// Copyright 2015 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package ast

import (
	"strings"

	"github.com/pingcap/errors"
	"github.com/pingcap/parser/auth"
	"github.com/pingcap/parser/model"
	"github.com/pingcap/parser/mysql"
)

var (
	_ DMLNode = &DeleteStmt{}
	_ DMLNode = &InsertStmt{}
	_ DMLNode = &UnionStmt{}
	_ DMLNode = &UpdateStmt{}
	_ DMLNode = &SelectStmt{}
	_ DMLNode = &ShowStmt{}
	_ DMLNode = &LoadDataStmt{}

	_ Node = &Assignment{}
	_ Node = &ByItem{}
	_ Node = &FieldList{}
	_ Node = &GroupByClause{}
	_ Node = &HavingClause{}
	_ Node = &Join{}
	_ Node = &Limit{}
	_ Node = &OnCondition{}
	_ Node = &OrderByClause{}
	_ Node = &SelectField{}
	_ Node = &TableName{}
	_ Node = &TableRefsClause{}
	_ Node = &TableSource{}
	_ Node = &UnionSelectList{}
	_ Node = &WildCardField{}
	_ Node = &WindowSpec{}
	_ Node = &PartitionByClause{}
	_ Node = &FrameClause{}
	_ Node = &FrameBound{}
)

// JoinType is join type, including cross/left/right/full.
type JoinType int

const (
	// CrossJoin is cross join type.
	CrossJoin JoinType = iota + 1
	// LeftJoin is left Join type.
	LeftJoin
	// RightJoin is right Join type.
	RightJoin
)

// Join represents table join.
type Join struct {
	node
	resultSetNode

	// Left table can be TableSource or JoinNode.
	Left ResultSetNode
	// Right table can be TableSource or JoinNode or nil.
	Right ResultSetNode
	// Tp represents join type.
	Tp JoinType
	// On represents join on condition.
	On *OnCondition
	// Using represents join using clause.
	Using []*ColumnName
	// NaturalJoin represents join is natural join.
	NaturalJoin bool
	// StraightJoin represents a straight join.
	StraightJoin bool
}

// Restore implements Node interface.
func (n *Join) Restore(ctx *RestoreCtx) error {
	if ctx.JoinLevel != 0 {
		ctx.WritePlain("(")
		defer ctx.WritePlain(")")
	}
	ctx.JoinLevel++
	if err := n.Left.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore Join.Left")
	}
	ctx.JoinLevel--
	if n.Right == nil {
		return nil
	}
	if n.NaturalJoin {
		ctx.WriteKeyWord(" NATURAL")
	}
	switch n.Tp {
	case LeftJoin:
		ctx.WriteKeyWord(" LEFT")
	case RightJoin:
		ctx.WriteKeyWord(" RIGHT")
	}
	if n.StraightJoin {
		ctx.WriteKeyWord(" STRAIGHT_JOIN ")
	} else {
		ctx.WriteKeyWord(" JOIN ")
	}
	ctx.JoinLevel++
	if err := n.Right.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore Join.Right")
	}
	ctx.JoinLevel--

	if n.On != nil {
		ctx.WritePlain(" ")
		if err := n.On.Restore(ctx); err != nil {
			return errors.Annotate(err, "An error occurred while restore Join.On")
		}
	}
	if len(n.Using) != 0 {
		ctx.WriteKeyWord(" USING ")
		ctx.WritePlain("(")
		for i, v := range n.Using {
			if i != 0 {
				ctx.WritePlain(",")
			}
			if err := v.Restore(ctx); err != nil {
				return errors.Annotate(err, "An error occurred while restore Join.Using")
			}
		}
		ctx.WritePlain(")")
	}

	return nil
}

// Accept implements Node Accept interface.
func (n *Join) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*Join)
	node, ok := n.Left.Accept(v)
	if !ok {
		return n, false
	}
	n.Left = node.(ResultSetNode)
	if n.Right != nil {
		node, ok = n.Right.Accept(v)
		if !ok {
			return n, false
		}
		n.Right = node.(ResultSetNode)
	}
	if n.On != nil {
		node, ok = n.On.Accept(v)
		if !ok {
			return n, false
		}
		n.On = node.(*OnCondition)
	}
	return v.Leave(n)
}

// TableName represents a table name.
type TableName struct {
	node
	resultSetNode

