package expression

import (
	"fmt"
	"strings"

	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

// ValueBuilder represents an item attribute value operand and implements the
// OperandBuilder interface. Methods and functions in the package take
// ValueBuilder as an argument and establishes relationships between operands.
// ValueBuilder should only be initialized using the function Value().
//
// Example:
//
//	// Create a ValueBuilder representing the string "aValue"
//	valueBuilder := expression.Value("aValue")
type ValueBuilder struct {
	value   interface{}
	options ValueBuilderOptions
}

// ValueBuilderOptions provides the options for how a value is built, and
// encoded in the expression.
type ValueBuilderOptions struct {
	// Use functional options to specify how the value will be encoded. If the
	// value is already an AttributeValue, the EncoderOptions will be ignored.
	EncoderOptions []func(*attributevalue.EncoderOptions)
}

// NameBuilder represents a name of a top level item attribute or a nested
// attribute. Since NameBuilder represents a DynamoDB Operand, it implements the
// OperandBuilder interface. Methods and functions in the package take
// NameBuilder as an argument and establishes relationships between operands.
// NameBuilder should only be initialized using the function Name().
//
// Example:
//
//	// Create a NameBuilder representing the item attribute "aName"
//	nameBuilder := expression.Name("aName")
type NameBuilder struct {
	names []string
}

// SizeBuilder represents the output of the function size ("someName"), which
// evaluates to the size of the item attribute defined by "someName". Since
// SizeBuilder represents an operand, SizeBuilder implements the OperandBuilder
// interface. Methods and functions in the package take SizeBuilder as an
// argument and establishes relationships between operands. SizeBuilder should
// only be initialized using the function Size().
//
// Example:
//
//	// Create a SizeBuilder representing the size of the item attribute
//	// "aName"
//	sizeBuilder := expression.Name("aName").Size()
type SizeBuilder struct {
	nameBuilder NameBuilder
}

// KeyBuilder represents either the partition key or the sort key, both of which
// are top level attributes to some item in DynamoDB. Since KeyBuilder
// represents an operand, KeyBuilder implements the OperandBuilder interface.
// Methods and functions in the package take KeyBuilder as an argument and
// establishes relationships between operands. However, KeyBuilder should only
// be used to describe Key Condition Expressions. KeyBuilder should only be
// initialized using the function Key().
//
// Example:
//
//	// Create a KeyBuilder representing the item key "aKey"
//	keyBuilder := expression.Key("aKey")
type KeyBuilder struct {
	key string
}

// setValueMode specifies the type of SetValueBuilder. The default value is
// unsetValue so that an UnsetParameterError when BuildOperand() is called on an
// empty SetValueBuilder.
type setValueMode int

const (
	unsetValue setValueMode = iota
	plusValueMode
	minusValueMode
	listAppendValueMode
	ifNotExistsValueMode
)

// SetValueBuilder represents the outcome of operator functions supported by the
// DynamoDB Set operation. The operator functions are the following:
//
//	Plus()  // Represents the "+" operator
//	Minus() // Represents the "-" operator
//	ListAppend()
//	IfNotExists()
//
// For documentation on the above functions,
// see: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET
// Since SetValueBuilder represents an operand, it implements the OperandBuilder
// interface. SetValueBuilder structs are used as arguments to the Set()
// function. SetValueBuilders should only initialize a SetValueBuilder using the
// functions listed above.
type SetValueBuilder struct {
	leftOperand  OperandBuilder
	rightOperand OperandBuilder
	mode         setValueMode
}

// Operand represents an item attribute name or value in DynamoDB. The
// relationship between Operands specified by various builders such as
// ConditionBuilders and UpdateBuilders for example is processed internally to
// write Condition Expressions and Update Expressions respectively.
type Operand struct {
	exprNode exprNode
}

// OperandBuilder represents the idea of Operand which are building blocks to
// DynamoDB Expressions. Package methods and functions can establish
// relationships between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// OperandBuilder and BuildOperand() are exported to allow package functions to
// take an interface as an argument.
type OperandBuilder interface {
	BuildOperand() (Operand, error)
}

