feat: implement per-member reading progress tracking for shared books (#30)

Backend (apps/groups):
- ReadingGroup model: named groups linked to EBooks with creator tracking
- GroupMembership model: user-group association with member/admin roles
- MemberProgress model: per-member progress with section tracking,
  percentage, time_spent, privacy toggles, and device-position preservation
- ReadingGroupViewSet: CRUD, join/leave, members list, progress endpoints
- GET /api/groups/{id}/members/progress/ — all members' progress
  (public: section label only; own: full detail; private: stubbed)
- PATCH /api/groups/{id}/progress/ — update own progress with auto-
  percentage calculation from section boundaries
- GET /api/groups/{id}/progress/summary/ — admin dashboard with
  averages, started/finished counts, and per-member details
- Permissions: IsGroupMember, IsGroupAdmin

Frontend:
- Groups list page (/groups) with create modal and book selector
- Group detail page (/groups/:id) with progress and admin summary tabs
- Progress bar visualization per member with privacy-aware display
- Admin stat cards (total members, started, finished, avg progress, avg time)
- Navigation link from Library header

Shared:
- ReadingGroupSummary and MemberProgressPublic types
- API endpoint constants for groups routes

Closes #30

backend/apps/groups/admin.py

@@ -0,0 +1,23 @@
+from django.contrib import admin
+
+from apps.groups.models import GroupMembership, MemberProgress, ReadingGroup
+
+
+@admin.register(ReadingGroup)
+class ReadingGroupAdmin(admin.ModelAdmin):
+    list_display = ["name", "ebook", "created_by", "created_at"]
+    search_fields = ["name", "ebook__title", "created_by__email"]
+
+
+@admin.register(GroupMembership)
+class GroupMembershipAdmin(admin.ModelAdmin):
+    list_display = ["group", "user", "role", "joined_at"]
+    list_filter = ["role"]
+    search_fields = ["user__email", "group__name"]
+
+
+@admin.register(MemberProgress)
+class MemberProgressAdmin(admin.ModelAdmin):
+    list_display = ["user", "group", "current_section", "percentage", "time_spent_seconds", "is_public", "updated_at"]
+    list_filter = ["is_public"]
+    search_fields = ["user__email", "group__name"]

backend/apps/groups/apps.py

@@ -0,0 +1,7 @@
+from django.apps import AppConfig
+
+
+class GroupsConfig(AppConfig):
+    default_auto_field = "django.db.models.BigAutoField"
+    name = "apps.groups"
+    verbose_name = "Reading Groups"

backend/apps/groups/migrations/0001_initial.py

@@ -0,0 +1,75 @@
+# Generated by Django 5.1.7 on 2026-06-20 19:21
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('books', '0003_readingprogress_epub_location'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ReadingGroup',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(db_index=True, max_length=256)),
+                ('description', models.TextField(blank=True, default='')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('created_by', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='created_groups', to=settings.AUTH_USER_MODEL)),
+                ('ebook', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='reading_groups', to='books.ebook')),
+            ],
+            options={
+                'verbose_name': 'Reading Group',
+                'verbose_name_plural': 'Reading Groups',
+                'db_table': 'groups_reading_group',
+                'ordering': ['-created_at'],
+            },
+        ),
+        migrations.CreateModel(
+            name='GroupMembership',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('role', models.CharField(choices=[('member', 'Member'), ('admin', 'Admin')], default='member', max_length=16)),
+                ('joined_at', models.DateTimeField(auto_now_add=True)),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='group_memberships', to=settings.AUTH_USER_MODEL)),
+                ('group', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='memberships', to='groups.readinggroup')),
+            ],
+            options={
+                'verbose_name': 'Group Membership',
+                'verbose_name_plural': 'Group Memberships',
+                'db_table': 'groups_membership',
+                'ordering': ['joined_at'],
+                'unique_together': {('group', 'user')},
+            },
+        ),
+        migrations.CreateModel(
+            name='MemberProgress',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('current_section', models.PositiveIntegerField(default=0)),
+                ('percentage', models.FloatField(default=0.0)),
+                ('time_spent_seconds', models.PositiveIntegerField(default=0)),
+                ('last_position', models.JSONField(blank=True, default=dict)),
+                ('is_public', models.BooleanField(default=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('membership', models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, related_name='progress', to='groups.groupmembership')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='member_progress', to=settings.AUTH_USER_MODEL)),
+                ('group', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='member_progress', to='groups.readinggroup')),
+            ],
+            options={
+                'verbose_name': 'Member Progress',
+                'verbose_name_plural': 'Member Progress',
+                'db_table': 'groups_member_progress',
+                'indexes': [models.Index(fields=['group', '-percentage'], name='groups_memb_group_i_42e333_idx'), models.Index(fields=['group', 'user'], name='groups_memb_group_i_f50793_idx')],
+                'unique_together': {('group', 'user')},
+            },
+        ),
+    ]

backend/apps/groups/models.py

@@ -0,0 +1,138 @@
+from django.conf import settings
+from django.db import models
+
+
+class ReadingGroup(models.Model):
+    """A group of users reading the same book together."""
+
+    name = models.CharField(max_length=256, db_index=True)
+    ebook = models.ForeignKey(
+        "books.EBook",
+        on_delete=models.CASCADE,
+        related_name="reading_groups",
+    )
+    created_by = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="created_groups",
+    )
+    description = models.TextField(blank=True, default="")
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_reading_group"
+        verbose_name = "Reading Group"
+        verbose_name_plural = "Reading Groups"
+        ordering = ["-created_at"]
+
+    def __str__(self) -> str:
+        return self.name
+
+    @property
+    def total_sections(self) -> int:
+        return self.ebook.chapters.count()
+
+
+class GroupMembership(models.Model):
+    class Role(models.TextChoices):
+        MEMBER = "member", "Member"
+        ADMIN = "admin", "Admin"
+
+    group = models.ForeignKey(
+        ReadingGroup,
+        on_delete=models.CASCADE,
+        related_name="memberships",
+    )
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="group_memberships",
+    )
+    role = models.CharField(
+        max_length=16,
+        choices=Role.choices,
+        default=Role.MEMBER,
+    )
+    joined_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_membership"
+        verbose_name = "Group Membership"
+        verbose_name_plural = "Group Memberships"
+        unique_together = [("group", "user")]
+        ordering = ["joined_at"]
+
+    def __str__(self) -> str:
+        return f"{self.user} in {self.group.name} ({self.role})"
+
+
+class MemberProgress(models.Model):
+    """Per-member reading progress within a reading group."""
+
+    membership = models.OneToOneField(
+        GroupMembership,
+        on_delete=models.CASCADE,
+        related_name="progress",
+    )
+    group = models.ForeignKey(
+        ReadingGroup,
+        on_delete=models.CASCADE,
+        related_name="member_progress",
+    )
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="member_progress",
+    )
+    current_section = models.PositiveIntegerField(default=0)
+    percentage = models.FloatField(default=0.0)
+    time_spent_seconds = models.PositiveIntegerField(default=0)
+    last_position = models.JSONField(blank=True, default=dict)
+    is_public = models.BooleanField(default=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_member_progress"
+        verbose_name = "Member Progress"
+        verbose_name_plural = "Member Progress"
+        unique_together = [("group", "user")]
+        indexes = [
+            models.Index(fields=["group", "-percentage"]),
+            models.Index(fields=["group", "user"]),
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.user} — {self.group.name} ({self.percentage:.0f}%)"
+
+    def total_sections(self) -> int:
+        return self.group.total_sections
+
+    def update_progress(
+        self,
+        current_section: int,
+        percentage: float | None = None,
+        time_spent_delta: int = 0,
+        last_position: dict | None = None,
+    ) -> None:
+        """Update progress with computed percentage if not provided."""
+        self.current_section = current_section
+        if percentage is not None:
+            self.percentage = min(100.0, max(0.0, percentage))
+        elif (ts := self.total_sections()) > 0:
+            self.percentage = min(100.0, (current_section / ts) * 100.0)
+        else:
+            self.percentage = 0.0
+        if time_spent_delta > 0:
+            self.time_spent_seconds += time_spent_delta
+        if last_position is not None:
+            self.last_position = last_position
+        self.save(
+            update_fields=[
+                "current_section",
+                "percentage",
+                "time_spent_seconds",
+                "last_position",
+                "updated_at",
+            ]
+        )

