From 0abbefb7739f8beeaf5189758fc037f90ae12c41 Mon Sep 17 00:00:00 2001
From: Johan Lindh <johan@linkdata.se>
Date: Mon, 25 Nov 2024 08:58:48 +0100
Subject: [PATCH] add TemplateReloader

---
 templatereloader/assets/test.html         |  0
 templatereloader/templatereloader.go      | 61 +++++++++++++++++++++++
 templatereloader/templatereloader_test.go | 36 +++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 templatereloader/assets/test.html
 create mode 100644 templatereloader/templatereloader.go
 create mode 100644 templatereloader/templatereloader_test.go

diff --git a/templatereloader/assets/test.html b/templatereloader/assets/test.html
new file mode 100644
index 0000000..e69de29
diff --git a/templatereloader/templatereloader.go b/templatereloader/templatereloader.go
new file mode 100644
index 0000000..5c952af
--- /dev/null
+++ b/templatereloader/templatereloader.go
@@ -0,0 +1,61 @@
+package templatereloader
+
+import (
+	"html/template"
+	"io/fs"
+	"path"
+	"time"
+
+	"github.com/linkdata/deadlock"
+	"github.com/linkdata/jaws"
+)
+
+// A TemplateReloader reloads and reparses templates if more than one second
+// has passed since the last Lookup.
+type TemplateReloader struct {
+	Path string // the file path we are loading from
+	mu   deadlock.RWMutex
+	when time.Time
+	curr *template.Template
+}
+
+// New returns a jaws.TemplateLookuper.
+//
+// If deadlock.Debug is false, it calls template.New("").ParseFS(fsys, fpath).
+//
+// If deadlock.Debug is true, fsys is ignored and it returns a TemplateReloader
+// that loads the templates using ParseGlob(relpath/fpath).
+func New(fsys fs.FS, fpath, relpath string) (jtl jaws.TemplateLookuper, err error) {
+	return create(deadlock.Debug, fsys, fpath, relpath)
+}
+
+func create(debug bool, fsys fs.FS, fpath, relpath string) (tl jaws.TemplateLookuper, err error) {
+	if !debug {
+		return template.New("").ParseFS(fsys, fpath)
+	}
+	var tmpl *template.Template
+	fpath = path.Join(relpath, fpath)
+	if tmpl, err = template.New("").ParseGlob(fpath); err == nil {
+		tl = &TemplateReloader{
+			Path: fpath,
+			when: time.Now(),
+			curr: tmpl,
+		}
+	}
+	return
+}
+
+func (tr *TemplateReloader) Lookup(name string) *template.Template {
+	tr.mu.RLock()
+	tl := tr.curr
+	d := time.Since(tr.when)
+	tr.mu.RUnlock()
+	if d > time.Second {
+		tr.mu.Lock()
+		defer tr.mu.Unlock()
+		tr.curr = template.Must(template.New("").ParseGlob(tr.Path))
+		tr.when = tr.when.Add(d)
+		tl = tr.curr
+	}
+	return tl.Lookup(name)
+}
diff --git a/templatereloader/templatereloader_test.go b/templatereloader/templatereloader_test.go
new file mode 100644
index 0000000..e774150
--- /dev/null
+++ b/templatereloader/templatereloader_test.go
@@ -0,0 +1,36 @@
+package templatereloader
+
+import (
+	"embed"
+	"testing"
+	"time"
+)
+
+//go:embed assets
+var assetsFS embed.FS
+
+func TestNew(t *testing.T) {
+	tl, err := New(assetsFS, "assets/*.html", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tr := tl.(*TemplateReloader)
+	tr.when = tr.when.Add(-time.Second * 2)
+
+	tmpl := tl.Lookup("test.html")
+	if tmpl == nil {
+		t.Fail()
+	}
+}
+
+func Test_create_no_debug(t *testing.T) {
+	tl, err := create(false, assetsFS, "assets/*.html", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	tmpl := tl.Lookup("test.html")
+	if tmpl == nil {
+		t.Fail()
+	}
+}