mwoods79 · Apr 30, 2026 · Apr 30, 2026 · Apr 30, 2026 · Apr 30, 2026 · Apr 30, 2026
diff --git a/lib/huddlz/communities/huddl.ex b/lib/huddlz/communities/huddl.ex
@@ -87,6 +87,7 @@ defmodule Huddlz.Communities.Huddl do
         :virtual_link,
         :is_private,
         :thumbnail_url,
+        :max_attendees,
         :creator_id,
         :group_id,
         :huddl_template_id
@@ -130,6 +131,7 @@ defmodule Huddlz.Communities.Huddl do
         :virtual_link,
         :is_private,
         :thumbnail_url,
+        :max_attendees,
         :huddl_template_id
       ]
 
@@ -160,6 +162,7 @@ defmodule Huddlz.Communities.Huddl do
       change Huddlz.Geocoding.ApplyProvidedCoordinates
       change {Huddlz.Geocoding.GeocodeChange, field: :physical_location}
       change Huddlz.Communities.Huddl.Changes.DefaultLocationFromGroup
+      change Huddlz.Communities.Huddl.Changes.EnforceCapacityFloor
     end
 
     read :by_status do
@@ -393,6 +396,12 @@ defmodule Huddlz.Communities.Huddl do
       public? true
     end
 
+    attribute :max_attendees, :integer do
+      allow_nil? true
+      public? true
+      constraints min: 1
+    end
+
     attribute :latitude, :float do
       allow_nil? true
       description "Geocoded latitude of physical_location or inherited from group"

diff --git a/lib/huddlz/communities/huddl/changes/enforce_capacity_floor.ex b/lib/huddlz/communities/huddl/changes/enforce_capacity_floor.ex
@@ -0,0 +1,42 @@
+defmodule Huddlz.Communities.Huddl.Changes.EnforceCapacityFloor do
+  @moduledoc """
+  Prevents organizers from reducing `max_attendees` below the current RSVP
+  count. Locks the huddl row inside the action's transaction so the check is
+  atomic with the update — no organizer/RSVP TOCTOU race.
+  """
+  use Ash.Resource.Change
+
+  alias Huddlz.Communities.Huddl
+
+  require Ash.Query
+
+  def change(changeset, _opts, _context) do
+    Ash.Changeset.before_action(changeset, fn cs ->
+      with true <- Ash.Changeset.changing_attribute?(cs, :max_attendees),
+           new_max when not is_nil(new_max) <-
+             Ash.Changeset.get_attribute(cs, :max_attendees) do
+        check_floor(cs, new_max)
+      else
+        _ -> cs
+      end
+    end)
+  end
+
+  defp check_floor(cs, new_max) do
+    huddl =
+      Huddl
+      |> Ash.Query.filter(id == ^cs.data.id)
+      |> Ash.Query.lock("FOR UPDATE")
+      |> Ash.Query.load(:rsvp_count)
+      |> Ash.read_one!(authorize?: false)
+
+    if new_max < huddl.rsvp_count do
+      Ash.Changeset.add_error(cs,
+        field: :max_attendees,
+        message: "cannot be less than the current RSVP count"
+      )
+    else
+      cs
+    end
+  end
+end
diff --git a/lib/huddlz/communities/huddl/changes/rsvp.ex b/lib/huddlz/communities/huddl/changes/rsvp.ex
@@ -2,36 +2,63 @@ defmodule Huddlz.Communities.Huddl.Changes.Rsvp do
   @moduledoc """
   Handles RSVP logic: creates an attendee record if one doesn't already exist.
   The rsvp_count is computed as an aggregate, so no manual counter management is needed.
+
+  Concurrency: locks the huddl row inside the action's transaction so that
+  concurrent RSVPs serialize on capacity checks and cannot overbook.
   """
   use Ash.Resource.Change
 
+  alias Huddlz.Communities.{Huddl, HuddlAttendee}
+
   require Ash.Query
 
   def change(changeset, _opts, %{actor: %{id: user_id}}) when not is_nil(user_id) do
-    huddl_id = changeset.data.id
-
-    existing =
-      Huddlz.Communities.HuddlAttendee
-      |> Ash.Query.for_read(:check_rsvp, %{huddl_id: huddl_id}, actor: %{id: user_id})
-      |> Ash.read_one(authorize?: false)
+    Ash.Changeset.before_action(changeset, &reserve_spot(&1, user_id))
+  end
 
-    case existing do
-      {:ok, nil} ->
-        Huddlz.Communities.HuddlAttendee
-        |> Ash.Changeset.for_create(:rsvp, %{huddl_id: huddl_id, user_id: user_id})
-        |> Ash.create!(authorize?: false)
+  def change(changeset, _opts, _context) do
+    Ash.Changeset.add_error(changeset, "An actor is required to RSVP")
+  end
 
