[VOL-2310] Logging - Implement dynamic log levels in OpenOLT adapter

Working on Logging design changes.

Change-Id: I99a8ab22eb291332bf6528c8912fcbf16873232f
diff --git a/pkg/config/configmanager.go b/pkg/config/configmanager.go
new file mode 100644
index 0000000..8f96b22
--- /dev/null
+++ b/pkg/config/configmanager.go
@@ -0,0 +1,215 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+
+ * http://www.apache.org/licenses/LICENSE-2.0
+
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package config
+
+import (
+	"context"
+	"fmt"
+	"github.com/opencord/voltha-lib-go/v3/pkg/db"
+	"github.com/opencord/voltha-lib-go/v3/pkg/db/kvstore"
+	"github.com/opencord/voltha-lib-go/v3/pkg/log"
+	"strings"
+)
+
+const (
+	defaultkvStoreConfigPath = "config"
+	kvStoreDataPathPrefix    = "/service/voltha"
+	kvStorePathSeparator     = "/"
+)
+
+// ConfigType represents the type for which config is created inside the kvstore
+// For example, loglevel
+type ConfigType int
+
+const (
+	ConfigTypeLogLevel ConfigType = iota
+	ConfigTypeKafka
+)
+
+func (c ConfigType) String() string {
+	return [...]string{"loglevel", "kafka"}[c]
+}
+
+// ChangeEvent represents the event recieved from watch
+// For example, Put Event
+type ChangeEvent int
+
+const (
+	Put ChangeEvent = iota
+	Delete
+)
+
+// ConfigChangeEvent represents config for the events recieved from watch
+// For example,ChangeType is Put ,ConfigAttribute default
+type ConfigChangeEvent struct {
+	ChangeType      ChangeEvent
+	ConfigAttribute string
+}
+
+// ConfigManager is a wrapper over backend to maintain Configuration of voltha components
+// in kvstore based persistent storage
+type ConfigManager struct {
+	backend             *db.Backend
+	KvStoreConfigPrefix string
+}
+
+// ComponentConfig represents a category of configuration for a specific VOLTHA component type
+// stored in a persistent storage pointed to by Config Manager
+// For example, one ComponentConfig instance will be created for loglevel config type for rw-core
+// component while another ComponentConfig instance will refer to connection config type for same
+// rw-core component. So, there can be multiple ComponentConfig instance created per component
+// pointing to different category of configuration.
+//
+// Configuration pointed to be by ComponentConfig is stored in kvstore as a list of key/value pairs
+// under the hierarchical tree with following base path
+// <Backend Prefix Path>/<Config Prefix>/<Component Name>/<Config Type>/
+//
+// For example, rw-core ComponentConfig for loglevel config entries will be stored under following path
+// /voltha/service/config/rw-core/loglevel/
+type ComponentConfig struct {
+	cManager         *ConfigManager
+	componentLabel   string
+	configType       ConfigType
+	changeEventChan  chan *ConfigChangeEvent
+	kvStoreEventChan chan *kvstore.Event
+}
+
+func NewConfigManager(kvClient kvstore.Client, kvStoreType, kvStoreHost string, kvStorePort, kvStoreTimeout int) *ConfigManager {
+
+	return &ConfigManager{
+		KvStoreConfigPrefix: defaultkvStoreConfigPath,
+		backend: &db.Backend{
+			Client:     kvClient,
+			StoreType:  kvStoreType,
+			Host:       kvStoreHost,
+			Port:       kvStorePort,
+			Timeout:    kvStoreTimeout,
+			PathPrefix: kvStoreDataPathPrefix,
+		},
+	}
+}
+
+// Initialize the component config
+func (cm *ConfigManager) InitComponentConfig(componentLabel string, configType ConfigType) *ComponentConfig {
+
+	return &ComponentConfig{
+		componentLabel:   componentLabel,
+		configType:       configType,
+		cManager:         cm,
+		changeEventChan:  nil,
+		kvStoreEventChan: nil,
+	}
+
+}
+
+func (c *ComponentConfig) makeConfigPath() string {
+
+	cType := c.configType.String()
+	return c.cManager.KvStoreConfigPrefix + kvStorePathSeparator +
+		c.componentLabel + kvStorePathSeparator + cType
+}
+
+// MonitorForConfigChange watch on the subkeys for the given key
+// Any changes to the subkeys for the given key will return an event channel
+// Then Event channel will be processed and  new event channel with required values will be created and return
+// For example, rw-core will be watching on <Backend Prefix Path>/<Config Prefix>/<Component Name>/<Config Type>/
+// will return an event channel for PUT,DELETE eventType.
