namespace :milestones do

  def generate_table_migration_sql(new_table:, old_table:, columns:)
    from_cols = ["id", *columns.keys]
    to_cols   = ["id", *columns.values]
    <<~SQL
      INSERT INTO #{new_table} (#{to_cols.join(", ")})
      SELECT #{from_cols.join(", ")} FROM #{old_table};
    SQL
  end

  def migrate_table!(new_table:, old_table:, columns:)
    puts "Migrating data from '#{old_table}' to '#{new_table}'..."
    result = ActiveRecord::Base.connection.execute(
      generate_table_migration_sql(old_table: old_table,
                                   new_table: new_table,
                                   columns:   columns)

    )
    puts "#{result.cmd_tuples} rows affected"
  end

  def populate_column!(table:, column:, value:)
    puts "Populating column '#{column}' from table '#{table}' with '#{value}'..."
    result = ActiveRecord::Base.connection.execute(
      "UPDATE #{table} SET #{column} = '#{value}';"
    )
    puts "#{result.cmd_tuples} rows affected"
  end

  def count_rows(table)
    ActiveRecord::Base.connection.query("SELECT COUNT(*) FROM #{table};")[0][0].to_i
  end

  desc "Migrate milestones and milestone status data after making the model polymorphic"
  task migrate: :environment do
    # This script copies all milestone-related data from the old tables to
    # the new ones (preserving all primary keys). All 3 of the new tables
    # must be empty.
    #
    # To clear the new tables to test this script:
    #
    #   DELETE FROM milestone_statuses;
    #   DELETE FROM milestones;
    #   DELETE FROM milestone_translations;
    #

    start = Time.now

    ActiveRecord::Base.transaction do
      migrate_table! old_table: "budget_investment_statuses",
                     new_table: "milestone_statuses",
                     columns: {"name"        => "name",
                               "description" => "description",
                               "hidden_at"   => "hidden_at",
                               "created_at"  => "created_at",
                               "updated_at"  => "updated_at"}

      migrate_table! old_table: "budget_investment_milestones",
                     new_table: "milestones",
                     columns: {"investment_id" => "milestoneable_id",
                               "title"         => "title",
                               "description"   => "description",
                               "created_at"    => "created_at",
                               "updated_at"    => "updated_at",
                               "publication_date" => "publication_date",
                               "status_id"     => "status_id"}

      populate_column! table:  "milestones",
                       column: "milestoneable_type",
                       value:  "Budget::Investment"

      migrate_table! old_table: "budget_investment_milestone_translations",
                     new_table: "milestone_translations",
                     columns: {"budget_investment_milestone_id" => "milestone_id",
                               "locale"      => "locale",
                               "created_at"  => "created_at",
                               "updated_at"  => "updated_at",
                               "title"       => "title",
                               "description" => "description"}

      Image.where(imageable_type: "Budget::Investment::Milestone").
            update_all(imageable_type: "Milestone")
      Document.where(documentable_type: "Budget::Investment::Milestone").
            update_all(documentable_type: "Milestone")

      puts "Verifying that all rows were copied..."

      {
        "budget_investment_milestones"             => "milestones",
        "budget_investment_statuses"               => "milestone_statuses",
        "budget_investment_milestone_translations" => "milestone_translations"
      }.each do |original_table, migrated_table|
        ActiveRecord::Base.connection.execute(
          "select setval('#{migrated_table}_id_seq', (select max(id) from #{migrated_table}));"
        )

        unless count_rows(original_table) == count_rows(migrated_table)
          raise "Number of rows of old and new tables do not match! Rolling back transaction..."
        end
      end
    end

    puts "Finished in %.3f seconds" % (Time.now - start)
  end
end