def filter_tracks
  # Does this need to be so high when JavaScript limits display to 14?
  @limit ||= 50

  # The query methods are responsible for adding their own offsets to this
  # hash map; that way, changing or removing a query method doesn't affect any
  # other method
  # If you need persistence with your implementation of pagination,
  # make a session/cookie instead of an instance variable
  @tracks_offset ||= {}
  @tracks_offset[:default] ||= 0

  # If you need persistence with your implementation of pagination,
  # make a session/cookie instead of an instance variable
  @result_track_ids ||= []

  @order ||= params[:order] || 'heavy_rotation'

  tracks = Track.ready.with_artist
  tracks = parse_params(params[:q], tracks)
  @result_count = tracks.count

  # Where is this used? Should this be an instance variable?
  searched = params[:q] && params[:q][:search].present?

  # Checks for heavy_rotation filter flag
  if heavy_rotation? @order
    @tracks = heavy_rotation
  else
    @tracks = order_by_params
  end

  render partial: "shared/results"
end

def order_by_params
  offset = @tracks_offset[:default]
  order = "tracks.#{@order}"

  # Are these fall-through conditionals or are both meant to be applied?
  order.match(/artist.*/) { |m| @order = @order.sub /tracks\./, '' }
  order.match(/title.*/) { |m| @order = @order.sub /tracks.(title)(.*)/i, 'LOWER(\1)\2' }

  unfiltered_results = tracks.offset(offset).order(@order, 'tracks.updated_at DESC').limit(@limit)
  top_results = validate_and_return_top_results unfiltered_results, @limit
  @tracks_offset[:default] += top_tracks[:offset]

  @tracks = top_tracks[:top_results]
end

def heavy_rotation
  week_ago = Time.now - 7.days
  two_weeks_ago = Time.now - 14.days
  three_months_ago = Time.now - 3.months

  # This will prevent the method from throwing an error
  # if you don't pass an argument to the query methods
  # However, if you have strict criteria for the queries and WANT to throw
  # an error then set @default = {} (easiest) or delete references to @default in
  # all the query methods
  @default = {
    date_range: two_weeks_ago,
    max_results: 5 }

  tracks_top_licensed(date_range: three_months_ago, max_results: 5) +
  tracks_top_listens(date_range: two_weeks_ago, max_results: 3) +
  tracks_top_downloaded(date_range: two_weeks_ago, max_results: 2) +
  tracks_staff_picks(date_range: three_months_ago, max_results: 4)

end

# check for heavy rotation filter flag
def heavy_rotation?(order_type)
  order_type == "heavy_rotation"
end

def validate_and_return_top_results(collection, max = 1)
  top_results = []
  i = 0 # offset incrementer

  until top_results.count >= max do
    # Checks if track has already appeared in the results
    unless @result_track_ids.include? collection[i].id

      # this will be returned in the method caller
      top_results << collection[i]

      # this is the point of reference to validate all your query method results
      @result_track_ids << collection[i].id
    end
    i += 1
  end

  { top_results: top_results, offset: i }
end

# mix in top licensed tracks within last 3 months
def tracks_top_licensed(args = {})
  args = @default.merge args
  max = args[:max_results]
  date_range = args[:date_range]

  # Adds own offset to #filter_tracks hash map => @tracks_offset
  @tracks_offset[:top_licensed] ||= 0

  unfiltered_results = Track.top_licensed
    .where("tracks.updated_at >= :date_range", date_range: date_range)
    .limit(@limit)
    .offset(@tracks_offset[:top_licensed])

  top_tracks = validate_and_return_top_results(unfiltered_results, max)

  # Add offset of your most recent query to the cumulative offset
  # so triggering 'view more'/pagination returns contiguous results
  @tracks_offset[:top_licensed] += top_tracks[:offset]

  top_tracks[:top_results]
end

# mix top listened to tracks within last two weeks
def tracks_top_listens(args = {})
  args = @default.merge args
  max = args[:max_results]
  date_range = args[:date_range]

  # Adds own offset to #filter_tracks hash map => @tracks_offset
  @tracks_offset[:top_listens] ||= 0

  unfiltered_results = Track.order('tracks.listens_count DESC')
    .where("tracks.updated_at >= :date_range", date_range: date_range)
    .limit(@limit)
    .offset(@tracks_offset[:top_listens])

  top_tracks = validate_and_return_top_results(unfiltered_results, max)
  @tracks_offset[:top_listens] += top_tracks[:offset]

  top_tracks[:top_results]
end

# mix top downloaded tracks within last two weeks
def tracks_top_downloaded(args = {})
  args = @default.merge args
  max = args[:max_results]
  date_range = args[:date_range]

  # Adds own offset to #filter_tracks hash map => @tracks_offset
  @tracks_offset[:top_downloaded] ||= 0

  unfiltered_results = Track.order('tracks.listens_count DESC')
    .where("tracks.updated_at >= :date_range", date_range: date_range)
    .limit(@limit)
    .offset(@tracks_offset[:top_downloaded])

  top_tracks = validate_and_return_top_results(unfiltered_results, max)
  @tracks_offset[:top_downloaded] += top_tracks[:offset]

  top_tracks[:top_results]
end

# mix in 25% of staff picks added within 3 months
def tracks_staff_picks(args = {})
  args = @default.merge args
  max = args[:max_results]
  date_range = args[:date_range]

  # Adds own offset to #filter_tracks hash map => @tracks_offset
  @tracks_offset[:staff_picks] ||= 0

  unfiltered_results = Track.ready
    .staff_picks
    .includes(:artist)
    .order("tracks.created_at DESC")
    .where("tracks.updated_at >= :date_range", date_range: date_range)

  top_tracks = validate_and_return_top_results(unfiltered_results, max)
  @tracks_offset[:staff_picks] += top_tracks[:offset]

  top_tracks[:top_results]
end