Allow translations to be overridden in the data folder

utils/merge_fs.go

@@ -0,0 +1,108 @@
+package utils
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"sort"
+)
+
+type MergeFS struct {
+	base    http.FileSystem
+	overlay http.FileSystem
+}
+
+func NewMergeFS(base, overlay http.FileSystem) http.FileSystem {
+	return &MergeFS{
+		base:    base,
+		overlay: overlay,
+	}
+}
+
+func (m MergeFS) Open(name string) (http.File, error) {
+	f, err := m.overlay.Open(name)
+	if err != nil {
+		return m.base.Open(name)
+	}
+
+	info, err := f.Stat()
+	if err != nil {
+		_ = f.Close()
+		return m.base.Open(name)
+	}
+
+	if !info.IsDir() {
+		return f, nil
+	}
+
+	baseDir, _ := m.base.Open(name)
+	defer func() {
+		_ = baseDir.Close()
+		_ = f.Close()
+	}()
+	return m.mergeDirs(name, info, baseDir, f)
+}
+
+func (m MergeFS) mergeDirs(name string, info os.FileInfo, baseDir http.File, overlayDir http.File) (http.File, error) {
+	merged := map[string]os.FileInfo{}
+
+	baseFiles, err := baseDir.Readdir(-1)
+	if err != nil {
+		return nil, err
+	}
+	sort.Slice(baseFiles, func(i, j int) bool { return baseFiles[i].Name() < baseFiles[j].Name() })
+
+	overlayFiles, err := overlayDir.Readdir(-1)
+	if err != nil {
+		overlayFiles = nil
+	}
+	sort.Slice(overlayFiles, func(i, j int) bool { return overlayFiles[i].Name() < overlayFiles[j].Name() })
+
+	for _, f := range baseFiles {
+		merged[f.Name()] = f
+	}
+	for _, f := range overlayFiles {
+		merged[f.Name()] = f
+	}
+
+	var entries []os.FileInfo
+	for _, i := range merged {
+		entries = append(entries, i)
+	}
+
+	sort.Slice(entries, func(i, j int) bool { return entries[i].Name() < entries[j].Name() })
+	return &mergedDir{
+		name:    name,
+		info:    info,
+		entries: entries,
+	}, nil
+}
+
+type mergedDir struct {
+	name    string
+	info    os.FileInfo
+	entries []os.FileInfo
+	pos     int
+}
+
+func (d mergedDir) Readdir(count int) ([]os.FileInfo, error) {
+	if d.pos >= len(d.entries) && count > 0 {
+		return nil, io.EOF
+	}
+	if count <= 0 || count > len(d.entries)-d.pos {
+		count = len(d.entries) - d.pos
+	}
+	e := d.entries[d.pos : d.pos+count]
+	d.pos += count
+	return e, nil
+}
+
+func (d mergedDir) Close() error               { return nil }
+func (d mergedDir) Stat() (os.FileInfo, error) { return d.info, nil }
+func (d mergedDir) Read(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("cannot Read from directory %s", d.name)
+}
+func (d mergedDir) Seek(offset int64, whence int) (int64, error) {
+	return 0, fmt.Errorf("unsupported Seek in directory %s", d.name)
+}