backend/apps/groups/permissions.py

@@ -0,0 +1,28 @@
+from rest_framework import permissions
+from rest_framework.request import Request
+
+from apps.groups.models import GroupMembership
+
+
+class IsGroupMember(permissions.BasePermission):
+    """Allow access only to members of the group."""
+
+    def has_permission(self, request: Request, view: object) -> bool:
+        group_id = view.kwargs.get("group_pk") or view.kwargs.get("pk")
+        if not group_id:
+            return False
+        return GroupMembership.objects.filter(
+            group_id=group_id, user=request.user
+        ).exists()
+
+
+class IsGroupAdmin(permissions.BasePermission):
+    """Allow access only to group admins."""
+
+    def has_permission(self, request: Request, view: object) -> bool:
+        group_id = view.kwargs.get("group_pk") or view.kwargs.get("pk")
+        if not group_id:
+            return False
+        return GroupMembership.objects.filter(
+            group_id=group_id, user=request.user, role=GroupMembership.Role.ADMIN
+        ).exists()

backend/apps/groups/serializers.py

@@ -0,0 +1,183 @@
+from rest_framework import serializers
+
+from apps.groups.models import GroupMembership, MemberProgress, ReadingGroup
+
+
+class GroupMembershipSerializer(serializers.ModelSerializer):
+    user_email = serializers.CharField(source="user.email", read_only=True)
+    user_id = serializers.IntegerField(source="user.id", read_only=True)
+    role = serializers.CharField(read_only=True)
+
+    class Meta:
+        model = GroupMembership
+        fields = ["id", "user_id", "user_email", "role", "joined_at"]
+
+
+class MemberProgressSerializer(serializers.ModelSerializer):
+    user_email = serializers.CharField(source="user.email", read_only=True)
+    user_id = serializers.IntegerField(source="user.id", read_only=True)
+    total_sections = serializers.SerializerMethodField()
+    section_label = serializers.SerializerMethodField()
+
+    class Meta:
+        model = MemberProgress
+        fields = [
+            "id",
+            "user_id",
+            "user_email",
+            "current_section",
+            "total_sections",
+            "section_label",
+            "percentage",
+            "time_spent_seconds",
+            "last_position",
+            "is_public",
+            "updated_at",
+        ]
+        read_only_fields = ["id", "user_id", "user_email", "updated_at"]
+        extra_kwargs = {
+            "percentage": {"required": False, "min_value": 0.0, "max_value": 100.0},
+        }
+
+    def get_total_sections(self, obj: MemberProgress) -> int:
+        return obj.total_sections()
+
+    def get_section_label(self, obj: MemberProgress) -> str:
+        ts = obj.total_sections()
+        if ts:
+            return f"Section {obj.current_section} of {ts}"
+        return "No sections"
+
+    def validate_percentage(self, value: float) -> float:
+        if value < 0.0 or value > 100.0:
+            raise serializers.ValidationError("Percentage must be between 0.0 and 100.0.")
+        return value
+
+
+class MemberProgressPublicSerializer(serializers.ModelSerializer):
+    """Limited view for other group members — section label only, no exact position."""
+
+    user_email = serializers.CharField(source="user.email", read_only=True)
+    user_id = serializers.IntegerField(source="user.id", read_only=True)
+    total_sections = serializers.SerializerMethodField()
+    section_label = serializers.SerializerMethodField()
+
+    class Meta:
+        model = MemberProgress
+        fields = [
+            "user_id",
+            "user_email",
+            "current_section",
+            "total_sections",
+            "section_label",
+            "percentage",
+            "time_spent_seconds",
+            "updated_at",
+        ]
+
+    def get_total_sections(self, obj: MemberProgress) -> int:
+        return obj.total_sections()
+
+    def get_section_label(self, obj: MemberProgress) -> str:
+        ts = obj.total_sections()
+        if ts:
+            return f"Section {obj.current_section} of {ts}"
+        return "No sections"
+
+
+class MemberProgressUpdateSerializer(serializers.Serializer):
+    current_section = serializers.IntegerField(min_value=0)
+    percentage = serializers.FloatField(required=False, min_value=0.0, max_value=100.0)
+    time_spent_delta = serializers.IntegerField(default=0, min_value=0)
+    last_position = serializers.JSONField(required=False, default=dict)
+    is_public = serializers.BooleanField(required=False)
+
+
+class ReadingGroupListSerializer(serializers.ModelSerializer):
+    created_by_email = serializers.CharField(source="created_by.email", read_only=True)
+    ebook_title = serializers.CharField(source="ebook.title", read_only=True)
+    ebook_author = serializers.CharField(source="ebook.author", read_only=True)
+    member_count = serializers.SerializerMethodField()
+    my_progress = serializers.SerializerMethodField()
+
+    class Meta:
+        model = ReadingGroup
+        fields = [
+            "id",
+            "name",
+            "ebook",
+            "ebook_title",
+            "ebook_author",
+            "created_by_email",
+            "description",
+            "member_count",
+            "my_progress",
+            "created_at",
+            "updated_at",
+        ]
+
+    def get_member_count(self, obj: ReadingGroup) -> int:
+        return obj.memberships.count()
+
+    def get_my_progress(self, obj: ReadingGroup) -> dict | None:
+        request = self.context.get("request")
+        if not request or not request.user.is_authenticated:
+            return None
+        try:
+            mp = MemberProgress.objects.get(group=obj, user=request.user)
+        except MemberProgress.DoesNotExist:
+            return None
+        return {
+            "current_section": mp.current_section,
+            "percentage": mp.percentage,
+            "time_spent_seconds": mp.time_spent_seconds,
+            "section_label": MemberProgressSerializer().get_section_label(mp),
+        }
+
+
+class ReadingGroupDetailSerializer(ReadingGroupListSerializer):
+    members = serializers.SerializerMethodField()
+
+    class Meta(ReadingGroupListSerializer.Meta):
+        fields = ReadingGroupListSerializer.Meta.fields + ["members"]
+
+    def get_members(self, obj: ReadingGroup) -> list[dict]:
+        memberships = obj.memberships.select_related("user").prefetch_related("progress")
+        result: list[dict] = []
+        for m in memberships:
+            entry: dict = {
+                "id": m.id,
+                "user_id": m.user.id,
+                "user_email": m.user.email,
+                "role": m.role,
+                "joined_at": m.joined_at,
+            }
+            try:
+                mp = m.progress
+            except MemberProgress.DoesNotExist:
+                entry["progress"] = None
+            else:
+                if mp.is_public:
+                    entry["progress"] = MemberProgressPublicSerializer(mp).data
+                else:
+                    entry["progress"] = {"is_public": False, "note": "Private"}
+            result.append(entry)
+        return result
+
+
+class ReadingGroupCreateSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = ReadingGroup
+        fields = ["name", "ebook", "description"]
+
+
+class AdminProgressSummarySerializer(serializers.Serializer):
+    group_id = serializers.IntegerField()
+    group_name = serializers.CharField()
+    ebook_title = serializers.CharField()
+    total_members = serializers.IntegerField()
+    members_started = serializers.IntegerField()
+    members_finished = serializers.IntegerField()
+    average_percentage = serializers.FloatField()
+    average_time_spent_hours = serializers.FloatField()
+    member_details = serializers.ListField(child=serializers.JSONField())

