feat: cache HN calls

Use Cachex to cache results from HN calls. This should theoretically reduce the
amount of calls this bot makes to the HN API.

Once again, this task is a purely academic pursuit.

lib/hn/client.ex

@@ -4,11 +4,12 @@ defmodule Hn.Client do
   """
   @link_regex ~r{^https://news.ycombinator.com/item\?id=(?<id>\d+)$}
   @escape_regex ~r/([_\[\]()~`>#+=|{}\.!-])/
+  @cache_ttl_sec 3_600
 
   @spec process_link(String.t()) :: {:ok, String.t()} | {:error, String.t()}
   def process_link(link) do
     with {:ok, id} <- get_id_from_link(link),
-         {:ok, hn_resp} <- Hn.API.fetch_item(id),
+         {:ok, hn_resp} <- fetch_item(id),
          {:ok, reply} <- parse_item(hn_resp, link) do
       {:ok, reply |> String.trim_trailing() |> escape_tg_reserved_chars()}
     else
@@ -18,6 +19,17 @@ defmodule Hn.Client do
     end
   end
 
+  defp fetch_item(id) do
+    Cachex.fetch(:hn_cache, id, fn id ->
+      {:commit, Hn.API.fetch_item(id), ttl: :timer.seconds(@cache_ttl_sec)}
+    end)
+    |> case do
+      {:ok, {:ok, hn_resp}} -> {:ok, hn_resp}
+      {:commit, {:ok, hn_resp}, _} -> {:ok, hn_resp}
+      _ -> :api_error
+    end
+  end
+
   defp get_id_from_link(link) do
     case Regex.named_captures(@link_regex, link) do
       %{"id" => id} -> {:ok, id}

lib/hntg/application.ex

@@ -12,7 +12,8 @@ defmodule Hntg.Application do
       # {Hntg.Worker, arg}
       {DNSCluster, query: Application.get_env(:hntg, :dns_cluster_query) || :ignore},
       Hntg.Server,
-      {Task.Supervisor, name: Hntg.TaskSupervisor}
+      {Task.Supervisor, name: Hntg.TaskSupervisor},
+      {Cachex, name: :hn_cache}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

mix.exs

@@ -29,6 +29,7 @@ defmodule Hntg.MixProject do
     [
       {:req, "~> 0.5.0"},
       {:dns_cluster, "~> 0.1.3"},
+      {:cachex, "~> 3.6"},
       {:mox, "~> 1.1", only: :test}
       # {:dep_from_hexpm, "~> 0.3.0"},
       # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}

