Added firmware endpoint

Necessary to handle the request and response of the firmware API endpoint.

lib/trmnl/api/endpoints/firmware.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "pipeable"
+
+module TRMNL
+  module API
+    module Endpoints
+      # Handles API request/response.
+      class Firmware
+        include Dependencies[:client, contract: "contracts.firmware", model: "models.firmware"]
+        include Pipeable
+
+        def call
+          pipe client.get("firmware/latest"),
+               try(:parse, catch: JSON::ParserError),
+               validate(contract, as: :to_h),
+               to(model, :for)
+        end
+      end
+    end
+  end
+end

spec/lib/trmnl/api/endpoints/firmware_spec.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe TRMNL::API::Endpoints::Firmware do
+  subject(:endpoint) { described_class.new client: }
+
+  include_context "with application dependencies"
+
+  let(:client) { TRMNL::API::Client.new http: }
+
+  describe "#call" do
+    let :http do
+      HTTP::Fake::Client.new do
+        get "/api/firmware/latest" do
+          headers["Content-Type"] = "application/json"
+          status 200
+
+          <<~JSON
+            {
+              "url": "https://test.io/FW1.2.3.bin",
+              "version": "1.2.3"
+            }
+          JSON
+        end
+      end
+    end
+
+    it "answers success" do
+      result = endpoint.call
+
+      expect(result).to be_success(
+        TRMNL::API::Models::Firmware[
+          url: "https://test.io/FW1.2.3.bin",
+          version: "1.2.3"
+        ]
+      )
+    end
+
+    context "with failure" do
+      let :http do
+        HTTP::Fake::Client.new do
+          get "/api/firmware/latest" do
+            headers["Content-Type"] = "application/json"
+            status 404
+
+            <<~JSON
+              {"error": "Danger!"}
+            JSON
+          end
+        end
+      end
+
+      it "answers failure" do
+        result = described_class.new(client:).call
+        expect(result).to match(Failure(be_a(HTTP::Response)))
+      end
+    end
+  end
+end