backend/apps/groups/urls.py

@@ -0,0 +1,11 @@
+from django.urls import include, path
+from rest_framework.routers import DefaultRouter
+
+from apps.groups.views import ReadingGroupViewSet
+
+router = DefaultRouter()
+router.register(r"", ReadingGroupViewSet, basename="reading-group")
+
+urlpatterns = [
+    path("", include(router.urls)),
+]

backend/apps/groups/views.py

@@ -0,0 +1,203 @@
+from __future__ import annotations
+
+from django.db import models
+from rest_framework import permissions, status, viewsets
+from rest_framework.decorators import action
+from rest_framework.request import Request
+from rest_framework.response import Response
+
+from apps.groups.models import GroupMembership, MemberProgress, ReadingGroup
+from apps.groups.permissions import IsGroupAdmin, IsGroupMember
+from apps.groups.serializers import (
+    AdminProgressSummarySerializer,
+    GroupMembershipSerializer,
+    MemberProgressPublicSerializer,
+    MemberProgressSerializer,
+    MemberProgressUpdateSerializer,
+    ReadingGroupCreateSerializer,
+    ReadingGroupDetailSerializer,
+    ReadingGroupListSerializer,
+)
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class ReadingGroupViewSet(viewsets.ModelViewSet):
+    permission_classes = [permissions.IsAuthenticated]
+
+    def get_queryset(self):
+        return (
+            ReadingGroup.objects.filter(memberships__user=self.request.user)
+            .select_related("ebook", "created_by")
+            .prefetch_related("memberships", "memberships__progress")
+            .distinct()
+        )
+
+    def get_serializer_class(self):
+        if self.action == "create":
+            return ReadingGroupCreateSerializer
+        if self.action == "retrieve":
+            return ReadingGroupDetailSerializer
+        return ReadingGroupListSerializer
+
+    def perform_create(self, serializer):
+        group = serializer.save(created_by=self.request.user)
+        # Creator automatically becomes admin member
+        GroupMembership.objects.create(
+            group=group,
+            user=self.request.user,
+            role=GroupMembership.Role.ADMIN,
+        )
+
+    # ── Membership ───────────────────────────────────────────────────────
+
+    @action(detail=True, methods=["post"], permission_classes=[IsGroupMember])
+    def join(self, request: Request, pk: int | None = None) -> Response:
+        """Join a reading group (public join link)."""
+        group = self.get_object()
+        membership, created = GroupMembership.objects.get_or_create(
+            group=group, user=request.user
+        )
+        if not created:
+            return Response({"detail": "Already a member."}, status=status.HTTP_200_OK)
+        MemberProgress.objects.get_or_create(
+            membership=membership,
+            group=group,
+            user=request.user,
+            defaults={"current_section": 0, "percentage": 0.0},
+        )
+        return Response({"detail": "Joined successfully."}, status=status.HTTP_201_CREATED)
+
+    @action(detail=True, methods=["post"], permission_classes=[IsGroupMember])
+    def leave(self, request: Request, pk: int | None = None) -> Response:
+        """Leave a reading group."""
+        group = self.get_object()
+        if group.created_by == request.user:
+            return Response(
+                {"error": "Group creator cannot leave. Transfer ownership or delete the group."},
+                status=status.HTTP_400_BAD_REQUEST,
+            )
+        GroupMembership.objects.filter(group=group, user=request.user).delete()
+        return Response(status=status.HTTP_204_NO_CONTENT)
+
+    @action(detail=True, methods=["get"], permission_classes=[IsGroupMember])
+    def members(self, request: Request, pk: int | None = None) -> Response:
+        """List group members with their progress."""
+        group = self.get_object()
+        memberships = (
+            group.memberships.select_related("user")
+            .prefetch_related("progress")
+            .all()
+        )
+        serializer = GroupMembershipSerializer(memberships, many=True)
+        return Response(serializer.data)
+
+    # ── Progress ─────────────────────────────────────────────────────────
+
+    @action(detail=True, methods=["get"], permission_classes=[IsGroupMember],
+            url_path="members/progress")
+    def members_progress(self, request: Request, pk: int | None = None) -> Response:
+        """Get progress for all group members.
+
+        Other members' progress shows section label only (no last_position).
+        Your own progress shows full detail.
+        """
+        group = self.get_object()
+        progress_qs = (
+            MemberProgress.objects.filter(group=group)
+            .select_related("user")
+            .order_by("-percentage")
+        )
+        result: list[dict] = []
+        for mp in progress_qs:
+            if mp.user == request.user:
+                result.append(MemberProgressSerializer(mp).data)
+            elif mp.is_public:
+                result.append(MemberProgressPublicSerializer(mp).data)
+            else:
+                result.append({
+                    "user_id": mp.user.id,
+                    "user_email": mp.user.email,
+                    "is_public": False,
+                    "note": "Private",
+                })
+        return Response(result)
+
+    @action(detail=True, methods=["get", "patch"], permission_classes=[IsGroupMember],
+            url_path="progress")
+    def my_progress(self, request: Request, pk: int | None = None) -> Response:
+        """Get or update my own progress in the group."""
+        group = self.get_object()
+        membership = GroupMembership.objects.get(group=group, user=request.user)
+        progress_obj, _created = MemberProgress.objects.get_or_create(
+            membership=membership,
+            group=group,
+            user=request.user,
+        )
+
+        if request.method == "GET":
+            serializer = MemberProgressSerializer(progress_obj)
+            return Response(serializer.data)
+
+        # PATCH — update progress
+        update_serializer = MemberProgressUpdateSerializer(data=request.data)
+        update_serializer.is_valid(raise_exception=True)
+        data = update_serializer.validated_data
+
+        progress_obj.update_progress(
+            current_section=data["current_section"],
+            percentage=data.get("percentage"),
+            time_spent_delta=data.get("time_spent_delta", 0),
+            last_position=data.get("last_position"),
+        )
+        if "is_public" in data:
+            progress_obj.is_public = data["is_public"]
+            progress_obj.save(update_fields=["is_public"])
+
+        serializer = MemberProgressSerializer(progress_obj)
+        return Response(serializer.data)
+
+    # ── Admin ────────────────────────────────────────────────────────────
+
+    @action(detail=True, methods=["get"], permission_classes=[IsGroupAdmin],
+            url_path="progress/summary")
+    def progress_summary(self, request: Request, pk: int | None = None) -> Response:
+        """Admin summary of all member progress."""
+        group = self.get_object()
+        progress_qs = MemberProgress.objects.filter(group=group).select_related("user")
+
+        total_members = group.memberships.count()
+        members_started = progress_qs.filter(current_section__gt=0).count()
+        members_finished = progress_qs.filter(percentage__gte=100.0).count()
+
+        avg_pct = progress_qs.aggregate(avg=models.Avg("percentage"))["avg"] or 0.0
+        avg_time = progress_qs.aggregate(avg=models.Avg("time_spent_seconds"))["avg"] or 0.0
+
+        member_details: list[dict] = []
+        for mp in progress_qs:
+            member_details.append({
+                "user_id": mp.user.id,
+                "user_email": mp.user.email,
+                "current_section": mp.current_section,
+                "percentage": mp.percentage,
+                "time_spent_seconds": mp.time_spent_seconds,
+                "is_public": mp.is_public,
+                "updated_at": mp.updated_at,
+            })
+
+        summary_data = {
+            "group_id": group.id,
+            "group_name": group.name,
+            "ebook_title": group.ebook.title,
+            "total_members": total_members,
+            "members_started": members_started,
+            "members_finished": members_finished,
+            "average_percentage": round(avg_pct, 1),
+            "average_time_spent_hours": round(avg_time / 3600.0, 1) if avg_time else 0.0,
+            "member_details": member_details,
+        }
+        serializer = AdminProgressSummarySerializer(data=summary_data)
+        serializer.is_valid(raise_exception=True)
+        return Response(serializer.data)

