user.contact_email,
-            telegram=user.telegram,
-            signal=user.signal,
-            nostr_npub=user.nostr_npub,
-        ),
-        slot_start=exchange.slot_start,
-        slot_end=exchange.slot_end,
-        direction=exchange.direction.value,
-        bitcoin_transfer_method=exchange.bitcoin_transfer_method.value,
-        eur_amount=exchange.eur_amount,
-        sats_amount=exchange.sats_amount,
-        market_price_eur=exchange.market_price_eur,
-        agreed_price_eur=exchange.agreed_price_eur,
-        premium_percentage=exchange.premium_percentage,
-        status=exchange.status.value,
-        created_at=exchange.created_at,
-        cancelled_at=exchange.cancelled_at,
-        completed_at=exchange.completed_at,
-    )
-
-
 @admin_trades_router.get("/upcoming", response_model=list[AdminExchangeResponse])
 async def get_upcoming_trades(
     db: AsyncSession = Depends(get_db),
@@ -722,7 +362,7 @@ async def get_upcoming_trades(
     )
     exchanges = result.scalars().all()
 
-    return [_to_admin_exchange_response(ex) for ex in exchanges]
+    return [ExchangeMapper.to_admin_response(ex) for ex in exchanges]
 
 
 @admin_trades_router.get("/past", response_model=list[AdminExchangeResponse])
@@ -783,7 +423,7 @@ async def get_past_trades(
     result = await db.execute(query)
     exchanges = result.scalars().all()
 
-    return [_to_admin_exchange_response(ex) for ex in exchanges]
+    return [ExchangeMapper.to_admin_response(ex) for ex in exchanges]
 
 
 @admin_trades_router.post("/{public_id}/complete", response_model=AdminExchangeResponse)
@@ -793,41 +433,11 @@ async def complete_trade(
     _current_user: User = Depends(require_permission(Permission.COMPLETE_EXCHANGE)),
 ) -> AdminExchangeResponse:
     """Mark a trade as completed. Only possible after slot time has passed."""
+    service = ExchangeService(db)
+    exchange = await service.get_exchange_by_public_id(public_id)
+    exchange = await service.complete_exchange(exchange)
 
-    result = await db.execute(
-        select(Exchange)
-        .options(joinedload(Exchange.user))
-        .where(Exchange.public_id == public_id)
-    )
-    exchange = result.scalar_one_or_none()
-
-    if not exchange:
-        raise HTTPException(
-            status_code=404,
-            detail="Trade not found",
-        )
-
-    # Check slot has passed
-    if exchange.slot_start > datetime.now(UTC):
-        raise HTTPException(
-            status_code=400,
-            detail="Cannot complete: trade slot has not yet started",
-        )
-
-    # Check status is BOOKED
-    if exchange.status != ExchangeStatus.BOOKED:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Cannot complete: status is '{exchange.status.value}'",
-        )
-
-    exchange.status = ExchangeStatus.COMPLETED
-    exchange.completed_at = datetime.now(UTC)
-
-    await db.commit()
-    await db.refresh(exchange)
-
-    return _to_admin_exchange_response(exchange)
+    return ExchangeMapper.to_admin_response(exchange)
 
 
 @admin_trades_router.post("/{public_id}/no-show", response_model=AdminExchangeResponse)
@@ -837,41 +447,11 @@ async def mark_no_show(
     _current_user: User = Depends(require_permission(Permission.COMPLETE_EXCHANGE)),
 ) -> AdminExchangeResponse:
     """Mark a trade as no-show. Only possible after slot time has passed."""
+    service = ExchangeService(db)
+    exchange = await service.get_exchange_by_public_id(public_id)
+    exchange = await service.mark_no_show(exchange)
 
-    result = await db.execute(
-        select(Exchange)
-        .options(joinedload(Exchange.user))
-        .where(Exchange.public_id == public_id)
-    )
-    exchange = result.scalar_one_or_none()
-
-    if not exchange:
-        raise HTTPException(
-            status_code=404,
-            detail="Trade not found",
-        )
-
-    # Check slot has passed
-    if exchange.slot_start > datetime.now(UTC):
-        raise HTTPException(
-            status_code=400,
-            detail="Cannot mark as no-show: trade slot has not yet started",
-        )
-
-    # Check status is BOOKED
-    if exchange.status != ExchangeStatus.BOOKED:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Cannot mark as no-show: status is '{exchange.status.value}'",
-        )
-
-    exchange.status = ExchangeStatus.NO_SHOW
-    exchange.completed_at = datetime.now(UTC)
-
-    await db.commit()
-    await db.refresh(exchange)
-
-    return _to_admin_exchange_response(exchange)
+    return ExchangeMapper.to_admin_response(exchange)
 