// Name creates a NameBuilder. The argument should represent the desired item
// attribute. It is possible to reference nested item attributes by using
// square brackets for lists and dots for maps. For documentation on specifying
// item attributes,
// see: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.Attributes.html
//
// Example:
//
//	// Specify a top-level attribute
//	name := expression.Name("TopLevel")
//	// Specify a nested attribute
//	nested := expression.Name("Record[6].SongList")
//	// Use Name() to create a condition expression
//	condition := expression.Name("foo").Equal(expression.Name("bar"))
func Name(name string) NameBuilder {
	if len(name) == 0 {
		return NameBuilder{}
	}

	return NameBuilder{
		names: strings.Split(name, "."),
	}
}

// AppendName to adds additional name fields, returning a new NameBuilder. Can
// be used to append list indexes and map fields to the Expression attribute
// name.
//
// Leading or trailing dots(`.`) for Names that are not created with
// NameNoDotSplit will result in an error when the expression is built. The
// dot(`.`) will be added automatically as needed.
func (nb NameBuilder) AppendName(field NameBuilder) NameBuilder {
	names := make([]string, 0, len(nb.names)+len(field.names))
	names = append(names, nb.names...)
	names = append(names, field.names...)

	// If the name being append starts with a list index it to the name being
	// appended to. This allows list indexes to be appended to names. If there
	// is a syntax error in the name, it will be caught when the expression is
	// built via BuildOperand method.
	if len(nb.names) != 0 && len(field.names) != 0 {
		lastLeftName := len(nb.names) - 1
		firstRightName := lastLeftName + 1

		v := names[firstRightName]
		end := strings.Index(v, "]")

		for len(v) > 0 && v[0] == '[' && end != -1 {
			names[lastLeftName] += v[0 : end+1]
			names[firstRightName] = v[end+1:]

			// Remove the name if it is empty after moving the index.
			if len(names[firstRightName]) == 0 {
				copy(names[firstRightName:], names[firstRightName+1:])
				names[len(names)-1] = ""
				names = names[:len(names)-1]

				break
			}

			v = v[end+1:]
			end = strings.Index(v, "]")
		}
	}

	return NameBuilder{
		names: names,
	}
}

// NameNoDotSplit returns a NameBuilder. The argument should represent the
// desired item attribute. The name will not be split on dots. The name may end
// with square brackets for list indexes. Square brackets will not be
// considered a part of the NameLiteral.
//
// Use NameBuilder.WithField method to add subsequent map field names.
// Use NameBuilder.WithListIndex method to add list index to the name.
//
// See: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.Attributes.html
//
// Example:
//
//	// Specify a name containing dots, and should not be split.
//	name := expression.NameLiteral("Top.Level")
//
//	// Specify a nested attribute
//	nested := expression.Name("Record[6].SongList")
//	// Use Name() to create a condition expression
//	condition := expression.Name("foo").Equal(expression.Name("bar"))
func NameNoDotSplit(name string) NameBuilder {
	return NameBuilder{
		names: []string{name},
	}
}

// Value creates a ValueBuilder and sets its value to the argument. The value
// will be marshalled using the attributevalue package, unless it is of
// type types.AttributeValue, where it will be used directly.
//
// Empty slices and maps will be encoded as their respective empty types.AttributeValue
// types. If a NULL value is required, pass a dynamodb.AttributeValue, e.g.:
// emptyList := &types.AttributeValueMemberNULL{Value: true}
//
// Example:
//
//	// Use Value() to create a condition expression
//	condition := expression.Name("foo").Equal(expression.Value(10))
//	// Use Value() to set the value of a set expression.
//	update := Set(expression.Name("greets"), expression.Value(&types.AttributeValueMemberS{Value: "hello"}))
func Value(value interface{}) ValueBuilder {
	return ValueBuilder{
		value: value,
	}
}

// ValueWithOptions creates a ValueBuilder and sets its value to the argument. The value
// will be marshalled using the attributevalue package, unless it is of
// type types.AttributeValue, where it will be used directly.
//
// The ValueBuilderOptions functional options parameter allows you to specify
// how the value will be encoded. Including options like AttributeValue
// encoding struct tag. If value is already a DynamoDB AttributeValue,
// encoding options will have not effect.
//
// Empty slices and maps will be encoded as their respective empty types.AttributeValue
// types. If a NULL value is required, pass a dynamodb.AttributeValue, e.g.:
// emptyList := &types.AttributeValueMemberNULL{Value: true}
//
// Example:
//
//	// Use Value() to create a condition expression
//	condition := expression.Name("foo").Equal(expression.Value(10))
//	// Use Value() to set the value of a set expression.
//	update := Set(expression.Name("greets"), expression.Value(&types.AttributeValueMemberS{Value: "hello"}))
func ValueWithOptions(value interface{}, optFns ...func(*ValueBuilderOptions)) ValueBuilder {
	var options ValueBuilderOptions
	for _, fn := range optFns {
		fn(&options)
	}

