import { Injectable, NotFoundException } from '@nestjs/common';
import {
  NOTIFICATION_PAGE_SIZE,
  type NotificationListView,
  type NotificationPayload,
  type NotificationType,
  type NotificationView,
} from '@dorfteich/shared';
import { Prisma, User } from '@prisma/client';
import { PinoLogger } from 'nestjs-pino';

import { PermissionService } from '../permissions/permission.service';
import { PrismaService } from '../prisma/prisma.service';

/**
 * Notification generation and the in-app center's data (issue #94).
 * Fan-out: everyone watching the page or its pond, minus the actors, and
 * only where page read permission holds at delivery time (a revoked
 * watcher gets nothing — permissions.md). The payload is denormalized so
 * the list renders without joins; it reflects the state at event time.
 */
@Injectable()
export class NotificationsService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly permissions: PermissionService,
    private readonly logger: PinoLogger,
  ) {
    this.logger.setContext(NotificationsService.name);
  }

  /**
   * Fans a page event out to its watchers. Never throws — a notification
   * failure must not break the write that caused it.
   */
  async fanoutPageEvent(type: NotificationType, pageId: string, actorIds: string[]): Promise<void> {
    try {
      await this.fanout(type, pageId, actorIds);
    } catch (error) {
      this.logger.warn({ pageId, type, err: error }, 'notification fan-out failed');
    }
  }

  private async fanout(type: NotificationType, pageId: string, actorIds: string[]): Promise<void> {
    const page = await this.prisma.page.findFirst({
      where: { id: pageId, deletedAt: null },
      select: { id: true, pondId: true, title: true, slug: true },
    });
    if (!page) return;
    const pond = await this.prisma.pond.findFirst({
      where: { id: page.pondId, deletedAt: null },
      select: { name: true, slug: true },
    });
    if (!pond) return;

    const watches = await this.prisma.watch.findMany({
      where: {
        OR: [
          { targetType: 'PAGE', targetId: page.id },
          { targetType: 'POND', targetId: page.pondId },
        ],
      },
      select: { userId: true },
    });
    const watcherIds = [...new Set(watches.map((watch) => watch.userId))].filter(
      (userId) => !actorIds.includes(userId),
    );
    if (watcherIds.length === 0) return;

    const actors = await this.prisma.user.findMany({
      where: { id: { in: actorIds } },
      select: { displayName: true },
    });
    const payload: NotificationPayload = {
      pageId: page.id,
      pageTitle: page.title,
      pageSlug: page.slug,
      pondSlug: pond.slug,
      pondName: pond.name,
      actorNames: actors.slice(0, 3).map((actor) => actor.displayName),
    };

    const watchers = await this.prisma.user.findMany({ where: { id: { in: watcherIds } } });
    for (const watcher of watchers) {
      // Delivery-time permission re-check: only watchers who may still read.
      if (!(await this.permissions.canAccessPage(watcher, page, 'read'))) continue;
      await this.prisma.notification.create({
        data: {
          userId: watcher.id,
          type,
          payload: payload as unknown as Prisma.InputJsonObject,
        },
      });
    }
  }

  async list(user: User, page: number): Promise<NotificationListView> {
    const where = { userId: user.id };
    const [total, unreadCount] = [
      await this.prisma.notification.count({ where }),
      await this.prisma.notification.count({ where: { ...where, readAt: null } }),
    ];
    const pageCount = Math.max(1, Math.ceil(total / NOTIFICATION_PAGE_SIZE));
    const current = Math.min(page, pageCount);
    const rows = await this.prisma.notification.findMany({
      where,
      // Unread first, newest first within each group.
      orderBy: [{ readAt: { sort: 'asc', nulls: 'first' } }, { createdAt: 'desc' }],
      skip: (current - 1) * NOTIFICATION_PAGE_SIZE,
      take: NOTIFICATION_PAGE_SIZE,
    });
    return {
      notifications: rows.map((row) => this.viewOf(row)),
      unreadCount,
      page: current,
      pageCount,
    };
  }

  async markRead(user: User, id: string): Promise<NotificationView> {
    const row = await this.prisma.notification.findFirst({ where: { id, userId: user.id } });
    if (!row) throw new NotFoundException();
    const updated = await this.prisma.notification.update({
      where: { id },
      data: { readAt: row.readAt ?? new Date() },
    });
    return this.viewOf(updated);
  }

  async markAllRead(user: User): Promise<void> {
    await this.prisma.notification.updateMany({
      where: { userId: user.id, readAt: null },
      data: { readAt: new Date() },
    });
  }

  private viewOf(row: {
    id: string;
    type: string;
    payload: Prisma.JsonValue;
    createdAt: Date;
    readAt: Date | null;
  }): NotificationView {
    return {
      id: row.id,
      type: row.type as NotificationType,
      payload: row.payload as unknown as NotificationView['payload'],
      createdAt: row.createdAt.toISOString(),
      readAt: row.readAt?.toISOString() ?? null,
    };
  }
}