feat(on_call): schedule editor layer reorder + unified resolver (chunk 3)

OnCall context
- move_layer/2: up/down position swap for schedule layers, mirror of
  move_escalation_rule/2 (tested for both directions + boundary no-op).

ScheduleLive.Show
- New move_layer event handler.
- Up/down arrow buttons on each layer card; the top arrow is disabled on
  the first layer, the bottom on the last (matches the escalation policy
  level reorder UX shipped in chunk 1).
- Replaced two per-hour walks (build_layer_spans + build_final_spans -
  ~672 resolve calls per render at 14 days) with Resolver.resolve_range/3
  + a small segments_to_spans/3 mapper. Per-layer view wraps each layer
  in a temporary single-layer %Schedule{} so the resolver code path is
  shared and overrides don't bleed into the per-layer strip.

Tests: 3 new context tests for move_layer, 1 new integration test for
the layer reorder UI. Full suite 10,214 / 0 failures. Format/dialyzer
clean.

CHANGELOG.txt

@@ -1,3 +1,21 @@
+2026-04-28
+feat(on_call): schedule editor layer reorder + unified resolver (chunk 3)
+  - OnCall.move_layer/2: up/down position swap for schedule layers (mirror
+    of move_escalation_rule/2). Tested for both directions + boundary no-op.
+  - ScheduleLive.Show: new move_layer event handler + up/down arrow buttons
+    on each layer card (top arrow disabled on first, bottom on last).
+  - ScheduleLive.Show timeline: replaced two per-hour walks
+    (build_layer_spans + build_final_spans, ~672 calls/render at 14 days)
+    with Resolver.resolve_range/3 + a small segments_to_spans/3 mapper.
+    Per-layer view wraps each layer in a temporary single-layer Schedule
+    struct so it reuses the same resolver code path.
+  - Tests: 3 new context tests for move_layer, 1 new integration test for
+    the layer reorder UI. Full suite 10,214 / 0 failures.
+  Files: lib/towerops/on_call.ex, lib/towerops_web/live/schedule_live/show.ex,
+         lib/towerops_web/live/schedule_live/show.html.heex,
+         test/towerops/on_call_test.exs,
+         test/towerops_web/live/schedule_live_test.exs
+
 2026-04-28
 feat(on_call): schedules list with gantt timeline (chunk 2)
   - Resolver.resolve_range/3 returns contiguous on-call segments across a

lib/towerops/on_call.ex

@@ -84,6 +84,48 @@ defmodule Towerops.OnCall do
     Repo.delete(layer)
   end
 
+  @doc """
+  Swaps a layer with its neighbour in the given direction (`:up` or `:down`).
+  Returns `{:ok, layer}` (unchanged when at the boundary), or `{:error, reason}`.
+  """
+  def move_layer(%Layer{} = layer, direction) when direction in [:up, :down] do
+    schedule_layers =
+      Layer
+      |> where([l], l.schedule_id == ^layer.schedule_id)
+      |> order_by([l], asc: l.position)
+      |> Repo.all()
+
+    case find_neighbour_layer(schedule_layers, layer, direction) do
+      nil ->
+        {:ok, layer}
+
+      neighbour ->
+        case swap_layer_positions(layer, neighbour) do
+          :ok -> {:ok, Repo.get!(Layer, layer.id)}
+          {:error, _} = err -> err
+        end
+    end
+  end
+
+  defp find_neighbour_layer(layers, layer, :up), do: Enum.find(layers, &(&1.position == layer.position - 1))
+
+  defp find_neighbour_layer(layers, layer, :down), do: Enum.find(layers, &(&1.position == layer.position + 1))
+
+  defp swap_layer_positions(a, b) do
+    a_pos = a.position
+    b_pos = b.position
+
+    fn ->
+      {:ok, _} = a |> Layer.changeset(%{position: b_pos}) |> Repo.update()
+      {:ok, _} = b |> Layer.changeset(%{position: a_pos}) |> Repo.update()
+    end
+    |> Repo.transaction()
+    |> case do
+      {:ok, _} -> :ok
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
   # --- Layer Members ---
 
