import { FieldPath, type QueryDocumentSnapshot } from 'firebase-admin/firestore';
import { NextRequest, NextResponse } from 'next/server';
import { getAdminAuth, getAdminFirestore } from '../../../lib/firebase-admin';

export const dynamic = 'force-dynamic';

const DEFAULT_PAGE_SIZE = 30;
const MAX_PAGE_SIZE = 50;

function isoDate(value: unknown): string | null {
  if (typeof value === 'string') {
    const date = new Date(value);
    return Number.isNaN(date.getTime()) ? null : date.toISOString();
  }
  if (value && typeof (value as { toDate?: unknown }).toDate === 'function') {
    const date = (value as { toDate: () => Date }).toDate();
    return Number.isNaN(date.getTime()) ? null : date.toISOString();
  }
  return null;
}

export async function GET(request: NextRequest) {
  try {
    const authorization = request.headers.get('authorization');
    if (!authorization?.startsWith('Bearer ')) {
      return NextResponse.json({ error: 'unauthorized' }, { status: 401 });
    }

    let callerUid: string;
    try {
      callerUid = (await getAdminAuth().verifyIdToken(authorization.slice(7).trim())).uid;
    } catch {
      return NextResponse.json({ error: 'unauthorized' }, { status: 401 });
    }

    const params = request.nextUrl.searchParams;
    const requestedSize = params.get('pageSize');
    const pageSize = requestedSize === null ? DEFAULT_PAGE_SIZE : Number(requestedSize);
    const cursor = params.get('cursor');
    if (!Number.isInteger(pageSize) || pageSize < 1 || pageSize > MAX_PAGE_SIZE ||
      (cursor !== null && (!cursor || cursor.length > 64 || /\s/.test(cursor)))) {
      return NextResponse.json({ error: 'invalid_request' }, { status: 400 });
    }

    const db = getAdminFirestore();
    const ridesCollection = db.collection('group_rides');
    let ridesQuery = ridesCollection
      .where('visibility', '==', 'public')
      .where('status', 'in', ['scheduled', 'assembling'])
      .orderBy('scheduledStartAt', 'asc')
      .orderBy(FieldPath.documentId(), 'asc');

    if (cursor) {
      const cursorDoc = await ridesCollection.doc(cursor).get();
      if (!cursorDoc.exists) {
        return NextResponse.json({ error: 'invalid_cursor' }, { status: 400 });
      }
      ridesQuery = ridesQuery.startAfter(cursorDoc);
    }

    const scanLimit = pageSize * 2;
    const rideSnapshot = await ridesQuery.limit(scanLimit).get();
    const candidates = rideSnapshot.docs.filter((ride: QueryDocumentSnapshot) => {
      const data = ride.data();
      const scheduledStartAt = isoDate(data.scheduledStartAt);
      return !('clubId' in data) && scheduledStartAt !== null &&
        new Date(scheduledStartAt).getTime() > Date.now() &&
        typeof data.organizerUid === 'string' && data.organizerUid.length > 0;
    });

    const callerBlocksSnapshot = await db
      .collection('users').doc(callerUid).collection('blocks').get();
    const blockedByCaller = new Set(callerBlocksSnapshot.docs.map((blocked) => blocked.id));
    const eligible = candidates.filter((ride) => !blockedByCaller.has(ride.data().organizerUid));
    const organizersToCheck = [...new Set(eligible
      .map((ride) => ride.data().organizerUid as string)
      .filter((uid) => uid !== callerUid))];
    const reverseBlocks = await Promise.all(organizersToCheck.map(async (organizerUid) => {
      const blocked = await db.collection('users').doc(organizerUid)
        .collection('blocks').doc(callerUid).get();
      return [organizerUid, blocked.exists] as const;
    }));
    const blockedCallers = new Set(reverseBlocks.filter(([, blocked]) => blocked).map(([uid]) => uid));
    const visible = eligible.filter((ride) => !blockedCallers.has(ride.data().organizerUid));
    const page = visible.slice(0, pageSize);

    const participantSnapshots = await Promise.all(page.map((ride) =>
      ride.ref.collection('participants').doc(callerUid).get()));
    const rides = page.map((ride, index) => {
      const data = ride.data();
      const meetingPoint = data.meetingPoint && typeof data.meetingPoint === 'object'
        ? data.meetingPoint as Record<string, unknown>
        : {};
      const participantStatus = participantSnapshots[index].data()?.status;
      const isOrganizer = data.organizerUid === callerUid;
      const userStatus = isOrganizer || participantStatus === 'accepted' || participantStatus === 'invited'
        ? 'joined'
        : participantStatus === 'requested' || participantStatus === 'waitlisted'
          ? participantStatus
          : 'none';
      const scheduledStartAt = isoDate(data.scheduledStartAt)!;

      return {
        id: ride.id,
        title: typeof data.title === 'string' ? data.title : 'Group ride',
        description: typeof data.description === 'string' ? data.description : '',
        region: typeof meetingPoint.address === 'string' ? meetingPoint.address
          : typeof meetingPoint.displayName === 'string' ? meetingPoint.displayName : 'Regional ride',
        meetingPoint: typeof meetingPoint.displayName === 'string' ? meetingPoint.displayName
          : typeof meetingPoint.address === 'string' ? meetingPoint.address : 'Rally point shared by organizer',
        scheduledStartAt,
        paceClassification: typeof data.paceClassification === 'string' ? data.paceClassification : 'Brisk Pace',
        discipline: typeof data.discipline === 'string' ? data.discipline : 'Sport / Canyon',
        formationProfile: typeof data.formationProfile === 'string' ? data.formationProfile : 'Staggered Dual Column [B]',
        joinPolicy: data.joinPolicy === 'open' || data.joinPolicy === 'inviteOnly' ? data.joinPolicy : 'requestToJoin',
        leadHandle: typeof data.organizerDisplayName === 'string' ? data.organizerDisplayName
          : typeof data.organizerHandle === 'string' ? data.organizerHandle : 'Rider',
        leadAvatarText: String(data.organizerDisplayName || data.organizerHandle || 'R').slice(0, 1).toUpperCase(),
        participantCount: typeof data.participantCount === 'number' ? data.participantCount : 1,
        participantLimit: typeof data.participantLimit === 'number' ? data.participantLimit : 12,
        distance: typeof data.routeDistanceMeters === 'number' && data.routeDistanceMeters > 0
          ? `${(data.routeDistanceMeters / 1609.34).toFixed(1)} Miles`
          : typeof data.distance === 'string' ? data.distance : 'Open Route',
        routeSnippet: typeof data.routeTitle === 'string' ? data.routeTitle : '',
        userStatus,
        isOrganizer,
        status: data.status,
        rideCode: ride.id,
      };
    });

    const hasMoreCandidates = rideSnapshot.docs.length === scanLimit;
    const hasMoreVisible = visible.length > pageSize;
    const nextCursor = hasMoreVisible
      ? page[page.length - 1]?.id
      : hasMoreCandidates ? rideSnapshot.docs[rideSnapshot.docs.length - 1]?.id : undefined;

    return NextResponse.json(
      { rides, nextCursor: nextCursor ?? null },
      { headers: { 'Cache-Control': 'no-store, max-age=0' } }
    );
  } catch (error) {
    console.error('[GROUP_RIDE_DISCOVERY] Failed to list public rides:', error);
    return NextResponse.json({ error: 'server_error' }, { status: 500 });
  }
}