 
 @admin_trades_router.post("/{public_id}/cancel", response_model=AdminExchangeResponse)
@@ -881,34 +461,11 @@ async def admin_cancel_trade(
     _current_user: User = Depends(require_permission(Permission.CANCEL_ANY_EXCHANGE)),
 ) -> AdminExchangeResponse:
     """Cancel any trade (admin only)."""
+    service = ExchangeService(db)
+    exchange = await service.get_exchange_by_public_id(public_id)
+    exchange = await service.cancel_exchange(exchange, _current_user, is_admin=True)
 
-    result = await db.execute(
-        select(Exchange)
-        .options(joinedload(Exchange.user))
-        .where(Exchange.public_id == public_id)
-    )
-    exchange = result.scalar_one_or_none()
-
-    if not exchange:
-        raise HTTPException(
-            status_code=404,
-            detail="Trade not found",
-        )
-
-    # Check status is BOOKED
-    if exchange.status != ExchangeStatus.BOOKED:
-        raise HTTPException(
-            status_code=400,
-            detail=f"Cannot cancel: status is '{exchange.status.value}'",
-        )
-
-    exchange.status = ExchangeStatus.CANCELLED_BY_ADMIN
-    exchange.cancelled_at = datetime.now(UTC)
-
-    await db.commit()
-    await db.refresh(exchange)
-
-    return _to_admin_exchange_response(exchange)
+    return ExchangeMapper.to_admin_response(exchange)
 
 
 # =============================================================================
@@ -918,13 +475,6 @@ async def admin_cancel_trade(
 admin_users_router = APIRouter(prefix="/api/admin/users", tags=["admin-users"])
 
 
-class UserSearchResult(BaseModel):
-    """Result item for user search."""
-
-    id: int
-    email: str
-
-
 @admin_users_router.get("/search", response_model=list[UserSearchResult])
 async def search_users(
     q: str = Query(..., min_length=1, description="Search query for user email"),

backend/routes/invites.py

@@ -9,11 +9,13 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from auth import require_permission
 from database import get_db
+from exceptions import BadRequestError, NotFoundError
 from invite_utils import (
     generate_invite_identifier,
     is_valid_identifier_format,
     normalize_identifier,
 )
+from mappers import InviteMapper
 from models import Invite, InviteStatus, Permission, User
 from pagination import calculate_offset, create_paginated_response
 from schemas import (
@@ -31,22 +33,6 @@ admin_router = APIRouter(prefix="/api/admin", tags=["admin"])
 MAX_INVITE_COLLISION_RETRIES = 3
 
 
-def _to_invite_response(invite: Invite) -> InviteResponse:
-    """Build an InviteResponse from an Invite with loaded relationships."""
-    return InviteResponse(
-        id=invite.id,
-        identifier=invite.identifier,
-        godfather_id=invite.godfather_id,
-        godfather_email=invite.godfather.email,
-        status=invite.status.value,
-        used_by_id=invite.used_by_id,
-        used_by_email=invite.used_by.email if invite.used_by else None,
-        created_at=invite.created_at,
-        spent_at=invite.spent_at,
-        revoked_at=invite.revoked_at,
-    )
-
-
 @router.get("/{identifier}/check", response_model=InviteCheckResponse)
 async def check_invite(
     identifier: str,
@@ -118,10 +104,7 @@ async def create_invite(
     result = await db.execute(select(User.id).where(User.id == data.godfather_id))
     godfather_id = result.scalar_one_or_none()
     if not godfather_id:
-        raise HTTPException(
-            status_code=status.HTTP_400_BAD_REQUEST,
-            detail="Godfather user not found",
-        )
+        raise BadRequestError("Godfather user not found")
 
     # Try to create invite with retry on collision
     invite: Invite | None = None
@@ -150,7 +133,7 @@ async def create_invite(
             status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
             detail="Failed to create invite",
         )
-    return _to_invite_response(invite)
+    return InviteMapper.to_response(invite)
 
