From 2a3c085fef8ac23cfd3f63878740f51f58890de8 Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Mon, 1 Jun 2020 22:24:18 -0400
Subject: [PATCH] Add item pagination

---
 lib/frenzy/paginator.ex                       | 28 +++++++++++++++++++
 lib/frenzy_web/controllers/feed_controller.ex | 15 ++++++++--
 lib/frenzy_web/templates/feed/show.html.eex   | 12 ++++++++
 lib/frenzy_web/views/feed_view.ex             | 27 +++++++++++++++++-
 4 files changed, 78 insertions(+), 4 deletions(-)
 create mode 100644 lib/frenzy/paginator.ex

diff --git a/lib/frenzy/paginator.ex b/lib/frenzy/paginator.ex
new file mode 100644
index 0000000..088ba03
--- /dev/null
+++ b/lib/frenzy/paginator.ex
@@ -0,0 +1,28 @@
+defmodule Frenzy.Paginator do
+  import Ecto.Query
+  alias Frenzy.{Repo, Item}
+
+  @spec paginate(query :: Ecto.Queryable.t(), params :: map()) :: Ecto.Query.t()
+
+  def paginate(query, %{"before" => before_id}) do
+    before = Repo.get(Item, before_id)
+
+    query
+    # |> where([o], o.id < ^before_id)
+    |> where([i], i.date < ^before.date)
+    |> order_by(desc: :date)
+  end
+
+  def paginate(query, %{"after" => after_id}) do
+    after_item = Repo.get(Item, after_id)
+
+    query
+    |> where([i], i.date > ^after_item.date)
+    |> order_by(asc: :date)
+  end
+
+  def paginate(query, _) do
+    query
+    |> order_by(desc: :date)
+  end
+end
diff --git a/lib/frenzy_web/controllers/feed_controller.ex b/lib/frenzy_web/controllers/feed_controller.ex
index 01d1628..c11818e 100644
--- a/lib/frenzy_web/controllers/feed_controller.ex
+++ b/lib/frenzy_web/controllers/feed_controller.ex
@@ -1,6 +1,6 @@
 defmodule FrenzyWeb.FeedController do
   use FrenzyWeb, :controller
-  alias Frenzy.{Repo, Group, Feed, Item, Pipeline}
+  alias Frenzy.{Repo, Group, Feed, Item, Pipeline, Paginator}
   alias FrenzyWeb.Router.Helpers, as: Routes
   alias FrenzyWeb.Endpoint
   import Ecto.Query
@@ -25,9 +25,18 @@ defmodule FrenzyWeb.FeedController do
 
   defp user_owns_feed(conn, _opts), do: conn
 
-  def show(conn, %{"id" => id}) do
+  def show(conn, %{"id" => id} = params) do
     feed = conn.assigns[:feed]
-    items = Repo.all(from Item, where: [feed_id: ^id, tombstone: false], order_by: [desc: :date])
+
+    items =
+      Item
+      |> where([i], i.feed_id == ^id)
+      |> Paginator.paginate(params)
+      |> limit(50)
+      |> Repo.all()
+      |> Enum.sort_by(fn item -> item.date end, fn a, b ->
+        DateTime.compare(a, b) == :gt
+      end)
 
     render(conn, "show.html", %{
       feed: feed,
diff --git a/lib/frenzy_web/templates/feed/show.html.eex b/lib/frenzy_web/templates/feed/show.html.eex
index d0e07a0..05e47aa 100644
--- a/lib/frenzy_web/templates/feed/show.html.eex
+++ b/lib/frenzy_web/templates/feed/show.html.eex
@@ -17,6 +17,12 @@
 
 <h3 class="mt-4">Items</h3>
 
+<%= unless is_nil(prev_page_path(@conn, @items)) do %>
+  <p class="text-center">
+    <a href="<%= prev_page_path(@conn, @items) %>" class="pagination-link">Newer</a>
+  </p>
+<% end %>
+
 <table class="table table-striped">
   <tbody>
     <%= for item <- @items do %>
@@ -34,3 +40,9 @@
     <% end %>
   </tbody>
 </table>
+
+<%= unless is_nil(next_page_path(@conn, @items)) do %>
+  <p class="text-center">
+    <a href="<%= next_page_path(@conn, @items) %>" class="pagination-link">Older</a>
+  </p>
+<% end %>
diff --git a/lib/frenzy_web/views/feed_view.ex b/lib/frenzy_web/views/feed_view.ex
index c6e727b..bbd346f 100644
--- a/lib/frenzy_web/views/feed_view.ex
+++ b/lib/frenzy_web/views/feed_view.ex
@@ -1,3 +1,28 @@
 defmodule FrenzyWeb.FeedView do
   use FrenzyWeb, :view
-end
\ No newline at end of file
+  alias Frenzy.{Repo, Item}
+  import Ecto.Query
+
+  @spec next_page_path(Plug.Conn.t(), [Frenzy.Item.t()]) :: String.t()
+  defp next_page_path(conn, items) do
+    %Item{id: id, date: date} = List.last(items)
+    has_older = Repo.exists?(from i in Item, where: i.date < ^date)
+
+    if has_older do
+      Phoenix.Controller.current_path(conn, %{before: id})
+    else
+      nil
+    end
+  end
+
+  @spec prev_page_path(Plug.Conn.t(), [Frenzy.Item.t()]) :: String.t()
+  defp prev_page_path(conn, [%Item{id: id, date: date} | _]) do
+    has_newer = Repo.exists?(from i in Item, where: i.date > ^date)
+
+    if has_newer do
+      Phoenix.Controller.current_path(conn, %{after: id})
+    else
+      nil
+    end
+  end
+end