html/render.go

package html

import (
	"fmt"
	"io"
	"strings"
)

const (
	defaultPWidth = 112
	unicodeNBSP   = 0xa0
)

type renderGuide struct {
	inline         bool
	inlineChildren bool
	void           bool
	script         bool
	verbatim       bool
}

type renderer struct {
	out           io.Writer
	originalOut   io.Writer
	indent        Indentation
	pwidth        int
	currentIndent string
	err           error
}

func mergeRenderingGuides(rgs []renderGuide) renderGuide {
	var rg renderGuide
	for _, rgi := range rgs {
		rg.inline = rg.inline || rgi.inline
		rg.inlineChildren = rg.inlineChildren || rgi.inlineChildren
		rg.void = rg.void || rgi.void
		rg.script = rg.script || rgi.script
		rg.verbatim = rg.verbatim || rgi.verbatim
	}

	return rg
}

func attributeEscape(value string) string {
	var rr []rune
	r := []rune(value)
	for i := range r {
		switch r[i] {
		case '"':
			rr = append(rr, []rune(""")...)
		case '&':
			rr = append(rr, []rune("&")...)
		default:
			rr = append(rr, r[i])
		}
	}

	return string(rr)
}

func htmlEscape(s string) string {
	var (
		rr              []rune
		lastWS, wsStart bool
	)

	r := []rune(s)
	for i := range r {
		switch r[i] {
		case '<':
			rr = append(rr, []rune("&lt;")...)
		case '>':
			rr = append(rr, []rune("&gt;")...)
		case '&':
			rr = append(rr, []rune("&amp;")...)
		case unicodeNBSP:
			rr = append(rr, []rune("&nbsp;")...)
		case ' ':
			if wsStart && lastWS {
				rr = append(rr[:len(rr)-1], []rune("&nbsp;&nbsp;")...)
			} else if lastWS {
				rr = append(rr, []rune("&nbsp;")...)
			} else {
				rr = append(rr, r[i])
			}
		default:
			rr = append(rr, r[i])
		}

		ws := r[i] == ' '
		wsStart = ws && !lastWS
		lastWS = ws
	}

	return string(rr)
}

func indentLines(indent string, s string) string {
	l := strings.Split(s, "\n")
	for i := range l {
		l[i] = fmt.Sprintf("%s%s", indent, l[i])
	}

	return strings.Join(l, "\n")
}

func (r *renderer) getPrintf(tagName string) func(f string, a ...any) {
	return func(f string, a ...any) {
		if r.err != nil {
			return
		}

		_, r.err = fmt.Fprintf(r.out, f, a...)
		if r.err != nil {
			r.err = fmt.Errorf("tag %s: %w", tagName, r.err)
		}
	}
}

func (r *renderer) renderAttributes(tagName string, a []Attributes) {
	printf := r.getPrintf(tagName)
	for _, ai := range a {
		for name, value := range ai {
			printf(" %s=\"%s\"", name, attributeEscape(value))
		}
	}
}

func (r *renderer) renderUnindented(name string, rg renderGuide, a []Attributes, children []any) {
	printf := r.getPrintf(name)
	printf("<%s", name)
	r.renderAttributes(name, a)
	printf(">")
	if rg.void {
		return
	}

	for _, c := range children {
		if ct, ok := c.(Tag); ok {
			ct(r)
			continue
		}

		s := fmt.Sprint(c)
		if s == "" {
			continue
		}

		if !rg.verbatim && !rg.script {
			s = htmlEscape(s)
		}

		printf(s)
	}

	printf("</%s>", name)
}

func (r *renderer) ensureWrapper() bool {
	if _, ok := r.out.(*wrapper); ok {
		return false
	}

	r.originalOut = r.out
	r.out = newWrapper(r.originalOut, r.pwidth, r.currentIndent)
	return true
}

func (r *renderer) clearWrapper() {
	w, ok := r.out.(*wrapper)
	if !ok {
		return
	}

