import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
import { SchedulerRegistry } from '@nestjs/schedule';
import { PrismaService } from '../prisma/prisma.service';
import { forSystem, forTenant } from '../prisma/prisma-tenant.extension';
import { TenderMailItem, TenderMailService } from './tender-mail.service';

/**
 * CronJob constructor — resolved at runtime via require() because `cron` is
 * a transitive dependency of @nestjs/schedule (not a direct api dep under
 * pnpm strict isolation, so `import { CronJob } from 'cron'` fails
 * type-check). Reuses the exact `TenderSchedulerService`/`DkvSchedulerService`
 * resolution workaround verbatim.
 */
// eslint-disable-next-line @typescript-eslint/no-require-imports
const CronJobClass: new (cronTime: string, onTick: () => void) => { start(): void } =
  // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
  require('cron').CronJob as new (cronTime: string, onTick: () => void) => { start(): void };

/**
 * TenderDigestScheduler — a SINGLE global cron job driving the tender-radar
 * digest send (NOTIFY-01). Deliberately mirrors `TenderSchedulerService`'s
 * poll-once-fan-out-many pattern, NOT `DkvSchedulerService`'s documented
 * "v1 single-tenant, find-first-row" pattern (RESEARCH.md Pitfall 1): there is
 * no per-tenant cron job and no per-tenant "active tenant" instance field.
 * One job, registered once, iterates every due user of every tenant via
 * `findMany` on every tick.
 *
 * Runs daily at 07:00 (server-local cron tick; due-date evaluation itself
 * is Europe/Berlin-aware for the weekly weekday check). Selects candidate
 * users as the distinct `userId`s that have at least one un-notified
 * `TenderMatch`, resolves each user's `TenderNotificationPref.digestInterval`
 * (missing row -> 'daily' default, D-01), and — for due users only — groups
 * their un-notified matches by saved-search profile name (D-02) into ONE
 * `TenderMailService.sendDigest` call. `TenderMatch.notifiedAt`/`notifiedChannel`
 * are stamped ONLY after a successful (non-skipped) send — the single
 * `notifiedAt IS NULL` eligibility gate that structurally prevents
 * double-sends across digest and instant channels (D-06).
 *
 * Robustness (Pitfall 6): each candidate user is processed inside its own
 * try/catch. A missing SMTP config, a send failure, or an unexpected thrown
 * error for one user/tenant leaves that user's matches `notifiedAt=NULL`
 * (retried on the next run) and never aborts the run for the remaining
 * users — a broken tenant must never take down every other tenant's digest.
 */
@Injectable()
export class TenderDigestScheduler implements OnModuleInit {
  private readonly logger = new Logger(TenderDigestScheduler.name);

  /** Name of the single, platform-global managed cron job. */
  private readonly JOB_NAME = 'tender-digest';

  /** Daily at 07:00 — a single platform-wide tick, no tenant dimension. */
  private readonly CRON_EXPR = '0 7 * * *';

  constructor(
    private readonly schedulerRegistry: SchedulerRegistry,
    private readonly prisma: PrismaService,
    private readonly mail: TenderMailService,
  ) {}

  /**
   * Registers the single global digest cron job on application startup.
   * Errors are caught and logged (never re-thrown) so a scheduling issue
   * never prevents the rest of the application from starting.
   */
  onModuleInit(): void {
    try {
      // Remove existing job if already registered (e.g. hot-reload/tests).
      try {
        this.schedulerRegistry.getCronJob(this.JOB_NAME).stop();
        this.schedulerRegistry.deleteCronJob(this.JOB_NAME);
      } catch {
        /* Job not yet registered — expected on first boot */
      }

      const job = new CronJobClass(this.CRON_EXPR, () => {
        this.runDigest().catch((err) =>
          this.logger.error(`Tender digest run failed: ${(err as Error).message}`),
        );
      });

      // Cast required: our minimal CronJob type doesn't match cron's full
      // type signature. At runtime the object IS a full CronJob —
      // SchedulerRegistry only calls stop() on it.
      // eslint-disable-next-line @typescript-eslint/no-explicit-any
      // URTEIL: BLEIBT (260921-m34, Aufgabe 3, D-01). Gemessen: ohne die
      // Zusicherung meldet tsc, dass das lokale `job` nur die Form
      // `{ start(): void }` hat, waehrend addCronJob() einen vollstaendigen
      // CronJob verlangt. Ursache ist der require()-Umweg aus 07-04 (pnpm-
      // Isolation, `cron` ist nur eine mittelbare Abhaengigkeit). Das
      // aufzuloesen hiesse, die Beschaffung der Klasse zu aendern — eine
      // Verhaltensaenderung — oder `cron` direkt aufzunehmen — eine neue
      // Abhaengigkeit. Beides ist hier verboten (D-03/D-04).
      this.schedulerRegistry.addCronJob(this.JOB_NAME, job as any);
      job.start();

      this.logger.log(
        `Tender digest scheduler registered: ${this.CRON_EXPR} (single global job — all tenants/users, no per-tenant dimension)`,
      );
    } catch (err) {
      this.logger.error(`Tender digest scheduler init failed: ${(err as Error).message}`);
    }
  }

