require File.join(File.dirname(__FILE__), "service")
require 'securerandom'

module Charrington
  class TransformRedshift
    include Service
    attr_accessor :event
    attr_reader :top_level_keys

    Error = Class.new(StandardError)
    EventNil = Class.new(Error)
    TableNameNil = Class.new(Error)
    ColumnBlacklist = Class.new(Error)

    KEY_FILTER_BLACKLIST = ['host','path','jwt','sequence']
    KEY_RAISE_BLACKLIST = ['inserted_at']

    def initialize(event)
      raise EventNil, "Event is nil" if event.nil?
      event = event.to_hash
      @event = drop_keys(event)
      @top_level_keys = @event.keys
      check_blacklist
    end

    def call
      handle_event_key(event)
      add_id_to_event(event)

      handle_key_transform(event, "anonymous_id", "anonymous_user")
      handle_key_transform(event, "sent_at", "published_at")
      handle_key_transform(event, "original_timestamp", "sent_at")
      handle_key_transform(event, "received_at", "sent_at")
      handle_key_transform(event, "timestamp", "sent_at")

      handle_meta_section(event)

      transform_session_stuff(event)

      event.delete_if {|k, _v| ['session', 'meta', 'published_at', 'anonymous_user'].include?(k) }

      event
    end

    private

    def handle_key_transform(hash, key_that_should_be_there, key_to_take_value_from)
      unless hash.has_key?(key_that_should_be_there)
        hash[key_that_should_be_there] = hash[key_to_take_value_from] || ""
      else
        hash
      end
    end

    def add_id_to_event(hash)
      hash["id"] = SecureRandom.hex(10)
    end

    def handle_event_key(hash)
      event_name = hash["event"] || ""

      hash["event_text"] = event_name

      hash["event"] = underscore_event_name(event_name)
    end

    def underscore_event_name(event_name)
      event_name.
      gsub(/::/, '/').
      gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
      gsub(/([a-z\d])([A-Z])/,'\1_\2').
      downcase.
      gsub(/[^a-z0-9]+/, "_").
      gsub(/\A_+/, "").
      gsub(/_+\z/, "")
    end

    def transform_session_stuff(hash)
      session_stuff = hash["session"] || {}

      session_stuff.each {|k, v| hash["context_#{k}"] = v }
    end

    def handle_meta_section(hash)
      meta_section = hash["meta"] || {}

      meta_section.each {|k, v| hash[k] = v }
    end

    def check_blacklist
      arr = []
      KEY_RAISE_BLACKLIST.each { |k| arr << k if event.keys.include?(k) }
      raise ColumnBlacklist, "Event contains these blacklisted keys: #{arr.join(",")}" unless arr.empty?
    end

    def drop_keys(event)
      event.delete_if {|k, _v| k.start_with?("@") || KEY_FILTER_BLACKLIST.include?(k) }
    end

    def flatten_hash(hash)
      hash.each_with_object({}) do |(k, v), acc|
        if v.is_a? Hash
          flatten_hash(v).map do |h_k, h_v|
            acc["#{k}_#{h_k}"] = h_v
          end
        else
          acc[k] = v
        end
      end
    end
  end
end