mix.lock

@@ -1,15 +1,20 @@
 %{
+  "cachex": {:hex, :cachex, "3.6.0", "14a1bfbeee060dd9bec25a5b6f4e4691e3670ebda28c8ba2884b12fe30b36bf8", [:mix], [{:eternal, "~> 1.2", [hex: :eternal, repo: "hexpm", optional: false]}, {:jumper, "~> 1.0", [hex: :jumper, repo: "hexpm", optional: false]}, {:sleeplocks, "~> 1.1", [hex: :sleeplocks, repo: "hexpm", optional: false]}, {:unsafe, "~> 1.0", [hex: :unsafe, repo: "hexpm", optional: false]}], "hexpm", "ebf24e373883bc8e0c8d894a63bbe102ae13d918f790121f5cfe6e485cc8e2e2"},
   "castore": {:hex, :castore, "1.0.8", "dedcf20ea746694647f883590b82d9e96014057aff1d44d03ec90f36a5c0dc6e", [:mix], [], "hexpm", "0b2b66d2ee742cb1d9cb8c8be3b43c3a70ee8651f37b75a8b982e036752983f1"},
   "dns_cluster": {:hex, :dns_cluster, "0.1.3", "0bc20a2c88ed6cc494f2964075c359f8c2d00e1bf25518a6a6c7fd277c9b0c66", [:mix], [], "hexpm", "46cb7c4a1b3e52c7ad4cbe33ca5079fbde4840dedeafca2baf77996c2da1bc33"},
+  "eternal": {:hex, :eternal, "1.2.2", "d1641c86368de99375b98d183042dd6c2b234262b8d08dfd72b9eeaafc2a1abd", [:mix], [], "hexpm", "2c9fe32b9c3726703ba5e1d43a1d255a4f3f2d8f8f9bc19f094c7cb1a7a9e782"},
   "finch": {:hex, :finch, "0.18.0", "944ac7d34d0bd2ac8998f79f7a811b21d87d911e77a786bc5810adb75632ada4", [:mix], [{:castore, "~> 0.1 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: false]}, {:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mint, "~> 1.3", [hex: :mint, repo: "hexpm", optional: false]}, {:nimble_options, "~> 0.4 or ~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_pool, "~> 0.2.6 or ~> 1.0", [hex: :nimble_pool, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "69f5045b042e531e53edc2574f15e25e735b522c37e2ddb766e15b979e03aa65"},
   "hpax": {:hex, :hpax, "1.0.0", "28dcf54509fe2152a3d040e4e3df5b265dcb6cb532029ecbacf4ce52caea3fd2", [:mix], [], "hexpm", "7f1314731d711e2ca5fdc7fd361296593fc2542570b3105595bb0bc6d0fad601"},
   "jason": {:hex, :jason, "1.4.4", "b9226785a9aa77b6857ca22832cffa5d5011a667207eb2a0ad56adb5db443b8a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "c5eb0cab91f094599f94d55bc63409236a8ec69a21a67814529e8d5f6cc90b3b"},
+  "jumper": {:hex, :jumper, "1.0.2", "68cdcd84472a00ac596b4e6459a41b3062d4427cbd4f1e8c8793c5b54f1406a7", [:mix], [], "hexpm", "9b7782409021e01ab3c08270e26f36eb62976a38c1aa64b2eaf6348422f165e1"},
   "mime": {:hex, :mime, "2.0.6", "8f18486773d9b15f95f4f4f1e39b710045fa1de891fada4516559967276e4dc2", [:mix], [], "hexpm", "c9945363a6b26d747389aac3643f8e0e09d30499a138ad64fe8fd1d13d9b153e"},
   "mint": {:hex, :mint, "1.6.2", "af6d97a4051eee4f05b5500671d47c3a67dac7386045d87a904126fd4bbcea2e", [:mix], [{:castore, "~> 0.1.0 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:hpax, "~> 0.1.1 or ~> 0.2.0 or ~> 1.0", [hex: :hpax, repo: "hexpm", optional: false]}], "hexpm", "5ee441dffc1892f1ae59127f74afe8fd82fda6587794278d924e4d90ea3d63f9"},
   "mox": {:hex, :mox, "1.1.0", "0f5e399649ce9ab7602f72e718305c0f9cdc351190f72844599545e4996af73c", [:mix], [], "hexpm", "d44474c50be02d5b72131070281a5d3895c0e7a95c780e90bc0cfe712f633a13"},
   "nimble_options": {:hex, :nimble_options, "1.1.1", "e3a492d54d85fc3fd7c5baf411d9d2852922f66e69476317787a7b2bb000a61b", [:mix], [], "hexpm", "821b2470ca9442c4b6984882fe9bb0389371b8ddec4d45a9504f00a66f650b44"},
   "nimble_pool": {:hex, :nimble_pool, "1.1.0", "bf9c29fbdcba3564a8b800d1eeb5a3c58f36e1e11d7b7fb2e084a643f645f06b", [:mix], [], "hexpm", "af2e4e6b34197db81f7aad230c1118eac993acc0dae6bc83bac0126d4ae0813a"},
   "req": {:hex, :req, "0.5.6", "8fe1eead4a085510fe3d51ad854ca8f20a622aae46e97b302f499dfb84f726ac", [:mix], [{:brotli, "~> 0.3.1", [hex: :brotli, repo: "hexpm", optional: true]}, {:ezstd, "~> 1.0", [hex: :ezstd, repo: "hexpm", optional: true]}, {:finch, "~> 0.17", [hex: :finch, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:mime, "~> 2.0.6 or ~> 2.1", [hex: :mime, repo: "hexpm", optional: false]}, {:nimble_csv, "~> 1.0", [hex: :nimble_csv, repo: "hexpm", optional: true]}, {:plug, "~> 1.0", [hex: :plug, repo: "hexpm", optional: true]}], "hexpm", "cfaa8e720945d46654853de39d368f40362c2641c4b2153c886418914b372185"},
+  "sleeplocks": {:hex, :sleeplocks, "1.1.3", "96a86460cc33b435c7310dbd27ec82ca2c1f24ae38e34f8edde97f756503441a", [:rebar3], [], "hexpm", "d3b3958552e6eb16f463921e70ae7c767519ef8f5be46d7696cc1ed649421321"},
   "stream_data": {:hex, :stream_data, "1.1.1", "fd515ca95619cca83ba08b20f5e814aaf1e5ebff114659dc9731f966c9226246", [:mix], [], "hexpm", "45d0cd46bd06738463fd53f22b70042dbb58c384bb99ef4e7576e7bb7d3b8c8c"},
   "telemetry": {:hex, :telemetry, "1.2.1", "68fdfe8d8f05a8428483a97d7aab2f268aaff24b49e0f599faa091f1d4e7f61c", [:rebar3], [], "hexpm", "dad9ce9d8effc621708f99eac538ef1cbe05d6a874dd741de2e689c47feafed5"},
+  "unsafe": {:hex, :unsafe, "1.0.2", "23c6be12f6c1605364801f4b47007c0c159497d0446ad378b5cf05f1855c0581", [:mix], [], "hexpm", "b485231683c3ab01a9cd44cb4a79f152c6f3bb87358439c6f68791b85c2df675"},
 }

test/hn/client_test.exs

@@ -5,6 +5,7 @@ defmodule Hn.ClientTest do
   alias Hn.Client
   alias Hn.API.Fixtures
 
+  setup :set_mox_from_context
   setup :verify_on_exit!
 
   describe "process_link/1" do
@@ -27,11 +28,27 @@ defmodule Hn.ClientTest do
       |> expect(:fetch_item, fn _id -> Fixtures.sample_valid_text_response() end)
 
       # ACT
-      assert {:ok, reply} = Client.process_link("https://news.ycombinator.com/item?id=00000000")
+      assert {:ok, reply} = Client.process_link("https://news.ycombinator.com/item?id=00000001")
 
       # ASSERT
       assert reply =~ "Link"
       refute reply =~ "Comments"
     end
+
+    test "multiple process_link/1 calls with the same link only fetches once" do
+      # ARRANGE
+      Hn.MockAPI
+      |> expect(:fetch_item, 1, fn _id -> Fixtures.sample_valid_link_response() end)
+
+      # ACT
+      Client.process_link("https://news.ycombinator.com/item?id=00000002")
+
+      # ASSERT
+      Hn.MockAPI
+      |> expect(:fetch_item, 0, fn _id -> Fixtures.sample_valid_link_response() end)
+
+      Client.process_link("https://news.ycombinator.com/item?id=00000002")
+      Client.process_link("https://news.ycombinator.com/item?id=00000002")
+    end
   end
 end