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 CryptoSellPrices
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 usd
21		EMPromise.all([cad, cad_to_usd]).then { |(a, b)| a * b }
22	end
23
24	def ticker_row_selector
25		raise NotImplementedError, "Subclass must implement"
26	end
27
28	def crypto_name
29		raise NotImplementedError, "Subclass must implement"
30	end
31
32	def cad
33		fetch_canadianbitcoins.then do |http|
34			cb = Nokogiri::HTML.parse(http.response)
35
36			row = cb.at(self.ticker_row_selector)
37			unless row.at("td").text == self.crypto_name
38				raise "#{crypto_name} row has moved"
39			end
40
41			BigDecimal(
42				row.at("td:nth-of-type(4)").text.match(/^\$(\d+\.\d+)/)[1]
43			)
44		end
45	end
46
47protected
48
49	def fetch_canadianbitcoins
50		EM::HttpRequest.new(
51			"https://www.canadianbitcoins.com",
52			tls: { verify_peer: true }
53		).aget
54	end
55
56	def cad_to_usd
57		@redis.get("cad_to_usd").then do |rate|
58			next rate.to_f if rate
59
60			EM.promise_defer {
61				# OXR gem is not async, so defer to threadpool
62				@oxr.update_rates
63				@oxr.get_rate("CAD", "USD")
64			}.then do |orate|
65				@redis.setex("cad_to_usd", 60 * 60, orate).then { orate }
66			end
67		end
68	end
69end
70
71class BCHSellPrices < CryptoSellPrices
72	def crypto_name
73		"Bitcoin Cash"
74	end
75
76	def ticker_row_selector
77		"#ticker > table > tbody > tr:nth-of-type(2)"
78	end
79end
80
81class BTCSellPrices < CryptoSellPrices
82	def crypto_name
83		"Bitcoin"
84	end
85
86	def ticker_row_selector
87		"#ticker > table > tbody > tr"
88	end
89end