DEV: add a remove_step method to Wizard (#24063)

Using Wizard.exclude_steps applies to all sites in a multisite cluster.
In order to exclude steps for individual sites at run-time, a new
instance method `remove_step` is being added.

lib/wizard.rb

@@ -54,6 +54,25 @@ class Wizard
     end
   end
 
+  def remove_step(step_id)
+    i = @steps.index { |step| step.id == step_id }
+    return if i.nil?
+
+    step = @steps.delete_at(i)
+
+    step.previous.next = step.next if step.previous
+
+    while step = step.next
+      step.index -= 1
+      if step.index == 0
+        step.previous = nil
+        @first_step = step
+      else
+        step.previous = @steps[step.index - 1]
+      end
+    end
+  end
+
   def self.exclude_step(step)
     @@excluded_steps << step
   end

spec/lib/wizard/wizard_spec.rb

@@ -56,6 +56,68 @@ RSpec.describe Wizard do
     end
   end
 
+  describe "remove_step" do
+    let(:user) { Fabricate.build(:moderator) }
+    let(:wizard) { Wizard.new(user) }
+    let(:step1) { wizard.create_step("first-step") }
+    let(:step2) { wizard.create_step("second-step") }
+    let(:step3) { wizard.create_step("third-step") }
+
+    before do
+      wizard.append_step(step1)
+      wizard.append_step(step2)
+      wizard.append_step(step3)
+    end
+
+    it "does nothing if step id doesn't match any steps" do
+      wizard.remove_step("nope")
+      expect(wizard.steps).to contain_exactly(step1, step2, step3)
+      expect(wizard.start).to eq(step1)
+    end
+
+    it "can remove the first step" do
+      wizard.remove_step(step1.id)
+      expect(wizard.steps).to contain_exactly(step2, step3)
+      expect(step2.index).to eq(0)
+      expect(step2.previous).to be_blank
+      expect(step2.next).to eq(step3)
+
+      expect(step3.index).to eq(1)
+      expect(step3.previous).to eq(step2)
+      expect(step3.next).to be_blank
+
+      expect(wizard.start).to eq(step2)
+    end
+
+    it "can remove a middle step" do
+      wizard.remove_step(step2.id)
+      expect(wizard.steps).to contain_exactly(step1, step3)
+      expect(step1.index).to eq(0)
+      expect(step1.previous).to be_blank
+      expect(step1.next).to eq(step3)
+
+      expect(step3.index).to eq(1)
+      expect(step3.previous).to eq(step1)
+      expect(step3.next).to be_blank
+
+      expect(wizard.start).to eq(step1)
+    end
+
+    it "can remove the last step" do
+      wizard.remove_step(step3.id)
+      expect(wizard.steps).to contain_exactly(step1, step2)
+      expect(step1.index).to eq(0)
+      expect(step1.previous).to be_blank
+      expect(step1.next).to eq(step2)
+
+      expect(step2.index).to eq(1)
+      expect(step2.previous).to eq(step1)
+      expect(step2.next).to be_blank
+
+      expect(wizard.start).to eq(step1)
+    end
+  end
+
   describe ".exclude_step" do
     let(:user) { Fabricate.build(:moderator) }
     let(:wizard) { Wizard.new(user) }