import type { Prisma, PrismaClient } from "@/generated/prisma/client";
import { NotificationChannel, NotificationDeliveryStatus, NotificationType } from "@/generated/prisma/enums";
import { notifySafely, resolveActivePushSubscriptions, resolveEmailAddress } from "./notification.service";
import type { EmailProvider } from "./providers/email-provider";
import type { PushProvider } from "./providers/push-provider";
import { getOwnerUserIds } from "./recipients";
import { renderEmailForNotification } from "./render-email";
import { getBranding } from "@/lib/business/branding";

/**
 * The background notification processor — the one place EMAIL and PUSH
 * deliveries actually get sent. Deliberately NOT a Next.js server
 * timer/interval (the brief's explicit "do not rely on in-memory Next.js
 * server timers" — a serverless/multi-instance deployment has no single
 * long-lived process to host one): this is a plain function meant to be
 * invoked by an external scheduler hitting the authenticated route
 * handler at src/app/api/cron/process-notifications/route.ts. See that
 * file's header comment for the recommended trigger frequency and
 * deployment notes.
 *
 * Locking: each due delivery is claimed with a single conditional
 * `updateMany` (`WHERE id = ? AND status = <the status it was in when we
 * read it>`) before doing any work. If two workers race for the same row,
 * exactly one's claim affects a row (MySQL row-level locking during the
 * UPDATE), and the loser sees `count: 0` and moves on — no separate lock
 * table, no SELECT ... FOR UPDATE transaction held open across a slow
 * network call to Brevo/a push service.
 *
 * Retry: only a `retryable` failure (timeout/rate-limit/5xx — see
 * BrevoEmailProvider.isRetryable / WebPushProvider.sendPush) is retried,
 * with a short exponential backoff (1 min, 5 min, 30 min) up to
 * MAX_ATTEMPTS; a permanent failure (invalid recipient, rejected payload,
 * auth failure, expired push subscription) or an exhausted retry budget
 * both end at FAILED, never retried again.
 */

const MAX_ATTEMPTS = 4;
const BACKOFF_MINUTES = [1, 5, 30] as const;
/** Failed deliveries for one business within a single processing run at or above this count raises OWNER_REPEATED_DELIVERY_FAILURE — see NotificationType in schema.prisma. */
const REPEATED_FAILURE_THRESHOLD = 3;

export interface ProcessNotificationsResult {
  claimed: number;
  sent: number;
  retried: number;
  failed: number;
  /** Another worker already claimed the row between our read and our claim attempt — not an error. */
  skippedAlreadyClaimed: number;
}

type DueDelivery = Prisma.NotificationDeliveryGetPayload<{ include: { notification: true } }>;

function backoffMinutesFor(attemptNumber: number): number {
  return BACKOFF_MINUTES[attemptNumber - 1] ?? BACKOFF_MINUTES[BACKOFF_MINUTES.length - 1] ?? 30;
}

export async function processDueNotificationDeliveries(
  prisma: PrismaClient,
  params: { emailProvider: EmailProvider; pushProvider?: PushProvider; now?: Date; batchSize?: number; businessId?: string },
): Promise<ProcessNotificationsResult> {
  const now = params.now ?? new Date();
  const batchSize = params.batchSize ?? 25;

  const due = await prisma.notificationDelivery.findMany({
    where: {
      channel: { in: [NotificationChannel.EMAIL, NotificationChannel.PUSH] },
      status: { in: [NotificationDeliveryStatus.PENDING, NotificationDeliveryStatus.SCHEDULED] },
      OR: [{ scheduledFor: null }, { scheduledFor: { lte: now } }],
      ...(params.businessId ? { notification: { businessId: params.businessId } } : {}),
    },
    orderBy: [{ scheduledFor: "asc" }, { createdAt: "asc" }],
    take: batchSize,
    include: { notification: true },
  });

  const result: ProcessNotificationsResult = { claimed: 0, sent: 0, retried: 0, failed: 0, skippedAlreadyClaimed: 0 };
  const failuresByBusiness = new Map<string, number>();

  for (const delivery of due) {
    const claim = await prisma.notificationDelivery.updateMany({
      where: { id: delivery.id, status: delivery.status },
      data: { status: NotificationDeliveryStatus.PROCESSING, lastAttemptedAt: now, attemptCount: { increment: 1 } },
    });
    if (claim.count === 0) {
      result.skippedAlreadyClaimed++;
      continue;
    }
    result.claimed++;
    const attemptNumber = delivery.attemptCount + 1;

    const outcome =
      delivery.channel === NotificationChannel.EMAIL
        ? await processEmailDelivery(prisma, delivery, params.emailProvider)
        : await processPushDelivery(prisma, delivery, params.pushProvider);

    if (outcome.status === "sent") {
      await prisma.notificationDelivery.update({
        where: { id: delivery.id },
        data: {
          status: NotificationDeliveryStatus.SENT,
          sentAt: new Date(),
          providerName: outcome.providerName,
          providerMessageId: outcome.providerMessageId,
        },
      });
      result.sent++;
      continue;
    }

    if (outcome.retryable && attemptNumber < MAX_ATTEMPTS) {
      await prisma.notificationDelivery.update({
        where: { id: delivery.id },
        data: {
          status: NotificationDeliveryStatus.PENDING,
          scheduledFor: new Date(now.getTime() + backoffMinutesFor(attemptNumber) * 60_000),
          failureReason: outcome.reason.slice(0, 500),
        },
      });
      result.retried++;
    } else {
      await prisma.notificationDelivery.update({
        where: { id: delivery.id },
        data: { status: NotificationDeliveryStatus.FAILED, failureReason: outcome.reason.slice(0, 500) },
      });
      result.failed++;
      failuresByBusiness.set(
        delivery.notification.businessId,
        (failuresByBusiness.get(delivery.notification.businessId) ?? 0) + 1,
      );
    }
  }