	if err := w.Flush(); err != nil {
		r.err = err
	}

	r.out = r.originalOut
}

func (r *renderer) renderInline(name string, rg renderGuide, a []Attributes, children []any) {
	newWrapper := r.ensureWrapper()
	printf := r.getPrintf(name)
	printf("<%s", name)
	r.renderAttributes(name, a)
	printf(">")
	if rg.void {
		if newWrapper {
			r.clearWrapper()
		}

		return
	}

	var lastBlock bool
	for _, c := range children {
		ct, isTag := c.(Tag)
		if !isTag && rg.verbatim {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			r.clearWrapper()
			s = indentLines(r.currentIndent+r.indent.Indent, s)
			printf("\n%s", s)
			lastBlock = true
			continue
		}

		if !isTag && rg.script {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			r.clearWrapper()
			printf("\n%s", s)
			lastBlock = true
			continue
		}

		if !isTag {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			if lastBlock {
				printf("\n%s", r.currentIndent)
			}

			if r.ensureWrapper() {
				newWrapper = true
			}

			s = htmlEscape(s)
			printf(s)
			lastBlock = false
			continue
		}

		var rgq renderGuidesQuery
		ct(&rgq)
		crg := mergeRenderingGuides(rgq.value)
		if crg.inline {
			if lastBlock {
				printf("\n%s", r.currentIndent)
			}

			if r.ensureWrapper() {
				newWrapper = true
			}

			ct(r)
			lastBlock = false
			continue
		}

		r.clearWrapper()
		cr := new(renderer)
		*cr = *r
		cr.currentIndent += cr.indent.Indent
		cr.pwidth -= len([]rune(cr.indent.Indent))
		if cr.pwidth < cr.indent.MinPWidth {
			cr.pwidth = cr.indent.MinPWidth
		}

		printf("\n%s", cr.currentIndent)
		ct(cr)
		if cr.err != nil {
			r.err = cr.err
		}

		lastBlock = true
	}

	if lastBlock {
		printf("\n%s", r.currentIndent)
	}

	printf("</%s>", name)
	if newWrapper {
		r.clearWrapper()
	}
}

func (r *renderer) renderBlock(name string, rg renderGuide, a []Attributes, children []any) {
	printf := r.getPrintf(name)
	printf("<%s", name)
	r.renderAttributes(name, a)
	printf(">")
	if rg.void {
		return
	}

	if len(children) == 0 {
		printf("</%s>", name)
		return
	}

	lastBlock := true
	originalIndent, originalWidth := r.currentIndent, r.pwidth
	r.currentIndent += r.indent.Indent
	r.pwidth -= len([]rune(r.indent.Indent))
	if r.pwidth < r.indent.MinPWidth {
		r.pwidth = r.indent.MinPWidth
	}

	for _, c := range children {
		ct, isTag := c.(Tag)
		if !isTag && rg.verbatim {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			r.clearWrapper()
			s = indentLines(r.currentIndent, s)
			printf("\n%s", s)
			lastBlock = true
			continue
		}

		if !isTag && rg.script {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			r.clearWrapper()
			printf("\n%s", s)
			lastBlock = true
			continue
		}

		if !isTag {
			s := fmt.Sprint(c)
			if s == "" {
				continue
			}

			if lastBlock {
				printf("\n%s", r.currentIndent)
			}

			r.ensureWrapper()
			s = htmlEscape(s)
			printf(s)
			lastBlock = false
			continue
		}

		var rgq renderGuidesQuery
		ct(&rgq)
		crg := mergeRenderingGuides(rgq.value)
		if crg.inline {
			if lastBlock {
				printf("\n%s", r.currentIndent)
			}

			r.ensureWrapper()
			ct(r)
			lastBlock = false
			continue
		}

		r.clearWrapper()
		cr := new(renderer)
		*cr = *r
		printf("\n%s", cr.currentIndent)
		ct(cr)
		if cr.err != nil {
			r.err = cr.err
		}

		lastBlock = true
	}

	r.clearWrapper()
	r.currentIndent, r.pwidth = originalIndent, originalWidth
	printf("\n%s</%s>", r.currentIndent, name)
}