	return ValueBuilder{
		value:   value,
		options: options,
	}
}

// Size creates a SizeBuilder representing the size of the item attribute
// specified by the argument NameBuilder. Size() is only valid for certain types
// of item attributes. For documentation,
// see: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html
// SizeBuilder is only a valid operand in Condition Expressions and Filter
// Expressions.
//
// Example:
//
//	// Use Size() to create a condition expression
//	condition := expression.Name("foo").Size().Equal(expression.Value(10))
//
// Expression Equivalent:
//
//	expression.Name("aName").Size()
//	"size (aName)"
func (nb NameBuilder) Size() SizeBuilder {
	return SizeBuilder{
		nameBuilder: nb,
	}
}

// Size creates a SizeBuilder representing the size of the item attribute
// specified by the argument NameBuilder. Size() is only valid for certain types
// of item attributes. For documentation,
// see: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html
// SizeBuilder is only a valid operand in Condition Expressions and Filter
// Expressions.
//
// Example:
//
//	// Use Size() to create a condition expression
//	condition := expression.Size(expression.Name("foo")).Equal(expression.Value(10))
//
// Expression Equivalent:
//
//	expression.Size(expression.Name("aName"))
//	"size (aName)"
func Size(nameBuilder NameBuilder) SizeBuilder {
	return nameBuilder.Size()
}

// Key creates a KeyBuilder. The argument should represent the desired partition
// key or sort key value. KeyBuilders should only be used to specify
// relationships for Key Condition Expressions. When referring to the partition
// key or sort key in any other Expression, use Name().
//
// Example:
//
//	// Use Key() to create a key condition expression
//	keyCondition := expression.Key("foo").Equal(expression.Value("bar"))
func Key(key string) KeyBuilder {
	return KeyBuilder{
		key: key,
	}
}

// Plus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Plus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Plus() to set the value of the item attribute "someName" to 5 + 10
//	update, err := expression.Set(expression.Name("someName"), expression.Plus(expression.Value(5), expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Plus(expression.Value(5), expression.Value(10))
//	// let :five and :ten be ExpressionAttributeValues for the values 5 and
//	// 10 respectively.
//	":five + :ten"
func Plus(leftOperand, rightOperand OperandBuilder) SetValueBuilder {
	return SetValueBuilder{
		leftOperand:  leftOperand,
		rightOperand: rightOperand,
		mode:         plusValueMode,
	}
}

// Plus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Plus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Plus() to set the value of the item attribute "someName" to the
//	// numeric value of item attribute "aName" incremented by 10
//	update, err := expression.Set(expression.Name("someName"), expression.Name("aName").Plus(expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Name("aName").Plus(expression.Value(10))
//	// let :ten be ExpressionAttributeValues representing the value 10
//	"aName + :ten"
func (nb NameBuilder) Plus(rightOperand OperandBuilder) SetValueBuilder {
	return Plus(nb, rightOperand)
}

// Plus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Plus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Plus() to set the value of the item attribute "someName" to 5 + 10
//	update, err := expression.Set(expression.Name("someName"), expression.Value(5).Plus(expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Value(5).Plus(expression.Value(10))
//	// let :five and :ten be ExpressionAttributeValues representing the value
//	// 5 and 10 respectively
//	":five + :ten"
func (vb ValueBuilder) Plus(rightOperand OperandBuilder) SetValueBuilder {
	return Plus(vb, rightOperand)
}

// Minus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Minus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Minus() to set the value of item attribute "someName" to 5 - 10
//	update, err := expression.Set(expression.Name("someName"), expression.Minus(expression.Value(5), expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Minus(expression.Value(5), expression.Value(10))
//	// let :five and :ten be ExpressionAttributeValues for the values 5 and
//	// 10 respectively.
//	":five - :ten"
func Minus(leftOperand, rightOperand OperandBuilder) SetValueBuilder {
	return SetValueBuilder{
		leftOperand:  leftOperand,
		rightOperand: rightOperand,
		mode:         minusValueMode,
	}
}

