module LiquidInterpolatable
  extend ActiveSupport::Concern

  included do
    validate :validate_interpolation
  end

  def valid?(context = nil)
    super
  rescue Liquid::Error
    errors.empty?
  end

  def validate_interpolation
    interpolated
  rescue Liquid::Error => e
    errors.add(:options, "has an error with Liquid templating: #{e.message}")
    false
  end

  # Return the current interpolation context.  Use this in your Agent
  # class to manipulate interpolation context for user.
  #
  # For example, to provide local variables:
  #
  #     # Create a new scope to define variables in:
  #     interpolation_context.stack {
  #       interpolation_context['_something_'] = 42
  #       # And user can say "{{_something_}}" in their options.
  #       value = interpolated['some_key']
  #     }
  #
  def interpolation_context
    @interpolation_context ||= Context.new(self)
  end

  # Take the given object as "self" in the current interpolation
  # context while running a given block.
  #
  # The most typical use case for this is to evaluate options for each
  # received event like this:
  #
  #     def receive(incoming_events)
  #       incoming_events.each do |event|
  #         interpolate_with(event) do
  #           # Handle each event based on "interpolated" options.
  #         end
  #       end
  #     end
  def interpolate_with(self_object)
    case self_object
    when nil
      yield
    else
      context = interpolation_context
      begin
        context.environments.unshift(self_object.to_liquid)
        yield
      ensure
        context.environments.shift
      end
    end
  end

  def interpolate_options(options, self_object = nil)
    interpolate_with(self_object) do
      case options
      when String
        interpolate_string(options)
      when ActiveSupport::HashWithIndifferentAccess, Hash
        options.each_with_object(ActiveSupport::HashWithIndifferentAccess.new) { |(key, value), memo|
          memo[key] = interpolate_options(value)
        }
      when Array
        options.map { |value| interpolate_options(value) }
      else
        options
      end
    end
  end

  def interpolated(self_object = nil)
    interpolate_with(self_object) do
      (@interpolated_cache ||= {})[[options, interpolation_context]] ||=
        interpolate_options(options)
    end
  end

  def interpolate_string(string, self_object = nil)
    interpolate_with(self_object) do
      Liquid::Template.parse(string).render!(interpolation_context)
    end
  end

  class Context < Liquid::Context
    def initialize(agent)
      super({}, {}, { agent: agent }, true)
    end

    def hash
      [@environments, @scopes, @registers].hash
    end

    def eql?(other)
      other.environments == @environments &&
        other.scopes == @scopes &&
        other.registers == @registers
    end
  end

  require 'uri'
  module Filters
    # Percent encoding for URI conforming to RFC 3986.
    # Ref: http://tools.ietf.org/html/rfc3986#page-12
    def uri_escape(string)
      CGI.escape(string) rescue string
    end

    # Escape a string for use in XPath expression
    def to_xpath(string)
      subs = string.to_s.scan(/\G(?:\A\z|[^"]+|[^']+)/).map { |x|
        case x
        when /"/
          %Q{'#{x}'}
        else
          %Q{"#{x}"}
        end
      }
      if subs.size == 1
        subs.first
      else
        'concat(' << subs.join(', ') << ')'
      end
    end
  end
  Liquid::Template.register_filter(LiquidInterpolatable::Filters)

  module Tags
    class Credential < Liquid::Tag
      def initialize(tag_name, name, tokens)
        super
        @credential_name = name.strip
      end

      def render(context)
        credential = context.registers[:agent].credential(@credential_name)
        raise "No user credential named '#{@credential_name}' defined" if credential.nil?
        credential
      end
    end
  end
  Liquid::Template.register_tag('credential', LiquidInterpolatable::Tags::Credential)
end