implement live-reloading dev server

Squashed commit of the following:

commit 02f077432202af4d633eb2cad81dfdaa6921317f
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 21:09:14 2024 +0200

    builder: only remove output directory if set and in dev mode

commit 47001e01c55fa6e74aafeda04ebc3e4e7c47eba0
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 21:03:37 2024 +0200

    implement live reload on dev server

commit 411ec969f61e4b73439f1c54ea29f75135ecc618
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:59:26 2024 +0200

    server: implement graceful shutdown

commit 5400132eb6eb1b638e0b3fd4265f51611c92d473
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:41:07 2024 +0200

    add some debug logs

commit 3c9b678197c044603950232d222f501ef74d7873
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:39:09 2024 +0200

    prefix log output with executable name

commit 300e24c179e390e9d3f5aeab4471c97f17f1fa64
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Sat Apr 27 20:29:42 2024 +0200

    don't panic inside internal packages, return error instead

commit fe2715d330402ad67fe866471bed89c7238ad2ec
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Fri Apr 26 01:18:29 2024 +0200

    config: use a table to configure CSP headers

commit d012553aaf78a436fa8871830b5d720a9e292d4b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 17:13:39 2024 +0200

    dev: create basic dev server to build and serve from a temporary directory

commit a1d11d3e69650d9b43ca1b1d7b7ccc05a808d5c1
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 13:02:22 2024 +0200

    remove unused redirect_other_hostnames config option

commit fd67b19b5c7f76f0c3579e8a05ef20a618e90be7
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:58:53 2024 +0200

    server: make port a string, which is what go uses

commit c798e8e736c0649008cade337158399470a9099b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:58:33 2024 +0200

    config: remove unused port variable

commit f94882b9001f3b0855e26b26b4a84b96e3deb22b
Author: Alan Pearce <alan@alanpearce.eu>
Date:   Thu Apr 25 12:49:10 2024 +0200

