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, 197 insertions, 0 deletions

diff --git a/internal/builder/builder.go b/internal/builder/builder.go
new file mode 100644
index 0000000..88e3f02
--- /dev/null
+++ b/internal/builder/builder.go
@@ -0,0 +1,197 @@
+package builder
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"log/slog"
+	"net/url"
+	"os"
+	"path"
+	"slices"
+
+	"website/internal/config"
+
+	cp "github.com/otiai10/copy"
+	"github.com/pkg/errors"
+)
+
+type IOConfig struct {
+	Source      string `conf:"default:.,short:s,flag:src"`
+	Destination string `conf:"default:website,short:d,flag:dest"`
+	BaseURL     config.URL
+	Development bool `conf:"default:false,flag:dev"`
+}
+
+func mkdirp(dirs ...string) error {
+	return os.MkdirAll(path.Join(dirs...), 0755)
+}
+
+func outputToFile(output io.Reader, filename ...string) error {
+	slog.Debug(fmt.Sprintf("outputting file %s", path.Join(filename...)))
+	file, err := os.OpenFile(path.Join(filename...), os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		return errors.WithMessage(err, "could not open output file")
+	}
+	defer file.Close()
+
+	if _, err := file.ReadFrom(output); err != nil {
+		return errors.WithMessage(err, "could not write output file")
+	}
+	return nil
+}
+
+func build(outDir string, config config.Config) error {
+	slog.Debug(fmt.Sprintf("output directory %s", outDir))
+	privateDir := path.Join(outDir, "private")
+	if err := mkdirp(privateDir); err != nil {
+		return errors.WithMessage(err, "could not create private directory")
+	}
+	publicDir := path.Join(outDir, "public")
+	if err := mkdirp(publicDir); err != nil {
+		return errors.WithMessage(err, "could not create public directory")
+	}
+
+	err := cp.Copy("static", publicDir, cp.Options{
+		PreserveTimes:     true,
+		PermissionControl: cp.AddPermission(0755),
+	})
+	if err != nil {
+		return errors.WithMessage(err, "could not copy static files")
+	}
+
+	if err := mkdirp(publicDir, "post"); err != nil {
+		return errors.WithMessage(err, "could not create post output directory")
+	}
+	slog.Debug("reading posts")
+	posts, tags, err := readPosts("content", "post", publicDir)
+	if err != nil {
+		return err
+	}
+
+	for _, post := range posts {
+		if err := mkdirp(publicDir, "post", post.Basename); err != nil {
+			return errors.WithMessage(err, "could not create directory for post")
+		}
+		slog.Debug("rendering post", "post", post.Basename)
+		output, err := renderPost(post, config)
+		if err != nil {
+			return errors.WithMessagef(err, "could not render post %s", post.Input)
+		}
+		if err := outputToFile(output, post.Output); err != nil {
+			return err
+		}
+	}
+
+	if err := mkdirp(publicDir, "tags"); err != nil {
+		return errors.WithMessage(err, "could not create directory for tags")
+	}
+	slog.Debug("rendering tags list")
+	output, err := renderTags(tags, config, "/tags")
+	if err != nil {
+		return errors.WithMessage(err, "could not render tags")
+	}
+	if err := outputToFile(output, publicDir, "tags", "index.html"); err != nil {
+		return err
+	}
+
+	for _, tag := range tags.ToSlice() {
+		matchingPosts := []Post{}
+		for _, post := range posts {
+			if slices.Contains(post.Taxonomies.Tags, tag) {
+				matchingPosts = append(matchingPosts, post)
+			}
+		}
+		if err := mkdirp(publicDir, "tags", tag); err != nil {
+			return errors.WithMessage(err, "could not create directory")
+		}
+		slog.Debug("rendering tags page", "tag", tag)
+		output, err := renderListPage(tag, config, matchingPosts, "/tags/"+tag)
+		if err != nil {
+			return errors.WithMessage(err, "could not render tag page")
+		}
+		if err := outputToFile(output, publicDir, "tags", tag, "index.html"); err != nil {
+			return err
+		}
+
+		slog.Debug("rendering tags feed", "tag", tag)
+		output, err = renderFeed(fmt.Sprintf("%s - %s", config.Title, tag), config, matchingPosts, tag)
+		if err != nil {
+			return errors.WithMessage(err, "could not render tag feed page")
+		}
+		if err := outputToFile(output, publicDir, "tags", tag, "atom.xml"); err != nil {
+			return err
+		}
+	}
+
+	slog.Debug("rendering list page")
+	listPage, err := renderListPage("", config, posts, "/post")
+	if err != nil {
+		return errors.WithMessage(err, "could not render list page")
+	}
+	if err := outputToFile(listPage, publicDir, "post", "index.html"); err != nil {
+		return err
+	}
+
+	slog.Debug("rendering feed")
+	feed, err := renderFeed(config.Title, config, posts, "feed")
+	if err != nil {
+		return errors.WithMessage(err, "could not render feed")
+	}
+	if err := outputToFile(feed, publicDir, "atom.xml"); err != nil {
+		return err
+	}
+
+	slog.Debug("rendering feed styles")
+	feedStyles, err := renderFeedStyles()
+	if err != nil {
+		return errors.WithMessage(err, "could not render feed styles")
+	}
+	if err := outputToFile(feedStyles, publicDir, "feed-styles.xsl"); err != nil {
+		return err
+	}
+
+	slog.Debug("rendering homepage")
+	homePage, err := renderHomepage(config, posts, "/")
+	if err != nil {
+		return errors.WithMessage(err, "could not render homepage")
+	}
+	if err := outputToFile(homePage, publicDir, "index.html"); err != nil {
+		return err
+	}
+
+	slog.Debug("rendering 404 page")
+	notFound, err := render404(config, "/404.html")
+	if err != nil {
+		return errors.WithMessage(err, "could not render 404 page")
+	}
+	if err := outputToFile(notFound, privateDir, "404.html"); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func BuildSite(ioConfig IOConfig) error {
+	config, err := config.GetConfig()
+	if err != nil {
+		log.Panic(errors.Errorf("could not get config: %v", err))
+	}
+	config.InjectLiveReload = ioConfig.Development
+
+	if ioConfig.BaseURL.URL != nil {
+		config.BaseURL.URL, err = url.Parse(ioConfig.BaseURL.String())
+		if err != nil {
+			log.Panic(errors.Errorf("highly unlikely: %v", err))
+		}
+	}
+
+	if ioConfig.Development && ioConfig.Destination != "website" {
+		err = os.RemoveAll(ioConfig.Destination)
+		if err != nil {
+			log.Panic(errors.Errorf("could not remove destination directory: %v", err))
+		}
+	}
+
+	return build(ioConfig.Destination, *config)
+}