 
 @admin_router.get("/invites", response_model=PaginatedInviteRecords)
@@ -197,7 +180,7 @@ async def list_all_invites(
     invites = result.scalars().all()
 
     # Build responses using preloaded relationships
-    records = [_to_invite_response(invite) for invite in invites]
+    records = [InviteMapper.to_response(invite) for invite in invites]
 
     return create_paginated_response(records, total, page, per_page)
 
@@ -213,16 +196,12 @@ async def revoke_invite(
     invite = result.scalar_one_or_none()
 
     if not invite:
-        raise HTTPException(
-            status_code=status.HTTP_404_NOT_FOUND,
-            detail="Invite not found",
-        )
+        raise NotFoundError("Invite")
 
     if invite.status != InviteStatus.READY:
-        raise HTTPException(
-            status_code=status.HTTP_400_BAD_REQUEST,
-            detail=f"Cannot revoke invite with status '{invite.status.value}'. "
-            "Only READY invites can be revoked.",
+        raise BadRequestError(
+            f"Cannot revoke invite with status '{invite.status.value}'. "
+            "Only READY invites can be revoked."
         )
 
     invite.status = InviteStatus.REVOKED
@@ -230,7 +209,7 @@ async def revoke_invite(
     await db.commit()
     await db.refresh(invite)
 
-    return _to_invite_response(invite)
+    return InviteMapper.to_response(invite)
 
 
 # All routers from this module for easy registration

backend/routes/profile.py

@@ -54,6 +54,7 @@ async def update_profile(
     )
 
     if errors:
+        # Keep field_errors format for backward compatibility with frontend
         raise HTTPException(
             status_code=422,
             detail={"field_errors": errors},

backend/schemas.py

@@ -277,3 +277,64 @@ class ConstantsResponse(BaseModel):
     roles: list[str]
     invite_statuses: list[InviteStatus]
     bitcoin_transfer_methods: list[BitcoinTransferMethod]
+
+
+# =============================================================================
+# Exchange Price/Config Schemas
+# =============================================================================
+
+
+class ExchangeConfigResponse(BaseModel):
+    """Exchange configuration for the frontend."""
+
+    eur_min: int
+    eur_max: int
+    eur_increment: int
+    premium_percentage: int
+
+
+class PriceResponse(BaseModel):
+    """Current BTC/EUR price for trading.
+
+    Note: The actual agreed price depends on trade direction (buy/sell)
+    and is calculated by the frontend using market_price and premium_percentage.
+    """
+
+    market_price: float  # Raw price from exchange
+    premium_percentage: int
+    timestamp: datetime
+    is_stale: bool
+
+
+class ExchangePriceResponse(BaseModel):
+    """Combined price and configuration response."""
+
+    price: PriceResponse | None  # None if price fetch failed
+    config: ExchangeConfigResponse
+    error: str | None = None
+
+
+class BookableSlot(BaseModel):
+    """A single bookable time slot."""
+
+    start_time: datetime
+    end_time: datetime
+
+
+class AvailableSlotsResponse(BaseModel):
+    """Response containing available slots for a date."""
+
+    date: date
+    slots: list[BookableSlot]
+
+
+# =============================================================================
+# Admin User Search Schemas
+# =============================================================================
+
+
+class UserSearchResult(BaseModel):
+    """Result item for user search."""
+
+    id: int
+    email: str

backend/services/__init__.py

@@ -0,0 +1,5 @@
+"""Service layer for business logic."""
+
+from services.exchange import ExchangeService
+
+__all__ = ["ExchangeService"]

