"""Transactional outbox for reliable domain event delivery.

Instead of publishing events directly to an in-process bus (which is lost
on crash/restart), domain events are written to the ``event_outbox`` table
**within the same database transaction** as the business operation.  A
background worker then polls the outbox and publishes events to the
in-process event bus.

Usage in services::

    from app.core.outbox import enqueue_outbox_event

    await enqueue_outbox_event(db, tenant_id, "contact.created", {
        "contact_id": str(contact.id),
        "tenant_id": str(tenant_id),
    })
    # ... later, the transaction commits and the event is durable.
"""

from __future__ import annotations

import logging
import uuid
from datetime import datetime, timedelta, timezone
from typing import Any

import redis.asyncio as aioredis
from sqlalchemy import text
from sqlalchemy.ext.asyncio import AsyncSession

logger = logging.getLogger(__name__)

# ── SQL statements (raw text for FOR UPDATE SKIP LOCKED) ────────────────────

_INSERT_SQL = text(
    """
    INSERT INTO event_outbox (tenant_id, event_name, payload, aggregate_type, aggregate_id, occurred_at, correlation_id, schema_version)
    VALUES (:tenant_id, :event_name, CAST(:payload AS JSONB), :aggregate_type, :aggregate_id, COALESCE(:occurred_at, now()), :correlation_id, COALESCE(:schema_version, 1))
    RETURNING id
    """
)

_CLAIM_SQL = text(
    """
    UPDATE event_outbox
       SET status = 'processing',
           updated_at = now()
     WHERE id IN (
         SELECT id FROM event_outbox
          WHERE status = 'pending'
            AND (next_retry_at IS NULL OR next_retry_at <= now())
          ORDER BY created_at
          LIMIT :batch_size
          FOR UPDATE SKIP LOCKED
     )
    RETURNING id, tenant_id, event_name, payload, attempts, max_attempts,
              aggregate_type, aggregate_id, occurred_at, correlation_id, schema_version
    """
)

_MARK_PUBLISHED_SQL = text(
    """
    UPDATE event_outbox
       SET status = 'published',
           published_at = now(),
           updated_at = now()
     WHERE id = :id
    """
)

_FAIL_SQL = text(
    """
    UPDATE event_outbox
       SET status = 'failed',
           updated_at = now()
     WHERE id = :id
    """
)

_RETRY_SQL = text(
    """
    UPDATE event_outbox
       SET status = 'pending',
           attempts = :attempts,
           next_retry_at = :next_retry_at,
           updated_at = now()
     WHERE id = :id
    """
)


def _json_payload(payload: dict[str, Any]) -> str:
    """Serialise payload to a JSON string suitable for JSONB cast."""
    import json

    return json.dumps(payload, default=str)


async def enqueue_outbox_event(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    event_name: str,
    payload: dict[str, Any],
    *,
    aggregate_type: str | None = None,
    aggregate_id: uuid.UUID | None = None,
    correlation_id: uuid.UUID | None = None,
    schema_version: int = 1,
) -> None:
    """Insert an event into the outbox table within the current transaction.

    The event is only persisted when the surrounding transaction commits.
    This guarantees at-least-once delivery — no event is lost even if the
    process crashes after the business operation but before the event is
    published.

    Args:
        db: Active async SQLAlchemy session (part of the business transaction).
        tenant_id: Tenant scope for the event.
        event_name: Logical event name (e.g. ``"crm.contact.created.v1"``).
        payload: Event payload dict (will be stored as JSONB).
        aggregate_type: Type of the aggregate (e.g. 'contact', 'task').
        aggregate_id: UUID of the aggregate entity.
        correlation_id: Optional correlation UUID for tracing across services.
        schema_version: Event schema version (default 1).
    """
    await db.execute(
        _INSERT_SQL,
        {
            "tenant_id": str(tenant_id),
            "event_name": event_name,
            "payload": _json_payload(payload),
            "aggregate_type": aggregate_type,
            "aggregate_id": str(aggregate_id) if aggregate_id else None,
            "occurred_at": None,  # DB defaults to NOW()
            "correlation_id": str(correlation_id) if correlation_id else None,
            "schema_version": schema_version,
        },
    )


async def _process_single_outbox_event(
    db: AsyncSession,
    event_bus,
    row: tuple,
) -> bool:
    """Process a single outbox event. Returns True if published successfully."""
    event_id = row[0]
    tenant_id = row[1]
    event_name = row[2]
    payload = row[3]
    attempts = row[4]
    max_attempts = row[5]
    aggregate_type = row[6] if len(row) > 6 else None
    aggregate_id = row[7] if len(row) > 7 else None
    occurred_at = row[8] if len(row) > 8 else None
    correlation_id = row[9] if len(row) > 9 else None
    schema_version = row[10] if len(row) > 10 else 1

