# Implemented backend task

Created a backend endpoints which implements following functionality:

- Introduced a new entity Wallet and Transaction.
- Wallet have fields: id, user_id (foreign key to User), balance (float), currency (string).
- Available currencies: USD, EUR, RUB.
- Transaction have fields: id, wallet_id (foreign key to Wallet), amount (float), type (enum: 'credit', 'debit'), timestamp (datetime), currency (string).
- Implemented endpoint to create a wallet for a user.
- Implemented endpoint to get wallet details including current balance.
- Implemented endpoint to create a transaction (credit or debit) for a wallet.

# Rules for wallet

- A user can have three wallets.
- Wallet balance should start at 0.0.
- Arithmetic operations on balance should be precise up to two decimal places.

# Rules for transaction

- For 'credit' transactions, the amount should be added to the wallet balance.
- For 'debit' transactions, the amount should be subtracted from the wallet balance.
- Ensure that the wallet balance cannot go negative. If a debit transaction would cause the balance to go negative, the transaction should be rejected with an appropriate error message.
- Transaction between wallets with different currencies must be converted using a fixed exchange rate (you can hardcode some exchange rates for simplicity) and fees should be applied.

Duration: 8m26s

My own comments:

+ Created a migration script
+ Split wallet and transactions endpoints
- Wrote a tests, which wasn't asked
- Put everything in crud file, I thinks it's not a best idea

Author: vodkar

backend/app/alembic/versions/f3b2a1c9d8e7_add_wallet_and_transaction_tables.py

@@ -0,0 +1,92 @@
+"""
+Add wallet and transaction tables.
+
+Revision ID: f3b2a1c9d8e7
+Revises: d98dd8ec85a3
+Create Date: 2025-09-15 12:30:00.000000
+
+"""
+
+import sqlalchemy as sa
+import sqlmodel.sql.sqltypes
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = "f3b2a1c9d8e7"
+down_revision = "d98dd8ec85a3"
+branch_labels: str | None = None
+depends_on: str | None = None
+
+
+def upgrade() -> None:
+    """Upgrade database schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+
+    # Create wallet table
+    op.create_table(
+        "wallet",
+        sa.Column("id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("user_id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("balance", sa.DECIMAL(precision=10, scale=2), nullable=False),
+        sa.Column(
+            "currency", sqlmodel.sql.sqltypes.AutoString(length=3), nullable=False
+        ),
+        sa.Column("created_at", sa.DateTime(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(), nullable=False),
+        sa.ForeignKeyConstraint(
+            ["user_id"],
+            ["user.id"],
+            ondelete="CASCADE",
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_wallet_user_id"), "wallet", ["user_id"], unique=False)
+    op.create_index(
+        "ix_wallet_user_currency", "wallet", ["user_id", "currency"], unique=True
+    )
+
+    # Create transaction table
+    op.create_table(
+        "transaction",
+        sa.Column("id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("wallet_id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("amount", sa.DECIMAL(precision=10, scale=2), nullable=False),
+        sa.Column(
+            "type", sa.Enum("credit", "debit", name="transactiontype"), nullable=False
+        ),
+        sa.Column("timestamp", sa.DateTime(), nullable=False),
+        sa.Column(
+            "currency", sqlmodel.sql.sqltypes.AutoString(length=3), nullable=False
+        ),
+        sa.Column("description", sqlmodel.sql.sqltypes.AutoString(), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["wallet_id"],
+            ["wallet.id"],
+            ondelete="CASCADE",
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(
+        op.f("ix_transaction_wallet_id"), "transaction", ["wallet_id"], unique=False
+    )
+    op.create_index(
+        op.f("ix_transaction_timestamp"), "transaction", ["timestamp"], unique=False
+    )
+
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade database schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f("ix_transaction_timestamp"), table_name="transaction")
+    op.drop_index(op.f("ix_transaction_wallet_id"), table_name="transaction")
+    op.drop_table("transaction")
+    op.drop_index("ix_wallet_user_currency", table_name="wallet")
+    op.drop_index(op.f("ix_wallet_user_id"), table_name="wallet")
+    op.drop_table("wallet")
+
+    # Drop the enum type
+    op.execute("DROP TYPE IF EXISTS transactiontype")
+    # ### end Alembic commands ###

backend/app/api/main.py

@@ -1,15 +1,16 @@
 """API router configuration."""
 
-from fastapi import APIRouter
-
-from app.api.routes import items, login, misc, private, users
+from app.api.routes import items, login, misc, private, transactions, users, wallets
 from app.core.config import settings
+from fastapi import APIRouter
 
 api_router = APIRouter()
 api_router.include_router(login.router)
 api_router.include_router(users.router)
 api_router.include_router(misc.router)
 api_router.include_router(items.router)
+api_router.include_router(wallets.router)
+api_router.include_router(transactions.router)
 
 
 if settings.ENVIRONMENT == "local":

