src/application/use_cases/ingest_ppg.py

"""
application/use_cases/ingest_ppg.py
─────────────────────────────────────
IngestPPGUseCase — ETL #1 orchestrator.

Responsibility:
    Accept a raw PPG payload from the API, validate it, persist it to the
    database, and publish a message to the queue for downstream processing.

Dependencies (injected via constructor — Dependency Inversion Principle):
    • PPGRepository   — stores the signal
    • MessageBroker   — publishes the event

This use case knows nothing about FastAPI, SQLAlchemy, or RabbitMQ.
"""
from __future__ import annotations

import json

from src.application.dto.ppg_dto import PPGIngestRequest, PPGIngestResponse
from src.domain.entities.ppg_signal import PPGSignal
from src.domain.interfaces.repositories.ppg_repository import PPGRepository
from src.domain.interfaces.services.message_broker import MessageBroker
from src.shared.constants import PPG_QUEUE_NAME
from src.shared.logger import get_logger

logger = get_logger(__name__)


class IngestPPGUseCase:
    """
    ETL #1: Extract → Transform → Load for incoming PPG signals.

    Steps:
        1. Extract  — build a validated PPGSignal entity from the request DTO.
        2. Transform — call ``entity.validate()`` to enforce domain rules.
        3. Load      — persist to database (``ppg_repo.add()``)
                       publish to queue   (``broker.publish()``).

    Usage::

        use_case = IngestPPGUseCase(ppg_repo=..., broker=...)
        response = await use_case.execute(request)
    """

    def __init__(
        self,
        ppg_repo: PPGRepository,
        broker: MessageBroker,
    ) -> None:
        """
        Args:
            ppg_repo: Any concrete PPGRepository (SQLAlchemy, in-memory, …).
            broker:   Any concrete MessageBroker (RabbitMQ, in-memory, …).
        """
        self._ppg_repo = ppg_repo
        self._broker = broker

    async def execute(self, request: PPGIngestRequest) -> PPGIngestResponse:
        """
        Run the ingestion pipeline for a single PPG signal.

        Args:
            request: Validated Pydantic DTO from the API route.

        Returns:
            PPGIngestResponse with the stored signal ID and queue status.

        Raises:
            InvalidSignalError: If the signal fails domain validation.
        """
        logger.info(
            "IngestPPGUseCase.execute — device=%s user=%s samples=%d",
            request.device_id,
            request.user_id,
            len(request.ppg_values),
        )

        # ── Step 1: EXTRACT — Build domain entity ─────────────────────────────
        signal = PPGSignal(
            device_id=request.device_id,
            user_id=request.user_id,
            sampling_rate=request.sampling_rate,
            ppg_values=request.ppg_values,
            duration_seconds=request.duration_seconds,
            timestamp=request.timestamp,
        )

        # ── Step 2: TRANSFORM — Domain validation ────────────────────────────
        signal.validate()
        logger.debug("Signal validated: %s", signal)

        # ── Step 3a: LOAD — Persist to database ──────────────────────────────
        persisted_signal = await self._ppg_repo.add(signal)
        logger.info("Signal persisted with id=%s", persisted_signal.id)

        # ── Step 3b: LOAD — Publish to message queue ─────────────────────────
        queued = False
        try:
            await self._broker.publish(
                queue_name=PPG_QUEUE_NAME,
                message=persisted_signal.to_dict(),
            )
            queued = True
            logger.info("Signal %s published to queue '%s'", persisted_signal.id, PPG_QUEUE_NAME)
        except Exception as exc:
            # Publishing failure is non-fatal: signal is already persisted.
            # Log the error so the ops team can replay the message if needed.
            logger.error(
                "Failed to publish signal %s to queue: %s",
                persisted_signal.id,
                exc,
                exc_info=True,
            )

        return PPGIngestResponse(
            signal_id=persisted_signal.id,
            user_id=persisted_signal.user_id,
            device_id=persisted_signal.device_id,
            num_samples=persisted_signal.num_samples,
            duration_seconds=persisted_signal.duration_seconds,
            queued=queued,
        )