# This code is based on Thoughtbot's guide to migrating from Paperclip
# to Active Storage:
# https://github.com/thoughtbot/paperclip/blob/master/MIGRATING.md
namespace :active_storage do
  desc "Copy paperclip's attachment database columns to active storage"
  task migrate_from_paperclip: :environment do
    logger = ApplicationLogger.new
    connection = ActiveRecord::Base.connection.raw_connection
    statement_name = "active_storage_statement"

    unless connection.exec("SELECT COUNT(*) FROM pg_prepared_statements WHERE name='#{statement_name}'").each_row.to_a[0][0] > 0
      connection.prepare(statement_name, <<-SQL)
        with rows as(
          INSERT INTO active_storage_blobs (
            key, filename, content_type, metadata, byte_size, checksum, created_at
          ) VALUES ($1, $2, $3, '{}', $4, $5, $6) RETURNING id
        )
        INSERT INTO active_storage_attachments (
          name, record_type, record_id, blob_id, created_at
        ) VALUES ($7, $8, $9, (SELECT id FROM rows), $10)
      SQL
    end

    Rails.application.eager_load!
    models = ActiveRecord::Base.descendants.reject(&:abstract_class?)

    ActiveRecord::Base.transaction do
      models.each do |model|
        next if model.name == "OldPassword" && !model.table_exists?

        attachments = model.column_names.map do |c|
          if c =~ /(.+)_file_name$/
            $1
          end
        end.compact

        if attachments.blank?
          next
        end

        model.find_each.each do |instance|
          attachments.each do |attachment|
            next if instance.send(:"storage_#{attachment}").attached?

            source = instance.send(attachment).path

            next if source.blank?

            file = File.read(source) if File.exist?(source)

            connection.exec_prepared(
              statement_name, [
                SecureRandom.uuid, # Alternatively instance.send("#{attachment}_file_name"),
                instance.send("#{attachment}_file_name"),
                instance.send("#{attachment}_content_type"),
                instance.send("#{attachment}_file_size"),
                file && Digest::MD5.base64digest(file) || SecureRandom.hex(32),
                instance.updated_at.iso8601,
                "storage_#{attachment}",
                model.name,
                instance.id,
                instance.updated_at.iso8601
              ])
          end
        end
      end
    end

    ActiveStorage::Attachment.find_each do |attachment|
      dest = ActiveStorage::Blob.service.path_for(attachment.blob.key)

      next if File.exist?(dest)

      name = attachment.name.delete_prefix("storage_")
      source = attachment.record.send(name).path

      if source && File.exist?(source)
        FileUtils.mkdir_p(File.dirname(dest))
        logger.info "Copying #{source} to #{dest}"
        FileUtils.cp(source, dest)
      end
    end
  end
end