From c16e705a4cabcd01731b77b38623491e16a618a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tim=20K=C3=A4chele?= <mail@timkaechele.me>
Date: Sat, 28 Oct 2023 14:06:21 +0200
Subject: [PATCH] Finish limit implementation

---
 lib/rex/limit.rb         |  40 ++++++
 spec/factories/limits.rb |   9 ++
 spec/limit_spec.rb       | 277 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 326 insertions(+)
 create mode 100644 spec/factories/limits.rb
 create mode 100644 spec/limit_spec.rb

diff --git a/lib/rex/limit.rb b/lib/rex/limit.rb
index 98007eb..e34bbd1 100644
--- a/lib/rex/limit.rb
+++ b/lib/rex/limit.rb
@@ -1,5 +1,10 @@
 module Rex
   class Limit
+    attr_reader(
+      :first_order,
+      :last_order,
+      :price
+    )
     def initialize(price)
       @price = price
       @first_order = nil
@@ -11,13 +16,24 @@ module Rex
       @first_order
     end
 
+    def count
+      @order_count
+    end
+
     def pop_first_order
+      return nil if empty?
+
       order = @first_order
       @first_order = @first_order.next_order
+      @first_order&.previous_order = nil
+
       if @first_order.nil?
         @last_order = nil
       end
 
+      order.next_order = nil
+      order.previous_order = nil
+
       @order_count -= 1
       order
     end
@@ -27,11 +43,35 @@ module Rex
         @first_order = order
       else
         @last_order.next_order = order
+        order.previous_order = @last_order
       end
       @last_order = order
       @order_count += 1
     end
 