backend/services/exchange.py

@@ -0,0 +1,392 @@
+"""Exchange service for business logic related to Bitcoin trading."""
+
+import uuid
+from datetime import UTC, date, datetime, time, timedelta
+
+from sqlalchemy import and_, select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from date_validation import validate_date_in_range
+from exceptions import (
+    BadRequestError,
+    ConflictError,
+    NotFoundError,
+    ServiceUnavailableError,
+)
+from models import (
+    Availability,
+    BitcoinTransferMethod,
+    Exchange,
+    ExchangeStatus,
+    PriceHistory,
+    TradeDirection,
+    User,
+)
+from repositories.price import PriceRepository
+from shared_constants import (
+    EUR_TRADE_INCREMENT,
+    EUR_TRADE_MAX,
+    EUR_TRADE_MIN,
+    LIGHTNING_MAX_EUR,
+    PREMIUM_PERCENTAGE,
+    PRICE_STALENESS_SECONDS,
+    SLOT_DURATION_MINUTES,
+)
+
+# Constants for satoshi calculations
+SATS_PER_BTC = 100_000_000
+
+
+class ExchangeService:
+    """Service for exchange-related business logic."""
+
+    def __init__(self, db: AsyncSession):
+        self.db = db
+        self.price_repo = PriceRepository(db)
+
+    def apply_premium_for_direction(
+        self,
+        market_price: float,
+        premium_percentage: int,
+        direction: TradeDirection,
+    ) -> float:
+        """
+        Apply premium to market price based on trade direction.
+
+        The premium is always favorable to the admin:
+        - When user BUYS BTC: user pays MORE (market * (1 + premium/100))
+        - When user SELLS BTC: user receives LESS (market * (1 - premium/100))
+        """
+        if direction == TradeDirection.BUY:
+            return market_price * (1 + premium_percentage / 100)
+        else:  # SELL
+            return market_price * (1 - premium_percentage / 100)
+
+    def calculate_sats_amount(
+        self,
+        eur_cents: int,
+        price_eur_per_btc: float,
+    ) -> int:
+        """
+        Calculate satoshi amount from EUR cents and price.
+
+        Args:
+            eur_cents: Amount in EUR cents (e.g., 10000 = €100)
+            price_eur_per_btc: Price in EUR per BTC
+
+        Returns:
+            Amount in satoshis
+        """
+        eur_amount = eur_cents / 100
+        btc_amount = eur_amount / price_eur_per_btc
+        return int(btc_amount * SATS_PER_BTC)
+
+    def is_price_stale(self, price_timestamp: datetime) -> bool:
+        """Check if a price is older than the staleness threshold."""
+        age_seconds = (datetime.now(UTC) - price_timestamp).total_seconds()
+        return age_seconds > PRICE_STALENESS_SECONDS
+
+    async def get_latest_price(self) -> PriceHistory | None:
+        """Get the most recent price from the database."""
+        return await self.price_repo.get_latest()
+
+    async def validate_slot_timing(self, slot_start: datetime) -> None:
+        """Validate slot timing - compute valid boundaries from slot duration."""
+        valid_minutes = tuple(range(0, 60, SLOT_DURATION_MINUTES))
+        if slot_start.minute not in valid_minutes:
+            raise BadRequestError(
+                f"Slot must be on {SLOT_DURATION_MINUTES}-minute boundary"
+            )
+        if slot_start.second != 0 or slot_start.microsecond != 0:
+            raise BadRequestError(
+                "Slot start time must not have seconds or microseconds"
+            )
+
+    async def validate_slot_availability(
+        self, slot_start: datetime, slot_date: date
+    ) -> None:
+        """Verify slot falls within availability."""
+        slot_start_time = slot_start.time()
+        slot_end_dt = slot_start + timedelta(minutes=SLOT_DURATION_MINUTES)
+        slot_end_time = slot_end_dt.time()
+
+        result = await self.db.execute(
+            select(Availability).where(
+                and_(
+                    Availability.date == slot_date,
+                    Availability.start_time <= slot_start_time,
+                    Availability.end_time >= slot_end_time,
+                )
+            )
+        )
+        matching_availability = result.scalar_one_or_none()
+
+        if not matching_availability:
+            slot_str = slot_start.strftime("%Y-%m-%d %H:%M")
+            raise BadRequestError(f"Selected slot at {slot_str} UTC is not available")
+
+    async def validate_price_not_stale(self) -> PriceHistory:
+        """Validate price exists and is not stale."""
+        cached_price = await self.get_latest_price()
+
+        if cached_price is None:
+            raise ServiceUnavailableError(
+                "Price data unavailable. Please try again later."
+            )
+
+        if self.is_price_stale(cached_price.timestamp):
