Use a general approach to access custom/static/builtin assets (#24022)

The idea is to use a Layered Asset File-system (modules/assetfs/layered.go)

For example: when there are 2 layers: "custom", "builtin", when access
to asset "my/page.tmpl", the Layered Asset File-system will first try to
use "custom" assets, if not found, then use "builtin" assets.

This approach will hugely simplify a lot of code, make them testable.

Other changes:

* Simplify the AssetsHandlerFunc code
* Simplify the `gitea embedded` sub-command code

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

4 files changed, 68 insertions, 11 deletions

diff --git a/modules/util/path.go b/modules/util/path.go
index 37d06e9813..1a68bc7488 100644
--- a/modules/util/path.go
+++ b/modules/util/path.go
@@ -74,29 +74,28 @@ const pathSeparator = string(os.PathSeparator)
 //
 //	{`/foo`, ``, `bar`} => `/foo/bar`
 //	{`/foo`, `..`, `bar`} => `/foo/bar`
-func FilePathJoinAbs(elem ...string) string {
-	elems := make([]string, len(elem))
+func FilePathJoinAbs(base string, sub ...string) string {
+	elems := make([]string, 1, len(sub)+1)
 
-	// POISX filesystem can have `\` in file names. Windows: `\` and `/` are both used for path separators
+	// POSIX filesystem can have `\` in file names. Windows: `\` and `/` are both used for path separators
 	// to keep the behavior consistent, we do not allow `\` in file names, replace all `\` with `/`
 	if isOSWindows() {
-		elems[0] = filepath.Clean(elem[0])
+		elems[0] = filepath.Clean(base)
 	} else {
-		elems[0] = filepath.Clean(strings.ReplaceAll(elem[0], "\\", pathSeparator))
+		elems[0] = filepath.Clean(strings.ReplaceAll(base, "\\", pathSeparator))
 	}
 	if !filepath.IsAbs(elems[0]) {
 		// This shouldn't happen. If there is really necessary to pass in relative path, return the full path with filepath.Abs() instead
 		panic(fmt.Sprintf("FilePathJoinAbs: %q (for path %v) is not absolute, do not guess a relative path based on current working directory", elems[0], elems))
 	}
-
-	for i := 1; i < len(elem); i++ {
-		if elem[i] == "" {
+	for _, s := range sub {
+		if s == "" {
 			continue
 		}
 		if isOSWindows() {
-			elems[i] = filepath.Clean(pathSeparator + elem[i])
+			elems = append(elems, filepath.Clean(pathSeparator+s))
 		} else {
-			elems[i] = filepath.Clean(pathSeparator + strings.ReplaceAll(elem[i], "\\", pathSeparator))
+			elems = append(elems, filepath.Clean(pathSeparator+strings.ReplaceAll(s, "\\", pathSeparator)))
 		}
 	}
 	// the elems[0] must be an absolute path, just join them together
diff --git a/modules/util/path_test.go b/modules/util/path_test.go
index 1d27c9bf0c..6a38bf4ace 100644
--- a/modules/util/path_test.go
+++ b/modules/util/path_test.go
@@ -207,6 +207,6 @@ func TestCleanPath(t *testing.T) {
 		}
 	}
 	for _, c := range cases {
-		assert.Equal(t, c.expected, FilePathJoinAbs(c.elems...), "case: %v", c.elems)
+		assert.Equal(t, c.expected, FilePathJoinAbs(c.elems[0], c.elems[1:]...), "case: %v", c.elems)
 	}
 }
diff --git a/modules/util/timer.go b/modules/util/timer.go
index daf96bda7e..d598fde73a 100644
--- a/modules/util/timer.go
+++ b/modules/util/timer.go
@@ -4,6 +4,7 @@
 package util
 
 import (
+	"sync"
 	"time"
 )
 
@@ -18,3 +19,30 @@ func StopTimer(t *time.Timer) bool {
 	}
 	return stopped
 }
+
+func Debounce(d time.Duration) func(f func()) {
+	type debouncer struct {
+		mu sync.Mutex
+		t  *time.Timer
+	}
+	db := &debouncer{}
+
+	return func(f func()) {
+		db.mu.Lock()
+		defer db.mu.Unlock()
+
+		if db.t != nil {
+			db.t.Stop()
+		}
+		var trigger *time.Timer
+		trigger = time.AfterFunc(d, func() {
+			db.mu.Lock()
+			defer db.mu.Unlock()
+			if trigger == db.t {
+				f()
+				db.t = nil
+			}
+		})
+		db.t = trigger
+	}
+}
diff --git a/modules/util/timer_test.go b/modules/util/timer_test.go
new file mode 100644
index 0000000000..602800c248
--- /dev/null
+++ b/modules/util/timer_test.go
@@ -0,0 +1,30 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDebounce(t *testing.T) {
+	var c int64
+	d := Debounce(50 * time.Millisecond)
+	d(func() { atomic.AddInt64(&c, 1) })
+	assert.EqualValues(t, 0, atomic.LoadInt64(&c))
+	d(func() { atomic.AddInt64(&c, 1) })
+	d(func() { atomic.AddInt64(&c, 1) })
+	time.Sleep(100 * time.Millisecond)
+	assert.EqualValues(t, 1, atomic.LoadInt64(&c))
+	d(func() { atomic.AddInt64(&c, 1) })
+	assert.EqualValues(t, 1, atomic.LoadInt64(&c))
+	d(func() { atomic.AddInt64(&c, 1) })
+	d(func() { atomic.AddInt64(&c, 1) })
+	d(func() { atomic.AddInt64(&c, 1) })
+	time.Sleep(100 * time.Millisecond)
+	assert.EqualValues(t, 2, atomic.LoadInt64(&c))
+}