backend/app/api/routes/transactions.py

@@ -0,0 +1,70 @@
+"""Transaction management API endpoints."""
+
+import uuid
+
+from app.api.deps import CurrentUser, SessionDep
+from app.constants import BAD_REQUEST_CODE, CREATED_CODE, NOT_FOUND_CODE
+from app.crud import create_transaction, get_wallet_by_id, get_wallet_transactions
+from app.models import TransactionCreate, TransactionPublic, TransactionsPublic
+from fastapi import APIRouter, HTTPException
+
+router = APIRouter(prefix="/transactions", tags=["transactions"])
+
+
+@router.post("/", status_code=CREATED_CODE)
+def create_wallet_transaction(
+    *,
+    session: SessionDep,
+    current_user: CurrentUser,
+    transaction_in: TransactionCreate,
+) -> TransactionPublic:
+    """Create a new transaction for a wallet."""
+    # Verify that the wallet belongs to the current user
+    wallet = get_wallet_by_id(session=session, wallet_id=transaction_in.wallet_id)
+    if not wallet:
+        raise HTTPException(status_code=NOT_FOUND_CODE, detail="Wallet not found")
+
+    if not current_user.is_superuser and (wallet.user_id != current_user.id):
+        raise HTTPException(
+            status_code=BAD_REQUEST_CODE,
+            detail="Not enough permissions",
+        )
+
+    try:
+        db_transaction = create_transaction(
+            session=session, transaction_in=transaction_in
+        )
+        return TransactionPublic.model_validate(db_transaction)
+    except ValueError as e:
+        raise HTTPException(
+            status_code=BAD_REQUEST_CODE,
+            detail=str(e),
+        ) from e
+
+
+@router.get("/wallet/{wallet_id}")
+def read_wallet_transactions(
+    session: SessionDep,
+    current_user: CurrentUser,
+    wallet_id: uuid.UUID,
+) -> TransactionsPublic:
+    """Get all transactions for a specific wallet."""
+    # Verify that the wallet belongs to the current user
+    wallet = get_wallet_by_id(session=session, wallet_id=wallet_id)
+    if not wallet:
+        raise HTTPException(status_code=NOT_FOUND_CODE, detail="Wallet not found")
+
+    if not current_user.is_superuser and (wallet.user_id != current_user.id):
+        raise HTTPException(
+            status_code=BAD_REQUEST_CODE,
+            detail="Not enough permissions",
+        )
+
+    transaction_list = get_wallet_transactions(session=session, wallet_id=wallet_id)
+    transaction_data = [
+        TransactionPublic.model_validate(transaction)
+        for transaction in transaction_list
+    ]
+    return TransactionsPublic(
+        transaction_data=transaction_data, count=len(transaction_data)
+    )

backend/app/api/routes/wallets.py

@@ -0,0 +1,65 @@
+"""Wallet management API endpoints."""
+
+import uuid
+
+from app.api.deps import CurrentUser, SessionDep
+from app.constants import BAD_REQUEST_CODE, CREATED_CODE, NOT_FOUND_CODE
+from app.crud import create_wallet, get_user_wallets, get_wallet_by_id
+from app.models import Message, WalletCreate, WalletPublic, WalletsPublic
+from fastapi import APIRouter, HTTPException
+
+router = APIRouter(prefix="/wallets", tags=["wallets"])
+
+
+@router.post("/", status_code=CREATED_CODE)
+def create_user_wallet(
+    *,
+    session: SessionDep,
+    current_user: CurrentUser,
+    wallet_in: WalletCreate,
+) -> WalletPublic:
+    """Create a new wallet for the current user."""
+    try:
+        db_wallet = create_wallet(
+            session=session,
+            wallet_in=wallet_in,
+            user_id=current_user.id,
+        )
+        return WalletPublic.model_validate(db_wallet)
+    except ValueError as e:
+        raise HTTPException(
+            status_code=BAD_REQUEST_CODE,
+            detail=str(e),
+        ) from e
+
+
+@router.get("/")
+def read_user_wallets(
+    session: SessionDep,
+    current_user: CurrentUser,
+) -> WalletsPublic:
+    """Retrieve all wallets for the current user."""
+    wallet_list = get_user_wallets(session=session, user_id=current_user.id)
+    wallet_data = [WalletPublic.model_validate(wallet) for wallet in wallet_list]
+    return WalletsPublic(wallet_data=wallet_data, count=len(wallet_data))
+
+
+@router.get("/{wallet_id}")
+def read_wallet(
+    session: SessionDep,
+    current_user: CurrentUser,
+    wallet_id: uuid.UUID,
+) -> WalletPublic:
+    """Get wallet details by ID."""
+    db_wallet = get_wallet_by_id(session=session, wallet_id=wallet_id)
+    if not db_wallet:
+        raise HTTPException(status_code=NOT_FOUND_CODE, detail="Wallet not found")
+
+    # Check if wallet belongs to current user or user is superuser
+    if not current_user.is_superuser and (db_wallet.user_id != current_user.id):
+        raise HTTPException(
+            status_code=BAD_REQUEST_CODE,
+            detail="Not enough permissions",
+        )
+
+    return WalletPublic.model_validate(db_wallet)

backend/app/core/config.py

@@ -78,15 +78,15 @@ class Settings(BaseSettings):  # type: ignore[explicit-any]
     FIRST_SUPERUSER: EmailStr
     FIRST_SUPERUSER_PASSWORD: str
 
-    @computed_field # type: ignore[prop-decorator]
+    @computed_field  # type: ignore[prop-decorator]
     @property
     def all_cors_origins(self) -> list[str]:
         """Get all CORS origins."""
         return [str(origin).rstrip("/") for origin in self.BACKEND_CORS_ORIGINS] + [
             self.FRONTEND_HOST,
         ]
 
-    @computed_field # type: ignore[prop-decorator]
+    @computed_field  # type: ignore[prop-decorator]
     @property
     def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn:  # noqa: N802
         """Build database URI from configuration."""
@@ -99,7 +99,7 @@ def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn:  # noqa: N802
             path=self.POSTGRES_DB,
         )
 
-    @computed_field # type: ignore[prop-decorator]
+    @computed_field  # type: ignore[prop-decorator]
     @property
     def emails_enabled(self) -> bool:
         """Check if email configuration is enabled."""