Infinite scroll example

paginate.rb

# frozen_string_literal: true

class Paginate
  def call(
    scope,
    direction: 'asc',
    field: nil,
    last_id: nil,
    field_value: nil,
    limit: nil
  )
    scope = order_scope(scope, field, direction)

    scope = filter(scope, field, direction, field_value)  if field && field_value
    scope = filter(scope, 'id',   direction, last_id, '') if last_id
    scope = scope.limit(limit) if limit

    scope
  end


  private

  COMPARERS = { asc: '>', desc: '<' }.freeze

  def order_scope(scope, field, direction)
    order_clause = field ? { field => direction } : {}
    scope.order(order_clause.merge(id: direction))
  end

  def filter(scope, field, direction, field_value, eq = '=')
    comparer = COMPARERS[direction.to_sym] + eq
    field = field.include?('.') ? field : (scope.table_name + ".#{field}")
    scope.where("#{field} #{comparer} ?", field_value)
  end
end