working on data retrieval endpoint

app/controllers/db_elements_controller.rb

+# frozen_string_literal: true
 class DbElementsController < ApplicationController
   before_action :authenticate_user!
 
   def index
-    req_elements = DbElement.find(params[:elements])
-    #make sure the user is allowed to view these elements
-    req_elements.each do |elem|
+    @elements = DbElement.find(JSON.decode(params[:elements]))
+    # make sure the user is allowed to view these elements
+    @elements.each do |elem|
       unless current_user.views_nilm?(elem.db_stream.db.nilm)
         head :unauthorized
         return
       end
     end
-    #make sure the time range makes sense
-    @start_time = params[:start_time].to_i
-    @end_time = params[:end_time].to_i
-    unless @end_time>@start_time
-      head :unprocessable_entity
+  end
+
+  def data
+    req_elements = DbElement.find(JSON.parse(params[:elements]))
+    # make sure the user is allowed to view these elements
+    req_elements.each do |elem|
+      unless current_user.views_nilm?(elem.db_stream.db.nilm)
+        head :unauthorized
         return
       end
-    #retrieve the data for the requested elements
+    end
+    # make sure the time range makes sense
+    start_time = (params[:start_time].to_i unless params[:start_time].nil?)
+    end_time = (params[:end_time].to_i unless params[:end_time].nil?)
+
+    # retrieve the data for the requested elements
     @service = LoadElementData.new
-    @service.run(req_elements, @start_time, @end_time)
+    @service.run(req_elements, start_time, end_time)
+    @start_time = @service.start_time
+    @end_time = @service.end_time
     render status: @service.success? ? :ok : :unprocessable_entity
   end
-
 end

app/services/data/load_element_data.rb

@@ -3,14 +3,20 @@
 # Loads data for specified elements
 class LoadElementData
   include ServiceStatus
-  attr_reader :data
+  attr_reader :data, :start_time, :end_time
 
   def initialize()
     super()
     @data = []
+    @start_time = nil
+    @end_time = nil
   end
 
   # load data for the array of specified elements
+  # start_time and end_time are unix us
+  # if start_time is nil it is set to earliest timestamp
+  # if end_time is nil it is set to latest timestamp
+  #
   # sets data
   # data:
   #   [{id: element_id, values: [...]},
@@ -25,12 +31,30 @@ class LoadElementData
         req_streams << elem.db_stream
       end
     end
+    #2 compute start and end times if nil
+    streams_with_data = req_streams.select{|stream| stream.total_time > 0}
+    if (start_time == nil || end_time == nil) && streams_with_data.empty?
+      add_error("no time bounds for requested elements, refresh database?")
+      return
+    end
+    @start_time = start_time
+    @end_time = end_time
+    if start_time == nil
+      @start_time = streams_with_data
+        .sort{|a,b| a.start_time < b.start_time }
+        .first.start_time
+    end
+    if end_time == nil
+      @end_time = streams_with_data
+        .sort{|a,b| a.end_time > b.end_time }
+        .first.end_time
+    end
     #2 pull data from streams
     combined_data = []
     req_streams.each do |stream|
       adapter = DbAdapter.new(stream.db.url)
       data_service = LoadStreamData.new(adapter)
-      data_service.run(stream, start_time, end_time)
+      data_service.run(stream, @start_time, @end_time)
       if data_service.success?
         combined_data.concat(data_service.data)
       else

app/views/db_elements/data.json.jbuilder

+json.data do
+  json.array! @service.data.each do |element_data|
+    json.element_id element_data[:id]
+    json.data element_data[:values]
+    json.start_time @start_time
+    json.end_time @end_time
+  end
+end
+
+json.partial! "helpers/messages", service: @service

app/views/db_elements/index.json.jbuilder

-json.data do
-  json.array! @service.data.each do |element_data|
-    elem = DbElement.find(element_data[:id])
-    json.extract! elem, *DbElement.json_keys
-    json.path elem.name_path
-    json.data element_data[:values]
-    json.start_time @start_time
-    json.end_time @end_time
-  end
-end
 
-json.partial! "helpers/messages", service: @service
+  json.array! @elements do |element|
+    json.extract! element, *DbElement.json_keys
+    json.path element.name_path
+  end

config/routes.rb

@@ -8,7 +8,11 @@ Rails.application.routes.draw do
   resources :dbs, only: [:show, :update]
   resources :db_folders, only: [:show, :update]
   resources :db_streams, only: [:update]
-  resources :db_elements, only: [:index]
+  resources :db_elements, only: [:index] do
+    collection do
+      get 'data'
+    end
+  end
 
   mount_devise_token_auth_for 'User', at: 'auth'
   resources :users, only: [:index, :create, :destroy]