Fix pagination on inventory tab at Token's page

This code was removed and it shouldn't :(. Besides bringing this code
back, I'm adding tests in the controller layer to make sure that it will
not happen anymore.

apps/block_scout_web/test/block_scout_web/controllers/tokens/inventory_controller_test.ex

@@ -0,0 +1,121 @@
+defmodule BlockScoutWeb.Tokens.InventoryControllerTest do
+  use BlockScoutWeb.ConnCase
+
+  describe "GET index/3" do
+    test "with invalid address hash", %{conn: conn} do
+      conn = get(conn, token_inventory_path(conn, :index, "invalid_address"))
+
+      assert html_response(conn, 404)
+    end
+
+    test "with a token that doesn't exist", %{conn: conn} do
+      address = build(:address)
+      conn = get(conn, token_inventory_path(conn, :index, address.hash))
+
+      assert html_response(conn, 404)
+    end
+
+    test "successfully renders the page", %{conn: conn} do
+      token_contract_address = insert(:contract_address)
+      token = insert(:token, type: "ERC-721", contract_address: token_contract_address)
+
+      transaction =
+        :transaction
+        |> insert()
+        |> with_block()
+
+      insert(
+        :token_transfer,
+        transaction: transaction,
+        token_contract_address: token_contract_address,
+        token: token
+      )
+
+      conn =
+        get(
+          conn,
+          token_inventory_path(conn, :index, token_contract_address.hash)
+        )
+
+      assert html_response(conn, 200)
+    end
+
+    test "returns next page of results based on last seen token balance", %{conn: conn} do
+      token = insert(:token, type: "ERC-721")
+
+      transaction =
+        :transaction
+        |> insert()
+        |> with_block()
+
+      second_page_token_balances =
+        Enum.map(
+          1..50,
+          &insert(
+            :token_transfer,
+            transaction: transaction,
+            token_contract_address: token.contract_address,
+            token: token,
+            token_id: &1 + 1000
+          )
+        )
+
+      conn =
+        get(conn, token_inventory_path(conn, :index, token.contract_address_hash), %{
+          "token_id" => "999"
+        })
+
+      assert Enum.map(conn.assigns.unique_tokens, & &1.token_id) == Enum.map(second_page_token_balances, & &1.token_id)
+    end
+
+    test "next_page_params exists if not on last page", %{conn: conn} do
+      token = insert(:token, type: "ERC-721")
+
+      transaction =
+        :transaction
+        |> insert()
+        |> with_block()
+
+      Enum.each(
+        1..51,
+        &insert(
+          :token_transfer,
+          transaction: transaction,
+          token_contract_address: token.contract_address,
+          token: token,
+          token_id: &1 + 1000
+        )
+      )
+
+      expected_next_page_params = %{
+        "token_id" => to_string(token.contract_address_hash),
+        "unique_token" => 1050
+      }
+
+      conn = get(conn, token_inventory_path(conn, :index, token.contract_address_hash))
+
+      assert conn.assigns.next_page_params == expected_next_page_params
+    end
+
+    test "next_page_params are empty if on last page", %{conn: conn} do
+      token = insert(:token, type: "ERC-721")
+
+      transaction =
+        :transaction
+        |> insert()
+        |> with_block()
+
+      insert(
+        :token_transfer,
+        transaction: transaction,
+        token_contract_address: token.contract_address,
+        token: token,
+        token_id: 1000
+      )
+
+      conn = get(conn, token_inventory_path(conn, :index, token.contract_address_hash))
+
+      refute conn.assigns.next_page_params
+    end
+  end
+end

apps/explorer/lib/explorer/chain/token_transfer.ex

@@ -135,6 +135,10 @@ defmodule Explorer.Chain.TokenTransfer do
 
   def page_token_transfer(query, %PagingOptions{key: nil}), do: query
 
+  def page_token_transfer(query, %PagingOptions{key: {token_id}}) do
+    where(query, [token_transfer], token_transfer.token_id > ^token_id)
+  end
+
   def page_token_transfer(query, %PagingOptions{key: {block_number, log_index}}) do
     where(
       query,

apps/explorer/test/explorer/chain_test.exs

@@ -3131,7 +3131,7 @@ defmodule Explorer.ChainTest do
           token_id: 29
         )
 
-      paging_options = %PagingOptions{key: {first_page.block_number, first_page.log_index}, page_size: 1}
+      paging_options = %PagingOptions{key: {first_page.token_id}, page_size: 1}
 
       unique_tokens_ids_paginated =
         token_contract_address.hash