backend/config/django.py

@@ -41,6 +41,7 @@ INSTALLED_APPS = [
     "apps.books",
     "apps.annotations",
     "apps.reader",
+    "apps.groups",
 ]
 
 MIDDLEWARE = [

backend/config/urls.py

@@ -8,6 +8,7 @@ urlpatterns = [
     path("api/books/", include("apps.books.urls")),
     path("api/annotations/", include("apps.annotations.urls")),
     path("api/reader/", include("apps.reader.urls")),
+    path("api/groups/", include("apps.groups.urls")),
 ]
 
 if settings.DEBUG:

frontend/src/App.tsx

@@ -12,6 +12,8 @@ const AddBookPage = lazy(() => import("./pages/AddBook").then((m) => ({ default:
 const SettingsPage = lazy(() => import("./pages/Settings").then((m) => ({ default: m.SettingsPage })));
 const BookmarksNotesPage = lazy(() => import("./components/annotations/BookmarksNotesPage").then((m) => ({ default: m.BookmarksNotesPage })));
 const ReadingPage = lazy(() => import("./pages/ReadingPage").then((m) => ({ default: m.default })));
+const ReadingGroupsPage = lazy(() => import("./pages/ReadingGroups").then((m) => ({ default: m.ReadingGroupsPage })));
+const GroupDetailPage = lazy(() => import("./pages/GroupDetail").then((m) => ({ default: m.GroupDetailPage })));
 
 const AuthPage = lazy(() => import("./pages/AuthPage"));
 
@@ -45,6 +47,8 @@ function AppRoutes() {
         <Route path="/add" element={<ProtectedRoute><AddBookPage /></ProtectedRoute>} />
         <Route path="/settings" element={<ProtectedRoute><SettingsPage /></ProtectedRoute>} />
         <Route path="/bookmarks-notes/:bookId?" element={<ProtectedRoute><BookmarksNotesPage /></ProtectedRoute>} />
+        <Route path="/groups" element={<ProtectedRoute><ReadingGroupsPage /></ProtectedRoute>} />
+        <Route path="/groups/:id" element={<ProtectedRoute><GroupDetailPage /></ProtectedRoute>} />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>
     </Suspense>

frontend/src/api/groups.ts

@@ -0,0 +1,81 @@
+import api from "./client";
+import type {
+  AdminProgressSummary,
+  CreateGroupPayload,
+  MemberProgressDetail,
+  MemberProgressEntry,
+  ReadingGroupDetail,
+  ReadingGroupSummary,
+  UpdateProgressPayload,
+} from "../types/groups";
+
+export const groupsApi = {
+  /* ── Groups ── */
+
+  async listGroups(): Promise<ReadingGroupSummary[]> {
+    const { data } = await api.get<ReadingGroupSummary[]>("/groups/");
+    if (Array.isArray(data)) return data;
+    return (data as { results: ReadingGroupSummary[] }).results ?? [];
+  },
+
+  async getGroup(id: number): Promise<ReadingGroupDetail> {
+    const { data } = await api.get<ReadingGroupDetail>(`/groups/${id}/`);
+    return data;
+  },
+
+  async createGroup(payload: CreateGroupPayload): Promise<ReadingGroupDetail> {
+    const { data } = await api.post<ReadingGroupDetail>("/groups/", payload);
+    return data;
+  },
+
+  async deleteGroup(id: number): Promise<void> {
+    await api.delete(`/groups/${id}/`);
+  },
+
+  /* ── Membership ── */
+
+  async joinGroup(id: number): Promise<{ detail: string }> {
+    const { data } = await api.post<{ detail: string }>(`/groups/${id}/join/`);
+    return data;
+  },
+
+  async leaveGroup(id: number): Promise<void> {
+    await api.post(`/groups/${id}/leave/`);
+  },
+
+  /* ── Progress ── */
+
+  async getMembersProgress(groupId: number): Promise<MemberProgressEntry[]> {
+    const { data } = await api.get<MemberProgressEntry[]>(
+      `/groups/${groupId}/members/progress/`,
+    );
+    return data;
+  },
+
+  async getMyProgress(groupId: number): Promise<MemberProgressDetail> {
+    const { data } = await api.get<MemberProgressDetail>(
+      `/groups/${groupId}/progress/`,
+    );
+    return data;
+  },
+
+  async updateMyProgress(
+    groupId: number,
+    payload: UpdateProgressPayload,
+  ): Promise<MemberProgressDetail> {
+    const { data } = await api.patch<MemberProgressDetail>(
+      `/groups/${groupId}/progress/`,
+      payload,
+    );
+    return data;
+  },
+
+  /* ── Admin ── */
+
+  async getProgressSummary(groupId: number): Promise<AdminProgressSummary> {
+    const { data } = await api.get<AdminProgressSummary>(
+      `/groups/${groupId}/progress/summary/`,
+    );
+    return data;
+  },
+};

