# Finds all column that reference a certain model name via a polymorphic association.
# This is helpful when renaming a table, because if you don't update the model names
# in these polymorphic belongs_to associations they will break.
class PolymorphicBelongsToFinder
  POLYMORPHIC_COLUMN_MATCH = /_type\Z/.freeze

  def initialize(old_model_name)
    @old_model_name = old_model_name
  end

  # Columns that reference the old model
  def problematic_columns
    problem_cols = []

    all_models.select do |model|
      polymorphic_columns_for(model).each do |col|
        if model.pluck(col).include?(old_model_name)
          problem_cols << model.column_for_attribute(col)
        end
      end
    end

    problem_cols
  end

  def print_report
    cols = problematic_columns

    if cols.any?
      puts "#{cols.count} polyorphic association(s) to #{old_model_name} were found"

      cols.each do |col|
        puts "#{col.table_name}.#{col.name} references #{old_model_name}"
      end
    else
      puts "No polyorphic associations to #{old_model_name} were found"
    end

    nil
  end

  private

  attr_reader :old_model_name

  def all_models
    (ApplicationRecord.subclasses | ActiveRecord::Base.subclasses).reject(&:abstract_class)
  end

  def polymorphic_columns_for(model)
    # Really just columns who's name matches polymorphic belongs_to naming
    # TODO: improve this to detect non-standard naming
    model.column_names.grep(POLYMORPHIC_COLUMN_MATCH)
  end
end

# Example:
# PolymorphicBelongsToFinder.new('OldModelName').print_report