  /**
   * Core digest run — the single global tick's fan-out over every due user
   * of every tenant. NEVER a per-tenant job, NEVER a first-row-only lookup (Pitfall 1).
   *
   * @param now - injectable clock for the weekly-weekday check (defaults to
   *   the real current time); tests pass a fixed date instead of faking the
   *   system clock.
   */
  async runDigest(now: Date = new Date()): Promise<void> {
    // Candidate users: distinct userId with at least one un-notified match,
    // across ALL tenants — a single findMany, never a per-tenant iteration.
    // SYSTEMGEBUNDEN (Etappe 3c, 260914-eym; die Etappe-3-Uebergabe aus
    // 260909-laa ist damit eingeloest): `forSystem()` liest TenderMatch
    // ALLER Mandanten NUR lesend (`system_read_policy ... FOR SELECT`,
    // Migration 20260914120000) — ohne diese Regel saehe der Digest nach dem
    // Scharfschalten 0 Kandidaten und wuerde stumm. Die Schleife unten
    // bleibt je Kandidatenzeile GEBUNDEN (bewusst ohne Benutzer, wie in 3b).
    // Eine LEERE Kandidatenliste ist Nichtstun: `notifiedAt` bleibt NULL.
    //
    // Zusaetzlich das denormalisierte tenantId der Treffer-Zeile mit
    // ausgewaehlt (nicht Teil von `distinct`), damit die Schleife unten
    // ueberhaupt an einen Mandanten binden KANN. Sonderfall, NICHT geloest:
    // ein Nutzer koennte Treffer unter zwei verschiedenen Mandanten haben
    // (der denormalisierte Wert kann bei einem Mandantenwechsel veralten) —
    // `distinct(['userId'])` liefert dann nur EINE der moeglichen
    // tenantId-Werte je Nutzer, welche ist von der internen Zeilenreihenfolge
    // abhaengig. Siehe docs/mandantentrennung-etappe2-fehlerrichtung.md.
    const systemPrisma = forSystem(this.prisma);
    const candidates: { userId: string; tenantId: string }[] = await systemPrisma.tenderMatch.findMany({
      where: { notifiedAt: null },
      select: { userId: true, tenantId: true },
      distinct: ['userId'],
    });

    if (!candidates.length) return;

    const weeklyDue = isMondayInBerlin(now);

    for (const { userId, tenantId } of candidates) {
      try {
        // Je-Treffer-Haelfte, gebunden an den Mandanten DIESER
        // Kandidatenzeile (260909-laa, Aufgabe 3) — ein einziger gebundener
        // Client fuer alle Zugriffe dieses Schleifendurchlaufs.
        //
        // Bewusst OHNE Benutzer (260911-nke, Etappe 3b): dieser Scheduler ist
        // ein Hintergrunddienst, kein Nutzer-CRUD-Aufrufer — er liest UND
        // schreibt fuer den Nutzer, nicht ALS ihn eingeloggt. Die `IS NULL
        // OR`-Form der Regeln macht das zur bewussten Eigenschaft: ohne
        // `userId` sieht dieser Zugriff den ganzen Mandanten, exakt wie vor
        // der Migration. Ein Systemkontext fuer Hintergrunddienste ist
        // Etappe 3c, nicht Teil dieser Aenderung.
        const tenantPrisma = forTenant(this.prisma, tenantId);

        const pref = await tenantPrisma.tenderNotificationPref.findUnique({
          where: { userId },
        });
        // Missing pref row -> daily default (D-01).
        const interval = pref?.digestInterval ?? 'daily';

        if (interval === 'off') continue;
        if (interval === 'weekly' && !weeklyDue) continue;
        // 'daily' (or any unrecognized value) -> due every run.

        const matches = await tenantPrisma.tenderMatch.findMany({
          where: { userId, notifiedAt: null },
          include: { tender: true, savedSearch: true },
          orderBy: { savedSearch: { name: 'asc' } },
        });
        if (!matches.length) continue;

        const user = await tenantPrisma.user.findUnique({ where: { id: userId } });
        // Kein Konto, oder ein Konto ohne Adresse (WINDOWS #15, kollidierte
        // AD-Adresse) -- die Zugehoerigkeit funktioniert, nur der
        // Mailversand wird uebersprungen (zugesagtes Verhalten).
        if (!user?.email) continue;

        const sections = groupMatchesByProfile(matches);
        const sent = await this.mail.sendDigest({ email: user.email }, user.tenantId, sections);

        if (sent) {
          await tenantPrisma.tenderMatch.updateMany({
            where: { id: { in: matches.map((m: { id: string }) => m.id) } },
            data: { notifiedAt: new Date(), notifiedChannel: 'digest' },
          });
        }
        // sent === false (no SMTP config or send failure) -> notifiedAt
        // stays NULL, this user's matches are retried on the next run.
      } catch (err) {
        // One broken user/tenant (DB error, malformed pref, etc.) must
        // never abort the run for the remaining users (Pitfall 6).
        this.logger.error(
          `Tender digest failed for user ${userId}: ${(err as Error).message}`,
        );
      }
    }
  }
}

/**
 * Groups a flat list of matches (each including its `savedSearch` and
 * `tender` relations) into the `{ profileName: tender[] }` shape
 * `TenderMailService.sendDigest` expects (D-02 — one mail, sectioned by
 * saved-search profile).
 */
function groupMatchesByProfile(
  matches: Array<{ savedSearch: { name: string }; tender: TenderMailItem }>,
): Record<string, TenderMailItem[]> {
  const sections: Record<string, TenderMailItem[]> = {};
  for (const match of matches) {
    const profileName = match.savedSearch.name;
    if (!sections[profileName]) sections[profileName] = [];
    sections[profileName].push(match.tender);
  }
  return sections;
}

/** True when `now` falls on a Monday in the Europe/Berlin timezone. */
function isMondayInBerlin(now: Date): boolean {
  const weekday = now.toLocaleDateString('en-US', {
    timeZone: 'Europe/Berlin',
    weekday: 'short',
  });
  return weekday === 'Mon';
}