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