frontend/src/pages/GroupDetail.tsx

@@ -0,0 +1,381 @@
+import React, { useCallback, useEffect, useState } from "react";
+import { useNavigate, useParams } from "react-router-dom";
+import { useTranslation } from "react-i18n-lite";
+import { groupsApi } from "../api/groups";
+import type {
+  AdminProgressSummary,
+  MemberProgressEntry,
+  ReadingGroupDetail,
+} from "../types/groups";
+import { useMediaQuery, BREAKPOINTS } from "../hooks/useMediaQuery";
+
+function isDetail(entry: MemberProgressEntry): entry is { user_id: number; is_public: boolean; id: number } {
+  return "id" in entry && "is_public" in entry;
+}
+
+export function GroupDetailPage() {
+  const { t } = useTranslation();
+  const { id } = useParams<{ id: string }>();
+  const navigate = useNavigate();
+  const isMobile = useMediaQuery(BREAKPOINTS.md);
+
+  const [group, setGroup] = useState<ReadingGroupDetail | null>(null);
+  const [progressEntries, setProgressEntries] = useState<MemberProgressEntry[]>([]);
+  const [adminSummary, setAdminSummary] = useState<AdminProgressSummary | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [tab, setTab] = useState<"progress" | "admin">("progress");
+
+  const isAdmin = group?.members.some(
+    (m) => m.user_id === (group as ReadingGroupDetail & { _myUserId?: number })._myUserId && m.role === "admin",
+  );
+
+  const loadGroup = useCallback(async () => {
+    if (!id) return;
+    setLoading(true);
+    setError(null);
+    try {
+      const groupId = Number(id);
+      if (Number.isNaN(groupId)) {
+        setError(t("groupDetail.invalidId") ?? "Invalid group ID");
+        return;
+      }
+      const [groupData, progressData] = await Promise.all([
+        groupsApi.getGroup(groupId),
+        groupsApi.getMembersProgress(groupId).catch(() => [] as MemberProgressEntry[]),
+      ]);
+      setGroup(groupData);
+      setProgressEntries(progressData);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to load group");
+    } finally {
+      setLoading(false);
+    }
+  }, [id, t]);
+
+  const loadAdminSummary = useCallback(async () => {
+    if (!id || !isAdmin) return;
+    try {
+      const summary = await groupsApi.getProgressSummary(Number(id));
+      setAdminSummary(summary);
+    } catch {
+      // Admin summary is optional
+    }
+  }, [id, isAdmin]);
+
+  useEffect(() => {
+    void loadGroup();
+  }, [loadGroup]);
+
+  useEffect(() => {
+    if (tab === "admin") {
+      void loadAdminSummary();
+    }
+  }, [tab, loadAdminSummary]);
+
+  const handleJoin = useCallback(async () => {
+    if (!id) return;
+    try {
+      await groupsApi.joinGroup(Number(id));
+      void loadGroup();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to join");
+    }
+  }, [id, loadGroup]);
+
+  const handleLeave = useCallback(async () => {
+    if (!id) return;
+    try {
+      await groupsApi.leaveGroup(Number(id));
+      navigate("/groups");
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to leave");
+    }
+  }, [id, navigate]);
+
+  const containerStyle: React.CSSProperties = {
+    maxWidth: 720,
+    margin: "0 auto",
+    padding: isMobile ? 16 : 24,
+    minHeight: "100vh",
+    background: "#f8f9fa",
+  };
+
+  const backButtonStyle: React.CSSProperties = {
+    display: "inline-flex",
+    alignItems: "center",
+    gap: 4,
+    padding: isMobile ? "10px 16px" : "8px 16px",
+    borderRadius: 8,
+    border: "1px solid #e5e7eb",
+    background: "#fff",
+    color: "#374151",
+    fontSize: isMobile ? 15 : 14,
+    cursor: "pointer",
+    marginBottom: 20,
+    minHeight: 44,
+  };
+
+  const tabBarStyle: React.CSSProperties = {
+    display: "flex",
+    gap: 0,
+    marginBottom: 20,
+    borderBottom: "2px solid #e5e7eb",
+  };
+
+  const tabStyle = (active: boolean): React.CSSProperties => ({
+    padding: "10px 20px",
+    fontSize: 14,
+    fontWeight: active ? 600 : 400,
+    color: active ? "#4f46e5" : "#6b7280",
+    background: "transparent",
+    border: "none",
+    borderBottom: active ? "2px solid #4f46e5" : "2px solid transparent",
+    cursor: "pointer",
+    marginBottom: -2,
+  });
+
+  if (loading) {
+    return (
+      <div style={containerStyle}>
+        <div style={{ height: 32, width: 100, background: "#e5e7eb", borderRadius: 6, marginBottom: 20 }} />
+        <div style={{ height: 28, width: "50%", background: "#e5e7eb", borderRadius: 6, marginBottom: 16 }} />
+        {[1, 2, 3].map((i) => (
+          <div key={i} style={{ height: 60, background: "#e5e7eb", borderRadius: 8, marginBottom: 8 }} />
+        ))}
+      </div>
+    );
+  }
+
+  if (error || !group) {
+    return (
+      <div style={containerStyle}>
+        <button onClick={() => navigate("/groups")} style={backButtonStyle}>
+          ← {t("groupDetail.back") ?? "Back"}
+        </button>
+        <div style={{ textAlign: "center", padding: "60px 20px" }}>
+          <div style={{ fontSize: 48, marginBottom: 16 }}>😕</div>
+          <p style={{ color: "#6b7280", fontSize: 16 }}>
+            {error ?? (t("groupDetail.notFound") ?? "Group not found")}
+          </p>
+        </div>
+      </div>
+    );
+  }
+
+  const isMember = group.members.some((m) => {
+    // Determine membership by matching progress data — user_id can come from members list
+    // We check if there's a progress entry with an "id" (indicates own data)
+    return progressEntries.some((e) => "id" in e);
+  });
+
+  return (
+    <div style={containerStyle}>
+      <button onClick={() => navigate("/groups")} style={backButtonStyle}>
+        ← {t("groupDetail.back") ?? "Back to Groups"}
+      </button>
+
+      {/* Header */}
+      <div style={{ marginBottom: 20 }}>
+        <h1 style={{ fontSize: isMobile ? 20 : 24, fontWeight: 700, color: "#1f2937", margin: "0 0 4px" }}>
+          {group.name}
+        </h1>
+        <p style={{ fontSize: 14, color: "#6b7280", margin: 0 }}>
+          {group.ebook_title} {group.ebook_author ? `— ${group.ebook_author}` : ""}
+        </p>
+      </div>
+
+      {/* Group actions */}
+      <div style={{ display: "flex", gap: 10, marginBottom: 20, flexWrap: "wrap" }}>
+        {!isMember ? (
+          <button
+            onClick={() => void handleJoin()}
+            style={{
+              padding: "10px 20px", borderRadius: 10, border: "none", background: "#4f46e5",
+              color: "#fff", fontSize: 14, fontWeight: 600, cursor: "pointer",
+            }}
+          >
+            {t("groupDetail.join") ?? "Join Group"}
+          </button>
+        ) : (
+          <>
+            <span style={{
+              fontSize: 13, color: "#16a34a", background: "#dcfce7",
+              padding: "4px 12px", borderRadius: 999, display: "inline-flex", alignItems: "center",
+            }}>
+              ✓ {t("groupDetail.member") ?? "Member"}
+            </span>
+            {group.created_by_email !== undefined /* can't check identity here, but leave is always available for non-creators */ && (
+              <button
+                onClick={() => void handleLeave()}
+                style={{
+                  padding: "10px 20px", borderRadius: 10, border: "1px solid #fca5a5",
+                  background: "#fff", color: "#b91c1c", fontSize: 14, cursor: "pointer",
+                }}
+              >
+                {t("groupDetail.leave") ?? "Leave Group"}
+              </button>
+            )}
+          </>
+        )}
+      </div>
+
+      {group.description && (
+        <p style={{ fontSize: 14, color: "#4b5563", marginBottom: 20, lineHeight: 1.6, background: "#fff", padding: isMobile ? 12 : 16, borderRadius: 10, border: "1px solid #e5e7eb" }}>
+          {group.description}
+        </p>
+      )}
+
+      {/* Tabs */}
+      <div style={tabBarStyle}>
+        <button style={tabStyle(tab === "progress")} onClick={() => setTab("progress")}>
+          {t("groupDetail.progressTab") ?? "Progress"}
+        </button>
+        {isAdmin && (
+          <button style={tabStyle(tab === "admin")} onClick={() => setTab("admin")}>
+            {t("groupDetail.adminTab") ?? "Admin Summary"}
+          </button>
+        )}
+      </div>
+
+      {/* Progress tab */}
+      {tab === "progress" && (
+        <div>
+          {progressEntries.length === 0 ? (
+            <div style={{ textAlign: "center", padding: "40px 20px", color: "#9ca3af" }}>
+              <p>{t("groupDetail.noProgress") ?? "No progress data yet."}</p>
+            </div>
+          ) : (
+            progressEntries.map((entry) => {
+              const isPrivate = "is_public" in entry && entry.is_public === false && "note" in entry;
+              const hasDetail = isDetail(entry);
+
+              return (
+                <div
+                  key={entry.user_id}
+                  style={{
+                    background: "#fff", borderRadius: 10, padding: isMobile ? 12 : 16,
+                    marginBottom: 10, border: "1px solid #e5e7eb",
+                    boxShadow: "0 1px 3px rgba(0,0,0,0.04)",
+                  }}
+                >
+                  <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 6 }}>
+                    <span style={{ fontSize: 15, fontWeight: 600, color: "#1f2937" }}>
+                      {entry.user_email}
+                      {hasDetail && " (you)"}
+                    </span>
+                    {isPrivate ? (
+                      <span style={{ fontSize: 12, color: "#9ca3af", fontStyle: "italic" }}>
+                        🔒 {t("groupDetail.private") ?? "Private"}
+                      </span>
+                    ) : "section_label" in entry && (
+                      <span style={{ fontSize: 13, color: "#4f46e5", fontWeight: 500 }}>
+                        {entry.section_label}
+                      </span>
+                    )}
+                  </div>
+
+                  {!isPrivate && "percentage" in entry && (
+                    <div style={{ display: "flex", alignItems: "center", gap: 10 }}>
+                      <div style={{
+                        flex: 1, height: 8, borderRadius: 4, background: "#e5e7eb", overflow: "hidden",
+                      }}>
+                        <div style={{
+                          height: "100%",
+                          width: `${Math.min(100, entry.percentage)}%`,
+                          background: hasDetail ? "#4f46e5" : "#818cf8",
+                          borderRadius: 4,
+                          transition: "width 0.3s ease",
+                        }} />
+                      </div>
+                      <span style={{ fontSize: 13, fontWeight: 600, color: "#374151", whiteSpace: "nowrap" }}>
+                        {Math.round(entry.percentage)}%
+                      </span>
+                    </div>
+                  )}
+
+                  {hasDetail && entry.last_position && Object.keys(entry.last_position).length > 0 && (
+                    <div style={{ marginTop: 8, fontSize: 12, color: "#9ca3af" }}>
+                      {t("groupDetail.lastPosition") ?? "Last position"}: {JSON.stringify(entry.last_position)}
+                    </div>
+                  )}
+                </div>
+              );
+            })
+          )}
+        </div>
+      )}
+
+      {/* Admin tab */}
+      {tab === "admin" && adminSummary && (
+        <div>
+          <div style={{
+            display: "grid",
+            gridTemplateColumns: "repeat(auto-fit, minmax(140px, 1fr))",
+            gap: 12,
+            marginBottom: 24,
+          }}>
+            <StatCard
+              label={t("groupDetail.totalMembers") ?? "Members"}
+              value={String(adminSummary.total_members)}
+            />
+            <StatCard
+              label={t("groupDetail.started") ?? "Started"}
+              value={String(adminSummary.members_started)}
+            />
+            <StatCard
+              label={t("groupDetail.finished") ?? "Finished"}
+              value={String(adminSummary.members_finished)}
+            />
+            <StatCard
+              label={t("groupDetail.avgProgress") ?? "Avg Progress"}
+              value={`${Math.round(adminSummary.average_percentage)}%`}
+            />
+            <StatCard
+              label={t("groupDetail.avgTime") ?? "Avg Time"}
+              value={`${adminSummary.average_time_spent_hours}h`}
+            />
+          </div>
+
+          <h3 style={{ fontSize: 15, fontWeight: 600, color: "#1f2937", marginBottom: 12 }}>
+            {t("groupDetail.memberDetails") ?? "Member Details"}
+          </h3>
+          {adminSummary.member_details.map((m) => (
+            <div
+              key={m.user_id}
+              style={{
+                background: "#fff", borderRadius: 10, padding: isMobile ? 12 : 14,
+                marginBottom: 8, border: "1px solid #e5e7eb",
+                display: "flex", justifyContent: "space-between", alignItems: "center",
+              }}
+            >
+              <div>
+                <span style={{ fontSize: 14, fontWeight: 500, color: "#1f2937" }}>{m.user_email}</span>
+                <span style={{ fontSize: 12, color: "#9ca3af", marginLeft: 8 }}>
+                  {m.is_public ? "👁" : "🔒"}
+                </span>
+              </div>
+              <div style={{ display: "flex", gap: 16, fontSize: 13, color: "#6b7280" }}>
+                <span>Section {m.current_section}</span>
+                <span style={{ fontWeight: 600, color: "#4f46e5" }}>{Math.round(m.percentage)}%</span>
+                <span>⏱ {Math.round(m.time_spent_seconds / 60)}m</span>
+              </div>
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  );
+}
+
+function StatCard({ label, value }: { label: string; value: string }) {
+  return (
+    <div style={{
+      background: "#fff", borderRadius: 10, padding: "14px 16px",
+      border: "1px solid #e5e7eb", textAlign: "center",
+    }}>
+      <div style={{ fontSize: 22, fontWeight: 700, color: "#4f46e5" }}>{value}</div>
+      <div style={{ fontSize: 12, color: "#6b7280", marginTop: 2 }}>{label}</div>
+    </div>
+  );
+}

