A monkey patch to switch the connection destination from pgbouncer to PostgreSQL only when `rake db:migrate`

db_migrate_monkey_patch.rake

# A monkey patch to switch the connection destination from pgbouncer to PostgreSQL only when `rake db:migrate`
#
# Usage: Put this file to `lib/tasks/db_migrate_monkey_patch.rake`
#
# https://gist.github.com/sue445/e82bbc8b626e4681f87182aa5981b68d

require "tmpdir"
require "fileutils"

module DbMigrateMonkeyPatch
  module InvokeWithChangeConnection
    def invoke(*args)
      Dir.mktmpdir("gitlab") do |dir|
        current_database_yml = "config/database.yml"
        backup_database_yml  = "#{dir}/database.yml"

        FileUtils.cp(current_database_yml, backup_database_yml)
        create_database_yml(current_database_yml)

        FileUtils.cp(current_database_yml, "config/database.yml.migrate")

        super
      ensure
        FileUtils.cp(backup_database_yml, current_database_yml)
      end
    end

    private

    def create_database_yml(path)
      db_config = {
        production: {
          adapter:  "postgresql",
          encoding: "unicode",
          database: ENV["DB_NAME"],
          host:     ENV["MASTER_DB_HOST"],
          port:     ENV["MASTER_DB_PORT"].to_i,
          username: ENV["MASTER_DB_USER"],
          password: ENV["MASTER_DB_PASS"],
          pool:     (ENV["DB_POOL"] || 10).to_i,
        }
      }

      File.open(path, "wb") do |f|
        f.write(db_config.deep_stringify_keys.to_yaml)
      end
    end
  end
end

Rake::Task["db:migrate"].singleton_class.prepend(DbMigrateMonkeyPatch::InvokeWithChangeConnection)