html/render.go

package html

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

const defaultPWidth = 112

type renderGuide struct {
	inline         bool
	inlineChildren bool
	void           bool
	script         bool
	preformatted   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.preformatted = rg.preformatted || rgi.preformatted
		rg.verbatim = rg.verbatim || rgi.verbatim
	}

	return rg
}

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) 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) writeEscaped(s string, nonbreakSpaces bool) {
	if r.err != nil {
		return
	}

	ew := newEscapeWriter(r.out, nonbreakSpaces)
	if _, r.err = ew.Write([]byte(s)); r.err != nil {
		return
	}

	r.err = ew.Flush()
}

func (r *renderer) copyEscaped(rd io.Reader, nonbreakSpaces bool) {
	if r.err != nil {
		return
	}

	ew := newEscapeWriter(r.out, nonbreakSpaces)
	if _, r.err = io.Copy(ew, rd); r.err != nil {
		return
	}

	r.err = ew.Flush()
}

func (r *renderer) writeIndented(indent, s string) {
	if r.err != nil {
		return
	}

	iw := newIndentWriter(r.out, indent)
	if _, r.err = iw.Write([]byte{'\n'}); r.err != nil {
		return
	}

	if _, r.err = iw.Write([]byte(s)); r.err != nil {
		return
	}

	r.err = iw.Flush()
}

func (r *renderer) copyIndented(indent string, rd io.Reader) {
	if r.err != nil {
		return
	}

	iw := newIndentWriter(r.out, indent)
	if _, r.err = iw.Write([]byte{'\n'}); r.err != nil {
		return
	}

	if _, r.err = io.Copy(iw, rd); r.err != nil {
		return
	}

	r.err = iw.Flush()
}

func (r *renderer) renderAttributes(tagName string, a []Attributes) {
	printf := r.getPrintf(tagName)
	isDeclaration := strings.HasPrefix(tagName, "!")
	for i, ai := range a {
		for j, name := range ai.names {
			if isDeclaration {
				f := " %s"
				if i == 0 && j == 0 {
					f = "%s"
				}

				printf(f, name)
				continue
			}

			value := ai.values[name]
			isTrue, _ := value.(bool)
			if isTrue {
				printf(" %s", name)
				continue
			}

			printf(" %s=\"%s\"", name, escapeAttribute(fmt.Sprint(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 c == nil {
			continue
		}

		rd, isReader := c.(io.Reader)
		if isReader && (rg.verbatim || rg.script) {
			if r.err == nil {
				_, r.err = io.Copy(r.out, rd)
			}

			continue
		}

		if isReader {
			r.copyEscaped(rd, !rg.preformatted)
			continue
		}

		if ct, ok := c.(Tag); ok {
			if rg.preformatted {
				ct = Preformatted(ct)
			}

			ct(r)
			continue
		}

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

		if rg.verbatim || rg.script {
			printf(s)
			continue
		}

		r.writeEscaped(s, !rg.preformatted)
	}

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

func indentLen(indent string) int {
	var l int
	r := []rune(indent)
	for _, ri := range r {
		if ri == '\t' {
			l += 8
			continue
		}

		l++
	}

	return l
}

func (r *renderer) renderChildTag(tagName string, rg renderGuide, lastBlock bool, ct Tag) (bool, bool) {
	printf := r.getPrintf(tagName)
	if rg.preformatted {
		cr := new(renderer)
		*cr = *r
		cr.indent = Indentation{}
		Preformatted(ct)(cr)
		return false, false
	}

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

		newWrapper := r.ensureWrapper()
		ct(r)
		return false, newWrapper
	}

	r.clearWrapper()
	cr := new(renderer)
	*cr = *r
	if rg.inline || rg.inlineChildren {
		cr.currentIndent += cr.indent.Indent
		cr.pwidth -= indentLen(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
	}

	return true, false
}

func (r *renderer) renderReaderChild(tagName string, rg renderGuide, lastBlock bool, rd io.Reader) bool {
	printf := r.getPrintf(tagName)
	if rg.script {
		r.clearWrapper()
		printf("\n")
		if r.err == nil {
			_, r.err = io.Copy(r.out, rd)
		}

		return false
	}

	if rg.verbatim {
		r.clearWrapper()
		indent := r.currentIndent
		if rg.inline || rg.inlineChildren {
			indent += r.indent.Indent
		}

		r.copyIndented(indent, rd)
		return false
	}

	if rg.preformatted {
		r.clearWrapper()
		r.copyEscaped(rd, false)
		return false
	}

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

	newWrapper := r.ensureWrapper()
	r.copyEscaped(rd, true)
	return newWrapper
}

func (r *renderer) renderChildScript(tagName string, c any) {
	s := fmt.Sprint(c)
	if s == "" {
		return
	}

	r.clearWrapper()
	printf := r.getPrintf(tagName)
	printf("\n%s", s)
}

func (r *renderer) renderVerbatimChild(rg renderGuide, c any) {
	s := fmt.Sprint(c)
	if s == "" {
		return
	}

	r.clearWrapper()
	if rg.preformatted {
		_, r.err = r.out.Write([]byte(s))
		return
	}

	indent := r.currentIndent
	if rg.inline || rg.inlineChildren {
		indent += r.indent.Indent
	}

	r.writeIndented(indent, s)
}

func (r *renderer) renderChildContent(tagName string, rg renderGuide, lastBlock bool, c any) bool {
	s := fmt.Sprint(c)
	if s == "" {
		return false
	}

	if rg.preformatted {
		r.writeEscaped(s, false)
		return false
	}

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

	newWrapper := r.ensureWrapper()
	r.writeEscaped(s, true)
	return newWrapper
}

func (r *renderer) renderIndented(name string, rg renderGuide, a []Attributes, children []any) {
	var newWrapper bool
	if rg.inline || rg.inlineChildren {
		newWrapper = r.ensureWrapper()
	}

	printf := r.getPrintf(name)
	printf("<%s", name)
	r.renderAttributes(name, a)
	printf(">")
	if rg.void {
		if newWrapper {
			r.clearWrapper()
		}

		return
	}

	if len(children) == 0 {
		printf("</%s>", name)
		if newWrapper {
			r.clearWrapper()
		}

		return
	}

	block := !rg.inline && !rg.inlineChildren
	lastBlock := block
	originalIndent, originalWidth := r.currentIndent, r.pwidth
	if block {
		r.currentIndent += r.indent.Indent
		r.pwidth -= indentLen(r.indent.Indent)
		if r.pwidth < r.indent.MinPWidth {
			r.pwidth = r.indent.MinPWidth
		}
	}

	if rg.preformatted {
		r.clearWrapper()
		printf("\n")
	}

	for _, c := range children {
		if c == nil {
			continue
		}

		if ct, isTag := c.(Tag); isTag {
			var nw bool
			lastBlock, nw = r.renderChildTag(name, rg, lastBlock, ct)
			if nw {
				newWrapper = true
			}

			continue
		}

		if rd, isReader := c.(io.Reader); isReader {
			if r.renderReaderChild(name, rg, lastBlock, rd) {
				newWrapper = true
			}

			lastBlock = rg.verbatim || rg.script
			continue
		}

		if rg.script {
			r.renderChildScript(name, c)
			lastBlock = true
			continue
		}

		if rg.verbatim {
			r.renderVerbatimChild(rg, c)
			lastBlock = true
			continue
		}

		if r.renderChildContent(name, rg, lastBlock, c) {
			newWrapper = true
		}

		lastBlock = false
	}

	if block {
		r.currentIndent, r.pwidth = originalIndent, originalWidth
		r.clearWrapper()
	}

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

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

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
	}

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