working on valuemonitor

valuemonitor.go

@@ -0,0 +1,81 @@
+package settings
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"sync"
+)
+
+type ValueMonitorParseFunc[T any] func(string) (T, error)
+
+type ValueMonitor[T any] struct {
+	mutex      sync.RWMutex
+	parent     *Settings
+	updates    <-chan string
+	key        string
+	parserFunc ValueMonitorParseFunc[T]
+	value      T
+}
+
+func (v *ValueMonitor[T]) GetValue() T {
+	v.mutex.RLock()
+	defer v.mutex.RUnlock()
+	return v.value
+}
+
+func (v *ValueMonitor[T]) maintenanceThread() {
+	ctx := v.parent.context
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case s, ok := <-v.updates:
+			if !ok {
+				return
+			}
+			t, err := v.parserFunc(s)
+			if err != nil {
+				log.Printf("ValueMonitor error parsing key %q value %q from channel: %v\n", v.key, s, err)
+				continue
+			}
+			func() {
+				v.mutex.RLock()
+				defer v.mutex.RUnlock()
+				v.value = t
+			}()
+		}
+	}
+}
+
+func NewValueMonitor[T any](settings *Settings, key string, parserFunc ValueMonitorParseFunc[T]) (*ValueMonitor[T], error) {
+	monitorChannel := make(chan string, 1)
+	err := settings.RegisterKeyToMonitor(key, monitorChannel)
+	if err != nil {
+		close(monitorChannel)
+		return nil, fmt.Errorf("error registering ValueMonitor %w", err)
+	}
+	initialString, ok := <-monitorChannel
+	if !ok {
+		close(monitorChannel)
+		return nil, errors.New("channel closed before reading initial value")
+	}
+	parsed, err := parserFunc(initialString)
+	if err != nil {
+		close(monitorChannel)
+		return nil, fmt.Errorf("error parsing initial value from %q: %v", initialString, err)
+	}
+	go func() {
+		<-settings.context.Done()
+		close(monitorChannel)
+	}()
+	results := &ValueMonitor[T]{
+		parent:     settings,
+		updates:    monitorChannel,
+		key:        key,
+		parserFunc: parserFunc,
+		value:      parsed,
+	}
+	go results.maintenanceThread()
+	return results, nil
+}