1 files changed, 149 insertions, 0 deletions
diff --git a/internal/mdedit/main.go b/internal/mdedit/main.go
new file mode 100644
index 0000000..67cfdde
--- /dev/null
+++ b/internal/mdedit/main.go
@@ -0,0 +1,149 @@
+// SPDX-FileCopyrightText: 2025 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: GPL-3.0-only
+
+package mdedit
+
+import (
+	"bytes"
+	"context"
+	_ "embed"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"time"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/extension"
+	"github.com/yuin/goldmark/renderer/html"
+)
+
+// Exec executes the mdedit applet and returns an exit code (0 for success, >0 for error).
+func Exec(args []string) int {
+	if len(args) != 2 {
+		os.Stderr.Write([]byte("  Usage: mdedit <file.md> <listenaddr>\nExample: mdedit todolist.md localhost:8080\n"))
+		return 1
+	}
+	markdownPath, listenAddress := args[0], args[1]
+
+	// prepare HTTP server
+	l := logic{markdownPath}
+	m := http.NewServeMux()
+	m.HandleFunc("GET /{$}", l.handleGetFile("index.html", embeddedHTML))
+	m.HandleFunc("GET /res.css", l.handleGetFile("res.css", embeddedCSS))
+	m.HandleFunc("GET /res.js", l.handleGetFile("res.js", embeddedJS))
+	m.HandleFunc("GET /data.html", l.handleGetDataHTML)
+	m.HandleFunc("GET /data.md", l.handleGetDataMarkdown)
+	m.HandleFunc("PUT /data.md", l.handlePutDataMarkdown)
+	s := &http.Server{Addr: listenAddress, Handler: m}
+
+	exitCode := &atomic.Int32{}
+	exitCode.Store(0)
+
+	// setup termination of HTTP server on SIGINT/SIGTERM
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	var wg sync.WaitGroup
+	wg.Go(func() {
+		for range ctx.Done() {
+		}
+		ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+		err := s.Shutdown(ctx)
+		if err != nil {
+			log.Println("shutdown error: " + err.Error())
+			exitCode.Store(1)
+		}
+		cancel()
+	})
+
+	// run HTTP server
+	log.Printf("listening on %s...\n", listenAddress)
+	err := s.ListenAndServe()
+	if err != http.ErrServerClosed {
+		log.Println("listen error: " + err.Error())
+		exitCode.Store(1)
+	}
+	stop()
+	wg.Wait()
+
+	return int(exitCode.Load())
+}
+
+type logic struct {
+	MarkdownPath string
+}
+
+var (
+	//go:embed res/index.html
+	embeddedHTML []byte
+	//go:embed res/style.css
+	embeddedCSS []byte
+	//go:embed res/app.js
+	embeddedJS []byte
+)
+
+// Handles `GET /` and `GET /res/...`.
+func (l logic) handleGetFile(name string, contents []byte) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		http.ServeContent(w, r, name, time.Time{}, bytes.NewReader(contents))
+	}
+}
+
+// Handles `GET /data.html`.
+func (l logic) handleGetDataHTML(w http.ResponseWriter, r *http.Request) {
+	buf, err := os.ReadFile(l.MarkdownPath)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	l.respondByRenderingMarkdown(w, buf)
+}
+
+// Handles `GET /data.md`.
+func (l logic) handleGetDataMarkdown(w http.ResponseWriter, r *http.Request) {
+	buf, err := os.ReadFile(l.MarkdownPath)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("X-Mdedit-Path", l.MarkdownPath)
+	http.ServeContent(w, r, "data.md", time.Time{}, bytes.NewReader(buf))
+}
+
+// Handles `PUT /data.md`.
+func (l logic) handlePutDataMarkdown(w http.ResponseWriter, r *http.Request) {
+	const maxSizeBytes = 8 * 1024 * 1024 // 8 MiB ought to be enough for a single Markdown file
+	buf, err := io.ReadAll(io.LimitReader(r.Body, maxSizeBytes))
+	if err != nil {
+		http.Error(w, "while reading request body: "+err.Error(), http.StatusInternalServerError)
+		return
+	}
+	err = os.WriteFile(l.MarkdownPath, buf, 0666)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	l.respondByRenderingMarkdown(w, buf)
+}
+
+var md = goldmark.New(
+	goldmark.WithExtensions(extension.GFM),
+	goldmark.WithRendererOptions(html.WithUnsafe()),
+)
+
+func (l logic) respondByRenderingMarkdown(w http.ResponseWriter, source []byte) {
+	var buf bytes.Buffer
+	err := md.Convert(source, &buf)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.Write(buf.Bytes())
+}