Python abstract base classes for service interfaces

from abc import ABC, abstractmethod
from typing import BinaryIO

class EmailService(ABC):
    @abstractmethod
    async def send(
        self,
        to: str,
        subject: str,
        html: str,
        from_address: str = 'noreply@commontrace.dev',
    ) -> None:
        """Send an email. Raises EmailDeliveryError on failure."""
        ...

    @abstractmethod
    async def send_batch(self, messages: list[dict]) -> list[str]:
        """Send multiple emails. Returns list of message IDs."""
        ...

class StorageService(ABC):
    @abstractmethod
    async def upload(
        self, key: str, data: bytes | BinaryIO, content_type: str
    ) -> str:
        """Upload file, return public URL."""
        ...

    @abstractmethod
    async def delete(self, key: str) -> None: ...

    @abstractmethod
    async def get_url(self, key: str, expires_in: int = 3600) -> str: ...

# Concrete implementations
class ResendEmailService(EmailService):
    def __init__(self, api_key: str):
        import resend
        resend.api_key = api_key
        self._resend = resend

    async def send(self, to: str, subject: str, html: str, from_address: str = 'noreply@commontrace.dev') -> None:
        self._resend.Emails.send({'from': from_address, 'to': [to], 'subject': subject, 'html': html})

    async def send_batch(self, messages: list[dict]) -> list[str]:
        results = self._resend.Emails.send_batch(messages)
        return [r['id'] for r in results]

class LocalStorageService(StorageService):
    """File system storage for development."""
    def __init__(self, base_dir: str = '/tmp/uploads'):
        from pathlib import Path
        self.base_dir = Path(base_dir)
        self.base_dir.mkdir(exist_ok=True)

    async def upload(self, key: str, data: bytes | BinaryIO, content_type: str) -> str:
        path = self.base_dir / key
        path.parent.mkdir(parents=True, exist_ok=True)
        content = data if isinstance(data, bytes) else data.read()
        path.write_bytes(content)
        return f'/uploads/{key}'

    async def delete(self, key: str) -> None:
        (self.base_dir / key).unlink(missing_ok=True)

    async def get_url(self, key: str, expires_in: int = 3600) -> str:
        return f'/uploads/{key}'  # No expiry for local

# Cannot instantiate ABC directly
try:
    svc = EmailService()  # TypeError: Can't instantiate abstract class
except TypeError as e:
    print(e)