from __future__ import annotations

from typing import Literal

from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app.core.config import get_settings
from app.models.audit import AuditEvent
from app.models.outbox import OutboxEvent
from app.schemas import N8nErrorHandlerStatus, N8nIntegrationStatus, N8nWorkflowEvidence

settings = get_settings()

# The 4 canonical Fleet Ops n8n workflows (see n8n/workflows/MANIFEST.md). Workflow 3
# (RAGcore Procedure Sync) is not built yet, so it always reports no evidence.
_CANONICAL_WORKFLOWS = (
    "Fleet Ops — Vehicle Return Orchestration",
    "Fleet Ops — Scheduled Data Quality Scan",
    "Fleet Ops — RAGcore Procedure Sync",
    "Fleet Ops — Workflow Error Handler",
)


def derive_n8n_status(db: Session) -> N8nIntegrationStatus:
    counts: dict[str, int] = dict(
        db.execute(
            select(OutboxEvent.delivery_status, func.count()).group_by(OutboxEvent.delivery_status)
        ).all()  # type: ignore[arg-type]
    )
    pending = counts.get("pending", 0)
    delivering = counts.get("delivering", 0)
    failed = counts.get("failed", 0)
    succeeded = counts.get("succeeded", 0)

    latest_success_at = db.scalar(
        select(func.max(OutboxEvent.updated_at)).where(OutboxEvent.delivery_status == "succeeded")
    )
    latest_failure_at = db.scalar(
        select(func.max(OutboxEvent.updated_at)).where(OutboxEvent.delivery_status == "failed")
    )

    state: Literal["disabled", "unavailable", "degraded", "operational", "no_evidence"]
    if not settings.n8n_dispatch_enabled:
        state = "disabled"
    elif failed > 0 and succeeded == 0:
        state = "unavailable"
    elif failed > 0:
        state = "degraded"
    elif succeeded > 0 or pending > 0 or delivering > 0:
        state = "operational"
    else:
        state = "no_evidence"

    # Scheduled scan evidence: only service-triggered runs count as n8n evidence, not
    # runs an operator triggered manually from the Data Quality page.
    latest_scan_at = db.scalar(
        select(func.max(AuditEvent.occurred_at)).where(
            AuditEvent.action == "data_quality_scan_run",
            AuditEvent.actor_type == "service",
        )
    )

    # Error handler evidence: registrations posted by the "Fleet Ops — Workflow Error
    # Handler" n8n workflow itself, which also doubles as proof that workflow is wired
    # up and firing correctly.
    total_failures_registered = (
        db.scalar(
            select(func.count(AuditEvent.id)).where(
                AuditEvent.action == "n8n_workflow_failure_registered"
            )
        )
        or 0
    )
    latest_failure_row = db.execute(
        select(AuditEvent.occurred_at, AuditEvent.after_json)
        .where(AuditEvent.action == "n8n_workflow_failure_registered")
        .order_by(AuditEvent.occurred_at.desc())
        .limit(1)
    ).first()
    latest_handler_failure_at = latest_failure_row[0] if latest_failure_row else None
    latest_handler_failure_workflow = (
        (latest_failure_row[1] or {}).get("workflow_name") if latest_failure_row else None
    )

    evidence_by_workflow = {
        "Fleet Ops — Vehicle Return Orchestration": latest_success_at,
        "Fleet Ops — Scheduled Data Quality Scan": latest_scan_at,
        "Fleet Ops — RAGcore Procedure Sync": None,
        "Fleet Ops — Workflow Error Handler": latest_handler_failure_at,
    }
    workflows = [
        N8nWorkflowEvidence(
            name=name,
            built=name != "Fleet Ops — RAGcore Procedure Sync",
            last_seen_at=evidence_by_workflow[name],
        )
        for name in _CANONICAL_WORKFLOWS
    ]

    return N8nIntegrationStatus(
        configured=bool(settings.n8n_webhook_url),
        dispatch_enabled=settings.n8n_dispatch_enabled,
        state=state,
        pending=pending,
        delivering=delivering,
        failed=failed,
        succeeded=succeeded,
        latest_success_at=latest_success_at,
        latest_failure_at=latest_failure_at,
        expected_workflow_count=len(_CANONICAL_WORKFLOWS),
        known_workflow_count=sum(1 for w in workflows if w.last_seen_at is not None),
        workflows=workflows,
        error_handler=N8nErrorHandlerStatus(
            total_failures_registered=total_failures_registered,
            latest_failure_at=latest_handler_failure_at,
            latest_failure_workflow=latest_handler_failure_workflow,
        ),
    )