   def add_layer_member(attrs) do

lib/towerops_web/live/schedule_live/show.ex

@@ -146,6 +146,17 @@ defmodule ToweropsWeb.ScheduleLive.Show do
     end
   end
 
+  def handle_event("move_layer", %{"id" => id, "direction" => direction}, socket) when direction in ["up", "down"] do
+    layer = Enum.find(socket.assigns.schedule.layers, &(&1.id == id))
+
+    if layer do
+      {:ok, _} = OnCall.move_layer(layer, String.to_existing_atom(direction))
+      {:noreply, reload_schedule(socket)}
+    else
+      {:noreply, socket}
+    end
+  end
+
   def handle_event("delete_layer", %{"id" => layer_id}, socket) do
     layer = Enum.find(socket.assigns.schedule.layers, &(&1.id == layer_id))
 
@@ -296,69 +307,35 @@ defmodule ToweropsWeb.ScheduleLive.Show do
   end
 
   defp build_layer_spans(layer, start_date, num_days) do
-    start_dt = DateTime.new!(start_date, ~T[00:00:00], "Etc/UTC")
-    total_hours = num_days * 24
-
-    0..(total_hours - 1)
-    |> Enum.map(fn hour_offset ->
-      dt = DateTime.add(start_dt, hour_offset * 3600, :second)
-      user = resolve_layer_only(layer, dt)
-      {hour_offset, user}
-    end)
-    |> Enum.chunk_by(fn {_, user} -> user && user.id end)
-    |> Enum.map(fn chunk ->
-      {start_offset, user} = List.first(chunk)
-      duration = length(chunk)
-
-      %{
-        user: user,
-        start_offset: start_offset,
-        duration: duration,
-        total_hours: total_hours
-      }
-    end)
-    |> Enum.reject(fn span -> is_nil(span.user) end)
+    # Resolve a single-layer "schedule" so we get per-layer coverage
+    # without overrides bleeding in. The Resolver only reads :layers and
+    # :overrides off the struct, so a stub keyword-style struct is fine.
+    layer_schedule = %Towerops.OnCall.Schedule{layers: [layer], overrides: []}
+    segments_to_spans(layer_schedule, start_date, num_days)
   end
 
   defp build_final_spans(schedule, start_date, num_days) do
-    start_dt = DateTime.new!(start_date, ~T[00:00:00], "Etc/UTC")
-    total_hours = num_days * 24
+    segments_to_spans(schedule, start_date, num_days)
+  end
 
-    0..(total_hours - 1)
-    |> Enum.map(fn hour_offset ->
-      dt = DateTime.add(start_dt, hour_offset * 3600, :second)
-      user = Resolver.resolve(schedule, dt)
-      {hour_offset, user}
-    end)
-    |> Enum.chunk_by(fn {_, user} -> user && user.id end)
-    |> Enum.map(fn chunk ->
-      {start_offset, user} = List.first(chunk)
-      duration = length(chunk)
+  defp segments_to_spans(schedule, start_date, num_days) do
+    total_hours = num_days * 24
+    {:ok, start_at} = DateTime.new(start_date, ~T[00:00:00], "Etc/UTC")
+    end_at = DateTime.add(start_at, total_hours * 3600, :second)
+
+    schedule
+    |> Resolver.resolve_range(start_at, end_at)
+    |> Enum.map(fn segment ->
+      start_offset = max(div(DateTime.diff(segment.start_at, start_at, :second), 3600), 0)
+      end_offset = min(div(DateTime.diff(segment.end_at, start_at, :second), 3600), total_hours)
+      duration = max(end_offset - start_offset, 1)
 
