blackfriday/node.go

package blackfriday

import (
	"bytes"
	"fmt"
)

// NodeType specifies a type of a single node of a syntax tree. Usually one
// node (and its type) corresponds to a single markdown feature, e.g. emphasis
// or code block.
type NodeType int

// Constants for identifying different types of nodes. See NodeType.
const (
	Document NodeType = iota
	BlockQuote
	List
	Item
	Paragraph
	Header
	HorizontalRule
	Emph
	Strong
	Del
	Link
	Image
	Text
	HTMLBlock
	CodeBlock
	Softbreak
	Hardbreak
	Code
	HTMLSpan
	Table
	TableCell
	TableHead
	TableBody
	TableRow
)

var nodeTypeNames = []string{
	Document:       "Document",
	BlockQuote:     "BlockQuote",
	List:           "List",
	Item:           "Item",
	Paragraph:      "Paragraph",
	Header:         "Header",
	HorizontalRule: "HorizontalRule",
	Emph:           "Emph",
	Strong:         "Strong",
	Del:            "Del",
	Link:           "Link",
	Image:          "Image",
	Text:           "Text",
	HTMLBlock:      "HTMLBlock",
	CodeBlock:      "CodeBlock",
	Softbreak:      "Softbreak",
	Hardbreak:      "Hardbreak",
	Code:           "Code",
	HTMLSpan:       "HTMLSpan",
	Table:          "Table",
	TableCell:      "TableCell",
	TableHead:      "TableHead",
	TableBody:      "TableBody",
	TableRow:       "TableRow",
}

func (t NodeType) String() string {
	return nodeTypeNames[t]
}

// ListData contains fields relevant to a List and Item node type.
type ListData struct {
	ListFlags       ListType
	Tight           bool   // Skip <p>s around list item data if true
	BulletChar      byte   // '*', '+' or '-' in bullet lists
	Delimiter       byte   // '.' or ')' after the number in ordered lists
	RefLink         []byte // If not nil, turns this list item into a footnote item and triggers different rendering
	IsFootnotesList bool   // This is a list of footnotes
}

// LinkData contains fields relevant to a Link node type.
type LinkData struct {
	Destination []byte // Destination is what goes into a href
	Title       []byte // Title is the tooltip thing that goes in a title attribute
	NoteID      int    // NoteID contains a serial number of a footnote, zero if it's not a footnote
	Footnote    *Node  // If it's a footnote, this is a direct link to the footnote Node. Otherwise nil.
}

// CodeBlockData contains fields relevant to a CodeBlock node type.
type CodeBlockData struct {
	IsFenced    bool   // Specifies whether it's a fenced code block or an indented one
	Info        []byte // This holds the info string
	FenceChar   byte
	FenceLength int
	FenceOffset int
}

// TableCellData contains fields relevant to a TableCell node type.
type TableCellData struct {
	IsHeader bool           // This tells if it's under the header row
	Align    CellAlignFlags // This holds the value for align attribute
}

// HeaderData contains fields relevant to a Header node type.
type HeaderData struct {
	Level        int    // This holds the heading level number
	HeaderID     string // This might hold header ID, if present
	IsTitleblock bool   // Specifies whether it's a title block
}

// Node is a single element in the abstract syntax tree of the parsed document.
// It holds connections to the structurally neighboring nodes and, for certain
// types of nodes, additional information that might be needed when rendering.
type Node struct {
	Type       NodeType // Determines the type of the node
	Parent     *Node    // Points to the parent
	FirstChild *Node    // Points to the first child, if any
	LastChild  *Node    // Points to the last child, if any
	Prev       *Node    // Previous sibling; nil if it's the first child
	Next       *Node    // Next sibling; nil if it's the last child

	Literal []byte // Text contents of the leaf nodes

	HeaderData    // Populated if Type is Header
	ListData      // Populated if Type is List
	CodeBlockData // Populated if Type is CodeBlock
	LinkData      // Populated if Type is Link
	TableCellData // Populated if Type is TableCell

	content []byte // Markdown content of the block nodes
	open    bool   // Specifies an open block node that has not been finished to process yet
}

// NewNode allocates a node of a specified type.
func NewNode(typ NodeType) *Node {
	return &Node{
		Type: typ,
		open: true,
	}
}

func (n *Node) String() string {
	ellipsis := ""
	snippet := n.Literal
	if len(snippet) > 16 {
		snippet = snippet[:16]
		ellipsis = "..."
	}
	return fmt.Sprintf("%s: '%s%s'", n.Type, snippet, ellipsis)
}

