module ActiveRecord
  # See ActiveRecord::Transactions::ClassMethods for documentation.
  module Transactions
    extend ActiveSupport::Concern
    ACTIONS = [:create, :destroy, :update]
    CALLBACK_WARN_MESSAGE = <<-EOF
Currently, Active Record will rescue any errors raised within
after_rollback/after_commit callbacks and print them to the logs. In the next
version, these errors will no longer be rescued. Instead, they will simply
bubble just like other Active Record callbacks.

You can opt into the new behavior and remove this warning by setting
config.active_record.raise_in_transactional_callbacks to true.
EOF

    included do
      define_callbacks :commit, :rollback,
                       terminator: ->(_, result) { result == false },
                       scope: [:kind, :name]

      mattr_accessor :raise_in_transactional_callbacks, instance_writer: false
      self.raise_in_transactional_callbacks = false
    end

    # = Active Record Transactions
    #
    # Transactions are protective blocks where SQL statements are only permanent
    # if they can all succeed as one atomic action. The classic example is a
    # transfer between two accounts where you can only have a deposit if the
    # withdrawal succeeded and vice versa. Transactions enforce the integrity of
    # the database and guard the data against program errors or database
    # break-downs. So basically you should use transaction blocks whenever you
    # have a number of statements that must be executed together or not at all.
    #
    # For example:
    #
    #   ActiveRecord::Base.transaction do
    #     david.withdrawal(100)
    #     mary.deposit(100)
    #   end
    #
    # This example will only take money from David and give it to Mary if neither
    # +withdrawal+ nor +deposit+ raise an exception. Exceptions will force a
    # ROLLBACK that returns the database to the state before the transaction
    # began. Be aware, though, that the objects will _not_ have their instance
    # data returned to their pre-transactional state.
    #
    # == Different Active Record classes in a single transaction
    #
    # Though the transaction class method is called on some Active Record class,
    # the objects within the transaction block need not all be instances of
    # that class. This is because transactions are per-database connection, not
    # per-model.
    #
    # In this example a +balance+ record is transactionally saved even
    # though +transaction+ is called on the +Account+ class:
    #
    #   Account.transaction do
    #     balance.save!
    #     account.save!
    #   end
    #
    # The +transaction+ method is also available as a model instance method.
    # For example, you can also do this:
    #
    #   balance.transaction do
    #     balance.save!
    #     account.save!
    #   end
    #
    # == Transactions are not distributed across database connections
    #
    # A transaction acts on a single database connection. If you have
    # multiple class-specific databases, the transaction will not protect
    # interaction among them. One workaround is to begin a transaction
    # on each class whose models you alter:
    #
    #   Student.transaction do
    #     Course.transaction do
    #       course.enroll(student)
    #       student.units += course.units
    #     end
    #   end
    #
    # This is a poor solution, but fully distributed transactions are beyond
    # the scope of Active Record.
    #
    # == +save+ and +destroy+ are automatically wrapped in a transaction
    #
    # Both +save+ and +destroy+ come wrapped in a transaction that ensures
    # that whatever you do in validations or callbacks will happen under its
    # protected cover. So you can use validations to check for values that
    # the transaction depends on or you can raise exceptions in the callbacks
    # to rollback, including <tt>after_*</tt> callbacks.
    #
    # As a consequence changes to the database are not seen outside your connection
    # until the operation is complete. For example, if you try to update the index
    # of a search engine in +after_save+ the indexer won't see the updated record.
    # The +after_commit+ callback is the only one that is triggered once the update
    # is committed. See below.
    #
    # == Exception handling and rolling back
    #
    # Also have in mind that exceptions thrown within a transaction block will
    # be propagated (after triggering the ROLLBACK), so you should be ready to
    # catch those in your application code.
    #
    # One exception is the <tt>ActiveRecord::Rollback</tt> exception, which will trigger
    # a ROLLBACK when raised, but not be re-raised by the transaction block.
    #
    # *Warning*: one should not catch <tt>ActiveRecord::StatementInvalid</tt> exceptions
    # inside a transaction block. <tt>ActiveRecord::StatementInvalid</tt> exceptions indicate that an
    # error occurred at the database level, for example when a unique constraint
    # is violated. On some database systems, such as PostgreSQL, database errors
    # inside a transaction cause the entire transaction to become unusable
