sq/libsq/ast/node.go

package ast

import (
	"fmt"
	"io"
	"reflect"
	"strings"

	antlr "github.com/antlr4-go/antlr/v4"
)

// Node is an AST node.
type Node interface {
	// ast returns the root AST node, or nil.
	ast() *AST

	// context returns the parse tree context.
	context() antlr.ParseTree

	// setContext sets the parse tree context, returning an error if illegal.
	setContext(ctx antlr.ParseTree) error

	// Parent returns the node's parent, which may be nil..
	Parent() Node

	// SetParent sets the node's parent, returning an error if illegal.
	SetParent(n Node) error

	// Children returns the node's children (which may be empty).
	Children() []Node

	// SetChildren sets the node's children, returning an error if illegal.
	SetChildren(children []Node) error

	// AddChild adds a child node, returning an error if illegal.
	AddChild(child Node) error

	// Text returns the node's raw text value.
	Text() string

	// String returns a debug-friendly string representation.
	String() string
}

// Selector is a Node marker interface for selector node types. A selector node
// models a selector such as ".first_name" or ".actor.last_name".
type Selector interface {
	Node
	selector()
}

// ResultColumn indicates a column selection expression Node such as a
// column name, or context-appropriate function, e.g. "COUNT(*)".
// See: https://www.sqlite.org/syntax/result-column.html
type ResultColumn interface {
	Node

	// String returns a log/debug-friendly representation.
	String() string

	// Alias returns the column alias, which may be empty.
	// For example, given the selector ".first_name:given_name", the
	// alias is "given_name".
	Alias() string

	// Text returns the raw text of the node, e.g. ".actor" or "1*2".
	Text() string

	resultColumn()
}

// baseNode is a base implementation of Node.
type baseNode struct {
	parent   Node
	ctx      antlr.ParseTree
	text     string
	children []Node
}

// ast implements ast.Node.
func (bn *baseNode) ast() *AST {
	if bn == nil {
		return nil
	}
	n := NodeRoot(bn.parent)
	if n == nil {
		return nil
	}

	if ast, ok := n.(*AST); ok {
		return ast
	}
	return nil
}

// Parent implements ast.Node.
func (bn *baseNode) Parent() Node {
	return bn.parent
}

// SetParent implements ast.Node.
func (bn *baseNode) SetParent(parent Node) error {
	bn.parent = parent
	return nil
}

// Children implements ast.Node.
func (bn *baseNode) Children() []Node {
	return bn.children
}

// AddChild always returns an error. Node implementations should
// implement a type-specific method that only accepts a child of
// an appropriate type for that node.
func (bn *baseNode) AddChild(child Node) error {
	return errorf(msgNodeNoAddChild, bn, child)
}

func (bn *baseNode) addChild(child Node) {
	// REVISIT: Why not call setParent() on child?
	// TODO: add child could be a generic function, returning
	// and error if the child is not of an appropriate type.
	bn.children = append(bn.children, child)
}

// SetChildren implements ast.Node. It always returns an error.
// Node implementations must provide their own type-specific
// implementation if they accept children.
func (bn *baseNode) SetChildren(children []Node) error {
	return errorf(msgNodeNoAddChildren, bn, len(children))
}

func (bn *baseNode) doSetChildren(children []Node) {
	// REVISIT: Why not call setParent() on each child?
	// TODO: doSetChildren could be a generic function, returning
	// and error if the children are not of an appropriate type.
	bn.children = children
}

// Text implements ast.Node.
func (bn *baseNode) Text() string {
	if bn.ctx == nil {
		return ""
	}

	return bn.ctx.GetText()
}

// context implements ast.Node.
func (bn *baseNode) context() antlr.ParseTree {
	return bn.ctx
}

// setContext implements ast.Node.
func (bn *baseNode) setContext(ctx antlr.ParseTree) error {
	bn.ctx = ctx
	return nil
}

// nodeString returns a default value suitable for use by Node.String().
func nodeString(n Node) string {
	return fmt.Sprintf("%T: %s", n, n.Text())
}