// Minus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Minus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Minus() to set the value of item attribute "someName" to the
//	// numeric value of "aName" decremented by 10
//	update, err := expression.Set(expression.Name("someName"), expression.Name("aName").Minus(expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Name("aName").Minus(expression.Value(10)))
//	// let :ten be ExpressionAttributeValues represent the value 10
//	"aName - :ten"
func (nb NameBuilder) Minus(rightOperand OperandBuilder) SetValueBuilder {
	return Minus(nb, rightOperand)
}

// Minus creates a SetValueBuilder to be used in as an argument to Set(). The
// arguments can either be NameBuilders or ValueBuilders. Minus() only supports
// DynamoDB Number types, so the ValueBuilder must be a Number and the
// NameBuilder must specify an item attribute of type Number.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.IncrementAndDecrement
//
// Example:
//
//	// Use Minus() to set the value of item attribute "someName" to 5 - 10
//	update, err := expression.Set(expression.Name("someName"), expression.Value(5).Minus(expression.Value(10)))
//
// Expression Equivalent:
//
//	expression.Value(5).Minus(expression.Value(10))
//	// let :five and :ten be ExpressionAttributeValues for the values 5 and
//	// 10 respectively.
//	":five - :ten"
func (vb ValueBuilder) Minus(rightOperand OperandBuilder) SetValueBuilder {
	return Minus(vb, rightOperand)
}

// ListAppend creates a SetValueBuilder to be used in as an argument to Set().
// The arguments can either be NameBuilders or ValueBuilders. ListAppend() only
// supports DynamoDB List types, so the ValueBuilder must be a List and the
// NameBuilder must specify an item attribute of type List.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.UpdatingListElements
//
// Example:
//
//	// Use ListAppend() to set item attribute "someName" to the item
//	// attribute "nameOfList" with "some" and "list" appended to it
//	update, err := expression.Set(expression.Name("someName"), expression.ListAppend(expression.Name("nameOfList"), expression.Value([]string{"some", "list"})))
//
// Expression Equivalent:
//
//	expression.ListAppend(expression.Name("nameOfList"), expression.Value([]string{"some", "list"})
//	// let :list be a ExpressionAttributeValue representing the list
//	// containing "some" and "list".
//	"list_append (nameOfList, :list)"
func ListAppend(leftOperand, rightOperand OperandBuilder) SetValueBuilder {
	return SetValueBuilder{
		leftOperand:  leftOperand,
		rightOperand: rightOperand,
		mode:         listAppendValueMode,
	}
}

// ListAppend creates a SetValueBuilder to be used in as an argument to Set().
// The arguments can either be NameBuilders or ValueBuilders. ListAppend() only
// supports DynamoDB List types, so the ValueBuilder must be a List and the
// NameBuilder must specify an item attribute of type List.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.UpdatingListElements
//
// Example:
//
//	// Use ListAppend() to set item attribute "someName" to the item
//	// attribute "nameOfList" with "some" and "list" appended to it
//	update, err := expression.Set(expression.Name("someName"), expression.Name("nameOfList").ListAppend(expression.Value([]string{"some", "list"})))
//
// Expression Equivalent:
//
//	expression.Name("nameOfList").ListAppend(expression.Value([]string{"some", "list"})
//	// let :list be a ExpressionAttributeValue representing the list
//	// containing "some" and "list".
//	"list_append (nameOfList, :list)"
func (nb NameBuilder) ListAppend(rightOperand OperandBuilder) SetValueBuilder {
	return ListAppend(nb, rightOperand)
}

// ListAppend creates a SetValueBuilder to be used in as an argument to Set().
// The arguments can either be NameBuilders or ValueBuilders. ListAppend() only
// supports DynamoDB List types, so the ValueBuilder must be a List and the
// NameBuilder must specify an item attribute of type List.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.UpdatingListElements
//
// Example:
//
//	// Use ListAppend() to set item attribute "someName" to a string list
//	// equal to {"a", "list", "some", "list"}
//	update, err := expression.Set(expression.Name("someName"), expression.Value([]string{"a", "list"}).ListAppend(expression.Value([]string{"some", "list"})))
//
// Expression Equivalent:
//
//	expression.Name([]string{"a", "list"}).ListAppend(expression.Value([]string{"some", "list"})
//	// let :list1 and :list2 be a ExpressionAttributeValue representing the
//	// list {"a", "list"} and {"some", "list"} respectively
//	"list_append (:list1, :list2)"
func (vb ValueBuilder) ListAppend(rightOperand OperandBuilder) SetValueBuilder {
	return ListAppend(vb, rightOperand)
}

