src/api/database.py

import logging
from typing import AsyncGenerator, List, Optional, Dict
from pydantic_settings import BaseSettings
from pydantic import PostgresDsn
import pg8000
from pg8000 import Connection
from pg8000.exceptions import DatabaseError as Pg8000DatabaseError
import asyncio
from contextlib import asynccontextmanager
from threading import Lock
from urllib.parse import urlparse

# Set up structured logging
logging.basicConfig(
    level=logging.INFO, format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
)
logger = logging.getLogger(__name__)


class DatabaseSettings(BaseSettings):
    db_url: PostgresDsn
    pool_size: int = 5  # Default pool size is 5

    class Config:
        env_file = ".env"


# Custom database errors
class DatabaseError(Exception):
    """Base exception for database errors."""

    pass


class ConnectionError(DatabaseError):
    """Exception raised when a database connection fails."""

    pass


class PoolExhaustedError(DatabaseError):
    """Exception raised when the connection pool is exhausted."""

    pass


class QueryExecutionError(DatabaseError):
    """Exception raised when a query execution fails."""

    pass


class HealthCheckError(DatabaseError):
    """Exception raised when a health check fails."""

    pass


class Database:
    def __init__(self, db_url: PostgresDsn, pool_size: int):
        self.db_url = db_url
        self.pool_size = pool_size
        self.pool: List[Connection] = []
        self.lock = Lock()

    async def connect(self) -> None:
        """Create a connection pool."""
        try:
            # Convert PostgresDsn to a string
            db_url_str = str(self.db_url)
            result = urlparse(db_url_str)
            for _ in range(self.pool_size):
                conn = pg8000.connect(
                    user=result.username,
                    password=result.password,
                    host=result.hostname,
                    port=result.port or 5432,
                    database=result.path.lstrip("/"),
                )
                self.pool.append(conn)
            logger.info(
                f"Database connection pool created with {self.pool_size} connections."
            )
        except Pg8000DatabaseError as e:
            logger.error(f"Failed to create database connection pool: {e}")
            raise ConnectionError("Failed to create database connection pool.") from e

    async def disconnect(self) -> None:
        """Close all connections in the pool."""
        with self.lock:
            for conn in self.pool:
                conn.close()
            self.pool.clear()
            logger.info("Database connection pool closed.")

    @asynccontextmanager
    async def get_connection(self) -> AsyncGenerator[Connection, None]:
        """Acquire a connection from the pool."""
        with self.lock:
            if not self.pool:
                logger.error("Connection pool is exhausted.")
                raise PoolExhaustedError("No available connections in the pool.")
            conn = self.pool.pop()
        try:
            yield conn
        except Pg8000DatabaseError as e:
            logger.error(f"Connection error: {e}")
            raise ConnectionError("Failed to use database connection.") from e
        finally:
            with self.lock:
                self.pool.append(conn)

    async def fetch(self, query: str, *args) -> Dict[str, List]:
        """
        Execute a SELECT query and return the results as a dictionary of lists.

        Args:
            query (str): The SQL query to execute.
            *args: Query parameters.

        Returns:
            Dict[str, List]: A dictionary where keys are column names and values are lists of column values.

        Raises:
            QueryExecutionError: If the query execution fails.
        """
        try:
            async with self.get_connection() as conn:
                cursor = conn.cursor()
                cursor.execute(query, args)
                rows = cursor.fetchall()
                columns = [desc[0] for desc in cursor.description]

                # Convert the list of dictionaries into a dictionary of lists
                data_dict = {column: [] for column in columns}
                for row in rows:
                    for i, value in enumerate(row):
                        data_dict[columns[i]].append(value)

                return data_dict
        except Pg8000DatabaseError as e:
            logger.error(f"Query execution failed: {e}")
            raise QueryExecutionError(f"Failed to execute query: {query}") from e

    async def execute(self, query: str, *args) -> None:
        """
        Execute an INSERT, UPDATE, or DELETE query.

        Args:
            query (str): The SQL query to execute.
            *args: Query parameters.

        Raises:
            QueryExecutionError: If the query execution fails.
        """
        try:
            async with self.get_connection() as conn:
                cursor = conn.cursor()
                cursor.execute(query, args)
                conn.commit()
        except Pg8000DatabaseError as e:
            logger.error(f"Query execution failed: {e}")
            raise QueryExecutionError(f"Failed to execute query: {query}") from e

    async def health_check(self) -> bool:
        """
        Perform a health check by executing a simple query (e.g., SELECT 1).

        Returns:
            bool: True if the database is healthy, False otherwise.

        Raises:
            HealthCheckError: If the health check fails.
        """
        try:
            async with self.get_connection() as conn:
                cursor = conn.cursor()
                cursor.execute("SELECT 1")
                result = cursor.fetchone()
                cursor.close()

                # Check if the result is as expected
                if result and result[0] == 1:
                    logger.info("Database health check succeeded.")
                    return True
                else:
                    logger.error("Database health check failed: Unexpected result.")
                    raise HealthCheckError("Unexpected result from health check query.")
        except Pg8000DatabaseError as e:
            logger.error(f"Health check failed: {e}")
            raise HealthCheckError("Failed to perform health check.") from e


# Dependency to get the database instance
async def get_db() -> AsyncGenerator[Database, None]:
    settings = DatabaseSettings()
    db = Database(db_url=settings.db_url, pool_size=settings.pool_size)
    await db.connect()
    try:
        yield db
    finally:
        await db.disconnect()


# Example usage
if __name__ == "__main__":

    async def main():
        settings = DatabaseSettings()
        db = Database(db_url=settings.db_url, pool_size=settings.pool_size)
        await db.connect()

        try:
            # Perform a health check
            is_healthy = await db.health_check()
            print(f"Database health check: {'Success' if is_healthy else 'Failure'}")
        except HealthCheckError as e:
            print(f"Health check failed: {e}")
        finally:
            await db.disconnect()

    asyncio.run(main())