  for (const [businessId, count] of failuresByBusiness) {
    if (count >= REPEATED_FAILURE_THRESHOLD) {
      await raiseRepeatedFailureNotice(prisma, businessId, now);
    }
  }

  return result;
}

type DeliveryOutcome =
  | { status: "sent"; providerName: string; providerMessageId?: string }
  | { status: "failed"; retryable: boolean; reason: string };

async function processEmailDelivery(prisma: PrismaClient, delivery: DueDelivery, emailProvider: EmailProvider): Promise<DeliveryOutcome> {
  try {
    const recipientEmail = await resolveEmailAddress(prisma, {
      recipientUserId: delivery.notification.recipientUserId ?? undefined,
      recipientCustomerId: delivery.notification.recipientCustomerId ?? undefined,
    });
    if (!recipientEmail) return { status: "failed", retryable: false, reason: "No email address on file for this recipient." };

    const email = await renderEmailForNotification(prisma, delivery.notification);
    if (!email) {
      return {
        status: "failed",
        retryable: false,
        reason: "Could not render email content — the business or referenced appointment/reward may have been deleted.",
      };
    }

    const sendResult = await emailProvider.sendEmail({
      to: { email: recipientEmail },
      sender: email.sender,
      subject: email.subject,
      html: email.html,
      text: email.text,
      idempotencyKey: delivery.id,
    });

    if (sendResult.status === "sent") {
      return { status: "sent", providerName: emailProvider.name, providerMessageId: sendResult.providerMessageId };
    }
    return { status: "failed", retryable: sendResult.retryable, reason: sendResult.reason };
  } catch (error) {
    return { status: "failed", retryable: true, reason: error instanceof Error ? error.message : "Unknown error while sending email." };
  }
}

/**
 * A PUSH delivery fans out to every active subscription this recipient
 * has (see PushSubscription in schema.prisma — a person can have several
 * devices, but there's only one PUSH NotificationDelivery row per
 * notification). Counted "sent" overall if at least one subscription
 * received it; any individual subscription the push service reports as
 * gone (404/410) is revoked immediately, regardless of the others'
 * outcome — that's real signal about that specific device, not about
 * this notification.
 */
async function processPushDelivery(prisma: PrismaClient, delivery: DueDelivery, pushProvider: PushProvider | undefined): Promise<DeliveryOutcome> {
  if (!pushProvider) return { status: "failed", retryable: true, reason: "No push provider configured." };

  try {
    const subscriptions = await resolveActivePushSubscriptions(prisma, {
      recipientUserId: delivery.notification.recipientUserId ?? undefined,
      recipientCustomerId: delivery.notification.recipientCustomerId ?? undefined,
    });
    if (subscriptions.length === 0) {
      return { status: "failed", retryable: false, reason: "No active push subscription for this recipient." };
    }

    let anySent = false;
    let lastFailureReason = "";
    let anyRetryable = false;

    // Every notify() call sets a subject (see notification.service.ts),
    // so this fallback is defensive rather than a normal path — but a
    // push notification's title is genuinely user-visible (shown by the
    // OS), so it still needs the business name, not the internal product
    // name, when reached.
    const fallbackTitle = delivery.notification.subject ?? (await getBranding()).name;

    for (const subscription of subscriptions) {
      const sendResult = await pushProvider.sendPush({
        subscription: { endpoint: subscription.endpoint, p256dhKey: subscription.p256dhKey, authKey: subscription.authKey },
        title: fallbackTitle,
        body: delivery.notification.bodyText,
        deepLinkPath: delivery.notification.deepLinkPath ?? undefined,
      });

      if (sendResult.status === "sent") {
        anySent = true;
        await prisma.pushSubscription.update({ where: { id: subscription.id }, data: { lastUsedAt: new Date() } }).catch(() => {});
        continue;
      }

      lastFailureReason = sendResult.reason;
      if (sendResult.subscriptionInvalid) {
        await prisma.pushSubscription.update({ where: { id: subscription.id }, data: { revokedAt: new Date() } }).catch(() => {});
      } else if (sendResult.retryable) {
        anyRetryable = true;
      }
    }

    if (anySent) return { status: "sent", providerName: pushProvider.name };
    return { status: "failed", retryable: anyRetryable, reason: lastFailureReason || "All subscriptions failed." };
  } catch (error) {
    return { status: "failed", retryable: true, reason: error instanceof Error ? error.message : "Unknown error while sending push." };
  }
}

async function raiseRepeatedFailureNotice(prisma: PrismaClient, businessId: string, now: Date): Promise<void> {
  const dayStamp = now.toISOString().slice(0, 10); // one notice per business per day, not one per processor run
  const ownerUserIds = await getOwnerUserIds(prisma, businessId);
  for (const ownerUserId of ownerUserIds) {
    await notifySafely(prisma, {
      businessId,
      type: NotificationType.OWNER_REPEATED_DELIVERY_FAILURE,
      recipientUserId: ownerUserId,
      subject: "Some notifications failed to send",
      bodyText: "Several notifications failed to send today. Check your notification settings, Brevo configuration, and push setup.",
      deepLinkPath: "/owner/notifications",
      idempotencyKey: `notify:owner-repeated-delivery-failure:${businessId}:${dayStamp}`,
    });
  }
}