// IfNotExists creates a SetValueBuilder to be used in as an argument to Set().
// The first argument must be a NameBuilder representing the name where the new
// item attribute is created. The second argument can either be a NameBuilder or
// a ValueBuilder. In the case that it is a NameBuilder, the value of the item
// attribute at the name specified becomes the value of the new item attribute.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.PreventingAttributeOverwrites
//
// Example:
//
//	// Use IfNotExists() to set item attribute "someName" to value 5 if
//	// "someName" does not exist yet. (Prevents overwrite)
//	update, err := expression.Set(expression.Name("someName"), expression.IfNotExists(expression.Name("someName"), expression.Value(5)))
//
// Expression Equivalent:
//
//	expression.IfNotExists(expression.Name("someName"), expression.Value(5))
//	// let :five be a ExpressionAttributeValue representing the value 5
//	"if_not_exists (someName, :five)"
func IfNotExists(name NameBuilder, setValue OperandBuilder) SetValueBuilder {
	return SetValueBuilder{
		leftOperand:  name,
		rightOperand: setValue,
		mode:         ifNotExistsValueMode,
	}
}

// IfNotExists creates a SetValueBuilder to be used in as an argument to Set().
// The first argument must be a NameBuilder representing the name where the new
// item attribute is created. The second argument can either be a NameBuilder or
// a ValueBuilder. In the case that it is a NameBuilder, the value of the item
// attribute at the name specified becomes the value of the new item attribute.
// More information: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.PreventingAttributeOverwrites
//
// Example:
//
//	// Use IfNotExists() to set item attribute "someName" to value 5 if
//	// "someName" does not exist yet. (Prevents overwrite)
//	update, err := expression.Set(
//	    expression.Name("someName"),
//	    expression.Name("someName").IfNotExists(expression.Value(5)),
//	)
//
// Expression Equivalent:
//
//	expression.Name("someName").IfNotExists(expression.Value(5))
//	// let :five be a ExpressionAttributeValue representing the value 5
//	"if_not_exists (someName, :five)"
func (nb NameBuilder) IfNotExists(rightOperand OperandBuilder) SetValueBuilder {
	return IfNotExists(nb, rightOperand)
}

// BuildOperand creates an Operand struct which are building blocks to DynamoDB
// Expressions. Package methods and functions can establish relationships
// between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// BuildOperand() aliases all strings to avoid stepping over DynamoDB's reserved
// words.
//
// More information on reserved words at http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html
func (nb NameBuilder) BuildOperand() (Operand, error) {
	if len(nb.names) == 0 {
		return Operand{}, newUnsetParameterError("BuildOperand", "NameBuilder")
	}

	node := exprNode{
		names: []string{},
	}

	fmtNames := make([]string, 0, len(nb.names))
	for _, word := range nb.names {
		var substr string
		if word == "" {
			return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
		}

		numOpenBrackets := strings.Count(word, "[")
		numCloseBrackets := strings.Count(word, "]")

		// mismatched brackets
		if numOpenBrackets != numCloseBrackets {
			return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
		}

		openPositions := make([]int, 0, numOpenBrackets)
		closePositions := make([]int, 0, numCloseBrackets)

		for i, char := range word {
			if char == '[' {
				openPositions = append(openPositions, i)
			} else if char == ']' {
				closePositions = append(closePositions, i)
			}
		}

		for idx := range closePositions {
			openPosition := openPositions[idx]
			closePosition := closePositions[idx]
			if openPosition > closePosition {
				return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
			}

			part := word[openPosition+1 : closePosition]
			if len(part) == 0 {
				return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
			}

			for _, c := range []byte(part) {
				if c < '0' || c > '9' {
					return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
				}
			}
		}

		if word[len(word)-1] == ']' {
			for j, char := range word {
				if char == '[' {
					substr = word[j:]
					word = word[:j]
					break
				}
			}
		}

		if word == "" {
			return Operand{}, newInvalidParameterError("BuildOperand", "NameBuilder")
		}