    # payload comes back as a dict from JSONB
    if isinstance(payload, str):
        import json
        payload_dict = json.loads(payload)
    else:
        payload_dict = payload

    try:
        # Enrich payload with standardized event envelope metadata
        payload_dict.setdefault("_event_id", str(event_id))
        payload_dict.setdefault("_event_name", event_name)
        payload_dict.setdefault("_event_timestamp", datetime.now(timezone.utc).isoformat())
        payload_dict.setdefault("_tenant_id", str(tenant_id))
        payload_dict.setdefault("_aggregate_type", aggregate_type)
        payload_dict.setdefault("_aggregate_id", str(aggregate_id) if aggregate_id else None)
        payload_dict.setdefault("_occurred_at", occurred_at.isoformat() if occurred_at else None)
        payload_dict.setdefault("_correlation_id", str(correlation_id) if correlation_id else None)
        payload_dict.setdefault("_schema_version", schema_version)

        # Idempotency check: has this event already been processed? (P1.5 fix)
        already_processed = await db.execute(
            text("SELECT 1 FROM consumer_inbox WHERE event_id = :eid AND status = 'processed' LIMIT 1"),
            {"eid": str(event_id)},
        )
        if already_processed.first():
            # Event was already processed by all consumers — mark as published
            await db.execute(_MARK_PUBLISHED_SQL, {"id": str(event_id)})
            logger.debug("Outbox event %s already processed, marking as published", event_id)
            return True

        results = await event_bus.publish_with_results(event_name, payload_dict)

        # Check if any handlers were registered at all
        handler_count = len(results)
        # If any handler raised, treat as failure
        handler_errors = [r for r in results if r is not None]
        if handler_errors:
            raise handler_errors[0]

        if handler_count == 0:
            # No handlers registered — mark as 'no_handlers' not 'published'
            await db.execute(
                text("UPDATE event_outbox SET status = 'no_handlers', published_at = now() WHERE id = :id"),
                {"id": str(event_id)},
            )
            logger.warning("Outbox event %s (%s) had no handlers registered", event_id, event_name)
        else:
            # Record in consumer_inbox for idempotency (P1.5 fix)
            await db.execute(
                text("INSERT INTO consumer_inbox (event_id, consumer_name, status, processed_at) VALUES (:eid, :name, 'processed', now()) ON CONFLICT DO NOTHING"),
                {"eid": str(event_id), "name": event_name},
            )
            await db.execute(_MARK_PUBLISHED_SQL, {"id": str(event_id)})
        return True
    except Exception as exc:
        logger.error(
            "Failed to publish outbox event %s (%s): %s",
            event_id, event_name, exc,
            exc_info=True,
        )
        new_attempts = attempts + 1
        if new_attempts >= max_attempts:
            await db.execute(_FAIL_SQL, {"id": str(event_id)})
            logger.warning(
                "Outbox event %s marked as failed after %d attempts",
                event_id, new_attempts,
            )
        else:
            backoff = timedelta(seconds=(2 ** new_attempts) * 10)
            next_retry = datetime.now(timezone.utc) + backoff
            await db.execute(
                _RETRY_SQL,
                {
                    "id": str(event_id),
                    "attempts": new_attempts,
                    "next_retry_at": next_retry,
                },
            )
        return False


async def process_outbox_batch(
    db: AsyncSession,
    redis: aioredis.Redis | None = None,
    batch_size: int = 50,
    tenant_ids: list[uuid.UUID] | None = None,
) -> int:
    """Process one batch of pending outbox events.

    Iterates over all tenants, setting tenant context for RLS before
    claiming and processing events for each tenant.

    Args:
        db: Async SQLAlchemy session for this batch (crm_worker role).
        redis: Optional Redis client (unused for now, reserved for future
               cross-process pub/sub).
        batch_size: Maximum events to process per tenant in one batch.
        tenant_ids: Optional list of tenant IDs to process. If None,
            all tenants are loaded from the database.

    Returns:
        Number of events successfully published.
    """
    from app.core.event_bus import get_event_bus

    event_bus = get_event_bus()
    published_count = 0

    # Load tenant IDs if not provided
    if tenant_ids is None:
        result = await db.execute(text("SELECT id FROM tenants"))
        tenant_ids = [row[0] for row in result]

    for tenant_id in tenant_ids:
        # Set tenant context for RLS — required for event_outbox and consumer_inbox
        await db.execute(
            text("SELECT set_config('app.current_tenant_id', :tid, true)"),
            {"tid": str(tenant_id)},
        )

        # Claim a batch of pending events for this tenant
        rows = (
            await db.execute(_CLAIM_SQL, {"batch_size": batch_size})
        ).fetchall()

        if not rows:
            continue

        for row in rows:
            published = await _process_single_outbox_event(db, event_bus, row)
            if published:
                published_count += 1

        # Commit after each tenant to release locks
        await db.commit()

    return published_count