import { createHmac } from 'crypto';
import { NextRequest, NextResponse } from 'next/server';
import { eq } from 'drizzle-orm';
import { db } from '@/lib/db';
import { jobs } from '@/lib/db/schema';
import { getUsersWithDueReviews } from '@/lib/db/queries';
import { reviewDigestEmail } from '@/lib/email/templates';
import { sendEmail } from '@/lib/email';

const BASE_URL = process.env.AUTH_URL ?? 'http://localhost:3000';

export function signUserId(userId: string): string {
  const secret = process.env.UNSUBSCRIBE_SECRET ?? 'dev-secret-change-in-prod';
  return createHmac('sha256', secret).update(userId).digest('hex');
}

export async function GET(request: NextRequest): Promise<NextResponse> {
  // Gate by env flag — feature is opt-in
  if (process.env.REVIEW_DIGEST_ENABLED !== 'true') {
    return NextResponse.json({ skipped: true, reason: 'REVIEW_DIGEST_ENABLED is not set' });
  }

  // Auth: Vercel Cron sends Authorization: Bearer <CRON_SECRET>
  const cronSecret = process.env.CRON_SECRET;
  if (cronSecret) {
    const auth = request.headers.get('Authorization');
    if (auth !== `Bearer ${cronSecret}`) {
      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
    }
  }

  const now = new Date();
  const dateKey = now.toISOString().slice(0, 10); // yyyy-mm-dd
  const recipients = await getUsersWithDueReviews(now);

  let sent = 0;
  let skipped = 0;

  for (const recipient of recipients) {
    const idempotencyKey = `digest:${recipient.userId}:${dateKey}`;

    // Idempotency: skip if already sent today
    const [existing] = await db
      .select({ id: jobs.id, status: jobs.status, attempts: jobs.attempts })
      .from(jobs)
      .where(eq(jobs.idempotencyKey, idempotencyKey))
      .limit(1);

    if (existing?.status === 'done') {
      skipped++;
      continue;
    }

    // Insert or update job row
    if (!existing) {
      await db.insert(jobs).values({
        type: 'review-digest',
        idempotencyKey,
        status: 'running',
        payloadJson: { userId: recipient.userId, date: dateKey },
        attempts: 1,
      }).onConflictDoNothing();
    } else {
      await db
        .update(jobs)
        .set({ status: 'running', attempts: (existing.attempts ?? 0) + 1 })
        .where(eq(jobs.id, existing.id));
    }

    const sig = signUserId(recipient.userId);
    const unsubscribeUrl = `${BASE_URL}/api/unsubscribe?userId=${encodeURIComponent(recipient.userId)}&sig=${sig}`;
    const reviewUrl = `${BASE_URL}/review`;

    const email = reviewDigestEmail({
      name: recipient.name,
      dueCount: recipient.dueCount,
      topConcepts: recipient.topConcepts,
      reviewUrl,
      unsubscribeUrl,
      locale: recipient.locale,
    });

    await sendEmail({ to: recipient.email, ...email });

    await db
      .update(jobs)
      .set({ status: 'done' })
      .where(eq(jobs.idempotencyKey, idempotencyKey));

    sent++;
  }

  return NextResponse.json({ sent, skipped, total: recipients.length, date: dateKey });
}