frontend/src/pages/Library.tsx

@@ -242,6 +242,7 @@ export function LibraryPage() {
             <>
               <button onClick={() => navigate("/add")} style={{ ...TOUCH_TARGET, fontSize: 20, background: "none", border: "none", cursor: "pointer", padding: 8 }} title={t("library.addBook")}>➕</button>
               <button onClick={() => navigate("/bookmarks-notes")} style={{ ...TOUCH_TARGET, fontSize: 20, background: "none", border: "none", cursor: "pointer", padding: 8 }} title={t("library.bookmarks")}>🔖</button>
+              <button onClick={() => navigate("/groups")} style={{ ...TOUCH_TARGET, fontSize: 20, background: "none", border: "none", cursor: "pointer", padding: 8 }} title="Reading Groups">👥</button>
               <button onClick={() => navigate("/settings")} style={{ ...TOUCH_TARGET, fontSize: 20, background: "none", border: "none", cursor: "pointer", padding: 8 }} title={t("library.settings")}>⚙️</button>
               <button onClick={logout} style={{ ...TOUCH_TARGET, fontSize: 20, background: "none", border: "none", cursor: "pointer", padding: 8 }} title={t("library.logout")}>🚪</button>
             </>
@@ -249,6 +250,7 @@ export function LibraryPage() {
             <>
               <button onClick={() => navigate("/add")} className="btn">+ {t("library.addBook")}</button>
               <button onClick={() => navigate("/bookmarks-notes")} className="btn btn-secondary">{t("library.bookmarks")}</button>
+              <button onClick={() => navigate("/groups")} className="btn btn-secondary">👥 Reading Groups</button>
               <button onClick={() => navigate("/settings")} className="btn btn-secondary">{t("library.settings")}</button>
               <button onClick={logout} className="btn btn-danger">{t("library.logout")}</button>
             </>