func (r *renderer) render(name string, children []any) {
	if r.err != nil {
		return
	}

	a, c, rgs := groupChildren(children)
	rg := mergeRenderingGuides(rgs)
	if r.indent.Indent == "" && r.indent.PWidth <= 0 {
		r.renderUnindented(name, rg, a, c)
		return
	}

	if rg.inline || rg.inlineChildren {
		r.renderInline(name, rg, a, c)
		return
	}

	r.renderBlock(name, rg, a, c)
}

/*
func getPrintf(out io.Writer) func(f string, a ...any) {
	return func(f string, a ...any) {
		if r.err != nil {
			return
		}

		_, r.err = fmt.Fprintf(r.out, f, a...)
		if r.err != nil {
			r.err = fmt.Errorf("tag %s: %w", name, r.err)
		}
	}
}

func renderAttributes(out io.Writer, a []Attributes) {
	printf := getPrintf(out)
	for _, ai := range a {
		for name, value := range ai {
			printf(" %s=\"%s\"", name, attributeEscape(value))
		}
	}
}

func renderUnindented(r *renderer, name string, rg renderGuide, a []Attributes, children []any) {
	printf := getPrintf(r.out)
	printf("<%s", name)
	renderAttributes(r.out, a)
	printf(">")
	if rg.void {
		return
	}

	for _, c := range children {
		if ct, ok := c.(Tag); ok {
			ct(r)
			continue
		}

		s := fmt.Sprint(c)
		if s == "" {
			continue
		}

		if !rg.verbatim && !rg.script {
			s = htmlEscape(s)
		}

		printf(s)
	}

	printf("</%s>", name)
}

func renderInline(r *renderer, name string, rg renderGuide, a []Attributes, children []any) {
	printf := getPrintf(r.out)
	printf("<%s", name)
	renderAttributes(r.out, a)
	printf(">")
	if rg.void {
		return
	}

	for _, c := range children {
		if ct, ok := c.(Tag); ok {
			var rgq renderGuidesQuery
			ct(&rgq)
			crg := mergeRenderingGuides(rgq.value)
			if crg.inline {
				ct(r)
				continue
			}

			printf("\n")
			cr := new(renderer)
			*cr = *r
			cr.currentIndent += cr.indent
			ct(cr)
			continue
		}

		s := fmt.Sprint(c)
		if s == "" {
			continue
		}

		if !rg.verbatim && !rg.script {
			s = htmlEscape(s)
		}

		printf(s)
	}

	printf("</%s>", name)
}

func renderBlock(r *renderer, name string, rg renderGuide, a []Attributes, children []any) {
	if r.direct == nil {
		r.direct = r.out
	}

	printf := getPrintf(r.direct)
	printf(r.currentIndent)
	printf("<%s", name)
	renderAttributes(r.direct, a)
	printf(">")
	if len(c) == 0 {
		printf("</%s>", name)
		return
	}

	if r.indent != "" {
		printf("\n")
	}

	var (
		inlineBuffer bytes.Buffer
		cr *renderer
		lastInline bool
	)

	for i, c := range children {
		if ct, ok := c.(Tag); ok {
			var rgq renderGuidesQuery
			ct(&rgq)
			crg := mergeRenderingGuides(rgq.value)
			if crg.inline {
				if cr == nil {
					cr = new(renderer)
					*cr = *r
					cr.currentIndent += cr.indent
				}

				cr.out = &inlineBuffer
				if !lastInline {
					printf(r.currentIndent + r.indent)
				}

				ct(cr)
				lastInline = true
				continue
			}

			inline := inlineBuffer.String()
			if inline != "" {
				// flush
				// newline
			}

			continue
		}

		lastInline = true
	}

	inline := inlineBuffer.String()
	if inline != "" {
		// flush inline
	}

	if r.indent != "" {
		printf("\n")
		printf(r.currentIndent)
	}

	printf("</%s>", name)
	if r.indent != "" {
		printf("\n")
	}
}

func render(r *renderer, name string, children []any) {
	if r.err != nil {
		return
	}

	a, c, rgs := groupChildren(children)
	rg := mergeRenderingGuides(rgs)
	if r.indent == "" {
		renderUnindented(r, name, rg, a, c)
		return
	}

	if rg.inline {
		// TODO:
		// - may need to wrap it here
		// - could use a wrapping buffer
		renderInline(r, name, rg, a, c)
		return
	}

	renderBlock(r, name, rg, a, c)