// Unlink removes node 'n' from the tree.
// It panics if the node is nil.
func (n *Node) Unlink() {
	if n.Prev != nil {
		n.Prev.Next = n.Next
	} else if n.Parent != nil {
		n.Parent.FirstChild = n.Next
	}
	if n.Next != nil {
		n.Next.Prev = n.Prev
	} else if n.Parent != nil {
		n.Parent.LastChild = n.Prev
	}
	n.Parent = nil
	n.Next = nil
	n.Prev = nil
}

// AppendChild adds a node 'child' as a child of 'n'.
// It panics if either node is nil.
func (n *Node) AppendChild(child *Node) {
	child.Unlink()
	child.Parent = n
	if n.LastChild != nil {
		n.LastChild.Next = child
		child.Prev = n.LastChild
		n.LastChild = child
	} else {
		n.FirstChild = child
		n.LastChild = child
	}
}

// InsertBefore inserts 'sibling' immediately before 'n'.
// It panics if either node is nil.
func (n *Node) InsertBefore(sibling *Node) {
	sibling.Unlink()
	sibling.Prev = n.Prev
	if sibling.Prev != nil {
		sibling.Prev.Next = sibling
	}
	sibling.Next = n
	n.Prev = sibling
	sibling.Parent = n.Parent
	if sibling.Prev == nil {
		sibling.Parent.FirstChild = sibling
	}
}

func (n *Node) isContainer() bool {
	switch n.Type {
	case Document:
		fallthrough
	case BlockQuote:
		fallthrough
	case List:
		fallthrough
	case Item:
		fallthrough
	case Paragraph:
		fallthrough
	case Header:
		fallthrough
	case Emph:
		fallthrough
	case Strong:
		fallthrough
	case Del:
		fallthrough
	case Link:
		fallthrough
	case Image:
		fallthrough
	case Table:
		fallthrough
	case TableHead:
		fallthrough
	case TableBody:
		fallthrough
	case TableRow:
		fallthrough
	case TableCell:
		return true
	default:
		return false
	}
}

func (n *Node) canContain(t NodeType) bool {
	if n.Type == List {
		return t == Item
	}
	if n.Type == Document || n.Type == BlockQuote || n.Type == Item {
		return t != Item
	}
	if n.Type == Table {
		return t == TableHead || t == TableBody
	}
	if n.Type == TableHead || n.Type == TableBody {
		return t == TableRow
	}
	if n.Type == TableRow {
		return t == TableCell
	}
	return false
}

// WalkStatus allows NodeVisitor to have some control over the tree traversal.
// It is returned from NodeVisitor and different values allow Node.Walk to
// decide which node to go to next.
type WalkStatus int

const (
	// GoToNext is the default traversal of every node.
	GoToNext WalkStatus = iota
	// SkipChildren tells walker to skip all children of current node.
	SkipChildren
	// Terminate tells walker to terminate the traversal.
	Terminate
)

// NodeVisitor is a callback to be called when traversing the syntax tree.
// Called twice for every node: once with entering=true when the branch is
// first visited, then with entering=false after all the children are done.
type NodeVisitor func(node *Node, entering bool) WalkStatus

// Walk is a convenience method that instantiates a walker and starts a
// traversal of subtree rooted at n.
func (n *Node) Walk(visitor NodeVisitor) {
	w := newNodeWalker(n)
	for w.current != nil {
		status := visitor(w.current, w.entering)
		switch status {
		case GoToNext:
			w.next()
		case SkipChildren:
			w.entering = false
			w.next()
		case Terminate:
			return
		}
	}
}

type nodeWalker struct {
	current  *Node
	root     *Node
	entering bool
}

func newNodeWalker(root *Node) *nodeWalker {
	return &nodeWalker{
		current:  root,
		root:     root,
		entering: true,
	}
}

func (nw *nodeWalker) next() {
	if (!nw.current.isContainer() || !nw.entering) && nw.current == nw.root {
		nw.current = nil
		return
	}
	if nw.entering && nw.current.isContainer() {
		if nw.current.FirstChild != nil {
			nw.current = nw.current.FirstChild
			nw.entering = true
		} else {
			nw.entering = false
		}
	} else if nw.current.Next == nil {
		nw.current = nw.current.Parent
		nw.entering = false
	} else {
		nw.current = nw.current.Next
		nw.entering = true
	}
}

func dump(ast *Node) {
	fmt.Println(dumpString(ast))
}

func dumpR(ast *Node, depth int) string {
	if ast == nil {
		return ""
	}
	indent := bytes.Repeat([]byte("\t"), depth)
	content := ast.Literal
	if content == nil {
		content = ast.content
	}
	result := fmt.Sprintf("%s%s(%q)\n", indent, ast.Type, content)
	for n := ast.FirstChild; n != nil; n = n.Next {
		result += dumpR(n, depth+1)
	}
	return result
}

func dumpString(ast *Node) string {
	return dumpR(ast, 0)
}