+            raise ServiceUnavailableError(
+                "Price is stale. Please refresh and try again."
+            )
+
+        return cached_price
+
+    async def validate_eur_amount(self, eur_amount: int) -> None:
+        """Validate EUR amount is within configured limits."""
+        if eur_amount < EUR_TRADE_MIN * 100:
+            raise BadRequestError(f"EUR amount must be at least €{EUR_TRADE_MIN}")
+        if eur_amount > EUR_TRADE_MAX * 100:
+            raise BadRequestError(f"EUR amount must be at most €{EUR_TRADE_MAX}")
+        if eur_amount % (EUR_TRADE_INCREMENT * 100) != 0:
+            raise BadRequestError(
+                f"EUR amount must be a multiple of €{EUR_TRADE_INCREMENT}"
+            )
+
+    async def validate_lightning_threshold(
+        self, bitcoin_transfer_method: BitcoinTransferMethod, eur_amount: int
+    ) -> None:
+        """Validate Lightning threshold."""
+        if (
+            bitcoin_transfer_method == BitcoinTransferMethod.LIGHTNING
+            and eur_amount > LIGHTNING_MAX_EUR * 100
+        ):
+            raise BadRequestError(
+                f"Lightning payments are only allowed for amounts up to "
+                f"€{LIGHTNING_MAX_EUR}. For amounts above €{LIGHTNING_MAX_EUR}, "
+                "please use onchain transactions."
+            )
+
+    async def check_existing_trade_on_date(
+        self, user: User, slot_date: date
+    ) -> Exchange | None:
+        """Check if user already has a trade on this date."""
+        existing_trade_query = select(Exchange).where(
+            and_(
+                Exchange.user_id == user.id,
+                Exchange.slot_start
+                >= datetime.combine(slot_date, time.min, tzinfo=UTC),
+                Exchange.slot_start
+                < datetime.combine(slot_date, time.max, tzinfo=UTC) + timedelta(days=1),
+                Exchange.status == ExchangeStatus.BOOKED,
+            )
+        )
+        result = await self.db.execute(existing_trade_query)
+        return result.scalar_one_or_none()
+
+    async def check_slot_already_booked(self, slot_start: datetime) -> Exchange | None:
+        """Check if slot is already booked (only consider BOOKED status)."""
+        slot_booked_query = select(Exchange).where(
+            and_(
+                Exchange.slot_start == slot_start,
+                Exchange.status == ExchangeStatus.BOOKED,
+            )
+        )
+        result = await self.db.execute(slot_booked_query)
+        return result.scalar_one_or_none()
+
+    async def create_exchange(
+        self,
+        user: User,
+        slot_start: datetime,
+        direction: TradeDirection,
+        bitcoin_transfer_method: BitcoinTransferMethod,
+        eur_amount: int,
+    ) -> Exchange:
+        """
+        Create a new exchange trade booking with all business validation.
+
+        Raises:
+            BadRequestError: For validation failures
+            ConflictError: If slot is already booked or user has trade on date
+            ServiceUnavailableError: If price is unavailable or stale
+        """
+        slot_date = slot_start.date()
+        validate_date_in_range(slot_date, context="book")
+
+        # Check if user already has a trade on this date
+        existing_trade = await self.check_existing_trade_on_date(user, slot_date)
+        if existing_trade:
+            raise BadRequestError(
+                f"You already have a trade booked on {slot_date.strftime('%Y-%m-%d')}. "
+                f"Only one trade per day is allowed. "
+                f"Trade ID: {existing_trade.public_id}"
+            )
+
+        # Validate EUR amount
+        await self.validate_eur_amount(eur_amount)
+
+        # Validate Lightning threshold
+        await self.validate_lightning_threshold(bitcoin_transfer_method, eur_amount)
+
+        # Validate slot timing
+        await self.validate_slot_timing(slot_start)
+
+        # Verify slot falls within availability
+        await self.validate_slot_availability(slot_start, slot_date)
+
+        # Get and validate price
+        cached_price = await self.validate_price_not_stale()
+
+        # Calculate agreed price based on direction
+        market_price = cached_price.price
+        agreed_price = self.apply_premium_for_direction(
+            market_price, PREMIUM_PERCENTAGE, direction
+        )
+
+        # Calculate sats amount based on agreed price
+        sats_amount = self.calculate_sats_amount(eur_amount, agreed_price)
+
+        # Check if slot is already booked
+        slot_booked = await self.check_slot_already_booked(slot_start)
+        if slot_booked:
+            slot_str = slot_start.strftime("%Y-%m-%d %H:%M")