    # until it's restarted from the beginning. Here is an example which
    # demonstrates the problem:
    #
    #   # Suppose that we have a Number model with a unique column called 'i'.
    #   Number.transaction do
    #     Number.create(i: 0)
    #     begin
    #       # This will raise a unique constraint error...
    #       Number.create(i: 0)
    #     rescue ActiveRecord::StatementInvalid
    #       # ...which we ignore.
    #     end
    #
    #     # On PostgreSQL, the transaction is now unusable. The following
    #     # statement will cause a PostgreSQL error, even though the unique
    #     # constraint is no longer violated:
    #     Number.create(i: 1)
    #     # => "PGError: ERROR:  current transaction is aborted, commands
    #     #     ignored until end of transaction block"
    #   end
    #
    # One should restart the entire transaction if an
    # <tt>ActiveRecord::StatementInvalid</tt> occurred.
    #
    # == Nested transactions
    #
    # +transaction+ calls can be nested. By default, this makes all database
    # statements in the nested transaction block become part of the parent
    # transaction. For example, the following behavior may be surprising:
    #
    #   User.transaction do
    #     User.create(username: 'Kotori')
    #     User.transaction do
    #       User.create(username: 'Nemu')
    #       raise ActiveRecord::Rollback
    #     end
    #   end
    #
    # creates both "Kotori" and "Nemu". Reason is the <tt>ActiveRecord::Rollback</tt>
    # exception in the nested block does not issue a ROLLBACK. Since these exceptions
    # are captured in transaction blocks, the parent block does not see it and the
    # real transaction is committed.
    #
    # In order to get a ROLLBACK for the nested transaction you may ask for a real
    # sub-transaction by passing <tt>requires_new: true</tt>. If anything goes wrong,
    # the database rolls back to the beginning of the sub-transaction without rolling
    # back the parent transaction. If we add it to the previous example:
    #
    #   User.transaction do
    #     User.create(username: 'Kotori')
    #     User.transaction(requires_new: true) do
    #       User.create(username: 'Nemu')
    #       raise ActiveRecord::Rollback
    #     end
    #   end
    #
    # only "Kotori" is created. This works on MySQL and PostgreSQL. SQLite3 version >= '3.6.8' also supports it.
    #
    # Most databases don't support true nested transactions. At the time of
    # writing, the only database that we're aware of that supports true nested
    # transactions, is MS-SQL. Because of this, Active Record emulates nested
    # transactions by using savepoints on MySQL and PostgreSQL. See
    # http://dev.mysql.com/doc/refman/5.6/en/savepoint.html
    # for more information about savepoints.
    #
    # === Callbacks
    #
    # There are two types of callbacks associated with committing and rolling back transactions:
    # +after_commit+ and +after_rollback+.
    #
    # +after_commit+ callbacks are called on every record saved or destroyed within a
    # transaction immediately after the transaction is committed. +after_rollback+ callbacks
    # are called on every record saved or destroyed within a transaction immediately after the
    # transaction or savepoint is rolled back.
    #
    # These callbacks are useful for interacting with other systems since you will be guaranteed
    # that the callback is only executed when the database is in a permanent state. For example,
    # +after_commit+ is a good spot to put in a hook to clearing a cache since clearing it from
    # within a transaction could trigger the cache to be regenerated before the database is updated.
    #
    # === Caveats
    #
    # If you're on MySQL, then do not use DDL operations in nested transactions
    # blocks that are emulated with savepoints. That is, do not execute statements
    # like 'CREATE TABLE' inside such blocks. This is because MySQL automatically
    # releases all savepoints upon executing a DDL operation. When +transaction+
    # is finished and tries to release the savepoint it created earlier, a
    # database error will occur because the savepoint has already been
    # automatically released. The following example demonstrates the problem:
    #
    #   Model.connection.transaction do                           # BEGIN
    #     Model.connection.transaction(requires_new: true) do  # CREATE SAVEPOINT active_record_1
    #       Model.connection.create_table(...)                    # active_record_1 now automatically released
    #     end                                                     # RELEASE savepoint active_record_1
    #                                                             # ^^^^ BOOM! database error!
    #   end
    #
    # Note that "TRUNCATE" is also a MySQL DDL statement!
    module ClassMethods
      # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
      def transaction(options = {}, &block)
        # See the ConnectionAdapters::DatabaseStatements#transaction API docs.
        connection.transaction(options, &block)
      end

