// createDescriptor implements the DescriptorAccessor interface.
func (p *planner) createDescriptor(plainKey sqlbase.DescriptorKey, descriptor sqlbase.DescriptorProto, ifNotExists bool) (bool, error) {
	idKey := plainKey.Key()
	// Check whether idKey exists.
	gr, err := p.txn.Get(idKey)
	if err != nil {
		return false, err
	}

	if gr.Exists() {
		if ifNotExists {
			// Noop.
			return false, nil
		}
		// Key exists, but we don't want it to: error out.
		return false, fmt.Errorf("%s %q already exists", descriptor.TypeName(), plainKey.Name())
	}

	// Increment unique descriptor counter.
	if ir, err := p.txn.Inc(keys.DescIDGenerator, 1); err == nil {
		descriptor.SetID(sqlbase.ID(ir.ValueInt() - 1))
	} else {
		return false, err
	}

	// TODO(pmattis): The error currently returned below is likely going to be
	// difficult to interpret.
	//
	// TODO(pmattis): Need to handle if-not-exists here as well.
	//
	// TODO(pmattis): This is writing the namespace and descriptor table entries,
	// but not going through the normal INSERT logic and not performing a precise
	// mimicry. In particular, we're only writing a single key per table, while
	// perfect mimicry would involve writing a sentinel key for each row as well.
	descKey := sqlbase.MakeDescMetadataKey(descriptor.GetID())

	b := client.Batch{}
	descID := descriptor.GetID()
	descDesc := sqlbase.WrapDescriptor(descriptor)
	if log.V(2) {
		log.Infof("CPut %s -> %d", idKey, descID)
		log.Infof("CPut %s -> %s", descKey, descDesc)
	}
	b.CPut(idKey, descID, nil)
	b.CPut(descKey, descDesc, nil)

	p.setTestingVerifyMetadata(func(systemConfig config.SystemConfig) error {
		if err := expectDescriptorID(systemConfig, idKey, descID); err != nil {
			return err
		}
		return expectDescriptor(systemConfig, descKey, descDesc)
	})

	return true, p.txn.Run(&b)
}

// createDescriptor implements the DescriptorAccessor interface.
func (p *planner) createDescriptor(
	plainKey sqlbase.DescriptorKey, descriptor sqlbase.DescriptorProto, ifNotExists bool,
) (bool, error) {
	idKey := plainKey.Key()

	if exists, err := p.descExists(idKey); err == nil && exists {
		if ifNotExists {
			// Noop.
			return false, nil
		}
		// Key exists, but we don't want it to: error out.
		return false, descriptorAlreadyExistsErr{descriptor, plainKey.Name()}
	} else if err != nil {
		return false, err
	}

	id, err := p.generateUniqueDescID()
	if err != nil {
		return false, err
	}

	return p.createDescriptorWithID(idKey, id, descriptor)
}

// getDescriptor implements the DescriptorAccessor interface.
func (p *planner) getDescriptor(plainKey sqlbase.DescriptorKey, descriptor sqlbase.DescriptorProto,
) (bool, error) {
	gr, err := p.txn.Get(plainKey.Key())
	if err != nil {
		return false, err
	}
	if !gr.Exists() {
		return false, nil
	}

	descKey := sqlbase.MakeDescMetadataKey(sqlbase.ID(gr.ValueInt()))
	desc := &sqlbase.Descriptor{}
	if err := p.txn.GetProto(descKey, desc); err != nil {
		return false, err
	}

	switch t := descriptor.(type) {
	case *sqlbase.TableDescriptor:
		table := desc.GetTable()
		table.MaybeUpgradeFormatVersion()
		// TODO(dan): Write the upgraded TableDescriptor back to kv. This will break
		// the ability to use a previous version of cockroach with the on-disk data,
		// but it's worth it to avoid having to do the upgrade every time the
		// descriptor is fetched. Our current test for this enforces compatibility
		// backward and forward, so that'll have to be extended before this is done.
		if table == nil {
			return false, errors.Errorf("%q is not a table", plainKey.Name())
		}
		if err := table.Validate(p.txn); err != nil {
			return false, err
		}
		*t = *table
	case *sqlbase.DatabaseDescriptor:
		database := desc.GetDatabase()
		if database == nil {
			return false, errors.Errorf("%q is not a database", plainKey.Name())
		}
		if err := database.Validate(); err != nil {
			return false, err
		}
		*t = *database
	}
	return true, nil
}

// getDescriptor implements the DescriptorAccessor interface.
func (p *planner) getDescriptor(plainKey sqlbase.DescriptorKey, descriptor sqlbase.DescriptorProto,
) (bool, error) {
	gr, err := p.txn.Get(plainKey.Key())
	if err != nil {
		return false, err
	}
	if !gr.Exists() {
		return false, nil
	}

	descKey := sqlbase.MakeDescMetadataKey(sqlbase.ID(gr.ValueInt()))
	desc := &sqlbase.Descriptor{}
	if err := p.txn.GetProto(descKey, desc); err != nil {
		return false, err
	}

	switch t := descriptor.(type) {
	case *sqlbase.TableDescriptor:
		table := desc.GetTable()
		if table == nil {
			return false, util.Errorf("%q is not a table", plainKey.Name())
		}
		*t = *table
	case *sqlbase.DatabaseDescriptor:
		database := desc.GetDatabase()
		if database == nil {
			return false, util.Errorf("%q is not a database", plainKey.Name())
		}
		*t = *database
	}

	if err := descriptor.Validate(); err != nil {
		return false, err
	}
	return true, nil
}