add Task::Import and tests, so we can pull diagrams from the PRO server.

lib/trailblazer/workflow/task/import.rb

@@ -0,0 +1,40 @@
+require "trailblazer/pro"
+
+module Trailblazer
+  module Workflow
+    module Task
+      class Import < Trailblazer::Activity::Railway
+        step Subprocess(Pro::Client::Connect), id: :connect,
+          Output(:failure) => End(:failure)
+        step :retrieve_document
+        fail :error_for_retrieve
+        step :store_document
+
+        def retrieve_document(ctx, session:, diagram_slug:, **)
+          id_token = session.id_token
+
+          ctx[:response] = response = Faraday.get(
+            "#{session.trailblazer_pro_host}/api/v1/diagrams/#{diagram_slug}/export",
+            {},
+            {'Content-Type'=>'application/json', "Accept": "application/json",
+              "Authorization": "Bearer #{id_token}"
+            }
+          )
+
+          return false unless response.status == 200 # TODO: abstract this for other users, and use "endpoint" paths.
+
+          ctx[:pro_json_document] = ctx[:response].body
+        end
+
+        def store_document(ctx, pro_json_document:, target_filename:, **)
+          File.write(target_filename, pro_json_document) > 0
+        end
+
+        def error_for_retrieve(ctx, response:, diagram_slug:, **)
+          ctx[:error_message] = %(Diagram #{diagram_slug.inspect} couldn't be retrieved. HTTP status: #{response.status})
+        end
+      end
+
+    end # Task
+  end
+end

test/import_task_test.rb

@@ -0,0 +1,32 @@
+require "test_helper"
+require "trailblazer/workflow/task/import" # FIXME.
+
+class ImportTaskTest < Minitest::Spec
+  let(:api_key) { "tpka_909ae987_c834_43e4_9869_2eefd2aa9bcf" }
+  let(:trailblazer_pro_host) { "https://testbackend-pro.trb.to" } # NOTE: it's a bit clumsy to share PRO testing knowledge across several gems, but this code belongs here.
+
+  let(:session_static_options) do
+    {
+      api_key: api_key,
+      trailblazer_pro_host: trailblazer_pro_host,
+      firebase_refresh_url: "https://securetoken.googleapis.com/v1/token?key=AIzaSyDVZOdUrI6wOji774hGU0yY_cQw9OAVwzs",
+    }
+  end # FIXME: do we need this?
+
+
+  it "Import retrieves editor JSON file" do
+  #@ Uninitialized sigin
+    initial_session = Trailblazer::Pro::Session::Uninitialized.new(trailblazer_pro_host: trailblazer_pro_host, api_key: api_key)
+
+    # 79d163 /tmp/79d163.json
+    signal, (ctx, _) = Trailblazer::Developer.wtf?(Trailblazer::Workflow::Task::Import, [{
+      session: initial_session,
+      diagram_slug: "79d163",
+      target_filename: "/tmp/79d163.json",
+    }, {}])
+
+    assert_equal signal.to_h[:semantic], :success
+    assert_equal File.read("/tmp/79d163.json").size, 4635
+    # output, _ = capture_io do
+  end
+end