class InfographicsController < ApplicationController
  # allows user to change their infographic title
  #
  # we need to authorize user: check if a user has permission to update
  # this infographic (check if a user owns it)
  # if we use gem 'cancancan', we can simply add
  #
  # load_and_authorize_resource
  #
  # to the top of our controller. It will use a before action to load
  # the resource into an instance variable and authorize it for every action.
  #
  def update
    # another option is to change this line
    @infographic = Infographic.find(params[:id])
    #
    # @infographic = Infographic.find_by!(id: 3, user: current_user)
    #
    # so we only use current_user variable (e.g. from gem 'devise')
    # or we can just add this line here (uses gem 'cancancan'):
    #
    # authorize! :update, @infographic
    #
    if @infographic.update_attributes(update_params)
      render json: @infographic
      # Codestyle concern: we have 'status: 422' two lines below
      # why there is no 'status: 200' here
      # and status: :ok is friendlier for human then status: 200
      #
      # We don't send location header (we need, since we updated object)
      #
      # We render all the object attributes (even if js-frontend/microservice/client
      # don't need all of them and shouldn't really know about existence of some of them)
      # because we skip the view layer
      # (some erb/jbuilder/rabl templates / ActiveModel::Serializer / fast_jsonapi)
      #
      # my variant:
      # render :show, status: :ok, location: @infographic
    else
      render json: { errors: @infographic.errors.full_messages }, status: 422
      # The main concern here is about error messages
      # right now it is useless for js-frontend/microservice/client since
      # js-frontend/microservice/client don't know what field the message is
      # related to:
      # {
      #   "errors": [
      #     "Title is too short (minimum is 5 characters)"
      #   ]
      # }
      # should be:
      # {
      #   "title": [
      #     "is too short (minimum is 5 characters)"
      #   ]
      # }
      #
      # codestyle concern: 'unprocessable_entity' is friendlier for human
      # then '422'
      #
      # my variant:
      # render json: { errors: @infographic.errors }, status: :unprocessable_entity
    end
  end

  private

  def update_params
    params.require(:infographic).permit(:title)
  end
end

# in general, this if-condition is useless here, since
# to get `status: 422` we need @infographic to be falsy and
# in a daily life it couldn't be falsy

# if `find` method couldn't find a record with id provided
# it raises `ActiveRecord::RecordNotFound` error

# but if we redefine `find` method like this (or any other way
# to return `nil` or `false`):

class Infographic < ApplicationRecord
  def self.find(id)
    Infographic.find_by(id: id)
  end
end

# it will return `nil` and thus we'll get `status: 422`

# frozen_string_literal: true

# you need to install Ruby Graph Library to use this solution
# `gem install rgl`
require 'rgl/adjacency'
require 'rgl/traversal'

POSSIBLE_TRIP = 'Trip is Possible'
IMPOSSIBLE_TRIP = 'Trip is impossible'

# @param start [String] start of the trip
# @param target [String] trip destination
# @param stations [Array<String>]
# @param station_links [Hash<String, Array<String>>]
# @return [String] if trip is possible
def check_trip(start, target, stations, station_links)
  graph = RGL::DirectedAdjacencyGraph.new

  stations.each { |station| graph.add_vertex(station) }
  station_links.each do |head, tails|
    tails.each { |tail| graph.add_edge head, tail }
  end
  graph.dfs_iterator(start).any?(target) ? POSSIBLE_TRIP : IMPOSSIBLE_TRIP
end

stations = %w[ADL BRI MEL SYD]
links = { 'ADL' => %w[MEL], 'MEL' => %w[ADL SYD], 'SYD' => %w[BRI] }
puts check_trip('ADL', 'BRI', stations, links) # => 'Trip is Possible'
puts check_trip('MEL', 'BRI', stations, links) # => 'Trip is Possible'
puts check_trip('SYD', 'ADL', stations, links) # => 'Trip is impossible'

# frozen_string_literal: true

POSSIBLE_TRIP = 'Trip is Possible'
IMPOSSIBLE_TRIP = 'Trip is impossible'

# @param start [String] start of the trip
# @param target [String] trip destination
# @param _stations [Array<String>]
# @param station_links [Hash<String, Array<String>>]
# @return [String] if trip is possible
def check_trip(start, target, _stations, station_links)
  visited = []
  queue = []
  queue.push(start)
  visited.push(start)
  while queue.any?
    node = queue.pop
    return POSSIBLE_TRIP if node == target

    station_links.fetch(node, []).each do |child|
      unless visited.include?(child)
        queue.push(child)
        visited.push(child)
      end
    end
  end
  IMPOSSIBLE_TRIP
end

stations = %w[ADL BRI MEL SYD]
links = { 'ADL' => %w[MEL], 'MEL' => %w[ADL SYD], 'SYD' => %w[BRI] }
puts check_trip('ADL', 'BRI', stations, links) # => 'Trip is Possible'
puts check_trip('ADL', 'BRI', stations, links) # => 'Trip is Possible'
puts check_trip('MEL', 'BRI', stations, links) # => 'Trip is Possible'
puts check_trip('SYD', 'ADL', stations, links) # => 'Trip is impossible'

# 1. Database indexes/indices
# 2. Eager loading associations
# 3. Conditional GETs (HTTP feature) caching
# 4. View Fragment Caching
# 5. !IMPORTANT: if nothing helps, just cache this stuff
#    using memcached/redis (Google: Rails Model Caching with Redis),
#    cache two queries: one for free user, one for paid user

# app/models/theme.rb
class Theme < ApplicationRecord
  has_one :snapshot

  scope :published, -> { where.not(published_at: nil) }
end

# app/models/snapshot.rb
class Snapshot < ApplicationRecord
  belongs_to :theme, touch: true # used to expire cache
  # ...
end

# app/controllers/themes_controller.rb
class ThemesController < ApplicationController
  def index
    # eager_loading snapshot association
    @themes =
      Theme
      .published
      .order(created_at: :desc)
      .eager_load(:snapshot)

    # using Conditional GETs (HTTP feature) caching
    return unless stale?([@themes, current_user])

    respond_to do |format|
      format.html
      format.json { render json: @themes }
    end
  end
end

# app/views/themes/index.html.erb
# using Fragment Caching
<% @themes.each do |theme| %>
  <li id="pikto-theme-item-<%= theme.id %>" class="theme-items">
    <div class="<%= 'protemplate' if theme.pro? && current_user.is_free? %>">
      <% cache theme do %>
        <% if theme.is_new? %>
          <i class="icon-tagnew"></i>
        <% end %>
        <% if theme.is_featured? %>
          <i class="icon-tagfeatured"></i>
        <% end %>
        <div class="the-infographic-img">
          <a href="#"><%= image_tag(theme.snapshot.url(:medium)) %></a>
        </div>
      <% end %>
    </div>
    <div class="infographic-details">
      <%= theme.title %>
    </div>
  </li>
<% end %>

# db/schema.rb
# using indexes/indices
create_table "snapshots", force: :cascade do |t|
  # ...
  t.integer "theme_id"
  t.index ["theme_id"], name: "index_snapshots_on_theme_id"
end

create_table "themes", force: :cascade do |t|
  # ...
  t.index ["published_at", "created_at"], name: "index_themes_on_published_at_and_created_at", order: { created_at: :desc }
end