Allow overrides for default task values via URL parameters

app/controllers/shipit/tasks_controller.rb

@@ -16,6 +16,7 @@ def index
     def new
       @definition = stack.find_task_definition(params[:definition_id])
       @task = stack.tasks.build(definition: @definition)
+      @task.definition.override_variables(params)
     end
 
     def show

app/models/shipit/task_definition.rb

@@ -40,6 +40,14 @@ def render_title(env)
       "This task (title: #{@title}) cannot be shown due to an incorrect variable name. Check your shipit.yml file"
     end
 
+    def override_variables(params)
+      variables.each do |var|
+        if params.key?(var.name)
+          var.override_value(params[var.name])
+        end
+      end
+    end
+
     def allow_concurrency?
       @allow_concurrency
     end

app/models/shipit/variable_definition.rb

@@ -15,6 +15,14 @@ def default_provided?
       @default_provided
     end
 
+    def override_value(value)
+      @override = value.to_s
+    end
+
+    def value
+      @override.presence || default
+    end
+
     def to_h
       {
         'name' => @name,

app/views/shipit/_variables.html.erb

@@ -9,7 +9,7 @@
           <% if variable.select %>
             <%= field.select variable.name, options_for_select([["Please select...", { disabled: "disabled" }]] + variable.select, variable.default || "Please select...") %>
           <% else %>
-            <%= field.text_field variable.name, value: variable.default %>
+            <%= field.text_field variable.name, value: variable.value %>
           <% end %>
           <%= field.label variable.name, variable.title || variable.name %>
         </p>

test/controllers/tasks_controller_test.rb

@@ -11,9 +11,16 @@ class TasksControllerTest < ActionController::TestCase
       session[:user_id] = shipit_users(:walrus).id
     end
 
-    test "tasks defined in the shipit.yml can be displayed" do
+    test "tasks defined in the shipit.yml can be displayed with default variable values" do
       get :new, params: { stack_id: @stack, definition_id: @definition.id }
       assert_response :ok
+      assert_select 'input[name="task[env][FOO]"][value="1"]'
+    end
+
+    test "it is possible to provide a default value override for a task" do
+      get :new, params: { stack_id: @stack, definition_id: @definition.id, FOO: '42' }
+      assert_response :ok
+      assert_select 'input[name="task[env][FOO]"][value="42"]'
     end
 
     test "tasks defined in the shipit.yml can't be triggered if the stack is being deployed" do