	Schema model.CIStr
	Name   model.CIStr

	DBInfo    *model.DBInfo
	TableInfo *model.TableInfo

	IndexHints []*IndexHint
}

// Restore implements Node interface.
func (n *TableName) Restore(ctx *RestoreCtx) error {
	if n.Schema.String() != "" {
		ctx.WriteName(n.Schema.String())
		ctx.WritePlain(".")
	}
	ctx.WriteName(n.Name.String())
	for _, value := range n.IndexHints {
		ctx.WritePlain(" ")
		if err := value.Restore(ctx); err != nil {
			return errors.Annotate(err, "An error occurred while splicing IndexHints")
		}
	}
	return nil
}

// IndexHintType is the type for index hint use, ignore or force.
type IndexHintType int

// IndexHintUseType values.
const (
	HintUse    IndexHintType = 1
	HintIgnore IndexHintType = 2
	HintForce  IndexHintType = 3
)

// IndexHintScope is the type for index hint for join, order by or group by.
type IndexHintScope int

// Index hint scopes.
const (
	HintForScan    IndexHintScope = 1
	HintForJoin    IndexHintScope = 2
	HintForOrderBy IndexHintScope = 3
	HintForGroupBy IndexHintScope = 4
)

// IndexHint represents a hint for optimizer to use/ignore/force for join/order by/group by.
type IndexHint struct {
	IndexNames []model.CIStr
	HintType   IndexHintType
	HintScope  IndexHintScope
}

// IndexHint Restore (The const field uses switch to facilitate understanding)
func (n *IndexHint) Restore(ctx *RestoreCtx) error {
	indexHintType := ""
	switch n.HintType {
	case 1:
		indexHintType = "USE INDEX"
	case 2:
		indexHintType = "IGNORE INDEX"
	case 3:
		indexHintType = "FORCE INDEX"
	default: // Prevent accidents
		return errors.New("IndexHintType has an error while matching")
	}

	indexHintScope := ""
	switch n.HintScope {
	case 1:
		indexHintScope = ""
	case 2:
		indexHintScope = " FOR JOIN"
	case 3:
		indexHintScope = " FOR ORDER BY"
	case 4:
		indexHintScope = " FOR GROUP BY"
	default: // Prevent accidents
		return errors.New("IndexHintScope has an error while matching")
	}
	ctx.WriteKeyWord(indexHintType)
	ctx.WriteKeyWord(indexHintScope)
	ctx.WritePlain(" (")
	for i, value := range n.IndexNames {
		if i > 0 {
			ctx.WritePlain(", ")
		}
		ctx.WriteName(value.O)
	}
	ctx.WritePlain(")")

	return nil
}

// Accept implements Node Accept interface.
func (n *TableName) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*TableName)
	return v.Leave(n)
}

// DeleteTableList is the tablelist used in delete statement multi-table mode.
type DeleteTableList struct {
	node
	Tables []*TableName
}

// Restore implements Node interface.
func (n *DeleteTableList) Restore(ctx *RestoreCtx) error {
	for i, t := range n.Tables {
		if i != 0 {
			ctx.WritePlain(",")
		}
		if err := t.Restore(ctx); err != nil {
			return errors.Annotatef(err, "An error occurred while restore DeleteTableList.Tables[%v]", i)
		}
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *DeleteTableList) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*DeleteTableList)
	if n != nil {
		for i, t := range n.Tables {
			node, ok := t.Accept(v)
			if !ok {
				return n, false
			}
			n.Tables[i] = node.(*TableName)
		}
	}
	return v.Leave(n)
}

// OnCondition represents JOIN on condition.
type OnCondition struct {
	node

	Expr ExprNode
}

// Restore implements Node interface.
func (n *OnCondition) Restore(ctx *RestoreCtx) error {
	ctx.WriteKeyWord("ON ")
	if err := n.Expr.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore OnCondition.Expr")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *OnCondition) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*OnCondition)
	node, ok := n.Expr.Accept(v)
	if !ok {
		return n, false
	}
	n.Expr = node.(ExprNode)
	return v.Leave(n)
}

// TableSource represents table source with a name.
type TableSource struct {
	node

	// Source is the source of the data, can be a TableName,
	// a SelectStmt, a UnionStmt, or a JoinNode.
	Source ResultSetNode