    re-organise module layout

1 files changed, 371 insertions, 0 deletions

diff --git a/internal/builder/template.go b/internal/builder/template.go
new file mode 100644
index 0000000..74d0418
--- /dev/null
+++ b/internal/builder/template.go
@@ -0,0 +1,371 @@
+package builder
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/url"
+	"os"
+	"strings"
+	"sync"
+	"time"
+	"website/internal/atom"
+	"website/internal/config"
+
+	"github.com/PuerkitoBio/goquery"
+	"github.com/a-h/htmlformat"
+	"github.com/antchfx/xmlquery"
+	"github.com/antchfx/xpath"
+	mapset "github.com/deckarep/golang-set/v2"
+	"golang.org/x/net/html"
+)
+
+var (
+	assetsOnce     sync.Once
+	css            string
+	countHTML      *goquery.Document
+	liveReloadHTML *goquery.Document
+	templates      map[string]*os.File = make(map[string]*os.File)
+)
+
+func loadTemplate(path string) (file *os.File, err error) {
+	if templates[path] == nil {
+		file, err = os.OpenFile(path, os.O_RDONLY, 0)
+		if err != nil {
+			return nil, err
+		}
+		templates[path] = file
+	}
+	file = templates[path]
+	return
+}
+
+var (
+	imgOnce     sync.Once
+	img         *goquery.Selection
+	urlTemplate *url.URL
+)
+
+type QuerySelection struct {
+	*goquery.Selection
+}
+
+type QueryDocument struct {
+	*goquery.Document
+}
+
+func NewDocumentFromReader(r io.Reader) (*QueryDocument, error) {
+	doc, err := goquery.NewDocumentFromReader(r)
+	return &QueryDocument{doc}, err
+}
+
+func (q *QueryDocument) Find(selector string) *QuerySelection {
+	return &QuerySelection{q.Document.Find(selector)}
+}
+
+func NewDocumentNoScript(r io.Reader) (*goquery.Document, error) {
+	root, err := html.ParseWithOptions(r, html.ParseOptionEnableScripting(false))
+	return goquery.NewDocumentFromNode(root), err
+}
+
+func (root QuerySelection) setImgURL(pageURL string, pageTitle string) QuerySelection {
+	clone := countHTML.Clone()
+	imgOnce.Do(func() {
+		var err error
+		img = clone.Find("img")
+		attr, _ := img.Attr("src")
+		if attr == "" {
+			panic("<img> does not have src attribute")
+		}
+		urlTemplate, err = url.Parse(attr)
+		if err != nil {
+			panic(err.Error())
+		}
+	})
+	q := urlTemplate.Query()
+	urlTemplate.RawQuery = ""
+	q.Set("p", pageURL)
+	q.Set("t", pageTitle)
+	output := urlTemplate.String() + "?" + q.Encode()
+	clone.Find("img").SetAttr("src", output)
+	root.AppendSelection(clone.Find("body").Children())
+	return root
+}
+
+func layout(filename string, config config.Config, pageTitle string, pageURL string) (*goquery.Document, error) {
+	html, err := loadTemplate(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer html.Seek(0, io.SeekStart)
+	assetsOnce.Do(func() {
+		var bytes []byte
+		bytes, err = os.ReadFile("templates/style.css")
+		if err != nil {
+			return
+		}
+		css = string(bytes)
+		countFile, err := os.OpenFile("templates/count.html", os.O_RDONLY, 0)
+		if err != nil {
+			return
+		}
+		defer countFile.Close()
+		countHTML, err = NewDocumentNoScript(countFile)
+		if config.InjectLiveReload {
+			liveReloadFile, err := os.OpenFile("templates/dev.html", os.O_RDONLY, 0)
+			if err != nil {
+				return
+			}
+			defer liveReloadFile.Close()
+			liveReloadHTML, err = goquery.NewDocumentFromReader(liveReloadFile)
+		}
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	doc, err := NewDocumentFromReader(html)
+	if err != nil {
+		return nil, err
+	}
+	doc.Find("html").SetAttr("lang", config.DefaultLanguage)
+	doc.Find("head > link[rel=alternate]").SetAttr("title", config.Title)
+	doc.Find("head > link[rel=canonical]").SetAttr("href", pageURL)
+	doc.Find(".title").SetText(config.Title)
+	doc.Find("title").Add(".p-name").SetText(pageTitle)
+	doc.Find("head > style").SetHtml(css)
+	doc.Find("body").setImgURL(pageURL, pageTitle)
+	if config.InjectLiveReload {
+		doc.Find("body").AppendSelection(liveReloadHTML.Find("body").Clone())
+	}
+	nav := doc.Find("nav")
+	navLink := doc.Find("nav a")
+	nav.Empty()
+	for _, link := range config.Menus["main"] {
+		nav.AppendSelection(navLink.Clone().SetAttr("href", link.URL).SetText(link.Name))
+	}
+	return doc.Document, nil
+}
+
+func renderPost(post Post, config config.Config) (r io.Reader, err error) {
+	doc, err := layout("templates/post.html", config, post.PostMatter.Title, post.URL)
+	if err != nil {
+		return nil, err
+	}
+	doc.Find(".title").AddClass("p-author h-card").SetAttr("rel", "author")
+	doc.Find(".h-entry .dt-published").
+		SetAttr("datetime", post.PostMatter.Date.UTC().Format(time.RFC3339)).
+		SetText(
+			post.PostMatter.Date.Format("2006-01-02"),
+		)
+	doc.Find(".h-entry .e-content").SetHtml(post.Content)
+	categories := doc.Find(".h-entry .p-categories")
+	tpl := categories.Find(".p-category").ParentsUntilSelection(categories)
+	tpl.Remove()
+	for _, tag := range post.Taxonomies.Tags {
+		cat := tpl.Clone()
+		cat.Find(".p-category").SetAttr("href", fmt.Sprintf("/tags/%s/", tag)).SetText("#" + tag)
+		categories.AppendSelection(cat)
+	}
+
+	return renderHTML(doc), nil
+}
+
+func renderTags(tags Tags, config config.Config, url string) (io.Reader, error) {
+	doc, err := layout("templates/tags.html", config, config.Title, url)
+	if err != nil {
+		return nil, err
+	}
+	tagList := doc.Find(".tags")
+	tpl := doc.Find(".h-feed")
+	tpl.Remove()
+	for _, tag := range mapset.Sorted(tags) {
+		li := tpl.Clone()
