market.rb

# Uses Steam Market backend URL to list cheapest knife available for CS:GO
# Checks if price is under the threshold and if so alert us

require 'httparty'
require 'nokogiri'

class Market
  def initialize
    # {"success":true,"start":0,"pagesize":100,"total_count":362,"results_html": ...}
    @url = "http://steamcommunity.com/market/search/render/?query=appid%3A730%20Covert%20Knife&start=0&count=1&sort_dir=asc&sort_column=price"
    @price_threshold = 10.00
  end

  def find_knife
    req = HTTParty.get(@url)
    html = req["results_html"]
    puts "Error: Unknown Response" unless html

    doc = Nokogiri::HTML(html)
    link = doc.css('a.market_listing_row_link')[0].attributes['href'].value
    price = doc.css('span[style="color:white"]')[0].content
    price = /(\d+.?\d+)/.match(price)
    return if price[0].to_i > @price_threshold
    puts "Knife Found! #{price} --- #{link}"
    # Knife Found! 63.17 --- http://steamcommunity.com/market/listings/730/%E2%98%85%20Gut%20Knife%20%7C%20Safari%20Mesh%20%28Field-Tested%29?filter=Covert
  end
end

# get them knives
market = Market.new
while true do
  market.find_knife
  sleep 60
end