      # This callback is called after a record has been created, updated, or destroyed.
      #
      # You can specify that the callback should only be fired by a certain action with
      # the +:on+ option:
      #
      #   after_commit :do_foo, on: :create
      #   after_commit :do_bar, on: :update
      #   after_commit :do_baz, on: :destroy
      #
      #   after_commit :do_foo_bar, on: [:create, :update]
      #   after_commit :do_bar_baz, on: [:update, :destroy]
      #
      # Note that transactional fixtures do not play well with this feature. Please
      # use the +test_after_commit+ gem to have these hooks fired in tests.
      def after_commit(*args, &block)
        set_options_for_callbacks!(args)
        set_callback(:commit, :after, *args, &block)
        unless ActiveRecord::Base.raise_in_transactional_callbacks
          ActiveSupport::Deprecation.warn(CALLBACK_WARN_MESSAGE)
        end
      end

      # This callback is called after a create, update, or destroy are rolled back.
      #
      # Please check the documentation of +after_commit+ for options.
      def after_rollback(*args, &block)
        set_options_for_callbacks!(args)
        set_callback(:rollback, :after, *args, &block)
        unless ActiveRecord::Base.raise_in_transactional_callbacks
          ActiveSupport::Deprecation.warn(CALLBACK_WARN_MESSAGE)
        end
      end

      private

      def set_options_for_callbacks!(args)
        options = args.last
        if options.is_a?(Hash) && options[:on]
          fire_on = Array(options[:on])
          assert_valid_transaction_action(fire_on)
          options[:if] = Array(options[:if])
          options[:if] << "transaction_include_any_action?(#{fire_on})"
        end
      end

      def assert_valid_transaction_action(actions)
        if (actions - ACTIONS).any?
          raise ArgumentError, ":on conditions for after_commit and after_rollback callbacks have to be one of #{ACTIONS.join(",")}"
        end
      end
    end

    # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
    def transaction(options = {}, &block)
      self.class.transaction(options, &block)
    end

    def destroy #:nodoc:
      with_transaction_returning_status { super }
    end

    def save(*) #:nodoc:
      rollback_active_record_state! do
        with_transaction_returning_status { super }
      end
    end

    def save!(*) #:nodoc:
      with_transaction_returning_status { super }
    end

    def touch(*) #:nodoc:
      with_transaction_returning_status { super }
    end

    # Reset id and @new_record if the transaction rolls back.
    def rollback_active_record_state!
      remember_transaction_record_state
      yield
    rescue Exception
      restore_transaction_record_state
      raise
    ensure
      clear_transaction_record_state
    end

    # Call the +after_commit+ callbacks.
    #
    # Ensure that it is not called if the object was never persisted (failed create),
    # but call it after the commit of a destroyed object.
    def committed!(should_run_callbacks = true) #:nodoc:
      run_callbacks :commit if should_run_callbacks && destroyed? || persisted?
    ensure
      force_clear_transaction_record_state
    end

    # Call the +after_rollback+ callbacks. The +force_restore_state+ argument indicates if the record
    # state should be rolled back to the beginning or just to the last savepoint.
    def rolledback!(force_restore_state = false, should_run_callbacks = true) #:nodoc:
      run_callbacks :rollback if should_run_callbacks
    ensure
      restore_transaction_record_state(force_restore_state)
      clear_transaction_record_state
    end

    # Add the record to the current transaction so that the +after_rollback+ and +after_commit+ callbacks
    # can be called.
    def add_to_transaction
      if self.class.connection.add_transaction_record(self)
        remember_transaction_record_state
      end
    end

    # Executes +method+ within a transaction and captures its return value as a
    # status flag. If the status is true the transaction is committed, otherwise
    # a ROLLBACK is issued. In any case the status flag is returned.
    #
    # This method is available within the context of an ActiveRecord::Base
    # instance.
    def with_transaction_returning_status
      status = nil
      self.class.transaction do
        add_to_transaction
        begin
          status = yield
        rescue ActiveRecord::Rollback
          clear_transaction_record_state
          status = nil
        end

        raise ActiveRecord::Rollback unless status
      end
      status
    end

    protected

    # Save the new record state and id of a record so it can be restored later if a transaction fails.
    def remember_transaction_record_state #:nodoc:
      @_start_transaction_state[:id] = id
      unless @_start_transaction_state.include?(:new_record)
        @_start_transaction_state[:new_record] = @new_record
      end
      unless @_start_transaction_state.include?(:destroyed)
        @_start_transaction_state[:destroyed] = @destroyed
      end
      @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) + 1
      @_start_transaction_state[:frozen?] = frozen?
    end

    # Clear the new record state and id of a record.
    def clear_transaction_record_state #:nodoc:
      @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
      force_clear_transaction_record_state if @_start_transaction_state[:level] < 1
    end

    # Force to clear the transaction record state.
    def force_clear_transaction_record_state #:nodoc:
      @_start_transaction_state.clear
    end

    # Restore the new record state and id of a record that was previously saved by a call to save_record_state.
    def restore_transaction_record_state(force = false) #:nodoc:
      unless @_start_transaction_state.empty?
        transaction_level = (@_start_transaction_state[:level] || 0) - 1
        if transaction_level < 1 || force
          restore_state = @_start_transaction_state
          thaw unless restore_state[:frozen?]
          @new_record = restore_state[:new_record]
          @destroyed  = restore_state[:destroyed]
          write_attribute(self.class.primary_key, restore_state[:id])
        end
      end
    end

    # Determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.
    def transaction_record_state(state) #:nodoc:
      @_start_transaction_state[state]
    end

    # Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
    def transaction_include_any_action?(actions) #:nodoc:
      actions.any? do |action|
        case action
        when :create
          transaction_record_state(:new_record)
        when :destroy
          destroyed?
        when :update
          !(transaction_record_state(:new_record) || destroyed?)
        end
      end
    end
  end
end