+		li.Find("a").SetAttr("href", fmt.Sprintf("/tags/%s/", tag)).SetText("#" + tag)
+		tagList.AppendSelection(li)
+	}
+	return renderHTML(doc), nil
+}
+
+func renderListPage(tag string, config config.Config, posts []Post, url string) (io.Reader, error) {
+	var title string
+	if len(tag) > 0 {
+		title = tag
+	} else {
+		title = config.Title
+	}
+	doc, err := layout("templates/list.html", config, title, url)
+	if err != nil {
+		return nil, err
+	}
+	feed := doc.Find(".h-feed")
+	tpl := feed.Find(".h-entry")
+	tpl.Remove()
+
+	doc.Find(".title").AddClass("p-author h-card").SetAttr("rel", "author")
+	if tag == "" {
+		doc.Find(".filter").Remove()
+	} else {
+		doc.Find(".filter").Find("h3").SetText("#" + tag)
+	}
+
+	for _, post := range posts {
+		entry := tpl.Clone()
+		entry.Find(".p-name").SetText(post.Title).SetAttr("href", post.URL)
+		entry.Find(".dt-published").
+			SetAttr("datetime", post.PostMatter.Date.UTC().Format(time.RFC3339)).
+			SetText(post.PostMatter.Date.Format("2006-01-02"))
+		feed.AppendSelection(entry)
+	}
+
+	return renderHTML(doc), nil
+}
+
+func renderHomepage(config config.Config, posts []Post, url string) (io.Reader, error) {
+	_, index, err := getPost("content/_index.md")
+	if err != nil {
+		return nil, err
+	}
+	doc, err := layout("templates/homepage.html", config, config.Title, url)
+	if err != nil {
+		return nil, err
+	}
+	doc.Find("body").AddClass("h-card")
+	doc.Find(".title").AddClass("p-name u-url")
+
+	html, err := renderMarkdown(index)
+	doc.Find("#content").SetHtml(html)
+
+	feed := doc.Find(".h-feed")
+	tpl := feed.Find(".h-entry")
+	tpl.Remove()
+
+	for _, post := range posts[0:3] {
+		entry := tpl.Clone()
+		entry.Find(".p-name").SetText(post.Title)
+		entry.Find(".u-url").SetAttr("href", post.URL)
+		entry.
+			Find(".dt-published").
+			SetAttr("datetime", post.PostMatter.Date.UTC().Format(time.RFC3339)).
+			SetText(post.PostMatter.Date.Format("2006-01-02"))
+
+		feed.AppendSelection(entry)
+	}
+	doc.Find(".u-email").
+		SetAttr("href", fmt.Sprintf("mailto:%s", config.Email)).
+		SetText(config.Email)
+
+	elsewhere := doc.Find(".elsewhere")
+	linkRelMe := elsewhere.Find(".u-url[rel=me]").ParentsUntil("ul")
+	linkRelMe.Remove()
+
+	for _, link := range config.Menus["me"] {
+		el := linkRelMe.Clone()
+		el.Find("a").SetAttr("href", link.URL).SetText(link.Name)
+		elsewhere.AppendSelection(el)
+	}
+
+	return renderHTML(doc), nil
+}
+
+func render404(config config.Config, url string) (io.Reader, error) {
+	doc, err := layout("templates/404.html", config, "404 Not Found", url)
+	if err != nil {
+		return nil, err
+	}
+	return renderHTML(doc), nil
+}
+
+func renderFeed(title string, config config.Config, posts []Post, specific string) (io.Reader, error) {
+	reader, err := loadTemplate("templates/feed.xml")
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Seek(0, io.SeekStart)
+	doc, err := xmlquery.Parse(reader)
+	feed := doc.SelectElement("feed")
+	feed.SelectElement("title").FirstChild.Data = title
+	feed.SelectElement("link").SetAttr("href", config.BaseURL.String())
+	feed.SelectElement("id").FirstChild.Data = atom.MakeTagURI(config, specific)
+	datetime, err := posts[0].Date.UTC().MarshalText()
+	feed.SelectElement("updated").FirstChild.Data = string(datetime)
+	tpl := feed.SelectElement("entry")
+	xmlquery.RemoveFromTree(tpl)
+
+	for _, post := range posts {
+		fullURL, err := url.JoinPath(config.BaseURL.String(), post.URL)
+		if err != nil {
+			return nil, err
+		}
+		text, err := xml.MarshalIndent(&atom.FeedEntry{
+			Title:   post.Title,
+			Link:    atom.MakeLink(fullURL),
+			Id:      atom.MakeTagURI(config, post.Basename),
+			Updated: post.Date.UTC(),
+			Summary: post.Description,
+			Author:  config.Title,
+			Content: atom.FeedContent{
+				Content: post.Content,
+				Type:    "html",
+			},
+		}, "  ", "    ")
+		if err != nil {
+			return nil, err
+		}
+		entry, err := xmlquery.ParseWithOptions(strings.NewReader(string(text)), xmlquery.ParserOptions{
+			Decoder: &xmlquery.DecoderOptions{
+				Strict:    false,
+				AutoClose: xml.HTMLAutoClose,
+				Entity:    xml.HTMLEntity,
+			},
+		})
+		if err != nil {
+			return nil, err
+		}
+		xmlquery.AddChild(feed, entry.SelectElement("entry"))
+	}
+
+	return strings.NewReader(doc.OutputXML(true)), nil
+}
+
+func renderFeedStyles() (io.Reader, error) {
+	reader, err := loadTemplate("templates/feed-styles.xsl")
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Seek(0, io.SeekStart)
+	nsMap := map[string]string{
+		"xsl":   "http://www.w3.org/1999/XSL/Transform",
+		"atom":  "http://www.w3.org/2005/Atom",
+		"xhtml": "http://www.w3.org/1999/xhtml",
+	}
+	doc, err := xmlquery.Parse(reader)
+	expr, err := xpath.CompileWithNS("//xhtml:style", nsMap)
+	if err != nil {
+		return nil, err
+	}
+	style := xmlquery.QuerySelector(doc, expr)
+	xmlquery.AddChild(style, &xmlquery.Node{
+		Type: xmlquery.TextNode,
+		Data: string(css),
+	})
+	return strings.NewReader(doc.OutputXML(true)), nil
+}
+
+func renderHTML(doc *goquery.Document) io.Reader {
+	r, w := io.Pipe()
+
+	// TODO: return errors to main thread
+	go func() {
+		w.Write([]byte("<!doctype html>\n"))
+		err := htmlformat.Nodes(w, []*html.Node{doc.Children().Get(0)})
+		if err != nil {
+			slog.Error("error rendering html", "error", err)
+			w.CloseWithError(err)
+			return
+		}
+		defer w.Close()
+	}()
+	return r
+}