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https://git.jolheiser.com/blog.git
My nonexistent blog
blog / blog.go
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package blog

import (
	"bytes"
	"errors"
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"net/url"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"github.com/bmatcuk/doublestar/v4"
	"github.com/pelletier/go-toml/v2"
	"gopkg.in/yaml.v3"
)

// Blog is a collection of [Article]
type Blog struct {
	indexTemplate   *template.Template
	articleTemplate *template.Template
	Articles        []Article
	Author          Author
}

// Article is a blog post/article
type Article struct {
	Filename string
	Content  template.HTML
	ArticleMeta
}

// ArticleMeta is the metadata of an [Article]
// The meta is parsed from frontmatter in an article
type ArticleMeta struct {
	Title    string
	Subtitle string
	Summary  string
	Time     time.Time
	Author   Author
	Tags     []string
	Category string
}

// Author is an author of a blog/post
type Author struct {
	Name  string
	Job   string
	Email string
	Links []Link
}

// Link is a link name and URL
type Link struct {
	Name string
	URL  LinkURL
}

// LinkURL is a URL
type LinkURL url.URL

func (l *LinkURL) UnmarshalText(data []byte) error {
	u, err := url.Parse(string(data))
	if err != nil {
		return err
	}
	*l = LinkURL(*u)
	return nil
}

// NewBlog constructs a new blog from articles in articleDir and templates in templateDir
func NewBlog(articleDir, templateDir string, author Author) (*Blog, error) {
	tmpl, err := parseTemplates(os.DirFS(templateDir))
	if err != nil {
		return nil, fmt.Errorf("could not parse templates in %q: %w", templateDir, err)
	}
	indexTmpl := tmpl.Lookup("index.tmpl")
	if indexTmpl == nil {
		indexTmpl = tmpl.Lookup("index")
		if indexTmpl == nil {
			return nil, errors.New("`index` template is required but was not found")
		}
	}
	articleTmpl := tmpl.Lookup("article.tmpl")
	if articleTmpl == nil {
		articleTmpl = tmpl.Lookup("article")
		if articleTmpl == nil {
			return nil, errors.New("`article` template is required but was not found")
		}
	}
	articles, err := parseArticles(os.DirFS(articleDir))
	if err != nil {
		return nil, fmt.Errorf("could not parse articles in %q: %w", articleDir, err)
	}
	return &Blog{
		indexTemplate:   indexTmpl,
		articleTemplate: articleTmpl,
		Articles:        articles,
		Author:          author,
	}, nil
}

// Index renders the blog index to w
func (b *Blog) Index(w io.Writer) error {
	byCat := make(map[string][]Article)
	for _, article := range b.Articles {
		byCat[article.Category] = append(byCat[article.Category], article)
	}
	return b.indexTemplate.Execute(w, map[string]any{
		"Articles":           b.Articles,
		"ArticlesByCategory": byCat,
		"Author":             b.Author,
	})
}

// Article renders an article to w
func (b *Blog) Article(w io.Writer, a Article) error {
	return b.articleTemplate.Execute(w, map[string]any{
		"Article": a,
		"Author":  b.Author,
	})
}

func parseTemplates(fs fs.FS) (*template.Template, error) {
	matches, err := doublestar.Glob(fs, "**/*.{tmpl,gohtml}")
	if err != nil {
		return nil, fmt.Errorf("could not glob templates: %w", err)
	}
	tmpl, err := template.New("").ParseFS(fs, matches...)
	if err != nil {
		return nil, fmt.Errorf("could not parse templates: %w", err)
	}
	return tmpl, nil
}

func parseArticles(fs fs.FS) ([]Article, error) {
	matches, err := doublestar.Glob(fs, "**/*.md")
	if err != nil {
		return nil, fmt.Errorf("could not glob articles: %w", err)
	}
	articles := make([]Article, 0, len(matches))
	for _, match := range matches {
		if err := func() error {
			fi, err := fs.Open(match)
			if err != nil {
				return err
			}
			defer fi.Close()

			content, err := io.ReadAll(fi)
			if err != nil {
				return err
			}

			article, err := parseArticle(string(content))
			if err != nil {
				return err
			}
			article.Filename = strings.TrimSuffix(filepath.Base(match), filepath.Ext(match))
			articles = append(articles, article)
			return nil
		}(); err != nil {
			return nil, err
		}
	}
	sort.SliceStable(articles, func(i, j int) bool {
		return articles[i].Time.After(articles[j].Time)
	})
	return articles, nil
}

func parseArticle(content string) (Article, error) {
	lines := strings.Split(content, "\n")

	start, end := -1, -1
	var isSep func(string) bool
	var decoder func([]byte, any) error

	for idx, line := range lines {
		if strings.TrimSpace(line) == "" {
			continue
		}
		if isSep != nil && isSep(line) {
			end = idx
			break
		}

		if isTOMLSeparator(line) {
			start = idx
			isSep = isTOMLSeparator
			decoder = toml.Unmarshal
			continue
		}

		if isYAMLSeparator(line) {
			start = idx
			isSep = isYAMLSeparator
			decoder = yaml.Unmarshal
			continue
		}
	}

	var meta ArticleMeta
	body := content
	if start != -1 && end != -1 {
		body = strings.Join(lines[end+1:], "\n")
		if err := decoder([]byte(strings.Join(lines[start+1:end], "\n")), &meta); err != nil {
			return Article{}, fmt.Errorf("could not parse frontmatter: %w", err)
		}
	}

	var buf bytes.Buffer
	err := Markdown.Convert([]byte(body), &buf)
	if err != nil {
		return Article{}, fmt.Errorf("could not convert article: %w", err)
	}

	return Article{
		Content:     template.HTML(buf.String()),
		ArticleMeta: meta,
	}, nil
}

func isTOMLSeparator(line string) bool {
	for _, char := range line {
		if char != '+' {
			return false
		}
	}
	return true
}

func isYAMLSeparator(line string) bool {
	for _, char := range line {
		if char != '-' {
			return false
		}
	}
	return true
}