frontend/src/pages/ReadingGroups.tsx

@@ -0,0 +1,288 @@
+import React, { useCallback, useEffect, useState } from "react";
+import { useNavigate } from "react-router-dom";
+import { useTranslation } from "react-i18n-lite";
+import { groupsApi } from "../api/groups";
+import { booksApi } from "../api/books";
+import type { ReadingGroupSummary } from "../types/groups";
+import type { EBookListItem } from "../types/book";
+import { useMediaQuery, BREAKPOINTS } from "../hooks/useMediaQuery";
+
+export function ReadingGroupsPage() {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const isMobile = useMediaQuery(BREAKPOINTS.md);
+
+  const [groups, setGroups] = useState<ReadingGroupSummary[]>([]);
+  const [ebooks, setEbooks] = useState<EBookListItem[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [showCreate, setShowCreate] = useState(false);
+  const [createName, setCreateName] = useState("");
+  const [createEbook, setCreateEbook] = useState<number | null>(null);
+  const [createDesc, setCreateDesc] = useState("");
+  const [creating, setCreating] = useState(false);
+
+  const loadGroups = useCallback(async () => {
+    try {
+      const data = await groupsApi.listGroups();
+      setGroups(data);
+      setError(null);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to load groups");
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  const loadEbooks = useCallback(async () => {
+    try {
+      const data = await booksApi.getEBooks();
+      setEbooks(data);
+    } catch {
+      // Ebook list is optional; groups page still works without it
+    }
+  }, []);
+
+  useEffect(() => {
+    void loadGroups();
+    void loadEbooks();
+  }, [loadGroups, loadEbooks]);
+
+  const handleCreate = useCallback(async () => {
+    if (!createName.trim() || createEbook === null) return;
+    setCreating(true);
+    try {
+      await groupsApi.createGroup({
+        name: createName.trim(),
+        ebook: createEbook,
+        description: createDesc.trim(),
+      });
+      setShowCreate(false);
+      setCreateName("");
+      setCreateEbook(null);
+      setCreateDesc("");
+      void loadGroups();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to create group");
+    } finally {
+      setCreating(false);
+    }
+  }, [createName, createEbook, createDesc, loadGroups]);
+
+  const containerStyle: React.CSSProperties = {
+    maxWidth: 720,
+    margin: "0 auto",
+    padding: isMobile ? 16 : 24,
+    minHeight: "100vh",
+    background: "#f8f9fa",
+  };
+
+  const headerBar: React.CSSProperties = {
+    display: "flex",
+    justifyContent: "space-between",
+    alignItems: "center",
+    marginBottom: 24,
+  };
+
+  const cardStyle: React.CSSProperties = {
+    background: "#fff",
+    borderRadius: 12,
+    padding: isMobile ? 14 : 18,
+    marginBottom: 12,
+    cursor: "pointer",
+    boxShadow: "0 1px 4px rgba(0,0,0,0.06)",
+    border: "1px solid #e5e7eb",
+  };
+
+  if (loading) {
+    return (
+      <div style={containerStyle}>
+        <div style={{ height: 24, width: 200, background: "#e5e7eb", borderRadius: 6, marginBottom: 24 }} />
+        {[1, 2, 3].map((i) => (
+          <div key={i} style={{ ...cardStyle, cursor: "default" }}>
+            <div style={{ height: 20, width: "60%", background: "#e5e7eb", borderRadius: 4, marginBottom: 8 }} />
+            <div style={{ height: 14, width: "40%", background: "#e5e7eb", borderRadius: 4 }} />
+          </div>
+        ))}
+      </div>
+    );
+  }
+
+  return (
+    <div style={containerStyle}>
+      <div style={headerBar}>
+        <h1 style={{ fontSize: isMobile ? 20 : 24, fontWeight: 700, color: "#1f2937", margin: 0 }}>
+          📚 {t("readingGroups.title") ?? "Reading Groups"}
+        </h1>
+        <button
+          onClick={() => setShowCreate(true)}
+          style={{
+            padding: isMobile ? "10px 18px" : "8px 18px",
+            borderRadius: 10,
+            border: "none",
+            background: "#4f46e5",
+            color: "#fff",
+            fontSize: 14,
+            fontWeight: 600,
+            cursor: "pointer",
+            minHeight: 40,
+          }}
+        >
+          + {t("readingGroups.create") ?? "New Group"}
+        </button>
+      </div>
+
+      {error && (
+        <div style={{ padding: "12px 16px", background: "#fef2f2", borderRadius: 8, color: "#b91c1c", marginBottom: 16, fontSize: 14 }}>
+          {error}
+        </div>
+      )}
+
+      {/* Create modal */}
+      {showCreate && (
+        <div style={{
+          position: "fixed", inset: 0, background: "rgba(0,0,0,0.4)",
+          display: "flex", alignItems: "center", justifyContent: "center", zIndex: 100,
+        }}>
+          <div style={{
+            background: "#fff", borderRadius: 16, padding: 24, maxWidth: 420, width: "90%",
+            boxShadow: "0 10px 40px rgba(0,0,0,0.15)",
+          }}>
+            <h2 style={{ fontSize: 18, fontWeight: 700, marginBottom: 16, color: "#1f2937" }}>
+              {t("readingGroups.createTitle") ?? "Create Reading Group"}
+            </h2>
+
+            <label style={{ fontSize: 13, color: "#6b7280", display: "block", marginBottom: 4 }}>
+              {t("readingGroups.groupName") ?? "Group Name"}
+            </label>
+            <input
+              type="text"
+              value={createName}
+              onChange={(e) => setCreateName(e.target.value)}
+              placeholder={t("readingGroups.namePlaceholder") ?? "e.g., Book Club June"}
+              style={{
+                width: "100%", padding: "10px 14px", borderRadius: 8, border: "1px solid #d1d5db",
+                fontSize: 14, marginBottom: 14, boxSizing: "border-box",
+              }}
+            />
+
+            <label style={{ fontSize: 13, color: "#6b7280", display: "block", marginBottom: 4 }}>
+              {t("readingGroups.selectBook") ?? "Select Book"}
+            </label>
+            <select
+              value={createEbook ?? ""}
+              onChange={(e) => setCreateEbook(e.target.value ? Number(e.target.value) : null)}
+              style={{
+                width: "100%", padding: "10px 14px", borderRadius: 8, border: "1px solid #d1d5db",
+                fontSize: 14, marginBottom: 14, boxSizing: "border-box", background: "#fff",
+              }}
+            >
+              <option value="">-- {t("readingGroups.choose") ?? "Choose"} --</option>
+              {ebooks.map((eb) => (
+                <option key={eb.id} value={eb.id}>
+                  {eb.title} {eb.author ? `— ${eb.author}` : ""}
+                </option>
+              ))}
+            </select>
+
+            <label style={{ fontSize: 13, color: "#6b7280", display: "block", marginBottom: 4 }}>
+              {t("readingGroups.description") ?? "Description"} ({t("common.optional") ?? "optional"})
+            </label>
+            <textarea
+              value={createDesc}
+              onChange={(e) => setCreateDesc(e.target.value)}
+              rows={3}
+              style={{
+                width: "100%", padding: "10px 14px", borderRadius: 8, border: "1px solid #d1d5db",
+                fontSize: 14, marginBottom: 18, boxSizing: "border-box", resize: "vertical",
+              }}
+            />
+
+            <div style={{ display: "flex", gap: 10, justifyContent: "flex-end" }}>
+              <button
+                onClick={() => setShowCreate(false)}
+                style={{
+                  padding: "10px 20px", borderRadius: 8, border: "1px solid #d1d5db",
+                  background: "#fff", color: "#374151", fontSize: 14, cursor: "pointer",
+                }}
+              >
+                {t("common.cancel") ?? "Cancel"}
+              </button>
+              <button
+                onClick={() => void handleCreate()}
+                disabled={creating || !createName.trim() || createEbook === null}
+                style={{
+                  padding: "10px 20px", borderRadius: 8, border: "none",
+                  background: (!createName.trim() || createEbook === null) ? "#9ca3af" : "#4f46e5",
+                  color: "#fff", fontSize: 14, fontWeight: 600, cursor: (!createName.trim() || createEbook === null) ? "not-allowed" : "pointer",
+                }}
+              >
+                {creating ? (t("common.creating") ?? "Creating...") : (t("readingGroups.create") ?? "Create")}
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+
+      {/* Group list */}
+      {groups.length === 0 ? (
+        <div style={{ textAlign: "center", padding: "60px 20px", color: "#6b7280" }}>
+          <div style={{ fontSize: 48, marginBottom: 12 }}>📖</div>
+          <p style={{ fontSize: 16, marginBottom: 16 }}>
+            {t("readingGroups.empty") ?? "No reading groups yet. Create one to read together!"}
+          </p>
+        </div>
+      ) : (
+        groups.map((g) => (
+          <div
+            key={g.id}
+            style={cardStyle}
+            onClick={() => navigate(`/groups/${g.id}`)}
+          >
+            <div style={{ display: "flex", justifyContent: "space-between", alignItems: "flex-start" }}>
+              <div>
+                <h2 style={{ fontSize: isMobile ? 16 : 17, fontWeight: 600, color: "#1f2937", margin: "0 0 4px" }}>
+                  {g.name}
+                </h2>
+                <p style={{ fontSize: 13, color: "#6b7280", margin: "0 0 6px" }}>
+                  {g.ebook_title} {g.ebook_author ? `— ${g.ebook_author}` : ""}
+                </p>
+              </div>
+              <span style={{
+                fontSize: 12, color: "#4f46e5", background: "#eef2ff",
+                padding: "2px 10px", borderRadius: 999, whiteSpace: "nowrap",
+                minHeight: 24, display: "inline-flex", alignItems: "center",
+              }}>
+                {g.member_count} {g.member_count === 1
+                  ? (t("readingGroups.member") ?? "member")
+                  : (t("readingGroups.members") ?? "members")}
+              </span>
+            </div>
+
+            {g.my_progress && (
+              <div style={{ marginTop: 8, display: "flex", alignItems: "center", gap: 8 }}>
+                <div style={{
+                  flex: 1, height: 6, borderRadius: 3, background: "#e5e7eb", overflow: "hidden",
+                }}>
+                  <div style={{
+                    height: "100%", width: `${Math.min(100, g.my_progress.percentage)}%`,
+                    background: "#4f46e5", borderRadius: 3, transition: "width 0.3s ease",
+                  }} />
+                </div>
+                <span style={{ fontSize: 12, color: "#6b7280", whiteSpace: "nowrap" }}>
+                  {g.my_progress.section_label}
+                </span>
+              </div>
+            )}
+
+            {g.description && (
+              <p style={{ fontSize: 13, color: "#9ca3af", margin: "8px 0 0", lineHeight: 1.5 }}>
+                {g.description}
+              </p>
+            )}
+          </div>
+        ))
+      )}
+    </div>
+  );
+}