       %{
-        user: user,
+        user: segment.user,
         start_offset: start_offset,
         duration: duration,
         total_hours: total_hours
       }
     end)
-    |> Enum.reject(fn span -> is_nil(span.user) end)
   end
-
-  defp resolve_layer_only(layer, datetime) do
-    with true <- DateTime.compare(datetime, layer.start_date) in [:gt, :eq],
-         members = Enum.sort_by(layer.members, & &1.position),
-         true <- members != [] do
-      elapsed = DateTime.diff(datetime, layer.start_date, :second)
-      rotation_secs = rotation_seconds(layer)
-      position = elapsed |> div(rotation_secs) |> rem(length(members))
-      Enum.at(members, position).user
-    else
-      _ -> nil
-    end
-  end
-
-  defp rotation_seconds(%{rotation_type: "daily", rotation_interval: i}), do: i * 86_400
-  defp rotation_seconds(%{rotation_type: "weekly", rotation_interval: i}), do: i * 604_800
-  defp rotation_seconds(%{rotation_interval: i}), do: i * 86_400
 end

lib/towerops_web/live/schedule_live/show.html.heex

@@ -338,8 +338,10 @@
         </p>
       </div>
     <% else %>
+      <% sorted_layers = Enum.sort_by(@schedule.layers, & &1.position) %>
+      <% layer_count = length(sorted_layers) %>
       <div class="space-y-4">
-        <%= for layer <- Enum.sort_by(@schedule.layers, & &1.position) do %>
+        <%= for {layer, idx} <- Enum.with_index(sorted_layers) do %>
           <div class="rounded-lg border border-gray-200 dark:border-white/10 bg-white dark:bg-gray-900 p-4">
             <div class="flex items-center justify-between mb-3">
               <div>
@@ -357,14 +359,37 @@
                   · Handoff at {Calendar.strftime(layer.handoff_time, "%H:%M")}
                 </p>
               </div>
-              <button
-                phx-click="delete_layer"
-                phx-value-id={layer.id}
-                data-confirm={t("Are you sure you want to delete this layer?")}
-                class="text-gray-400 hover:text-red-500 dark:hover:text-red-400 transition-colors"
-              >
-                <.icon name="hero-trash" class="h-4 w-4" />
-              </button>
+              <div class="flex items-center gap-1">
+                <button
+                  phx-click="move_layer"
+                  phx-value-id={layer.id}
+                  phx-value-direction="up"
+                  class="text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 disabled:opacity-30 disabled:hover:text-gray-400"
+                  disabled={idx == 0}
+                  title={t("Move up")}
+                >
+                  <.icon name="hero-arrow-up" class="h-4 w-4" />
+                </button>
+                <button
+                  phx-click="move_layer"
+                  phx-value-id={layer.id}
+                  phx-value-direction="down"
+                  class="text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 disabled:opacity-30 disabled:hover:text-gray-400"
+                  disabled={idx == layer_count - 1}
+                  title={t("Move down")}
+                >
+                  <.icon name="hero-arrow-down" class="h-4 w-4" />
+                </button>
+                <button
+                  phx-click="delete_layer"
+                  phx-value-id={layer.id}
+                  data-confirm={t("Are you sure you want to delete this layer?")}
+                  class="text-gray-400 hover:text-red-500 dark:hover:text-red-400 transition-colors ml-1"
+                  title={t("Delete")}
+                >
+                  <.icon name="hero-trash" class="h-4 w-4" />
+                </button>
+              </div>
             </div>
 