+// Then values from event channel will be processed and  stored in kvStoreEventChan.
+func (c *ComponentConfig) MonitorForConfigChange(ctx context.Context) chan *ConfigChangeEvent {
+	key := c.makeConfigPath()
+
+	log.Debugw("monitoring-for-config-change", log.Fields{"key": key})
+
+	c.changeEventChan = make(chan *ConfigChangeEvent, 1)
+
+	c.kvStoreEventChan = c.cManager.backend.CreateWatch(ctx, key, true)
+
+	go c.processKVStoreWatchEvents()
+
+	return c.changeEventChan
+}
+
+// processKVStoreWatchEvents process event channel recieved from the backend for any ChangeType
+// It checks for the EventType is valid or not.For the valid EventTypes creates ConfigChangeEvent and send it on channel
+func (c *ComponentConfig) processKVStoreWatchEvents() {
+
+	ccKeyPrefix := c.makeConfigPath()
+	log.Debugw("processing-kvstore-event-change", log.Fields{"key-prefix": ccKeyPrefix})
+	ccPathPrefix := c.cManager.backend.PathPrefix + ccKeyPrefix + kvStorePathSeparator
+	for watchResp := range c.kvStoreEventChan {
+
+		if watchResp.EventType == kvstore.CONNECTIONDOWN || watchResp.EventType == kvstore.UNKNOWN {
+			log.Warnw("received-invalid-change-type-in-watch-channel-from-kvstore", log.Fields{"change-type": watchResp.EventType})
+			continue
+		}
+
+		// populating the configAttribute from the received Key
+		// For Example, Key received would be <Backend Prefix Path>/<Config Prefix>/<Component Name>/<Config Type>/default
+		// Storing default in configAttribute variable
+		ky := fmt.Sprintf("%s", watchResp.Key)
+
+		c.changeEventChan <- &ConfigChangeEvent{
+			ChangeType:      ChangeEvent(watchResp.EventType),
+			ConfigAttribute: strings.TrimPrefix(ky, ccPathPrefix),
+		}
+	}
+}
+
+func (c *ComponentConfig) RetrieveAll(ctx context.Context) (map[string]string, error) {
+	key := c.makeConfigPath()
+
+	log.Debugw("retreiving-list", log.Fields{"key": key})
+	data, err := c.cManager.backend.List(ctx, key)
+	if err != nil {
+		return nil, err
+	}
+
+	// Looping through the data recieved from the backend for the given key
+	// Trimming the required key and value from data and  storing as key/value pair
+	// For Example, recieved key would be <Backend Prefix Path>/<Config Prefix>/<Component Name>/<Config Type>/default and value \"DEBUG\"
+	// Then in default will be stored as key and DEBUG will be stored as value in map[string]string
+	res := make(map[string]string)
+	ccPathPrefix := c.cManager.backend.PathPrefix + kvStorePathSeparator + key + kvStorePathSeparator
+	for attr, val := range data {
+		res[strings.TrimPrefix(attr, ccPathPrefix)] = strings.Trim(fmt.Sprintf("%s", val.Value), "\"")
+	}
+
+	return res, nil
+}
+
+func (c *ComponentConfig) Save(configKey string, configValue string, ctx context.Context) error {
+	key := c.makeConfigPath() + "/" + configKey
+
+	log.Debugw("saving-key", log.Fields{"key": key, "value": configValue})
+
+	//save the data for update config
+	if err := c.cManager.backend.Put(ctx, key, configValue); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (c *ComponentConfig) Delete(configKey string, ctx context.Context) error {
+	//construct key using makeConfigPath
+	key := c.makeConfigPath() + "/" + configKey
+
+	log.Debugw("deleting-key", log.Fields{"key": key})
+	//delete the config
+	if err := c.cManager.backend.Delete(ctx, key); err != nil {
+		return err
+	}
+	return nil
+}