-        changeset
+  defp reserve_spot(cs, user_id) do
+    huddl = lock_huddl!(cs.data.id)
 
-      {:ok, _} ->
-        changeset
+    case fetch_existing_rsvp(huddl.id, user_id) do
+      {:ok, nil} -> claim_or_reject(cs, huddl, user_id)
+      {:ok, _attendee} 
8000
-> cs
+      {:error, error} -> Ash.Changeset.add_error(cs, error)
+    end
+  end
 
-      {:error, error} ->
-        Ash.Changeset.add_error(changeset, error)
+  defp claim_or_reject(cs, huddl, user_id) do
+    if at_capacity?(huddl) do
+      Ash.Changeset.add_error(cs, "This huddl is full")
+    else
+      create_rsvp!(huddl.id, user_id)
+      cs
     end
   end
 
-  def change(changeset, _opts, _context) do
-    Ash.Changeset.add_error(changeset, "An actor is required to RSVP")
+  defp lock_huddl!(huddl_id) do
+    Huddl
+    |> Ash.Query.filter(id == ^huddl_id)
+    |> Ash.Query.lock("FOR UPDATE")
+    |> Ash.Query.load(:rsvp_count)
+    |> Ash.read_one!(authorize?: false)
+  end
+
+  defp fetch_existing_rsvp(huddl_id, user_id) do
+    HuddlAttendee
+    |> Ash.Query.for_read(:check_rsvp, %{huddl_id: huddl_id}, actor: %{id: user_id})
+    |> Ash.read_one(authorize?: false)
+  end
+
+  defp at_capacity?(%{max_attendees: nil}), do: false
+  defp at_capacity?(%{max_attendees: max, rsvp_count: count}), do: count >= max
+
+  defp create_rsvp!(huddl_id, user_id) do
+    HuddlAttendee
+    |> Ash.Changeset.for_create(:rsvp, %{huddl_id: huddl_id, user_id: user_id})
+    |> Ash.create!(authorize?: false)
   end
 end
diff --git a/lib/huddlz_web/components/community_components.ex b/lib/huddlz_web/components/community_components.ex
@@ -181,10 +181,14 @@ defmodule HuddlzWeb.CommunityComponents do
               {@huddl.physical_location}
             </span>
           <% end %>
-          <%= if @huddl.rsvp_count > 0 do %>
+          <%= if @huddl.max_attendees || @huddl.rsvp_count > 0 do %>
             <span class="flex items-center gap-1">
               <.icon name="hero-user-group" class="h-3.5 w-3.5" />
-              {@huddl.rsvp_count} attending
+              <%= if @huddl.max_attendees do %>
+                {capacity_label(@huddl)}
+              <% else %>
+                {@huddl.rsvp_count} attending
+              <% end %>
             </span>
           <% end %>
           <%= if @distance do %>
@@ -194,6 +198,16 @@ defmodule HuddlzWeb.CommunityComponents do
             </span>
           <% end %>
         </div>
+        <%= if @huddl.max_attendees do %>
+          <div class="mt-3">
+            <div class="flex items-center justify-between text-xs">
+              <span class={capacity_status_class(@huddl)}>{capacity_status(@huddl)}</span>
+            </div>
+            <div class="mt-1.5 h-1.5 bg-base-200 overflow-hidden">
+              <div class="h-full bg-primary" style={"width: #{capacity_percent(@huddl)}%"}></div>
+            </div>
+          </div>
+        <% end %>
       </div>
     </.link>
     """
@@ -324,6 +338,38 @@ defmodule HuddlzWeb.CommunityComponents do
   defp type_icon(:hybrid), do: "hero-globe-alt"
   defp type_icon(_), do: "hero-calendar"
 
