// writeMutation writes the mutation to the table descriptor. If the
// State or the Direction is undefined, these values are populated via
// picking random values before the mutation is written.
func (mt mutationTest) writeMutation(m sqlbase.DescriptorMutation) {
	if m.Direction == sqlbase.DescriptorMutation_NONE {
		// randomly pick ADD/DROP mutation if this is the first mutation, or
		// pick the direction already chosen for the first mutation.
		if len(mt.tableDesc.Mutations) > 0 {
			m.Direction = mt.tableDesc.Mutations[0].Direction
		} else {
			m.Direction = sqlbase.DescriptorMutation_DROP
			if rand.Intn(2) == 0 {
				m.Direction = sqlbase.DescriptorMutation_ADD
			}
		}
	}
	if m.State == sqlbase.DescriptorMutation_UNKNOWN {
		// randomly pick DELETE_ONLY/WRITE_ONLY state.
		r := rand.Intn(2)
		if r == 0 {
			m.State = sqlbase.DescriptorMutation_DELETE_ONLY
		} else {
			m.State = sqlbase.DescriptorMutation_WRITE_ONLY
		}
	}
	mt.tableDesc.Mutations = append(mt.tableDesc.Mutations, m)
	if err := mt.tableDesc.ValidateTable(); err != nil {
		mt.Fatal(err)
	}
	if err := mt.kvDB.Put(
		context.TODO(),
		sqlbase.MakeDescMetadataKey(mt.tableDesc.ID),
		sqlbase.WrapDescriptor(mt.tableDesc),
	); err != nil {
		mt.Fatal(err)
	}
}

// writeColumnMutation adds column as a mutation and writes the
// descriptor to the DB.
func (mt mutationTest) writeColumnMutation(column string, m sqlbase.DescriptorMutation) {
	_, i, err := mt.tableDesc.FindColumnByNormalizedName(column)
	if err != nil {
		mt.Fatal(err)
	}
	col := mt.tableDesc.Columns[i]
	mt.tableDesc.Columns = append(mt.tableDesc.Columns[:i], mt.tableDesc.Columns[i+1:]...)
	m.Descriptor_ = &sqlbase.DescriptorMutation_Column{Column: &col}
	mt.writeMutation(m)
}

// writeIndexMutation adds index as a mutation and writes the
// descriptor to the DB.
func (mt mutationTest) writeIndexMutation(index string, m sqlbase.DescriptorMutation) {
	tableDesc := mt.tableDesc
	_, i, err := tableDesc.FindIndexByNormalizedName(index)
	if err != nil {
		mt.Fatal(err)
	}
	idx := tableDesc.Indexes[i]
	tableDesc.Indexes = append(tableDesc.Indexes[:i], tableDesc.Indexes[i+1:]...)
	m.Descriptor_ = &sqlbase.DescriptorMutation_Index{Index: &idx}
	mt.writeMutation(m)
}