// nodeReplace replaces old with new. That is, nu becomes a child
// of old's parent.
func nodeReplace(old, nu Node) error {
	err := nu.setContext(old.context())
	if err != nil {
		return err
	}

	parent := old.Parent()

	index := nodeChildIndex(parent, old)
	if index < 0 {
		return errorf("parent %T(%s) does not appear to have child %T(%s)", parent, parent.Text(), old, old.Text())
	}
	siblings := parent.Children()
	siblings[index] = nu

	return parent.SetChildren(siblings)
}

// nodesAreOnlyOfType returns an error if the type of any non-nil element
// of nodes is not contained in types.
func nodesAreOnlyOfType(nodes []Node, types ...reflect.Type) error {
	m := map[reflect.Type]struct{}{}
	typeNames := make([]string, 0, len(types))
	for _, typ := range types {
		m[typ] = struct{}{}
		typeNames = append(typeNames, typ.Name())
	}

	for i, node := range nodes {
		if node == nil {
			continue
		}

		if _, ok := m[reflect.TypeOf(node)]; !ok {
			return errorf("node[%d] {%s} is not an allowed type in [%s]", i, node, strings.Join(typeNames, ", "))
		}
	}

	return nil
}

// NodeRoot returns the root node of the tree containing node.
// This returned node should be an *ast.AST.
func NodeRoot(node Node) Node {
	if node == nil {
		return nil
	}

	if node.Parent() == nil {
		return node
	}

	return NodeRoot(node.Parent())
}

// NodeNextSibling returns the node's next sibling, or nil.
func NodeNextSibling(node Node) Node {
	if node == nil {
		return nil
	}

	parent := node.Parent()
	if parent == nil {
		return nil
	}

	i := nodeChildIndex(parent, node)
	if i < 0 {
		return nil
	}

	children := parent.Children()
	if i >= len(children)-1 {
		return nil
	}

	return children[i+1]
}

// NodePrevSibling returns the node's previous sibling, or nil.
func NodePrevSibling(node Node) Node {
	if node == nil {
		return nil
	}

	parent := node.Parent()
	if parent == nil {
		return nil
	}

	i := nodeChildIndex(parent, node)
	if i < 1 {
		return nil
	}

	children := parent.Children()
	return children[i-1]
}

// NodesHavingText returns any node whose node.Text()
// method returns text.
func NodesHavingText(tree Node, text string) []Node {
	if tree == nil {
		return nil
	}

	var nodes []Node

	w := NewWalker(tree)
	w.AddVisitor(typeNode, func(w *Walker, node Node) error {
		nodeText := node.Text()
		if nodeText == text {
			nodes = append(nodes, node)
		}
		return nil
	})

	if err := w.Walk(); err != nil {
		panic(err)
	}
	return nodes
}

// nodeChildIndex returns the index of child in parent's children, or -1.
func nodeChildIndex(parent, child Node) int {
	for i, node := range parent.Children() {
		if node == child {
			return i
		}
	}

	return -1
}

// nodeFirstChild returns the first child of parent, or nil.
func nodeFirstChild(parent Node) Node { //nolint:unused
	if parent == nil {
		return nil
	}

	children := parent.Children()
	if len(children) == 0 {
		return nil
	}

	return children[0]
}

// nodeFirstChild returns the last child of parent, or nil.
func nodeLastChild(parent Node) Node {
	if parent == nil {
		return nil
	}

	children := parent.Children()
	if len(children) == 0 {
		return nil
	}

	return children[len(children)-1]
}

// nodesWithType returns a new slice containing each member of nodes that is
// of the specified type.
func nodesWithType(nodes []Node, typ reflect.Type) []Node {
	s := make([]Node, 0)

	for _, n := range nodes {
		if reflect.TypeOf(n) == typ {
			s = append(s, n)
		}
	}
	return s
}

