require 'rest_client'

module Scrivito

  class ContentServiceObjQueries
    def initialize(queries)
      @queries = queries
      @open_queries = queries.dup
      @results = {}
    end

    def open_queries
      @open_queries[0..99]
    end

    def handle_response(response)
      objs = {}
      response["objs"].each do |obj|
        objs[obj["_id"].first] = obj
      end

      queries_to_delete = []
      response["results"].each_with_index do |response, i|
        query = @open_queries[i]
        if response["continuation_handle"]
          query[:continuation_handle] = response["continuation_handle"]
        else
          queries_to_delete << i
        end
        result = (@results[query.__id__] ||= [])
        response["refs"].each do |obj_ref|
          id = obj_ref["id"]
          # TODO fetch missing ObjData from Service
          result << (objs[id] or raise "Data for Obj with id #{id} missing!")
        end
      end
      queries_to_delete.reverse_each {|i| @open_queries.delete_at(i) }
    end

    def results
      @queries.map {|query| @results[query.__id__] || [] }
    end

    def finished?
      open_queries.empty?
    end
  end

  class CmsBackend
    BLOB_DATA_CACHE_PREFIX = 'blob_data'.freeze
    VALID_INDEX_NAMES = %w[id path ppath permalink].freeze

    class << self
      def instance
        @instance ||= new
      end
    end

    def initialize
      @query_counter = 0
    end

    def begin_caching
      @caching = true
    end

    def end_caching
      CmsCacheStorage.cache.clear
      @caching = false
    end

    def caching?
      !!@caching
    end

    def query_counter
      @query_counter
    end

    def find_workspace_data_by_id(id)
      workspace_data_from_cache = WorkspaceDataFromService.find_from_cache(id)
      from_content_state_id = workspace_data_from_cache.try(:content_state_id)

      request_params = {:workspace_id => id}
      request_params[:content_state_id] = from_content_state_id if from_content_state_id

      raw_data = if id == 'published' && workspace_data_from_cache
        begin
          ContentService.query('workspaces/query', request_params, timeout: 1)
        rescue CommunicationError => e
          warn_backend_not_available(id, from_content_state_id, e.message)
          return workspace_data_from_cache
        end
      else
        ContentService.query('workspaces/query', request_params)
      end

      if raw_workspace_data = raw_data['workspace']
        workspace_data = WorkspaceDataFromService.new(raw_workspace_data)
        workspace_data.store_in_cache if from_content_state_id != workspace_data.content_state_id
        workspace_data
      end
    end

    def find_obj_data_by(revision, index, keys)
      find_obj_data_filtering_deleted_by(revision, index, keys, false)
    end

    def find_obj_data_including_deleted_by(revision, index, keys)
      find_obj_data_filtering_deleted_by(revision, index, keys, true)
    end

    def find_blob_data_by_id(id)
      cache_key = "#{BLOB_DATA_CACHE_PREFIX}/#{id}"
      if data_from_cache = CmsCacheStorage.cache.read(cache_key)
        data_from_cache
      else
        data_from_database = find_blob_data_from_database_by(id)
        if maxage = data_from_database['maxage']
          CmsCacheStorage.cache.write(cache_key, data_from_database, :expires_in => maxage)
        end
        data_from_database
      end
    end

    private

    def find_obj_data_filtering_deleted_by(revision, index, keys, include_deleted)
      index = index.to_s
      assert_valid_index_name(index)
      raw_data = find_raw_data_from_cache_or_database_by(revision, index, keys)

      raw_data.map do |raw_result|
        raw_result.each_with_object([]) do |raw_data, result|
          next if raw_data['_modification'] == ['deleted'] && !include_deleted
          result << ObjDataFromService.new(raw_data)
        end
      end
    end

    def find_raw_data_from_cache_or_database_by(revision, index, keys)
      keys_from_database = []
      # load results from cache
      results_from_cache = keys.map do |key|
        find_raw_data_from_cache_by(revision, index, key).tap do |objs|
          keys_from_database << key unless objs
        end
      end

      # load cache misses from database and store them in cache
      results_from_database =
          find_raw_data_from_database_by(revision, index, keys_from_database)
      keys_from_database.each_with_index do |key, key_number|
        store_raw_data_list_in_cache(revision, index, key, results_from_database[key_number])
      end

      # combine the results
      results_from_cache.map do |objs_from_cache|
        objs_from_cache || results_from_database.shift
      end
    end

    def find_raw_data_from_cache_by(revision, index, key)
      ContentStateCaching.find_obj_data(revision.content_state, index, key) if caching?
    end

    def find_raw_data_from_database_by(revision, index, keys)
      return [] if keys.blank?
      instrumenter = ActiveSupport::Notifications.instrumenter
      instrumenter.instrument(
        "cms_load.scrivito", :name => "Obj Load", :index => index, :keys => keys
      ) do
        @query_counter += 1
        queries = ContentServiceObjQueries.new(keys.map {|key| {:type => index, :param => key} })
        queries.handle_response(request_content_service(queries, revision)) until queries.finished?
        queries.results
      end
    end

    def request_content_service(queries, revision)
      ContentService.query('objs/query', content_service_request_params(queries, revision))
    end

    def content_service_request_params(queries, revision)
      params = {
        queries: queries.open_queries,
        revision_id: revision.id,
        include_deleted: true
      }

      # Not every revision has a workspace,
      # e.g. when requesting with the base revision of the current workspace.
      params[:workspace_id] = revision.workspace.id if revision.workspace

      params
    end

    UNIQUE_INDICES = [:id, :path, :permalink].freeze

    def store_raw_data_list_in_cache(revision, index, key, raw_data_list)
      raw_data_list.each do |values|
        UNIQUE_INDICES.each do |unique_index|
          unique_index_values = values["_#{unique_index}"]
          if unique_index_values.present?
            store_item_in_cache(revision, unique_index, unique_index_values.first, [values])
          end
        end
      end
      unless UNIQUE_INDICES.include?(index)
        store_item_in_cache(revision, index, key, raw_data_list)
      end
    end

    def store_item_in_cache(revision, index, key, item)
      ContentStateCaching.store_obj_data(revision.content_state, index, key, item)
    end

    def find_blob_data_from_database_by(id)
      @query_counter += 1
      ContentService.query('blobs/query', :blob_ids => [id])['blobs'][id]
    end

    def assert_valid_index_name(index)
      raise ArgumentError, "invalid index name '#{index}'" unless VALID_INDEX_NAMES.include?(index)
    end

    def warn_backend_not_available(workspace_id, content_state_id, error_message)
      message = <<-EOS
        Couldn't connect to content service for workspace with id=#{workspace_id} and content_state_id=#{content_state_id}.
        #{error_message}
        Serving from cache.
      EOS
      Rails.logger.warn(message)
    end

  end

end