fetch ERC721 token instance by token_id

apps/block_scout_web/lib/block_scout_web/controllers/tokens/instance_controller.ex

@@ -0,0 +1,16 @@
+defmodule BlockScoutWeb.Tokens.InstanceController do
+  use BlockScoutWeb, :controller
+
+  alias Explorer.Chain
+
+  def show(conn, %{"id" => token_id, "token_address_hash" => token_address_hash}) do
+    with {:ok, token_address} <- Chain.hash_to_address(token_address_hash, []),
+         {:ok, token_transfer} <-
+           Chain.erc721_token_instance_from_token_id_and_token_address(token_id, token_address.hash) do
+      json(conn, token_transfer)
+    else
+      _ ->
+        not_found(conn)
+    end
+  end
+end

apps/block_scout_web/lib/block_scout_web/web_router.ex

@@ -178,6 +178,13 @@ defmodule BlockScoutWeb.WebRouter do
         only: [:index],
         as: :inventory
       )
+
+      resources(
+        "/token_instance",
+        Tokens.InstanceController,
+        only: [:show],
+        as: :instance
+      )
     end
 
     resources(

apps/explorer/lib/explorer/chain.ex

@@ -2959,6 +2959,21 @@ defmodule Explorer.Chain do
     |> Repo.all()
   end
 
+  @spec erc721_token_instance_from_token_id_and_token_address(binary(), Hash.Address.t()) :: TokenTransfer.t() | nil
+  def erc721_token_instance_from_token_id_and_token_address(token_id, token_contract_address) do
+    query =
+      from(tt in TokenTransfer,
+        where: tt.token_contract_address_hash == ^token_contract_address and tt.token_id == ^token_id,
+        order_by: [desc: tt.block_number],
+        limit: 1
+      )
+
+    case Repo.one(query) do
+      nil -> {:error, :not_found}
+      token_instance -> {:ok, token_instance}
+    end
+  end
+
   @spec address_to_coin_balances(Hash.Address.t(), [paging_options]) :: []
   def address_to_coin_balances(address_hash, options) do
     paging_options = Keyword.get(options, :paging_options, @default_paging_options)

apps/explorer/test/explorer/chain_test.exs

@@ -82,6 +82,25 @@ defmodule Explorer.ChainTest do
     end
   end
 
+  describe "ERC721_token_instance_from_token_id_and_token_address/2" do
+    test "return ERC721 token instance" do
+      contract_address = insert(:address)
+
+      token_id = 10
+
+      insert(:token_transfer,
+        from_address: contract_address,
+        token_contract_address: contract_address,
+        token_id: token_id
+      )
+
+      assert {:ok, result} =
+               Chain.erc721_token_instance_from_token_id_and_token_address(token_id, contract_address.hash)
+
+      assert result.token_id == Decimal.new(token_id)
+    end
+  end
+
   describe "address_to_logs/2" do
     test "fetches logs" do
       %Address{hash: address_hash} = address = insert(:address)