+    # Assumption when calling: the order is part of the limit
+    def remove_order(order)
+      if @first_order == order
+        @first_order = order.next_order
+      end
+
+      if @last_order == order
+        @last_order = order.previous_order
+      end
+
+      previous_order = order.previous_order
+      next_order = order.next_order
+
+      previous_order&.next_order = next_order
+      next_order&.previous_order = previous_order
+
+      order.previous_order = nil
+      order.next_order = nil
+      @order_count -= 1
+
+      order
+    end
+
     def empty?
       @order_count == 0
     end
diff --git a/spec/factories/limits.rb b/spec/factories/limits.rb
new file mode 100644
index 0000000..75d8c73
--- /dev/null
+++ b/spec/factories/limits.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :limit, class: Rex::Limit do
+    transient do
+      price { 100 }
+    end
+  end
+end
diff --git a/spec/limit_spec.rb b/spec/limit_spec.rb
new file mode 100644
index 0000000..b96aadc
--- /dev/null
+++ b/spec/limit_spec.rb
@@ -0,0 +1,277 @@
+# frozen_string_literal: true
+
+RSpec.describe Rex::Limit do
+  let(:instance) { described_class.new(100) }
+  let(:order_a) { build(:order) }
+  let(:order_b) { build(:order) }
+  let(:order_c) { build(:order) }
+
+  describe "#add_order" do
+    context "when limit has no orders yet" do
+      it "increases the count by one" do
+        expect do
+          instance.add_order(order_a)
+        end.to change(instance, :count).by(1)
+      end
+
+      it "sets the first and last order correctly" do
+        instance.add_order(order_a)
+
+        expect(instance.first_order).to eq(order_a)
+        expect(instance.last_order).to eq(order_a)
+      end
+
+      it "does not change the previous/next order values" do
+        instance.add_order(order_a)
+
+        expect(order_a.previous_order).to eq(nil)
+        expect(order_a.next_order).to eq(nil)
+      end
+    end
+
+    context "when limit orders already in it" do
+      before do
+        instance.add_order(order_a)
+      end
+
+      it "increases the count by one" do
+        expect do
+          instance.add_order(order_b)
+        end.to change(instance, :count).by(1)
+      end
+
+      it "sets the first and last order correctly" do
+        instance.add_order(order_b)
+
+        expect(instance.first_order).to eq(order_a)
+        expect(instance.last_order).to eq(order_b)
+      end
+
+      it "does not change the previous/next order values" do
+        instance.add_order(order_b)
+
+        expect(order_a.previous_order).to eq(nil)
+        expect(order_a.next_order).to eq(order_b)
+
+        expect(order_b.previous_order).to eq(order_a)
+        expect(order_b.next_order).to eq(nil)
+      end
+    end
+  end
+
+  describe "#peek_first_order" do
+    subject { instance.peek_first_order }
+
+    context "when limit is empty" do
+      it { is_expected.to eq(nil) }
+    end
+
+    context "when limit has one item" do
+      before do
+        instance.add_order(order_a)
+      end
+
+      it "returns the first first order" do
+        expect(subject).to eq(order_a)
+      end
+    end
+
+    context "when limit has two items" do
+      before do
+        instance.add_order(order_a)
+        instance.add_order(order_b)
+      end
+
+      it "returns the first order" do
+        expect(subject).to eq(order_a)
+      end
+    end
+  end
+
+  describe "#pop_first_order" do
+    context "when limit is empty" do
+      it "returns nil" do
+        expect(instance.pop_first_order).to eq(nil)
+      end
+
+      it "does not change the count" do
+        expect { instance.pop_first_order }.not_to change(instance, :count)
+      end
+    end
+
+    context "when limit has two orders" do
+      before do
+        instance.add_order(order_a)
+        instance.add_order(order_b)
+      end
+
+      it "decrements the count by 1" do
+        expect { instance.pop_first_order }.to change(instance, :count).by(-1)
+      end
+
+      it "returns the first order" do
+        expect(instance.pop_first_order).to eq(order_a)
+      end
+
+      it "adjusts the first order" do
+        expect { instance.pop_first_order }.to change(instance, :first_order).from(order_a).to(order_b)
+      end
+
+      it "sets the previous/next order accordingly" do
+        popped_order = instance.pop_first_order
+
+        expect(popped_order.next_order).to eq(nil)
+        expect(popped_order.previous_order).to eq(nil)
+      end
+
+      it "updates the previous/next order links of the new first order" do
+        instance.pop_first_order
+        new_first_order = instance.peek_first_order
+
+        expect(new_first_order.previous_order).to eq(nil)
+        expect(new_first_order.next_order).to eq(nil)
+      end
+    end
+
+    context "when limit has only one order" do
+      before do
+        instance.add_order(order_a)
+      end
+
+      it "decrements the count by 1" do
+        expect { instance.pop_first_order }.to change(instance, :count).to(0)
+      end
+
+      it "returns the first order" do
+        expect(instance.pop_first_order).to eq(order_a)
+      end
+
+      it "adjusts the first order" do
+        expect { instance.pop_first_order }.to change(instance, :first_order).from(order_a).to(nil)
+      end
+
+      it "sets the previous/next of the returned order to nil" do
+        popped_order = instance.pop_first_order
+
+        expect(popped_order.next_order).to eq(nil)
+        expect(popped_order.previous_order).to eq(nil)
+      end
+
+      it "sets the first/last order correctly" do
+        instance.pop_first_order
+
+        expect(instance.first_order).to eq(nil)
+        expect(instance.last_order).to eq(nil)
+      end
+    end
+  end
+
+  describe "#remove_order" do
+    context "when the order is the first order" do
+      before do
+        instance.add_order(order_a)
+      end
+
+      it "decrements the count by 1" do
+        expect { instance.remove_order(order_a) }.to change(instance, :count).by(-1)
+      end
+
+      it "returns the removed order" do
+        expect(instance.remove_order(order_a)).to eq(order_a)
+      end
+
+      it "adjusts the previous/next order of the removed order" do
+        instance.remove_order(order_a)
+
+        expect(order_a.previous_order).to eq(nil)
+        expect(order_a.next_order).to eq(nil)
+      end
+
+      it "adjusts the first/last order in the limit" do
+        instance.remove_order(order_a)
+
+        expect(instance.first_order).to eq(nil)
+        expect(instance.last_order).to eq(nil)
+      end
+    end
+
+    context "when the order is the last order" do
+      before do
+        instance.add_order(order_a)
+        instance.add_order(order_b)
+      end
+
+      it "decrements the count by 1" do
+        expect { instance.remove_order(order_b) }.to change(instance, :count).by(-1)
+      end
+
+      it "returns the removed order" do
+        expect(instance.remove_order(order_b)).to eq(order_b)
+      end
+
+      it "adjusts the previous/next order of the removed order" do
+        instance.remove_order(order_b)
+
+        expect(order_b.previous_order).to eq(nil)
+        expect(order_b.next_order).to eq(nil)
+      end
+
+      it "adjusts the first/last order in the limit" do
+        instance.remove_order(order_b)
+
+        expect(instance.first_order).to eq(order_a)
+        expect(instance.last_order).to eq(order_a)
+      end
+    end
+
+    context "when the order is the in the middle of the queue" do
+      before do
+        instance.add_order(order_a)
+        instance.add_order(order_b)
+        instance.add_order(order_c)
+      end
+
+      it "decrements the count by 1" do
+        expect { instance.remove_order(order_b) }.to change(instance, :count).by(-1)
+      end
+
+      it "returns the removed order" do
+        expect(instance.remove_order(order_b)).to eq(order_b)
+      end
+
+      it "adjusts the previous/next order of the removed order" do
+        instance.remove_order(order_b)
+
+        expect(order_b.previous_order).to eq(nil)
+        expect(order_b.next_order).to eq(nil)
+      end
+
+      it "does not adjust the first/last order in the limit" do
+        instance.remove_order(order_b)
+
+        expect(instance.first_order).to eq(order_a)
+        expect(instance.last_order).to eq(order_c)
+      end
+
+      it "adjusts the previous/next order of the remaining orders" do
+        instance.remove_order(order_b)
+
+        expect(order_a.previous_order).to eq(nil)
+        expect(order_a.next_order).to eq(order_c)
+
+        expect(order_c.previous_order).to eq(order_a)
+        expect(order_c.next_order).to eq(nil)
+      end
+
+      it "ends up in a valid state after deleting all the orders" do
+        [order_a, order_b, order_c].shuffle.each do |order|
+          instance.remove_order(order)
+        end
+
+        expect(instance.first_order).to eq(nil)
+        expect(instance.last_order).to eq(nil)
+        expect(instance.count).to eq(0)
+      end
+    end
+  end
+end