1 files changed, 220 insertions, 0 deletions
diff --git a/config.go b/config.go
new file mode 100644
index 0000000..7164e93
--- /dev/null
+++ b/config.go
@@ -0,0 +1,220 @@
+package main
+
+import (
+	"log"
+	"os"
+	"path"
+	"strings"
+	"sync/atomic"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+type Lang struct {
+	Code string
+	Name string
+}
+
+// Wrapper over atomic.Value; contains []string
+type atomicStringSlice struct {
+	v atomic.Value
+}
+// Wrapper over atomic.Value; contains []Lang
+type atomicLangSlice struct {
+	v atomic.Value
+}
+
+// A config that is just a list of lines of text
+type lineListConfig struct {
+	path  string
+	items atomicStringSlice
+}
+
+// A config that is list of two-column lines sepparated by a tab character
+type langListConfig struct {
+	path  string
+	langs atomicLangSlice
+}
+
+// Interface for all types of configs that can be updated/reloaded
+type updatableConfig interface {
+	update() error
+}
+
+// The data type that will watch for changes in some updatableConfig types and
+// call their update() methods on changes
+type configWatcher struct {
+	lists   map[string]updatableConfig
+	watcher *fsnotify.Watcher
+	dirpath string
+}
+
+var watcher configWatcher
+
+func (v *atomicStringSlice) Load() []string {
+	return v.v.Load().([]string)
+}
+
+func (v *atomicStringSlice) Store(val []string) {
+	v.v.Store(val)
+}
+
+func (v *atomicLangSlice) Load() []Lang {
+	return v.v.Load().([]Lang)
+}
+
+func (v *atomicLangSlice) Store(val []Lang) {
+	v.v.Store(val)
+}
+
+// Re-read the file of this and update the items list.
+func (c *lineListConfig) update() error {
+	data, err := os.ReadFile(c.path)
+	if err != nil {
+		return err
+	}
+
+	// Cut the string into substrings line by line omitting empty lines.
+	s := string(data)
+	sep := "\n"
+	items := make([]string, 0, 8)
+	for {
+		if i := strings.Index(s, sep); i >= 0 {
+			sub := s[:i]
+			if len(sub) > 0 {
+				items = append(items, sub)
+			}
+			s = s[i+len(sep):]
+			continue
+		}
+		break
+	}
+	c.items.Store(items)
+
+	return nil
+}
+
+// Return the slice of strings atomically
+func (c *lineListConfig) getList() []string {
+	return c.items.Load()
+}
+
+// Re-read the file of this and update the items list.
+func (c *langListConfig) update() error {
+	data, err := os.ReadFile(c.path)
+	if err != nil {
+		return err
+	}
+
+	// Cut the string into substring line by line omitting empty lines, and
+	// sepparating the code and the name of the language.
+	s := string(data)
+	sep := "\n"
+	langs := make([]Lang, 0, 8)
+	for {
+		if i := strings.Index(s, sep); i >= 0 {
+			sub := s[:i]
+			if len(sub) > 0 {
+				cols := strings.SplitN(sub, "\t", 2)
+				if len(cols) < 2 {
+					log.Println("WARNING: bad language format:", sub)
+				} else {
+					langs = append(langs, Lang{ cols[0], cols[1] })
+				}
+			}
+			s = s[i+len(sep):]
+			continue
+		}
+		break
+	}
+	c.langs.Store(langs)
+
+	return nil
+}
+
+// Return the slice of strings atomically
+func (c *langListConfig) getList() []Lang {
+	return c.langs.Load()
+}
+
+// Make a new lineListConfig from the file that is inside the configWatcher dir
+// with the name give in this method. The name of the file will be automatically
+// watched by the configWatcher. Returns a new instance of a lineListConfig if
+// there were no errors.
+func newLineListConfig(name string) (*lineListConfig, error) {
+	var err error
+	path := path.Join(watcher.dirpath, name)
+
+	c := &lineListConfig{path: path}
+	err = c.update()
+	watcher.lists[path] = c
+
+	return c, err
+}
+
+// Make a new langListConfig; the same story as with lineListConfig
+func newLangListConfig(name string) (*langListConfig, error) {
+	var err error
+	path := path.Join(watcher.dirpath, name)
+
+	c := &langListConfig{path: path}
+	err = c.update()
+	watcher.lists[path] = c
+
+	return c, err
+}
+
+// Initialize and start the config watcher.
+func startConfigWatcher(path string) error {
+	var err error
+
+	watcher.lists = make(map[string]updatableConfig)
+	watcher.dirpath = path
+
+	watcher.watcher, err = fsnotify.NewWatcher()
+	if err != nil {
+		return err
+	}
+	err = watcher.watcher.Add(path)
+	if err != nil {
+		return err
+	}
+
+	go func() {
+		for {
+			select {
+			case e, ok := <-watcher.watcher.Events:
+				if !ok {
+					return
+				}
+				if e.Has(fsnotify.Write) {
+					cl, ok := watcher.lists[e.Name]
+					if ok {
+						if err := cl.update(); err != nil {
+							log.Println(
+								"read error: couldn't update", e.Name, ":", err,
+							)
+							break
+						}
+						log.Println("reloaded config list from file:", e.Name)
+					}
+				}
+			case err, ok := <-watcher.watcher.Errors:
+				if !ok {
+					return
+				}
+				log.Println("watcher error:", err)
+			}
+		}
+	}()
+
+	return err
+}
+
+// Stop the configList watcher.
+func stopConfigWatcher() {
+	err := watcher.watcher.Close()
+	if err != nil {
+		log.Println("watcher error: on close:", err)
+	}
+}