type pageMap struct {
	s *Site
	*contentMap
}
type pageMaps struct {
	workers *para.Workers
	pmaps   []*pageMap
}

type contentNode struct {
	p *pageState
	// Set if source is a file.
	// We will soon get other sources.
	fi hugofs.FileMetaInfo
	// The source path. Unix slashes. No leading slash.
	path string
	...
}

type pageState struct {
	// This slice will be of same length as the number of global slice of output
	// formats (for all sites).
	pageOutputs []*pageOutput
	// This will be shifted out when we start to render a new output format.
	*pageOutput
	// Common for all output formats.
	*pageCommon
	...
}

// hugo-playground/hugolib/page__new.go
// line 97
// Prepare output formats for all sites.
// We do this even if this page does not get rendered on
// its own. It may be referenced via .Site.GetPage and
// it will then need an output format.
ps.pageOutputs = make([]*pageOutput, len(ps.s.h.renderFormats))

package main
import (
	"fmt"
	"html/template"
)
func main() {
	outputFormats := createOutputFormats()
	renderFormats := initRenderFormats(outputFormats)
	s := &site{
		outputFormats: outputFormats,
		renderFormats: renderFormats,
	}
	ps := &pageState{
		pageOutputs: nil,
		pageOutput:  nil,
		pageCommon:  &pageCommon{m: &pageMeta{kind: KindPage}},
	}
	ps.init(s)
	// prepare
	ps.pageOutput = ps.pageOutputs[0]
	// render
	fmt.Println(ps.targetPaths().TargetFilename)
	fmt.Println(ps.Content())
	fmt.Println(ps.m.kind)
}
type site struct {
	outputFormats map[string]Formats
	renderFormats Formats
}
type pageState struct {
	// This slice will be of same length as the number of global slice of output
	// formats (for all sites).
	pageOutputs []*pageOutput
	// This will be shifted out when we start to render a new output format.
	*pageOutput
	// Common for all output formats.
	*pageCommon
}
func (p *pageState) init(s *site) {
	pp := newPagePaths(s)
	p.pageOutputs = make([]*pageOutput, len(s.renderFormats))
	for i, f := range s.renderFormats {
		ft, found := pp.targetPaths[f.Name]
		if !found {
			panic("target path not found")
		}
		providers := struct{ targetPather }{ft}
		po := &pageOutput{
			f:                      f,
			pagePerOutputProviders: providers,
			ContentProvider:        nil,
		}
		contentProvider := newPageContentOutput(po)
		po.ContentProvider = contentProvider
		p.pageOutputs[i] = po
	}
}
func newPageContentOutput(po *pageOutput) *pageContentOutput {
	cp := &pageContentOutput{
		f: po.f,
	}
	initContent := func() {
		cp.content = template.HTML("<p>hello content</p>")
	}
	cp.initMain = func() {
		initContent()
	}
	return cp
}
func newPagePaths(s *site) pagePaths {
	outputFormats := s.renderFormats
	targets := make(map[string]targetPathsHolder)
	for _, f := range outputFormats {
		target := "/" + "blog" + "/" + f.BaseName +
			"." + f.MediaType.SubType
		paths := TargetPaths{
			TargetFilename: target,
		}
		targets[f.Name] = targetPathsHolder{
			paths: paths,
		}
	}
	return pagePaths{
		targetPaths: targets,
	}
}
type pagePaths struct {
	targetPaths map[string]targetPathsHolder
}
type targetPathsHolder struct {
	paths TargetPaths
}
func (t targetPathsHolder) targetPaths() TargetPaths {
	return t.paths
}
type pageOutput struct {
	f Format
	// These interface provides the functionality that is specific for this
	// output format.
	pagePerOutputProviders
	ContentProvider
	// May be nil.
	cp *pageContentOutput
}
// pageContentOutput represents the Page content for a given output format.
type pageContentOutput struct {
	f        Format
	initMain func()
	content  template.HTML
}
func (p *pageContentOutput) Content() any {
	p.initMain()
	return p.content
}
// these will be shifted out when rendering a given output format.
type pagePerOutputProviders interface {
	targetPather
}
type targetPather interface {
	targetPaths() TargetPaths
}
type TargetPaths struct {
	// Where to store the file on disk relative to the publish dir. OS slashes.
	TargetFilename string
}
type ContentProvider interface {
	Content() any
}
type pageCommon struct {
	m *pageMeta
}
type pageMeta struct {
	// kind is the discriminator that identifies the different page types
	// in the different page collections. This can, as an example, be used
	// to to filter regular pages, find sections etc.
	// Kind will, for the pages available to the templates, be one of:
	// page, home, section, taxonomy and term.
	// It is of string type to make it easy to reason about in
	// the templates.
	kind string
}
func initRenderFormats(
	outputFormats map[string]Formats) Formats {
	return outputFormats[KindPage]
}
func createOutputFormats() map[string]Formats {
	m := map[string]Formats{
		KindPage: {HTMLFormat},
	}
	return m
}
const (
	KindPage = "page"
)
var HTMLType = newMediaType("text", "html")
// HTMLFormat An ordered list of built-in output formats.
var HTMLFormat = Format{
	Name:      "HTML",
	MediaType: HTMLType,
	BaseName:  "index",
}
func newMediaType(main, sub string) Type {
	t := Type{
		MainType:  main,
		SubType:   sub,
		Delimiter: "."}
	return t
}
type Type struct {
	MainType  string `json:"mainType"`  // i.e. text
	SubType   string `json:"subType"`   // i.e. html
	Delimiter string `json:"delimiter"` // e.g. "."
}
type Format struct {
	// The Name is used as an identifier. Internal output formats (i.e. HTML and RSS)
	// can be overridden by providing a new definition for those types.
	Name string `json:"name"`
	MediaType Type `json:"-"`
	// The base output file name used when not using "ugly URLs", defaults to "index".
	BaseName string `json:"baseName"`
}
type Formats []Format

