require 'yaml'
require 'erb'
require 'imgur'

module Paperclip
  module Storage
    module Imgur

      # Specify credentials in a file, path, string or hash.
      # Required fields: client_id, client_secret, refresh_token
      def self.extended(base)
        base.instance_eval do
          imgur_credentials = parse_credentials(@options[:imgur_credentials])
          imgur_options = @options[:imgur_options] || {}
          environment = defined?(Rails) ? Rails.env : imgur_options[:environment].to_s

          # Use credentials for the current Rails environment, if any
          @imgur_credentials = (imgur_credentials[environment] || imgur_credentials).symbolize_keys
        end
      end

      # We have to trust that any Imgur hash stored into *_file_name represents an existing Imgur image.
      # This assumption let us avoid the latency of a network call.
      # If not, someone has touched where he shouldn't!
      def exists?(style_name = default_style)
        if original_filename
          true
        else
          false
        end
      end

      def flush_writes
        @queued_for_write.each do |style, file| #style is 'original' etc...

          begin
            image = imgur_session.image.image_upload(file)
            image_id = image.id
          rescue
            # Sometimes there are API or network errors.
            # In this cases, we don't store anything.
            image_id = nil
          end

          # We cannot use update_attribute because it internally calls save, and save calls
          # flush_writes again, and it will end up in a stack overflow due excessive recursion
          instance.update_column :"#{name}_#{:file_name}", image_id
        end
        after_flush_writes
        @queued_for_write = {}
      end

      def flush_deletes
        @queued_for_delete.each do |path|
          imgur_session.image.image_delete(path) # Doesn't matter if the image doesn't really exists
        end
        @queued_for_delete = []
      end

      # Returns the image's URL.
      # We don't use imgur_session.find to avoid the latency of a network call.
      def url(size = default_style)
        image_id = instance.send("#{name}_#{:file_name}")

        return @url_generator.for(size, {}) if image_id.nil? || image_id.empty? # Show Paperclip's default missing image path

        ::Imgur::Image.new(id: image_id).url(size)
      end

      # Returns the path of the attachment.
      # It's exactly the Imgur hash.
      def path(style_name = default_style)
        original_filename
      end

      def copy_to_local_file(style, destination_path)
        # TO BE DONE
        #local_file = File.open(destination_path, 'wb')
        #local_file.write(imgur_session.get_file(path(style)))
        #local_file.close
      end

      private

      def imgur_session
        @imgur_session ||= ::Imgur::Session.instance(@imgur_credentials)
      end

      def parse_credentials(credentials = nil)
        if credentials.nil? && defined?(Rails)
          credentials = "#{Rails.root}/config/imgur.yml"
        end

        credentials = case credentials
                      when File
                        YAML.load(ERB.new(File.read(credentials.path)).result)
                      when String, Pathname
                        YAML.load(ERB.new(File.read(credentials)).result)
                      end

        return credentials.stringify_keys if credentials.respond_to? :stringify_keys

        raise ArgumentError, 'Please specify Imgur credentials via a file, string or hash.'
      end
    end
  end
end