working on valuemonitor

settings.go

@@ -1,8 +1,10 @@
 package settings
 
 import (
+	"bufio"
 	"bytes"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -24,11 +26,67 @@ var (
 )
 
 type Settings struct {
-	mutex      sync.RWMutex
-	contents   map[string]string
-	filename   string
-	modtime    time.Time
-	LogUpdates atomic.Bool
+	mutex       sync.RWMutex
+	context     context.Context
+	contents    map[string]string
+	monitorKeys map[string]chan<- string
+	filename    string
+	modtime     time.Time
+	LogUpdates  atomic.Bool
+}
+
+func insertOrTimeout(ctx context.Context, c chan<- string, s string) error {
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case c <- s:
+		return nil
+	}
+}
+
+func (s *Settings) RegisterKeyToMonitor(key string, updateOutputChannel chan<- string) error {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+	if s.monitorKeys == nil {
+		s.monitorKeys = make(map[string]chan<- string, 1)
+	}
+	if _, found := s.monitorKeys[key]; found {
+		return fmt.Errorf("key %q already in monitorKeys map", key)
+	}
+	if err := insertOrTimeout(s.context, updateOutputChannel, s.contents[key]); err != nil {
+		return fmt.Errorf("error inserting: %w", err)
+	}
+	s.monitorKeys[key] = updateOutputChannel
+	return nil
+}
+
+func (s *Settings) Dump() ([]byte, error) {
+	var buffer bytes.Buffer
+	if err := s.DumpToWriter(&buffer); err != nil {
+		return nil, err
+	}
+	return buffer.Bytes(), nil
+}
+
+func (s *Settings) DumpToWriter(w io.Writer) error {
+	writer := bufio.NewWriter(w)
+	s.mutex.RLock()
+	defer s.mutex.RUnlock()
+	var index int
+	for k, v := range s.contents {
+		writer.WriteString(fmt.Sprintf("%s=%s", k, v))
+		if index < len(s.contents)-1 {
+			writer.WriteByte('\n')
+		}
+		index++
+	}
+	return writer.Flush()
+}
+
+func (s *Settings) DumpToJson() ([]byte, error) {
+	s.mutex.RLock()
+	defer s.mutex.RUnlock()
+	return json.Marshal(s.contents)
 }
 
 func (s *Settings) GetFilename() string {
@@ -68,6 +126,9 @@ func (s *Settings) lockedSetKeyValue(key, value string) bool {
 		log.Printf("Settings::lockedKeyValue %s: storing key '%s' with value '%s'\n", baseFilename, key, value)
 	}
 	s.contents[strings.Clone(key)] = strings.Clone(value)
+	if updateChannel, found := s.monitorKeys[key]; found {
+		insertOrTimeout(s.context, updateChannel, value)
+	}
 	return true
 }
 
@@ -132,10 +193,10 @@ func (s *Settings) Update() error {
 	return s.lockedUpdate()
 }
 
-func (s *Settings) maintenanceRoutine(ctx context.Context) {
+func (s *Settings) maintenanceRoutine() {
 	for {
 		select {
-		case <-ctx.Done():
+		case <-s.context.Done():
 			return
 		case <-time.After(MaintenanceRoutinePace):
 			err := s.Update()
@@ -154,6 +215,7 @@ func NewSettings(filename string, logUpdates bool) *Settings {
 
 func NewSettingsWithContext(ctx context.Context, filename string, logUpdates bool) *Settings {
 	settings := &Settings{
+		context:  ctx,
 		contents: make(map[string]string),
 		filename: strings.Clone(filename),
 	}
@@ -161,7 +223,7 @@ func NewSettingsWithContext(ctx context.Context, filename string, logUpdates boo
 	if err := settings.lockedUpdate(); err != nil && (!errors.Is(err, os.ErrNotExist) || WarnIfFileNotFound) {
 		log.Printf("NewSettingsWithContext %s error from initial update: %v\n", filepath.Base(filename), err)
 	}
-	go settings.maintenanceRoutine(ctx)
+	go settings.maintenanceRoutine()
 	return settings
 }