	// AsName is the alias name of the table source.
	AsName model.CIStr
}

// Restore implements Node interface.
func (n *TableSource) Restore(ctx *RestoreCtx) error {
	needParen := false
	switch n.Source.(type) {
	case *SelectStmt, *UnionStmt:
		needParen = true
	}
	if needParen {
		ctx.WritePlain("(")
	}
	if err := n.Source.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore TableSource.Source")
	}
	if needParen {
		ctx.WritePlain(")")
	}
	if asName := n.AsName.String(); asName != "" {
		ctx.WriteKeyWord(" AS ")
		ctx.WriteName(asName)
	}

	return nil
}

// Accept implements Node Accept interface.
func (n *TableSource) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*TableSource)
	node, ok := n.Source.Accept(v)
	if !ok {
		return n, false
	}
	n.Source = node.(ResultSetNode)
	return v.Leave(n)
}

// SelectLockType is the lock type for SelectStmt.
type SelectLockType int

// Select lock types.
const (
	SelectLockNone SelectLockType = iota
	SelectLockForUpdate
	SelectLockInShareMode
)

// String implements fmt.Stringer.
func (slt SelectLockType) String() string {
	switch slt {
	case SelectLockNone:
		return "none"
	case SelectLockForUpdate:
		return "for update"
	case SelectLockInShareMode:
		return "in share mode"
	}
	return "unsupported select lock type"
}

// WildCardField is a special type of select field content.
type WildCardField struct {
	node

	Table  model.CIStr
	Schema model.CIStr
}

// Restore implements Node interface.
func (n *WildCardField) Restore(ctx *RestoreCtx) error {
	if schema := n.Schema.String(); schema != "" {
		ctx.WriteName(schema)
		ctx.WritePlain(".")
	}
	if table := n.Table.String(); table != "" {
		ctx.WriteName(table)
		ctx.WritePlain(".")
	}
	ctx.WritePlain("*")
	return nil
}

// Accept implements Node Accept interface.
func (n *WildCardField) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*WildCardField)
	return v.Leave(n)
}

// SelectField represents fields in select statement.
// There are two type of select field: wildcard
// and expression with optional alias name.
type SelectField struct {
	node

	// Offset is used to get original text.
	Offset int
	// WildCard is not nil, Expr will be nil.
	WildCard *WildCardField
	// Expr is not nil, WildCard will be nil.
	Expr ExprNode
	// AsName is alias name for Expr.
	AsName model.CIStr
	// Auxiliary stands for if this field is auxiliary.
	// When we add a Field into SelectField list which is used for having/orderby clause but the field is not in select clause,
	// we should set its Auxiliary to true. Then the TrimExec will trim the field.
	Auxiliary bool
}

// Restore implements Node interface.
func (n *SelectField) Restore(ctx *RestoreCtx) error {
	if n.WildCard != nil {
		if err := n.WildCard.Restore(ctx); err != nil {
			return errors.Annotate(err, "An error occurred while restore SelectField.WildCard")
		}
	}
	if n.Expr != nil {
		if err := n.Expr.Restore(ctx); err != nil {
			return errors.Annotate(err, "An error occurred while restore SelectField.Expr")
		}
	}
	if asName := n.AsName.String(); asName != "" {
		ctx.WriteKeyWord(" AS ")
		ctx.WriteName(asName)
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *SelectField) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*SelectField)
	if n.Expr != nil {
		node, ok := n.Expr.Accept(v)
		if !ok {
			return n, false
		}
		n.Expr = node.(ExprNode)
	}
	return v.Leave(n)
}

// FieldList represents field list in select statement.
type FieldList struct {
	node

	Fields []*SelectField
}

// Restore implements Node interface.
func (n *FieldList) Restore(ctx *RestoreCtx) error {
	for i, v := range n.Fields {
		if i != 0 {
			ctx.WritePlain(", ")
		}
		if err := v.Restore(ctx); err != nil {
			return errors.Annotatef(err, "An error occurred while restore FieldList.Fields[%d]", i)
		}
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *FieldList) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*FieldList)
	for i, val := range n.Fields {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Fields[i] = node.(*SelectField)
	}
	return v.Leave(n)
}

// TableRefsClause represents table references clause in dml statement.
type TableRefsClause struct {
	node

	TableRefs *Join
}

// Restore implements Node interface.
func (n *TableRefsClause) Restore(ctx *RestoreCtx) error {
	if err := n.TableRefs.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore TableRefsClause.TableRefs")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *TableRefsClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*TableRefsClause)
	node, ok := n.TableRefs.Accept(v)
	if !ok {
		return n, false
	}
	n.TableRefs = node.(*Join)
	return v.Leave(n)
}