+  def event_full?(%{max_attendees: nil}), do: false
+  def event_full?(huddl), do: huddl.rsvp_count >= huddl.max_attendees
+
+  def capacity_label(huddl), do: "#{huddl.rsvp_count}/#{huddl.max_attendees} spots filled"
10000
;
+
+  def capacity_percent(%{max_attendees: nil}), do: 0
+
+  def capacity_percent(huddl) do
+    min(round(huddl.rsvp_count / huddl.max_attendees * 100), 100)
+  end
+
+  def capacity_status(huddl), do: capacity_status_for_tier(capacity_tier(huddl))
+  def capacity_status_class(huddl), do: capacity_status_class_for_tier(capacity_tier(huddl))
+
+  defp capacity_tier(huddl) do
+    cond do
+      event_full?(huddl) -> :full
+      capacity_percent(huddl) >= 80 -> :almost_full
+      capacity_percent(huddl) >= 50 -> :filling_up
+      true -> :plenty
+    end
+  end
+
+  defp capacity_status_for_tier(:full), do: "Event Full"
+  defp capacity_status_for_tier(:almost_full), do: "Almost full"
+  defp capacity_status_for_tier(:filling_up), do: "Filling up"
+  defp capacity_status_for_tier(:plenty), do: "Plenty of space"
+
+  defp capacity_status_class_for_tier(:full), do: "font-semibold text-error"
+  defp capacity_status_class_for_tier(:almost_full), do: "font-semibold text-warning"
+  defp capacity_status_class_for_tier(_), do: "font-semibold text-success"
+
   defp truncate(text, max_length) when is_binary(text) and byte_size(text) > max_length do
     String.slice(text, 0, max_length) <> "..."
   end

diff --git a/lib/huddlz_web/live/huddl_live/edit.ex b/lib/huddlz_web/live/huddl_live/edit.ex
@@ -104,7 +104,8 @@ defmodule HuddlzWeb.HuddlLive.Edit do
     initial_params = %{
       "date" => Date.to_iso8601(date),
       "start_time" => Calendar.strftime(start_time, "%H:%M"),
-      "duration_minutes" => to_string(duration_minutes)
+      "duration_minutes" => to_string(duration_minutes),
+      "max_attendees" => if(huddl.max_attendees, do: to_string(huddl.max_attendees), else: "")
     }
 
     initial_params = maybe_add_recurring_params(initial_params, huddl)

diff --git a/lib/huddlz_web/live/huddl_live/form_component.ex b/lib/huddlz_web/live/huddl_live/form_component.ex
@@ -33,6 +33,14 @@ defmodule HuddlzWeb.HuddlLive.FormComponent do
 
     <.duration_picker field={@form[:duration_minutes]} label="Duration" />
 
+    <.input
+      field={@form[:max_attendees]}
+      type="number"
+      label="Max Attendees"
+      min="1"
+      placeholder="Leave blank for unlimited"
+    />
+
     <%= if @calculated_end_time do %>
       <div class="border border-primary/20 p-3 bg-primary/5 flex items-center gap-2 text-sm">
         <.icon name="hero-clock" class="h-5 w-5" />

diff --git a/lib/huddlz_web/live/huddl_live/show.ex b/lib/huddlz_web/live/huddl_live/show.ex
@@ -89,9 +89,15 @@ defmodule HuddlzWeb.HuddlLive.Show do
                 </button>
               </div>
             <% else %>
-              <.button phx-click="rsvp">
-                RSVP to this huddl
-              </.button>
+              <%= if event_full?(@huddl) do %>
+                <div class="text-error font-semibold">
+                  <.icon name="hero-x-circle" class="h-5 w-5 inline" /> Event Full
+                </div>
+              <% else %>
+                <.button phx-click="rsvp">
+                  RSVP to this huddl
+                </.button>
+              <% end %>
             <% end %>
           <% end %>
         </:actions>
@@ -120,6 +126,23 @@ defmodule HuddlzWeb.HuddlLive.Show do
           {@huddl.description || "No description provided."}
         </p>
 
+        <%= if @huddl.max_attendees do %>
+          <div class="mt-6 border border-base-300 p-4">
+            <div class="flex items-center justify-between gap-3 text-sm">
+              <span class="font-medium flex items-center gap-2">
+                <.icon name="hero-user-group" class="h-4 w-4" />
+                {capacity_label(@huddl)}
+              </span>
+              <span class={capacity_status_class(@huddl)}>
+                {capacity_status(@huddl)}
+              </span>
+            </div>
+            <div class="mt-3 h-2 bg-base-200 overflow-hidden">
+              <div class="h-full bg-primary" style={"width: #{capacity_percent(@huddl)}%"}></div>
+            </div>
+          </div>
+        <% end %>
+
         <dl class="mt-6">
           <div class="flex items-start gap-3 py-3">
             <dt class="w-32 shrink-0 font-medium text-base-content/50">Status</dt>

diff --git a/priv/repo/migrations/20260430014356_add_max_attendees_to_huddlz.exs b/priv/repo/migrations/20260430014356_add_max_attendees_to_huddlz.exs
@@ -0,0 +1,21 @@
+defmodule Huddlz.Repo.Migrations.AddMaxAttendeesToHuddlz do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:huddlz) do
+      add :max_attendees, :bigint
+    end
+  end
+
+  def down do
+    alter table(:huddlz) do
+      remove :max_attendees
+    end
+  end
+end