from __future__ import annotations

import hashlib
import hmac
import uuid
from datetime import UTC, datetime
from pathlib import Path

from fastapi import APIRouter, Depends, Header
from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app.api.deps import get_db
from app.core.config import get_settings
from app.core.errors import AppError
from app.models.audit import AuditEvent
from app.models.outbox import OutboxEvent
from app.schemas import (
    N8nHeartbeatIn,
    N8nHeartbeatResult,
    ProcedureDocumentOut,
    ProcedureListOut,
    ProcedureSyncResultIn,
    ProcedureSyncResultResult,
    ReturnCallbackIn,
    ScanResultOut,
    WorkflowErrorReportIn,
    WorkflowErrorReportResult,
)
from app.services.audit import record_audit_event
from app.services.data_quality import run_scan
from app.services.knowledge.procedures import iter_procedure_documents

router = APIRouter(prefix="/api/v1/integrations/n8n", tags=["integrations"])
settings = get_settings()

_CANONICAL_WORKFLOW_NAMES = frozenset(
    {
        "Fleet Ops — Vehicle Return Orchestration",
        "Fleet Ops — Scheduled Data Quality Scan",
        "Fleet Ops — RAGcore Procedure Sync",
        "Fleet Ops — Workflow Error Handler",
    }
)


def _require_service_token(service_token: str) -> None:
    # Constant-time comparison: a plain ``!=`` leaks how many leading bytes matched.
    if not hmac.compare_digest(
        service_token.encode("utf-8"), settings.n8n_callback_token.encode("utf-8")
    ):
        raise AppError("UNAUTHORIZED_SERVICE", "Invalid service token.", status_code=401)


def _lock_idempotency_key(db: Session, namespace: str, key: str) -> None:
    """Serialize callback check+insert by a stable, transaction-scoped key."""
    digest = hashlib.sha256(f"{namespace}:{key}".encode()).digest()
    lock_id = int.from_bytes(digest[:8], byteorder="big", signed=True)
    db.scalar(select(func.pg_advisory_xact_lock(lock_id)))


@router.post("/heartbeat", response_model=N8nHeartbeatResult)
def workflow_heartbeat(
    body: N8nHeartbeatIn,
    service_token: str = Header(..., alias="X-Service-Token"),
    db: Session = Depends(get_db),
) -> N8nHeartbeatResult:
    """Authenticated, idempotent execution evidence from a canonical n8n workflow."""
    _require_service_token(service_token)
    if body.workflow_name not in _CANONICAL_WORKFLOW_NAMES:
        raise AppError("UNKNOWN_WORKFLOW", "Unknown Fleet Ops workflow.", status_code=422)
    _lock_idempotency_key(db, "n8n_workflow_heartbeat", f"{body.execution_id}:{body.status}")
    already_recorded = (
        db.scalar(
            select(AuditEvent.id).where(
                AuditEvent.action == "n8n_workflow_heartbeat",
                AuditEvent.metadata_json["execution_id"].astext == body.execution_id,
                AuditEvent.after_json["status"].astext == body.status,
            )
        )
        is not None
    )
    if not already_recorded:
        record_audit_event(
            db,
            actor_type="service",
            actor_label="n8n workflow heartbeat",
            action="n8n_workflow_heartbeat",
            entity_type="automation",
            after={
                "workflow_id": body.workflow_id,
                "workflow_name": body.workflow_name,
                "status": body.status,
            },
            metadata={"execution_id": body.execution_id},
        )
        db.commit()
    return N8nHeartbeatResult(
        status="already_registered" if already_recorded else "registered",
        execution_id=body.execution_id,
        occurred_at=datetime.now(UTC),
    )


@router.post("/return-callback")
def return_callback(
    body: ReturnCallbackIn,
    idempotency_key: str = Header(..., alias="Idempotency-Key"),
    service_token: str = Header(..., alias="X-Service-Token"),
    db: Session = Depends(get_db),
) -> dict:
    _require_service_token(service_token)

    try:
        event_id = uuid.UUID(idempotency_key)
    except ValueError as exc:
        raise AppError(
            "INVALID_IDEMPOTENCY_KEY", "Idempotency-Key must be the event's UUID.", status_code=422
        ) from exc

    event = db.scalar(select(OutboxEvent).where(OutboxEvent.event_id == event_id).with_for_update())
    if event is None:
        raise AppError("EVENT_NOT_FOUND", "No outbox event matches this event ID.", status_code=404)
    if body.event_id != event_id:
        raise AppError(
            "CALLBACK_EVENT_MISMATCH",
            "Callback event_id does not match Idempotency-Key.",
            status_code=409,
        )
    try:
        expected_correlation_id = uuid.UUID(str(event.payload_json["correlation_id"]))
    except (KeyError, TypeError, ValueError) as exc:
        raise AppError(
            "INVALID_EVENT_CORRELATION",
            "The stored outbox event has no valid correlation ID.",
            status_code=409,
        ) from exc
    if body.correlation_id != expected_correlation_id:
        raise AppError(
            "CALLBACK_CORRELATION_MISMATCH",
            "Callback correlation_id does not match the outbox event.",
            status_code=409,
        )