frontend/src/types/groups.ts

@@ -0,0 +1,104 @@
+/* ── Reading Groups ── */
+
+export interface MemberProgressPublic {
+  user_id: number;
+  user_email: string;
+  current_section: number;
+  total_sections: number;
+  section_label: string;
+  percentage: number;
+  time_spent_seconds: number;
+  updated_at: string;
+}
+
+export interface MemberProgressDetail {
+  id: number;
+  user_id: number;
+  user_email: string;
+  current_section: number;
+  total_sections: number;
+  section_label: string;
+  percentage: number;
+  time_spent_seconds: number;
+  last_position: Record<string, unknown>;
+  is_public: boolean;
+  updated_at: string;
+}
+
+export interface MemberProgressPrivateStub {
+  user_id: number;
+  user_email: string;
+  is_public: false;
+  note: string;
+}
+
+export type MemberProgressEntry =
+  | MemberProgressDetail
+  | MemberProgressPublic
+  | MemberProgressPrivateStub;
+
+export interface GroupMember {
+  id: number;
+  user_id: number;
+  user_email: string;
+  role: "member" | "admin";
+  joined_at: string;
+  progress: MemberProgressPublic | { is_public: false; note: string } | null;
+}
+
+export interface ReadingGroupSummary {
+  id: number;
+  name: string;
+  ebook: number;
+  ebook_title: string;
+  ebook_author: string;
+  created_by_email: string;
+  description: string;
+  member_count: number;
+  my_progress: {
+    current_section: number;
+    percentage: number;
+    time_spent_seconds: number;
+    section_label: string;
+  } | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface ReadingGroupDetail extends ReadingGroupSummary {
+  members: GroupMember[];
+}
+
+export interface CreateGroupPayload {
+  name: string;
+  ebook: number;
+  description?: string;
+}
+
+export interface UpdateProgressPayload {
+  current_section: number;
+  percentage?: number;
+  time_spent_delta?: number;
+  last_position?: Record<string, unknown>;
+  is_public?: boolean;
+}
+
+export interface AdminProgressSummary {
+  group_id: number;
+  group_name: string;
+  ebook_title: string;
+  total_members: number;
+  members_started: number;
+  members_finished: number;
+  average_percentage: number;
+  average_time_spent_hours: number;
+  member_details: {
+    user_id: number;
+    user_email: string;
+    current_section: number;
+    percentage: number;
+    time_spent_seconds: number;
+    is_public: boolean;
+    updated_at: string;
+  }[];
+}

packages/shared/src/types.ts

@@ -215,4 +215,36 @@ export interface PaginatedResponse<T> {
 export interface ApiError {
   detail?: string;
   [key: string]: unknown;
+}
+
+// ---- Reading Groups ----
+
+export interface ReadingGroupSummary {
+  id: number;
+  name: string;
+  ebook: number;
+  ebook_title: string;
+  ebook_author: string;
+  created_by_email: string;
+  description: string;
+  member_count: number;
+  my_progress: {
+    current_section: number;
+    percentage: number;
+    time_spent_seconds: number;
+    section_label: string;
+  } | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface MemberProgressPublic {
+  user_id: number;
+  user_email: string;
+  current_section: number;
+  total_sections: number;
+  section_label: string;
+  percentage: number;
+  time_spent_seconds: number;
+  updated_at: string;
 }

packages/shared/src/utils.ts

@@ -114,4 +114,13 @@ export const API_ENDPOINTS = {
     bookmarkDetail: (id: string) => `/api/annotations/bookmarks/${id}/`,
     noteDetail: (id: string) => `/api/annotations/notes/${id}/`,
   },
+  groups: {
+    list: "/api/groups/",
+    detail: (id: number) => `/api/groups/${id}/`,
+    membersProgress: (id: number) => `/api/groups/${id}/members/progress/`,
+    myProgress: (id: number) => `/api/groups/${id}/progress/`,
+    progressSummary: (id: number) => `/api/groups/${id}/progress/summary/`,
+    join: (id: number) => `/api/groups/${id}/join/`,
+    leave: (id: number) => `/api/groups/${id}/leave/`,
+  },
 } as const;