             <%!-- Members --%>

priv/static/changelog.txt

@@ -1,3 +1,7 @@
+2026-04-28 — Schedule Layer Reorder
+* Added up/down reorder controls to layers on the schedule detail page
+* Schedule timelines now use the same per-day rendering engine as the schedules list
+
 2026-04-28 — Schedules Timeline View
 * New gantt-style schedules list shows who's on call across a date window
 * Date navigation (Today / prev / next) and 1/2/4-week range selector

test/towerops/on_call_test.exs

@@ -353,6 +353,60 @@ defmodule Towerops.OnCallTest do
     end
   end
 
+  describe "move_layer/2" do
+    test "swaps positions with the neighbour above when direction is :up", %{organization: org} do
+      schedule = schedule_fixture(org.id)
+      {:ok, l0} = OnCall.create_layer(layer_attrs(schedule.id, 0))
+      {:ok, l1} = OnCall.create_layer(layer_attrs(schedule.id, 1))
+
+      {:ok, _} = OnCall.move_layer(l1, :up)
+
+      reloaded = OnCall.get_schedule!(schedule.id)
+      by_id = Map.new(reloaded.layers, &{&1.id, &1.position})
+      assert by_id[l0.id] == 1
+      assert by_id[l1.id] == 0
+    end
+
+    test "is a no-op at the top boundary", %{organization: org} do
+      schedule = schedule_fixture(org.id)
+      {:ok, l0} = OnCall.create_layer(layer_attrs(schedule.id, 0))
+
+      assert {:ok, returned} = OnCall.move_layer(l0, :up)
+      assert returned.id == l0.id
+      assert returned.position == 0
+    end
+
+    test "swaps with the neighbour below when direction is :down", %{organization: org} do
+      schedule = schedule_fixture(org.id)
+      {:ok, l0} = OnCall.create_layer(layer_attrs(schedule.id, 0))
+      {:ok, l1} = OnCall.create_layer(layer_attrs(schedule.id, 1))
+
+      {:ok, _} = OnCall.move_layer(l0, :down)
+
+      by_id =
+        schedule.id
+        |> OnCall.get_schedule!()
+        |> Map.fetch!(:layers)
+        |> Map.new(&{&1.id, &1.position})
+
+      assert by_id[l0.id] == 1
+      assert by_id[l1.id] == 0
+    end
+  end
+
+  defp layer_attrs(schedule_id, position) do
+    %{
+      name: "Layer #{position}",
+      position: position,
+      rotation_type: "weekly",
+      rotation_interval: 1,
+      handoff_time: ~T[09:00:00],
+      handoff_day: 1,
+      start_date: ~U[2026-01-01 09:00:00Z],
+      schedule_id: schedule_id
+    }
+  end
+
   describe "who_is_on_call/2" do
     test "resolves who is on call from schedule id", %{user: user, organization: org} do
       schedule = schedule_fixture(org.id)

test/towerops_web/live/schedule_live_test.exs

@@ -199,6 +199,39 @@ defmodule ToweropsWeb.ScheduleLiveTest do
       assert html =~ "Covers weekday shifts"
     end
 
+    test "can reorder layers via the up/down buttons", %{conn: conn, organization: organization} do
+      schedule = schedule_fixture(organization.id)
+
+      l0 =
+        layer_fixture(schedule.id, %{
+          name: "Top Layer",
+          position: 0,
+          rotation_type: "weekly",
+          handoff_time: ~T[09:00:00],
+          start_date: ~U[2026-01-01 09:00:00Z]
+        })
+
+      l1 =
+        layer_fixture(schedule.id, %{
+          name: "Bottom Layer",
+          position: 1,
+          rotation_type: "weekly",
+          handoff_time: ~T[09:00:00],
+          start_date: ~U[2026-01-01 09:00:00Z]
+        })
+
+      {:ok, view, _html} = live(conn, ~p"/schedules/#{schedule.id}")
+
+      view
+      |> element(~s|button[phx-click="move_layer"][phx-value-id="#{l1.id}"][phx-value-direction="up"]|)
+      |> render_click()
+
+      reloaded = OnCall.get_schedule!(schedule.id)
+      by_id = Map.new(reloaded.layers, &{&1.id, &1.position})
+      assert by_id[l0.id] == 1
+      assert by_id[l1.id] == 0
+    end
+
     test "shows Currently On-Call section with no one on-call", %{
       conn: conn,
       organization: organization