		// Create a string with special characters that can be substituted later: $p
		node.names = append(node.names, word)
		fmtNames = append(fmtNames, "$n"+substr)
	}
	node.fmtExpr = strings.Join(fmtNames, ".")
	return Operand{
		exprNode: node,
	}, nil
}

// BuildOperand creates an Operand struct which are building blocks to DynamoDB
// Expressions. Package methods and functions can establish relationships
// between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// BuildOperand() aliases all strings to avoid stepping over DynamoDB's reserved
// words.
// More information on reserved words at http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html
func (vb ValueBuilder) BuildOperand() (Operand, error) {
	var (
		expr types.AttributeValue
		err  error
	)

	switch v := vb.value.(type) {
	case types.AttributeValueMemberS:
		expr = &v
	case types.AttributeValueMemberN:
		expr = &v
	case types.AttributeValueMemberB:
		expr = &v
	case types.AttributeValueMemberSS:
		expr = &v
	case types.AttributeValueMemberNS:
		expr = &v
	case types.AttributeValueMemberBS:
		expr = &v
	case types.AttributeValueMemberM:
		expr = &v
	case types.AttributeValueMemberL:
		expr = &v
	case types.AttributeValueMemberNULL:
		expr = &v
	case types.AttributeValueMemberBOOL:
		expr = &v
	case types.AttributeValue:
		expr = v
	default:
		expr, err = attributevalue.MarshalWithOptions(vb.value, vb.options.EncoderOptions...)
		if err != nil {
			return Operand{}, newInvalidParameterError("BuildOperand", "ValueBuilder")
		}
	}

	// Create a string with special characters that can be substituted later: $v
	operand := Operand{
		exprNode: exprNode{
			values:  []types.AttributeValue{expr},
			fmtExpr: "$v",
		},
	}
	return operand, nil
}

// BuildOperand creates an Operand struct which are building blocks to DynamoDB
// Expressions. Package methods and functions can establish relationships
// between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// BuildOperand() aliases all strings to avoid stepping over DynamoDB's reserved
// words.
// More information on reserved words at http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html
func (sb SizeBuilder) BuildOperand() (Operand, error) {
	operand, err := sb.nameBuilder.BuildOperand()
	operand.exprNode.fmtExpr = "size (" + operand.exprNode.fmtExpr + ")"

	return operand, err
}

// BuildOperand creates an Operand struct which are building blocks to DynamoDB
// Expressions. Package methods and functions can establish relationships
// between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// BuildOperand() aliases all strings to avoid stepping over DynamoDB's reserved
// words.
// More information on reserved words at http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html
func (kb KeyBuilder) BuildOperand() (Operand, error) {
	if kb.key == "" {
		return Operand{}, newUnsetParameterError("BuildOperand", "KeyBuilder")
	}

	ret := Operand{
		exprNode: exprNode{
			names:   []string{kb.key},
			fmtExpr: "$n",
		},
	}

	return ret, nil
}

// BuildOperand creates an Operand struct which are building blocks to DynamoDB
// Expressions. Package methods and functions can establish relationships
// between operands, representing DynamoDB Expressions. The method
// BuildOperand() is called recursively when the Build() method on the type
// Builder is called. BuildOperand() should never be called externally.
// BuildOperand() aliases all strings to avoid stepping over DynamoDB's reserved
// words.
// More information on reserved words at http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ReservedWords.html
func (svb SetValueBuilder) BuildOperand() (Operand, error) {
	if svb.mode == unsetValue {
		return Operand{}, newUnsetParameterError("BuildOperand", "SetValueBuilder")
	}

	left, err := svb.leftOperand.BuildOperand()
	if err != nil {
		return Operand{}, err
	}
	leftNode := left.exprNode

	right, err := svb.rightOperand.BuildOperand()
	if err != nil {
		return Operand{}, err
	}
	rightNode := right.exprNode

	node := exprNode{
		children: []exprNode{leftNode, rightNode},
	}

	switch svb.mode {
	case plusValueMode:
		node.fmtExpr = "$c + $c"
	case minusValueMode:
		node.fmtExpr = "$c - $c"
	case listAppendValueMode:
		node.fmtExpr = "list_append($c, $c)"
	case ifNotExistsValueMode:
		node.fmtExpr = "if_not_exists($c, $c)"
	default:
		return Operand{}, fmt.Errorf("build operand error: unsupported mode: %v", svb.mode)
	}

	return Operand{
		exprNode: node,
	}, nil
}