/blog/index.html
<p>hello content</p>
page
Program exited.

// We create a pageOutput for every output format combination, even if this
// particular page isn't configured to be rendered to that format.
type pageOutput struct {
	...
	// These interface provides the functionality that is specific for this
	// output format.
	pagePerOutputProviders
	page.ContentProvider
	page.TableOfContentsProvider
	page.PageRenderProvider
	// May be nil.
	cp *pageContentOutput
}

package main
import (
	"bytes"
	"fmt"
	"io"
	"os"
	"path/filepath"
)
// publisher needs to know:
// 1: what to publish
// 2: where to publish
func main() {
	// 1
	// src is template executed result
	// it is the source that we need to publish
	// take a look at template executor example
	// https://c.sunwei.xyz/template-executor.html
	src := &bytes.Buffer{}
	src.Write([]byte("template executed result"))
	b := &bytes.Buffer{}
	transformers := createTransformerChain()
	if err := transformers.Apply(b, src); err != nil {
		fmt.Println(err)
		return
	}
	dir, _ := os.MkdirTemp("", "hugo")
	defer os.RemoveAll(dir)
	// 2
	// targetPath is from pageState
	// this is where we need to publish
	// take a look at page state example
	// https://c.sunwei.xyz/page-state.html
	targetPath := filepath.Join(dir, "index.html")
	if err := os.WriteFile(
		targetPath,
		bytes.TrimSuffix(b.Bytes(), []byte("\n")),
		os.ModePerm); err != nil {
		panic(err)
	}
	fmt.Println("1. what to publish: ", string(b.Bytes()))
	fmt.Println("2. where to publish: ", dir)
}
func (c *Chain) Apply(to io.Writer, from io.Reader) error {
	fb := &bytes.Buffer{}
	if _, err := fb.ReadFrom(from); err != nil {
		return err
	}
	tb := &bytes.Buffer{}
	ftb := &fromToBuffer{from: fb, to: tb}
	for i, tr := range *c {
		if i > 0 {
			panic("switch from/to and reset to")
		}
		if err := tr(ftb); err != nil {
			continue
		}
	}
	_, err := ftb.to.WriteTo(to)
	return err
}
func createTransformerChain() Chain {
	transformers := NewEmpty()
	transformers = append(transformers, func(ft FromTo) error {
		content := ft.From().Bytes()
		w := ft.To()
		tc := bytes.Replace(
			content,
			[]byte("result"), []byte("transferred result"), 1)
		_, _ = w.Write(tc)
		return nil
	})
	return transformers
}
// Chain is an ordered processing chain. The next transform operation will
// receive the output from the previous.
type Chain []Transformer
// Transformer is the func that needs to be implemented by a transformation step.
type Transformer func(ft FromTo) error
// FromTo is sent to each transformation step in the chain.
type FromTo interface {
	From() BytesReader
	To() io.Writer
}
// BytesReader wraps the Bytes method, usually implemented by bytes.Buffer, and an
// io.Reader.
type BytesReader interface {
	// Bytes The slice given by Bytes is valid for use only until the next buffer modification.
	// That is, if you want to use this value outside of the current transformer step,
	// you need to take a copy.
	Bytes() []byte
	io.Reader
}
// NewEmpty creates a new slice of transformers with a capacity of 20.
func NewEmpty() Chain {
	return make(Chain, 0, 2)
}
// Implements contentTransformer
// Content is read from the from-buffer and rewritten to to the to-buffer.
type fromToBuffer struct {
	from *bytes.Buffer
	to   *bytes.Buffer
}
func (ft fromToBuffer) From() BytesReader {
	return ft.from
}
func (ft fromToBuffer) To() io.Writer {
	return ft.to
}