	// --

	printf("<%s", name)

	printf(">")
	if r.indent != "" && !rg.inline && len(c) > 0 {
		printf("\n")
	}

	if rg.void {
		return
	}

	var inlineBuffer *bytes.Buffer

	// TODO:
	// - avoid rendering an inline buffer into another inline buffer
	// - why?
	// - or, if inline, just use the inline buffer without indentation
	// - check the wrapping again, if it preserves or eliminates the spaces the right way
	for i, ci := range c {
		// tag && rg.inline && crg.inline
		// tag && rg.inline && !crg.inline
		// tag && !rg.inline && crg.inline
		// tag && !rg.inline && !crg.inline
		// !tag && rg.inline && crg.inline
		// !tag && rg.inline && !crg.inline
		// !tag && !rg.inline && crg.inline
		// !tag && !rg.inline && !crg.inline

		if tag, ok := ci.(Tag); ok {
			if rg.inline {
				if inlineBuffer == nil {
					inlineBuffer = bytes.NewBuffer(nil)
				}

				var rgq renderGuidesQuery
				tag(&rgq)
				crg := mergeRenderingGuides(rgq.value)
				if r.indent != "" && !crg.inline && inlineBuffer.Len() > 0 {
					w := r.pwidth
					if w == 0 {
						w = defaultPWidth
					}

					inlineBuffer = wrap(inlineBuffer, w, "")
					if _, err := io.Copy(r.out, inlineBuffer); err != nil {
						r.err = err
						return
					}

					inlineBuffer = bytes.NewBuffer(nil)
				}

				if i > 0 && r.indent != "" && !crg.inline {
					printf("\n")
				}

				rr := new(renderer)
				*rr = *r
				rr.indent = ""
				rr.currentIndent = ""
				tag(rr)
			} else {
				var rgq renderGuidesQuery
				tag(&rgq)
				crg := mergeRenderingGuides(rgq.value)
				if r.indent != "" && !crg.inline && inlineBuffer.Len() > 0 {
					w := r.pwidth
					if w == 0 {
						w = defaultPWidth
					}

					inlineBuffer = wrap(inlineBuffer, w, r.currentIndent+r.indent)
					if _, err := io.Copy(r.out, inlineBuffer); err != nil {
						r.err = err
						return
					}

					inlineBuffer = bytes.NewBuffer(nil)
				}

				if i > 0 && r.indent != "" && !crg.inline {
					printf("\n")
				}

				rr := new(renderer)
				*rr = *r
				rr.currentIndent += r.indent
				if r.indent != "" && crg.inline {
					rr.out = inlineBuffer
				}

				tag(rr)
			}

			continue
		}

		s := fmt.Sprint(ci)
		if s == "" {
			continue
		}

		if !rg.verbatim && !rg.script {
			s = htmlEscape(s)
		}

		if r.indent == "" {
			printf(s)
			continue
		}

		inlineBuffer.WriteString(s)
	}

	if r.indent != "" && inlineBuffer.Len() > 0 {
		w := r.pwidth
		if w == 0 {
			w = defaultPWidth
		}

		var indent string
		if !rg.inline && !rg.script {
			indent = r.currentIndent + r.indent
		}

		inlineBuffer = wrap(inlineBuffer, w, indent)
		if _, err := io.Copy(r.out, inlineBuffer); err != nil {
			r.err = err
			return
		}

		if !rg.inline {
			printf("\n")
		}
	}

	if !rg.inline {
		printf(r.currentIndent)
	}

	printf("</%s>", name)
	if r.indent != "" && !rg.inline {
		printf("\n")
	}
}
*/