// ByItem represents an item in order by or group by.
type ByItem struct {
	node

	Expr ExprNode
	Desc bool
}

// Restore implements Node interface.
func (n *ByItem) Restore(ctx *RestoreCtx) error {
	if err := n.Expr.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore ByItem.Expr")
	}
	if n.Desc {
		ctx.WriteKeyWord(" DESC")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *ByItem) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*ByItem)
	node, ok := n.Expr.Accept(v)
	if !ok {
		return n, false
	}
	n.Expr = node.(ExprNode)
	return v.Leave(n)
}

// GroupByClause represents group by clause.
type GroupByClause struct {
	node
	Items []*ByItem
}

// Restore implements Node interface.
func (n *GroupByClause) Restore(ctx *RestoreCtx) error {
	ctx.WriteKeyWord("GROUP BY ")
	for i, v := range n.Items {
		if i != 0 {
			ctx.WritePlain(",")
		}
		if err := v.Restore(ctx); err != nil {
			return errors.Annotatef(err, "An error occurred while restore GroupByClause.Items[%d]", i)
		}
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *GroupByClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*GroupByClause)
	for i, val := range n.Items {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Items[i] = node.(*ByItem)
	}
	return v.Leave(n)
}

// HavingClause represents having clause.
type HavingClause struct {
	node
	Expr ExprNode
}

// Restore implements Node interface.
func (n *HavingClause) Restore(ctx *RestoreCtx) error {
	ctx.WriteKeyWord("HAVING ")
	if err := n.Expr.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore HavingClause.Expr")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *HavingClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*HavingClause)
	node, ok := n.Expr.Accept(v)
	if !ok {
		return n, false
	}
	n.Expr = node.(ExprNode)
	return v.Leave(n)
}

// OrderByClause represents order by clause.
type OrderByClause struct {
	node
	Items    []*ByItem
	ForUnion bool
}

// Restore implements Node interface.
func (n *OrderByClause) Restore(ctx *RestoreCtx) error {
	ctx.WriteKeyWord("ORDER BY ")
	for i, item := range n.Items {
		if i != 0 {
			ctx.WritePlain(",")
		}
		if err := item.Restore(ctx); err != nil {
			return errors.Annotatef(err, "An error occurred while restore OrderByClause.Items[%d]", i)
		}
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *OrderByClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*OrderByClause)
	for i, val := range n.Items {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Items[i] = node.(*ByItem)
	}
	return v.Leave(n)
}

// SelectStmt represents the select query node.
// See https://dev.mysql.com/doc/refman/5.7/en/select.html
type SelectStmt struct {
	dmlNode
	resultSetNode

	// SelectStmtOpts wraps around select hints and switches.
	*SelectStmtOpts
	// Distinct represents whether the select has distinct option.
	Distinct bool
	// From is the from clause of the query.
	From *TableRefsClause
	// Where is the where clause in select statement.
	Where ExprNode
	// Fields is the select expression list.
	Fields *FieldList
	// GroupBy is the group by expression list.
	GroupBy *GroupByClause
	// Having is the having condition.
	Having *HavingClause
	// WindowSpecs is the window specification list.
	WindowSpecs []WindowSpec
	// OrderBy is the ordering expression list.
	OrderBy *OrderByClause
	// Limit is the limit clause.
	Limit *Limit
	// LockTp is the lock type
	LockTp SelectLockType
	// TableHints represents the table level Optimizer Hint for join type
	TableHints []*TableOptimizerHint
	// IsAfterUnionDistinct indicates whether it's a stmt after "union distinct".
	IsAfterUnionDistinct bool
	// IsInBraces indicates whether it's a stmt in brace.
	IsInBraces bool
}

