1# frozen_string_literal: true
 2
 3require "em-http"
 4require "em_promise"
 5require "em-synchrony/em-http" # For aget vs get
 6require "money/bank/open_exchange_rates_bank"
 7require "nokogiri"
 8
 9require_relative "em"
10
11class BTCSellPrices
12	def initialize(redis, oxr_app_id)
13		@redis = redis
14		@oxr = Money::Bank::OpenExchangeRatesBank.new(
15			Money::RatesStore::Memory.new
16		)
17		@oxr.app_id = oxr_app_id
18	end
19
20	def cad
21		fetch_canadianbitcoins.then do |http|
22			canadianbitcoins = Nokogiri::HTML.parse(http.response)
23
24			bitcoin_row = canadianbitcoins.at("#ticker > table > tbody > tr")
25			raise "Bitcoin row has moved" unless bitcoin_row.at("td").text == "Bitcoin"
26
27			BigDecimal.new(
28				bitcoin_row.at("td:nth-of-type(3)").text.match(/^\$(\d+\.\d+)/)[1]
29			)
30		end
31	end
32
33	def usd
34		EMPromise.all([cad, cad_to_usd]).then { |(a, b)| a * b }
35	end
36
37protected
38
39	def fetch_canadianbitcoins
40		EM::HttpRequest.new(
41			"https://www.canadianbitcoins.com",
42			tls: { verify_peer: true }
43		).aget
44	end
45
46	def cad_to_usd
47		@redis.get("cad_to_usd").then do |rate|
48			next rate.to_f if rate
49
50			EM.promise_defer {
51				# OXR gem is not async, so defer to threadpool
52				oxr.update_rates
53				oxr.get_rate("CAD", "USD")
54			}.then do |orate|
55				@redis.set("cad_to_usd", orate, ex: 60 * 60).then { orate }
56			end
57		end
58	end
59end