/**
 * Phase B alert framework — service layer.
 *
 * This is the skeleton: types, function shapes, and behaviour stubs. The
 * actual rule evaluators live in `alert-rules.ts` (PR2). The cron
 * dispatcher will compose this service with that catalogue.
 */

import { and, eq, isNull, sql } from 'drizzle-orm';
import { createHash } from 'crypto';

import { db } from '@/lib/db';
import { alerts, type Alert, type AlertSeverity, type AlertRuleId } from '@/lib/db/schema/insights';
import { emitToRoom } from '@/lib/socket/server';

export interface AlertCandidate {
  ruleId: AlertRuleId;
  severity: AlertSeverity;
  title: string;
  body?: string;
  link: string;
  entityType?: string;
  entityId?: string;
  metadata?: Record<string, unknown>;
}

/**
 * Stable identity hash so re-evaluations of the same condition upsert
 * onto the same row (via `idx_alerts_fingerprint_open`).
 */
export function fingerprintFor(
  c: Pick<AlertCandidate, 'ruleId' | 'entityType' | 'entityId'>,
): string {
  return createHash('sha1')
    .update(`${c.ruleId}|${c.entityType ?? ''}|${c.entityId ?? ''}`)
    .digest('hex');
}

/**
 * Apply a batch of rule outputs against the open-alert table:
 * - upsert open alerts (rule still firing)
 * - resolve any open alert in scope whose fingerprint isn't in this batch
 */
export async function reconcileAlertsForPort(
  portId: string,
  ruleId: AlertRuleId,
  candidates: AlertCandidate[],
): Promise<void> {
  // Insert new / leave existing — only one open row per fingerprint
  // thanks to the partial unique index. Track newly inserted rows so we
  // can emit `alert:created` to the port room.
  for (const c of candidates) {
    const fingerprint = fingerprintFor(c);
    const inserted = await db
      .insert(alerts)
      .values({
        portId,
        ruleId: c.ruleId,
        severity: c.severity,
        title: c.title,
        body: c.body,
        link: c.link,
        entityType: c.entityType,
        entityId: c.entityId,
        fingerprint,
        metadata: c.metadata ?? {},
      })
      .onConflictDoNothing()
      .returning({ id: alerts.id });
    if (inserted[0]) {
      emitToRoom(`port:${portId}`, 'alert:created', {
        alertId: inserted[0].id,
        portId,
        ruleId: c.ruleId,
        severity: c.severity,
        title: c.title,
        link: c.link,
      });
    }
  }

  // Auto-resolve open alerts for this rule whose fingerprint disappeared.
  const liveFingerprints = new Set(candidates.map((c) => fingerprintFor(c)));
  const open = await db.query.alerts.findMany({
    where: and(eq(alerts.portId, portId), eq(alerts.ruleId, ruleId), isNull(alerts.resolvedAt)),
  });
  const stale = open.filter((a) => !liveFingerprints.has(a.fingerprint));
  for (const a of stale) {
    await db
      .update(alerts)
      .set({ resolvedAt: sql`now()` })
      .where(eq(alerts.id, a.id));
    emitToRoom(`port:${portId}`, 'alert:resolved', {
      alertId: a.id,
      portId,
      ruleId,
    });
  }
}

export async function dismissAlert(alertId: string, userId: string): Promise<void> {
  const [row] = await db
    .update(alerts)
    .set({ dismissedAt: sql`now()`, dismissedBy: userId })
    .where(eq(alerts.id, alertId))
    .returning({ id: alerts.id, portId: alerts.portId });
  if (row) {
    emitToRoom(`port:${row.portId}`, 'alert:dismissed', { alertId: row.id, portId: row.portId });
  }
}

export async function acknowledgeAlert(alertId: string, userId: string): Promise<void> {
  await db
    .update(alerts)
    .set({ acknowledgedAt: sql`now()`, acknowledgedBy: userId })
    .where(eq(alerts.id, alertId));
}

export interface ListAlertsOptions {
  severity?: AlertSeverity[];
  includeDismissed?: boolean;
  includeResolved?: boolean;
}

export async function listAlertsForPort(
  portId: string,
  options: ListAlertsOptions = {},
): Promise<Alert[]> {
  const conditions = [eq(alerts.portId, portId)];
  if (!options.includeResolved) conditions.push(isNull(alerts.resolvedAt));
  if (!options.includeDismissed) conditions.push(isNull(alerts.dismissedAt));
  return db.query.alerts.findMany({
    where: and(...conditions),
    orderBy: (a, { desc }) => [desc(a.firedAt)],
    limit: 100,
  });
}