// Restore implements Node interface.
func (n *SelectStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *SelectStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}

	n = newNode.(*SelectStmt)
	if n.TableHints != nil && len(n.TableHints) != 0 {
		newHints := make([]*TableOptimizerHint, len(n.TableHints))
		for i, hint := range n.TableHints {
			node, ok := hint.Accept(v)
			if !ok {
				return n, false
			}
			newHints[i] = node.(*TableOptimizerHint)
		}
		n.TableHints = newHints
	}

	if n.From != nil {
		node, ok := n.From.Accept(v)
		if !ok {
			return n, false
		}
		n.From = node.(*TableRefsClause)
	}

	if n.Where != nil {
		node, ok := n.Where.Accept(v)
		if !ok {
			return n, false
		}
		n.Where = node.(ExprNode)
	}

	if n.Fields != nil {
		node, ok := n.Fields.Accept(v)
		if !ok {
			return n, false
		}
		n.Fields = node.(*FieldList)
	}

	if n.GroupBy != nil {
		node, ok := n.GroupBy.Accept(v)
		if !ok {
			return n, false
		}
		n.GroupBy = node.(*GroupByClause)
	}

	if n.Having != nil {
		node, ok := n.Having.Accept(v)
		if !ok {
			return n, false
		}
		n.Having = node.(*HavingClause)
	}

	for i, spec := range n.WindowSpecs {
		node, ok := spec.Accept(v)
		if !ok {
			return n, false
		}
		n.WindowSpecs[i] = *node.(*WindowSpec)
	}

	if n.OrderBy != nil {
		node, ok := n.OrderBy.Accept(v)
		if !ok {
			return n, false
		}
		n.OrderBy = node.(*OrderByClause)
	}

	if n.Limit != nil {
		node, ok := n.Limit.Accept(v)
		if !ok {
			return n, false
		}
		n.Limit = node.(*Limit)
	}

	return v.Leave(n)
}

// UnionSelectList represents the select list in a union statement.
type UnionSelectList struct {
	node

	Selects []*SelectStmt
}

// Restore implements Node interface.
func (n *UnionSelectList) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *UnionSelectList) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*UnionSelectList)
	for i, sel := range n.Selects {
		node, ok := sel.Accept(v)
		if !ok {
			return n, false
		}
		n.Selects[i] = node.(*SelectStmt)
	}
	return v.Leave(n)
}

// UnionStmt represents "union statement"
// See https://dev.mysql.com/doc/refman/5.7/en/union.html
type UnionStmt struct {
	dmlNode
	resultSetNode

	SelectList *UnionSelectList
	OrderBy    *OrderByClause
	Limit      *Limit
}

// Restore implements Node interface.
func (n *UnionStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *UnionStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*UnionStmt)
	if n.SelectList != nil {
		node, ok := n.SelectList.Accept(v)
		if !ok {
			return n, false
		}
		n.SelectList = node.(*UnionSelectList)
	}
	if n.OrderBy != nil {
		node, ok := n.OrderBy.Accept(v)
		if !ok {
			return n, false
		}
		n.OrderBy = node.(*OrderByClause)
	}
	if n.Limit != nil {
		node, ok := n.Limit.Accept(v)
		if !ok {
			return n, false
		}
		n.Limit = node.(*Limit)
	}
	return v.Leave(n)
}

// Assignment is the expression for assignment, like a = 1.
type Assignment struct {
	node
	// Column is the column name to be assigned.
	Column *ColumnName
	// Expr is the expression assigning to ColName.
	Expr ExprNode
}

// Restore implements Node interface.
func (n *Assignment) Restore(ctx *RestoreCtx) error {
	if err := n.Column.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore Assignment.Column")
	}
	ctx.WritePlain("=")
	if err := n.Expr.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore Assignment.Expr")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *Assignment) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*Assignment)
	node, ok := n.Column.Accept(v)
	if !ok {
		return n, false
	}
	n.Column = node.(*ColumnName)
	node, ok = n.Expr.Accept(v)
	if !ok {
		return n, false
	}
	n.Expr = node.(ExprNode)
	return v.Leave(n)
}

// LoadDataStmt is a statement to load data from a specified file, then insert this rows into an existing table.
// See https://dev.mysql.com/doc/refman/5.7/en/load-data.html
type LoadDataStmt struct {
	dmlNode

	IsLocal     bool
	Path        string
	Table       *TableName
	Columns     []*ColumnName
	FieldsInfo  *FieldsClause
	LinesInfo   *LinesClause
	IgnoreLines uint64
}

// Restore implements Node interface.
func (n *LoadDataStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *LoadDataStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*LoadDataStmt)
	if n.Table != nil {
		node, ok := n.Table.Accept(v)
		if !ok {
			return n, false
		}
		n.Table = node.(*TableName)
	}
	for i, val := range n.Columns {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Columns[i] = node.(*ColumnName)
	}
	return v.Leave(n)
}

