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			unless bitcoin_row.at("td").text == "Bitcoin"
26				raise "Bitcoin row has moved"
27			end
28
29			BigDecimal(
30				bitcoin_row.at("td:nth-of-type(4)").text.match(/^\$(\d+\.\d+)/)[1]
31			)
32		end
33	end
34
35	def usd
36		EMPromise.all([cad, cad_to_usd]).then { |(a, b)| a * b }
37	end
38
39protected
40
41	def fetch_canadianbitcoins
42		EM::HttpRequest.new(
43			"https://www.canadianbitcoins.com",
44			tls: { verify_peer: true }
45		).aget
46	end
47
48	def cad_to_usd
49		@redis.get("cad_to_usd").then do |rate|
50			next rate.to_f if rate
51
52			EM.promise_defer {
53				# OXR gem is not async, so defer to threadpool
54				@oxr.update_rates
55				@oxr.get_rate("CAD", "USD")
56			}.then do |orate|
57				@redis.setex("cad_to_usd", 60 * 60, orate).then { orate }
58			end
59		end
60	end
61end