// NodeUnwrap "unwraps" node returning the lowest single contained node.
// False is returned if node (or any of its descendants), has more than one
// child. If node has no children, it is returned directly. This function
// is useful for "unwrapping" a node that is contained in an outer node. For
// example, an ExprNode may often contain just a single LiteralNode.
func NodeUnwrap[T Node](node Node) (T, bool) {
	var result T
	var ok bool
	if node == nil {
		return result, false
	}

	var children []Node
	for {
		children = node.Children()
		switch len(children) {
		case 0:
			result, ok = node.(T)
			return result, ok
		case 1:
			node = children[0]
			continue
		default:
			return result, false
		}
	}
}

// FindNodes returns the nodes of type T in ast.
func FindNodes[T Node](ast *AST) []T {
	var nodes []T
	if ast == nil {
		return nodes
	}
	w := NewWalker(ast)
	w.AddVisitor(reflect.TypeOf((*T)(nil)).Elem(), func(w *Walker, node Node) error {
		nodes = append(nodes, node.(T))
		return nil
	})

	_ = w.Walk()
	return nodes
}

// FindFirstNode returns the first node of type T in ast, or
// nil if no such node exists.
func FindFirstNode[T Node](ast *AST) T {
	var node T
	w := NewWalker(ast)
	w.AddVisitor(reflect.TypeOf((*T)(nil)).Elem(), func(w *Walker, n Node) error {
		node, _ = n.(T)
		return io.EOF // Return any error to halt the walk.
	})

	_ = w.Walk()
	return node
}

// NodePrevSegmentChild returns the first child of the
// previous segment, where the child must be of type T, or
// an error if the child is not of type T.
func NodePrevSegmentChild[T Node](node Node) (T, error) {
	var (
		result T
		parent Node
		seg    *SegmentNode
		ok     bool
	)

	if node == nil {
		return result, errorf("node is nil")
	}

	seg, ok = node.(*SegmentNode)
	if !ok {
		for {
			parent = node.Parent()
			if parent == nil {
				return result, errorf("unable to find segment in node {%T} ancestry", node)
			}

			seg, ok = parent.(*SegmentNode)
			if ok {
				break
			}

			if seg == nil {
				// Can't happen?
				return result, errorf("unable to find segment in node {%T} ancestry", node)
			}
		}
	}

	prevSeg := seg.Prev()
	if prevSeg == nil {
		return result, errorf("expected preceding segment")
	}

	prevSegChildren := prevSeg.Children()
	if len(prevSegChildren) == 0 {
		return result, errorf("expected preceding segment to have children")
	}

	result, ok = prevSegChildren[0].(T)
	if ok {
		return result, nil
	}

	return result, errorf("expected preceding segment to have child of type {%T} but got {%T}",
		result, prevSegChildren[0])
}

// Results from reflect.TypeOf for node types.
var (
	typeAST                = reflect.TypeOf((*AST)(nil))
	typeColSelectorNode    = reflect.TypeOf((*ColSelectorNode)(nil))
	typeExprNode           = reflect.TypeOf((*ExprNode)(nil))
	typeFuncNode           = reflect.TypeOf((*FuncNode)(nil))
	typeGroupByNode        = reflect.TypeOf((*GroupByNode)(nil))
	typeHavingNode         = reflect.TypeOf((*HavingNode)(nil))
	typeHandleNode         = reflect.TypeOf((*HandleNode)(nil))
	typeJoinNode           = reflect.TypeOf((*JoinNode)(nil))
	typeNode               = reflect.TypeOf((*Node)(nil)).Elem()
	_                      = reflect.TypeOf((*OperatorNode)(nil))
	typeOrderByNode        = reflect.TypeOf((*OrderByNode)(nil))
	typeRowRangeNode       = reflect.TypeOf((*RowRangeNode)(nil))
	typeSegmentNode        = reflect.TypeOf((*SegmentNode)(nil))
	_                      = reflect.TypeOf((*Selector)(nil)).Elem()
	typeSelectorNode       = reflect.TypeOf((*SelectorNode)(nil))
	typeTblColSelectorNode = reflect.TypeOf((*TblColSelectorNode)(nil))
	typeTblSelectorNode    = reflect.TypeOf((*TblSelectorNode)(nil))
	typeUniqueNode         = reflect.TypeOf((*UniqueNode)(nil))
)