// FieldsClause represents fields references clause in load data statement.
type FieldsClause struct {
	Terminated string
	Enclosed   byte
	Escaped    byte
}

// LinesClause represents lines references clause in load data statement.
type LinesClause struct {
	Starting   string
	Terminated string
}

// InsertStmt is a statement to insert new rows into an existing table.
// See https://dev.mysql.com/doc/refman/5.7/en/insert.html
type InsertStmt struct {
	dmlNode

	IsReplace   bool
	IgnoreErr   bool
	Table       *TableRefsClause
	Columns     []*ColumnName
	Lists       [][]ExprNode
	Setlist     []*Assignment
	Priority    mysql.PriorityEnum
	OnDuplicate []*Assignment
	Select      ResultSetNode
}

// Restore implements Node interface.
func (n *InsertStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *InsertStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}

	n = newNode.(*InsertStmt)
	if n.Select != nil {
		node, ok := n.Select.Accept(v)
		if !ok {
			return n, false
		}
		n.Select = node.(ResultSetNode)
	}

	node, ok := n.Table.Accept(v)
	if !ok {
		return n, false
	}
	n.Table = node.(*TableRefsClause)

	for i, val := range n.Columns {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Columns[i] = node.(*ColumnName)
	}
	for i, list := range n.Lists {
		for j, val := range list {
			node, ok := val.Accept(v)
			if !ok {
				return n, false
			}
			n.Lists[i][j] = node.(ExprNode)
		}
	}
	for i, val := range n.Setlist {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Setlist[i] = node.(*Assignment)
	}
	for i, val := range n.OnDuplicate {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.OnDuplicate[i] = node.(*Assignment)
	}
	return v.Leave(n)
}

// DeleteStmt is a statement to delete rows from table.
// See https://dev.mysql.com/doc/refman/5.7/en/delete.html
type DeleteStmt struct {
	dmlNode

	// TableRefs is used in both single table and multiple table delete statement.
	TableRefs *TableRefsClause
	// Tables is only used in multiple table delete statement.
	Tables       *DeleteTableList
	Where        ExprNode
	Order        *OrderByClause
	Limit        *Limit
	Priority     mysql.PriorityEnum
	IgnoreErr    bool
	Quick        bool
	IsMultiTable bool
	BeforeFrom   bool
	// TableHints represents the table level Optimizer Hint for join type.
	TableHints []*TableOptimizerHint
}

// Restore implements Node interface.
func (n *DeleteStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *DeleteStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}

	n = newNode.(*DeleteStmt)
	node, ok := n.TableRefs.Accept(v)
	if !ok {
		return n, false
	}
	n.TableRefs = node.(*TableRefsClause)

	node, ok = n.Tables.Accept(v)
	if !ok {
		return n, false
	}
	n.Tables = node.(*DeleteTableList)

	if n.Where != nil {
		node, ok = n.Where.Accept(v)
		if !ok {
			return n, false
		}
		n.Where = node.(ExprNode)
	}
	if n.Order != nil {
		node, ok = n.Order.Accept(v)
		if !ok {
			return n, false
		}
		n.Order = node.(*OrderByClause)
	}
	if n.Limit != nil {
		node, ok = n.Limit.Accept(v)
		if !ok {
			return n, false
		}
		n.Limit = node.(*Limit)
	}
	return v.Leave(n)
}

// UpdateStmt is a statement to update columns of existing rows in tables with new values.
// See https://dev.mysql.com/doc/refman/5.7/en/update.html
type UpdateStmt struct {
	dmlNode

	TableRefs     *TableRefsClause
	List          []*Assignment
	Where         ExprNode
	Order         *OrderByClause
	Limit         *Limit
	Priority      mysql.PriorityEnum
	IgnoreErr     bool
	MultipleTable bool
	TableHints    []*TableOptimizerHint
}

// Restore implements Node interface.
func (n *UpdateStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *UpdateStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*UpdateStmt)
	node, ok := n.TableRefs.Accept(v)
	if !ok {
		return n, false
	}
	n.TableRefs = node.(*TableRefsClause)
	for i, val := range n.List {
		node, ok = val.Accept(v)
		if !ok {
			return n, false
		}
		n.List[i] = node.(*Assignment)
	}
	if n.Where != nil {
		node, ok = n.Where.Accept(v)
		if !ok {
			return n, false
		}
		n.Where = node.(ExprNode)
	}
	if n.Order != nil {
		node, ok = n.Order.Accept(v)
		if !ok {
			return n, false
		}
		n.Order = node.(*OrderByClause)
	}
	if n.Limit != nil {
		node, ok = n.Limit.Accept(v)
		if !ok {
			return n, false
		}
		n.Limit = node.(*Limit)
	}
	return v.Leave(n)
}