    # Idempotent by event ID: n8n or our own dispatcher may redeliver the same event
    # (e.g. a lost response after a timeout), so this callback must not double-record.
    already_recorded = (
        db.scalar(
            select(AuditEvent.id).where(
                AuditEvent.action == "n8n_return_followup_recorded",
                AuditEvent.metadata_json["event_id"].astext == str(event_id),
            )
        )
        is not None
    )
    if not already_recorded:
        record_audit_event(
            db,
            actor_type="service",
            actor_label="n8n",
            action="n8n_return_followup_recorded",
            entity_type="booking",
            correlation_id=expected_correlation_id,
            after={"follow_up": body.follow_up, "summary": body.summary},
            metadata={"event_id": str(event_id)},
        )
        db.commit()

    return {
        "status": "recorded",
        "event_id": str(event_id),
        "occurred_at": datetime.now(UTC).isoformat(),
    }


@router.post("/scheduled-scan", response_model=ScanResultOut)
def scheduled_scan(
    service_token: str = Header(..., alias="X-Service-Token"),
    db: Session = Depends(get_db),
) -> ScanResultOut:
    """Triggered by the scheduled n8n quality-scan workflow. Narrow, read-mostly, and
    safe to call repeatedly: run_scan() only ever creates an issue for a condition that
    doesn't already have one open, so a duplicate or overlapping trigger does no
    duplicate domain work -- it just reports zero new issues for anything already known."""
    _require_service_token(service_token)

    result = run_scan(db, actor_label="n8n scheduled scan", actor_type="service")
    return ScanResultOut(created=result.created)


@router.post("/workflow-error", response_model=WorkflowErrorReportResult)
def workflow_error(
    body: WorkflowErrorReportIn,
    service_token: str = Header(..., alias="X-Service-Token"),
    db: Session = Depends(get_db),
) -> WorkflowErrorReportResult:
    """Receives a bounded, secret-free failure report from the central n8n "Fleet Ops --
    Workflow Error Handler" workflow, which is attached as the Error Workflow on every
    other Fleet Ops n8n workflow. Idempotent on execution_id: n8n may redeliver the same
    error report (e.g. after a timed-out response), so this must not double-record."""
    _require_service_token(service_token)
    _lock_idempotency_key(db, "n8n_workflow_failure", body.execution_id)

    already_recorded = (
        db.scalar(
            select(AuditEvent.id).where(
                AuditEvent.action == "n8n_workflow_failure_registered",
                AuditEvent.metadata_json["execution_id"].astext == body.execution_id,
            )
        )
        is not None
    )
    if not already_recorded:
        record_audit_event(
            db,
            actor_type="service",
            actor_label="n8n error handler",
            action="n8n_workflow_failure_registered",
            entity_type="automation",
            correlation_id=body.correlation_id,
            after={
                "workflow_id": body.workflow_id,
                "workflow_name": body.workflow_name,
                "error_category": body.error_category,
                "error_summary": body.error_summary,
                "trigger_context": body.trigger_context,
                "attempt": body.attempt,
                "retry_action": body.retry_action,
                "failed_at": body.failed_at.isoformat(),
            },
            metadata={"execution_id": body.execution_id},
        )
        db.commit()

    return WorkflowErrorReportResult(
        status="already_registered" if already_recorded else "registered",
        execution_id=body.execution_id,
        occurred_at=datetime.now(UTC),
    )


@router.get("/procedures", response_model=ProcedureListOut)
def list_procedures(service_token: str = Header(..., alias="X-Service-Token")) -> ProcedureListOut:
    """Read-only source list for the RAGcore Procedure Sync workflow: every procedure
    Markdown file Fleet Ops ships, across every supported language, with a stable
    per-document id (source_id) and a content hash so the caller can detect changes
    without re-fetching content it already has."""
    _require_service_token(service_token)

    documents = [
        ProcedureDocumentOut(
            id=doc.source_id,
            language=doc.language,
            document_id=doc.document_id,
            title=doc.title,
            version=doc.version,
            content=doc.content,
            content_hash=doc.content_hash,
        )
        for doc in iter_procedure_documents(Path(settings.knowledge_dir))
    ]
    return ProcedureListOut(documents=documents)


@router.post("/procedures-sync-result", response_model=ProcedureSyncResultResult)
def procedures_sync_result(
    body: ProcedureSyncResultIn,
    service_token: str = Header(..., alias="X-Service-Token"),
    db: Session = Depends(get_db),
) -> ProcedureSyncResultResult:
    """Receives a summary (counts only, no document content) from the n8n "Fleet Ops --
    RAGcore Procedure Sync" workflow once it finishes uploading procedures to RAGcore.
    Idempotent on execution_id, matching the workflow-error and return-callback pattern."""
    _require_service_token(service_token)
    _lock_idempotency_key(db, "n8n_procedure_sync", body.execution_id)

    already_recorded = (
        db.scalar(
            select(AuditEvent.id).where(
                AuditEvent.action == "n8n_procedures_synced",
                AuditEvent.metadata_json["execution_id"].astext == body.execution_id,
            )
        )
        is not None
    )
    if not already_recorded:
        record_audit_event(
            db,
            actor_type="service",
            actor_label="n8n procedure sync",
            action="n8n_procedures_synced",
            entity_type="automation",
            after={"synced": body.synced, "failed": body.failed},
            metadata={"execution_id": body.execution_id},
        )
        db.commit()

    return ProcedureSyncResultResult(
        status="already_registered" if already_recorded else "registered",
        execution_id=body.execution_id,
        occurred_at=datetime.now(UTC),
    )