#
# Obtain energy prices from Entsoe (transparancy platform)
# See https://transparency.entsoe.eu/content/static_content/Static%20content/web%20api/Guide.html
#

require 'open-uri'
require 'nokogiri'

class Entsoe 

  URL = 'https://transparency.entsoe.eu'
  
  attr_reader :storage_cost

  def initialize(api_key = "c2287e07-0c26-4950-b430-22b7f75a8f2e")
    @api_key = api_key
    @kwh_prices = {}  
    @storage_cost = 0.05 # how much does it cost to store 1 kwh in battery
  end
  
  def price_at(formatted_hour)
    unless @kwh_prices.key?(formatted_hour)
      p "Fetching Entsoe tariffs for %s" % formatted_hour
      @kwh_prices.merge!(query_day_ahead_prices(Date.parse(formatted_hour)))
    end
    @kwh_prices[formatted_hour]
  end
  
  def prices_at(date)
    hour_start = date.beginning_of_day
    day_end = hour_start.advance(days: 1)
    result = {}
    while(hour_start < day_end) do
        formatted_hour = hour_start.strftime("%F-%H")
        result.merge!({ formatted_hour => price_at(formatted_hour)})
        hour_start = hour_start.advance(:hours => 1)
    end
    result    
  end
  
  def high_low_hours(date)
    sorted_prices = prices_at(date).to_a.sort_by(&:last) # sort according to price 
    highest_hour = sorted_prices.last[0] 
    
    # From Apr-Oct: do not charge; every hour that has cost > charge_rate is a high_hour
    if [4,5,6,7,8,9,10].include?(date.month)
      lowest_hour = "" # effectively no charging from grid
      high_hours = sorted_prices.select{|p| p[1] > storage_cost}
    else      
      lowest_hour = sorted_prices.first[0]
      
      # calculate hours where rate > charge_rate + storage_cost (typically 0.05)
      charge_rate = sorted_prices.first[1] # assume we charge at lowest hour
      high_hours = sorted_prices.select{|p| p[1] > charge_rate + storage_cost}.to_h.keys
      
      # reset lowest_hour (effectively not charging), when price difference smaller than storage_cost
      highest_price  = sorted_prices.last[1]
      lowest_hour = "" if (highest_price-charge_rate) < storage_cost
    end
    
    return lowest_hour,highest_hour,high_hours
  end
  
  def query_day_ahead_prices(date)
    start_date = date.beginning_of_day
    end_date = date.end_of_day
    
    # A44 - Document type => Price Document
    # NL =  '10YNL----------L'
    
    domain = '10YNL----------L'      
    url = URL + "/api?securityToken=%s&documentType=A44&in_Domain=%s&out_Domain=%s&periodStart=%s&periodEnd=%s" % [@api_key, domain, domain, start_date.strftime("%Y%m%d%H%M"), end_date.strftime("%Y%m%d%H00")]
    #p url
    
    base_request(date, url)
  end
  
  private
  
    # get position and amount from XML snippet
    # <Point>
    #  <position>1</position>
    #  <price.amount>196.23</price.amount>
    # </Point>
    #
    # convert price to EUR per kwh, including VAT (21%)
    #
    def parse_point(xml)
      return xml.children[1].text.to_i, ((xml.children[3].text.to_f/1000)*1.21).round(5)
    end
  
    def base_request(date, url)
      formatted_date = date.strftime("%F")
      
      doc = Nokogiri::XML(URI.open(url))
      prices = doc.xpath('.//xmlns:Point').map{|p| parse_point(p)}
      
      #returns a hash with keys formatted "yyyy-mm-dd-hr" and values price (per kwh)
      prices.map{|p| ["%s-%02d" % [formatted_date,(p[0]-1)], p[1]]}.to_h
    end
end