// Limit is the limit clause.
type Limit struct {
	node

	Count  ExprNode
	Offset ExprNode
}

// Restore implements Node interface.
func (n *Limit) Restore(ctx *RestoreCtx) error {
	ctx.WriteKeyWord("LIMIT ")
	if n.Offset != nil {
		if err := n.Offset.Restore(ctx); err != nil {
			return errors.Annotate(err, "An error occurred while restore Limit.Offset")
		}
		ctx.WritePlain(",")
	}
	if err := n.Count.Restore(ctx); err != nil {
		return errors.Annotate(err, "An error occurred while restore Limit.Count")
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *Limit) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	if n.Count != nil {
		node, ok := n.Count.Accept(v)
		if !ok {
			return n, false
		}
		n.Count = node.(ExprNode)
	}
	if n.Offset != nil {
		node, ok := n.Offset.Accept(v)
		if !ok {
			return n, false
		}
		n.Offset = node.(ExprNode)
	}

	n = newNode.(*Limit)
	return v.Leave(n)
}

// ShowStmtType is the type for SHOW statement.
type ShowStmtType int

// Show statement types.
const (
	ShowNone = iota
	ShowEngines
	ShowDatabases
	ShowTables
	ShowTableStatus
	ShowColumns
	ShowWarnings
	ShowCharset
	ShowVariables
	ShowStatus
	ShowCollation
	ShowCreateTable
	ShowGrants
	ShowTriggers
	ShowProcedureStatus
	ShowIndex
	ShowProcessList
	ShowCreateDatabase
	ShowEvents
	ShowStatsMeta
	ShowStatsHistograms
	ShowStatsBuckets
	ShowStatsHealthy
	ShowPlugins
	ShowProfiles
	ShowMasterStatus
	ShowPrivileges
	ShowErrors
)

// ShowStmt is a statement to provide information about databases, tables, columns and so on.
// See https://dev.mysql.com/doc/refman/5.7/en/show.html
type ShowStmt struct {
	dmlNode
	resultSetNode

	Tp          ShowStmtType // Databases/Tables/Columns/....
	DBName      string
	Table       *TableName  // Used for showing columns.
	Column      *ColumnName // Used for `desc table column`.
	Flag        int         // Some flag parsed from sql, such as FULL.
	Full        bool
	User        *auth.UserIdentity // Used for show grants.
	IfNotExists bool               // Used for `show create database if not exists`

	// GlobalScope is used by show variables
	GlobalScope bool
	Pattern     *PatternLikeExpr
	Where       ExprNode
}

// Restore implements Node interface.
func (n *ShowStmt) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *ShowStmt) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*ShowStmt)
	if n.Table != nil {
		node, ok := n.Table.Accept(v)
		if !ok {
			return n, false
		}
		n.Table = node.(*TableName)
	}
	if n.Column != nil {
		node, ok := n.Column.Accept(v)
		if !ok {
			return n, false
		}
		n.Column = node.(*ColumnName)
	}
	if n.Pattern != nil {
		node, ok := n.Pattern.Accept(v)
		if !ok {
			return n, false
		}
		n.Pattern = node.(*PatternLikeExpr)
	}

	switch n.Tp {
	case ShowTriggers, ShowProcedureStatus, ShowProcessList, ShowEvents:
		// We don't have any data to return for those types,
		// but visiting Where may cause resolving error, so return here to avoid error.
		return v.Leave(n)
	}

	if n.Where != nil {
		node, ok := n.Where.Accept(v)
		if !ok {
			return n, false
		}
		n.Where = node.(ExprNode)
	}
	return v.Leave(n)
}

// WindowSpec is the specification of a window.
type WindowSpec struct {
	node

	Name model.CIStr
	// Ref is the reference window of this specification. For example, in `w2 as (w1 order by a)`,
	// the definition of `w2` references `w1`.
	Ref model.CIStr

	PartitionBy *PartitionByClause
	OrderBy     *OrderByClause
	Frame       *FrameClause
}