+            raise ConflictError(
+                f"This slot at {slot_str} UTC has already been booked. "
+                "Select another slot."
+            )
+
+        # Create the exchange
+        slot_end_dt = slot_start + timedelta(minutes=SLOT_DURATION_MINUTES)
+        exchange = Exchange(
+            user_id=user.id,
+            slot_start=slot_start,
+            slot_end=slot_end_dt,
+            direction=direction,
+            bitcoin_transfer_method=bitcoin_transfer_method,
+            eur_amount=eur_amount,
+            sats_amount=sats_amount,
+            market_price_eur=market_price,
+            agreed_price_eur=agreed_price,
+            premium_percentage=PREMIUM_PERCENTAGE,
+            status=ExchangeStatus.BOOKED,
+        )
+
+        self.db.add(exchange)
+
+        try:
+            await self.db.commit()
+            await self.db.refresh(exchange)
+        except IntegrityError as e:
+            await self.db.rollback()
+            # This should rarely happen now since we check explicitly above,
+            # but keep it for other potential integrity violations
+            raise ConflictError(
+                "Database constraint violation. Please try again."
+            ) from e
+
+        return exchange
+
+    async def get_exchange_by_public_id(
+        self, public_id: uuid.UUID, user: User | None = None
+    ) -> Exchange:
+        """
+        Get an exchange by public ID, optionally checking ownership.
+
+        Raises:
+            NotFoundError: If exchange not found or user doesn't own it
+                (for security, returns 404)
+        """
+        query = select(Exchange).where(Exchange.public_id == public_id)
+        result = await self.db.execute(query)
+        exchange = result.scalar_one_or_none()
+
+        if not exchange:
+            raise NotFoundError("Trade")
+
+        # Check ownership if user is provided - return 404 for security
+        # (prevents info leakage)
+        if user and exchange.user_id != user.id:
+            raise NotFoundError("Trade")
+
+        return exchange
+
+    async def cancel_exchange(
+        self, exchange: Exchange, user: User, is_admin: bool = False
+    ) -> Exchange:
+        """
+        Cancel an exchange trade.
+
+        Raises:
+            BadRequestError: If cancellation is not allowed
+            NotFoundError: If user doesn't own the exchange (when not admin,
+                returns 404 for security)
+        """
+        if not is_admin and exchange.user_id != user.id:
+            raise NotFoundError("Trade")
+
+        if exchange.status != ExchangeStatus.BOOKED:
+            raise BadRequestError(f"Cannot cancel: status is '{exchange.status.value}'")
+
+        if exchange.slot_start <= datetime.now(UTC):
+            raise BadRequestError("Cannot cancel: trade slot time has already passed")
+
+        exchange.status = (
+            ExchangeStatus.CANCELLED_BY_ADMIN
+            if is_admin
+            else ExchangeStatus.CANCELLED_BY_USER
+        )
+        exchange.cancelled_at = datetime.now(UTC)
+
+        await self.db.commit()
+        await self.db.refresh(exchange)
+
+        return exchange
+
+    async def complete_exchange(self, exchange: Exchange) -> Exchange:
+        """
+        Mark an exchange as completed.
+
+        Raises:
+            BadRequestError: If completion is not allowed
+        """
+        if exchange.slot_start > datetime.now(UTC):
+            raise BadRequestError("Cannot complete: trade slot has not yet started")
+
+        if exchange.status != ExchangeStatus.BOOKED:
+            raise BadRequestError(
+                f"Cannot complete: status is '{exchange.status.value}'"
+            )
+
+        exchange.status = ExchangeStatus.COMPLETED
+        exchange.completed_at = datetime.now(UTC)
+
+        await self.db.commit()
+        await self.db.refresh(exchange)
+
+        return exchange
+
+    async def mark_no_show(self, exchange: Exchange) -> Exchange:
+        """
+        Mark an exchange as no-show.
+
+        Raises:
+            BadRequestError: If marking as no-show is not allowed
+        """
+        if exchange.slot_start > datetime.now(UTC):
+            raise BadRequestError(
+                "Cannot mark as no-show: trade slot has not yet started"
+            )
+
+        if exchange.status != ExchangeStatus.BOOKED:
+            raise BadRequestError(
+                f"Cannot mark as no-show: status is '{exchange.status.value}'"
+            )
+
+        exchange.status = ExchangeStatus.NO_SHOW
+        exchange.completed_at = datetime.now(UTC)
+
+        await self.db.commit()
+        await self.db.refresh(exchange)
+
+        return exchange