Finish basic order book implementation

This commit is contained in:
Tim Kächele 2023-10-28 18:01:24 +02:00
parent c16e705a4c
commit 57436c9eb0
2 changed files with 142 additions and 12 deletions

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@ -3,29 +3,62 @@ require "rbtree"
module Rex
class OrderBook
def initialize
@sell_side = tree_with_limit_default
@buy_side = tree_with_limit_default
@sell_side = RBTree.new
@buy_side = RBTree.new
@order_ids = {} # order_id => order
end
def add_order(order)
side = if order.is_buy
@buy_side
else
@sell_side
end
side = side_for_order(order)
side[order.price] ||= Limit.new(order.price)
side[order.price].add_order(order)
order_ids[order.id] = order
end
def cancel_order(order_id)
def remove_order(order_id)
order = order_ids[order_id]
return nil if order.nil?
side = side_for_order(order)
limit = side[order.price]
limit.remove_order(order)
if limit.empty?
side.delete(limit.price)
end
order_ids.delete(order.id)
end
alias_method :cancel_order, :remove_order
def highest_buy_order
buy_side.last&.[](1)&.peek_first_order
end
def lowest_sell_order
sell_side.first&.[](1)&.peek_first_order
end
def best_buy_price
buy_side.last&.[](0)
end
def best_sell_price
sell_side.first&.[](0)
end
private
def tree_with_limit_default
tree = RBTree.new
tree.default_proc = ->(tree, key) { tree[key] = Limit.new(key) }
tree
attr_reader :order_ids, :buy_side, :sell_side
def side_for_order(order)
if order.is_buy
buy_side
else
sell_side
end
end
end
end

97
spec/order_book_spec.rb Normal file
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@ -0,0 +1,97 @@
# frozen_string_literal: true
RSpec.describe Rex::OrderBook do
let(:instance) { described_class.new }
describe "#add_order" do
let(:order_a) { build(:order, is_buy: true, price: 100) }
it "adds the order to the order book" do
instance.add_order(order_a)
expect(instance.best_buy_price).to eq(100)
end
context "with multiple orders at the same price" do
let(:order_b) { build(:order, is_buy: true, price: 100) }
it "regards the new order as the best buy price" do
instance.add_order(order_a)
instance.add_order(order_b)
expect(instance.best_buy_price).to eq(100)
expect(instance.highest_buy_order).to eq(order_a)
end
end
context "with multiple orders at the different price levels" do
let(:order_b) { build(:order, is_buy: true, price: 120) }
it "regards the new order as the best buy price" do
instance.add_order(order_b)
instance.add_order(order_a)
expect(instance.best_buy_price).to eq(120)
expect(instance.highest_buy_order).to eq(order_b)
end
end
context "with multiple orders on different sides" do
let(:order_b) { build(:order, is_buy: false, price: 120) }
it "returns the correct prices for both sides" do
instance.add_order(order_a)
instance.add_order(order_b)
expect(instance.best_buy_price).to eq(100)
expect(instance.best_sell_price).to eq(120)
end
end
end
describe "#highest_buy_order" do
context "when there is nothing in the book" do
it "returns nil " do
expect(instance.highest_buy_order).to eq(nil)
end
end
end
describe "#lowest_sell_Order" do
context "when there is nothing in the book" do
it "returns nil " do
expect(instance.highest_buy_order).to eq(nil)
end
end
end
describe "#cancel_order" do
let(:buy_order) { build(:order, is_buy: true, price: 100) }
let(:sell_order) { build(:order, is_buy: false, price: 121) }
before do
instance.add_order(buy_order)
end
context "when it is the last order for the given price" do
it "removes the order from the side" do
instance.cancel_order(buy_order.id)
expect(instance.best_buy_price).to eq(nil)
end
end
context "an order on the sell side is removed" do
before do
instance.add_order(buy_order)
instance.add_order(sell_order)
end
it "does not affect the buy side" do
instance.cancel_order(sell_order.id)
expect(instance.best_buy_price).to eq(100)
end
end
end
end