// Restore implements Node interface.
func (n *WindowSpec) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *WindowSpec) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*WindowSpec)
	if n.PartitionBy != nil {
		node, ok := n.PartitionBy.Accept(v)
		if !ok {
			return n, false
		}
		n.PartitionBy = node.(*PartitionByClause)
	}
	if n.OrderBy != nil {
		node, ok := n.OrderBy.Accept(v)
		if !ok {
			return n, false
		}
		n.OrderBy = node.(*OrderByClause)
	}
	if n.Frame != nil {
		node, ok := n.Frame.Accept(v)
		if !ok {
			return n, false
		}
		n.Frame = node.(*FrameClause)
	}
	return v.Leave(n)
}

// PartitionByClause represents partition by clause.
type PartitionByClause struct {
	node

	Items []*ByItem
}

// Restore implements Node interface.
func (n *PartitionByClause) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *PartitionByClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*PartitionByClause)
	for i, val := range n.Items {
		node, ok := val.Accept(v)
		if !ok {
			return n, false
		}
		n.Items[i] = node.(*ByItem)
	}
	return v.Leave(n)
}

// FrameType is the type of window function frame.
type FrameType int

// Window function frame types.
// MySQL only supports `ROWS` and `RANGES`.
const (
	Rows = iota
	Ranges
	Groups
)

// FrameClause represents frame clause.
type FrameClause struct {
	node

	Type   FrameType
	Extent FrameExtent
}

// Restore implements Node interface.
func (n *FrameClause) Restore(ctx *RestoreCtx) error {
	return errors.New("Not implemented")
}

// Accept implements Node Accept interface.
func (n *FrameClause) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*FrameClause)
	node, ok := n.Extent.Start.Accept(v)
	if !ok {
		return n, false
	}
	n.Extent.Start = *node.(*FrameBound)
	node, ok = n.Extent.End.Accept(v)
	if !ok {
		return n, false
	}
	n.Extent.End = *node.(*FrameBound)
	return v.Leave(n)
}

// FrameExtent represents frame extent.
type FrameExtent struct {
	Start FrameBound
	End   FrameBound
}

// FrameType is the type of window function frame bound.
type BoundType int

// Frame bound types.
const (
	Following = iota
	Preceding
	CurrentRow
)

// FrameBound represents frame bound.
type FrameBound struct {
	node

	Type      BoundType
	UnBounded bool
	Expr      ExprNode
	// `Unit` is used to indicate the units in which the `Expr` should be interpreted.
	// For example: '2:30' MINUTE_SECOND.
	Unit ExprNode
}

// Restore implements Node interface.
func (n *FrameBound) Restore(ctx *RestoreCtx) error {
	if n.UnBounded {
		ctx.WriteKeyWord("UNBOUNDED")
	}
	switch n.Type {
	case CurrentRow:
		ctx.WriteKeyWord("CURRENT ROW")
	case Preceding, Following:
		if n.Unit != nil {
			ctx.WriteKeyWord("INTERVAL ")
		}
		if n.Expr != nil {
			if err := n.Expr.Restore(ctx); err != nil {
				return errors.Annotate(err, "An error occurred while restore FrameBound.Expr")
			}
		}
		if n.Unit != nil {
			// Here the Unit string should not be quoted.
			// TODO: This is a temporary workaround that should be changed once something like "Keyword Expression" is implemented.
			var sb strings.Builder
			n.Unit.Restore(NewRestoreCtx(0, &sb))
			ctx.WritePlain(" ")
			ctx.WriteKeyWord(sb.String())
		}
		if n.Type == Preceding {
			ctx.WriteKeyWord(" PRECEDING")
		} else {
			ctx.WriteKeyWord(" FOLLOWING")
		}
	}
	return nil
}

// Accept implements Node Accept interface.
func (n *FrameBound) Accept(v Visitor) (Node, bool) {
	newNode, skipChildren := v.Enter(n)
	if skipChildren {
		return v.Leave(newNode)
	}
	n = newNode.(*FrameBound)
	if n.Expr != nil {
		node, ok := n.Expr.Accept(v)
		if !ok {
			return n, false
		}
		n.Expr = node.(ExprNode)
	}
	if n.Unit != nil {
		node, ok := n.Unit.Accept(v)
		if !ok {
			return n, false
		}
		n.Unit = node.(ExprNode)
	}
	return v.Leave(n)
}