VOL-2999 - Reworked how Proxies are created & used.

Added DB Paths to separate location specification logic from entry access logic.
Also merged Update() and AddWithID() and renamed to Set().

Change-Id: I9ed5eafd63c180dddc5845a166554f89bda12325
diff --git a/db/model/proxy.go b/db/model/proxy.go
index 997ebe4..cd35507 100644
--- a/db/model/proxy.go
+++ b/db/model/proxy.go
@@ -20,10 +20,12 @@
 	"context"
 	"errors"
 	"fmt"
+	"reflect"
+	"strings"
+
 	"github.com/gogo/protobuf/proto"
 	"github.com/opencord/voltha-lib-go/v3/pkg/db"
 	"github.com/opencord/voltha-lib-go/v3/pkg/log"
-	"reflect"
 )
 
 // RequestTimestamp attribute used to store a timestamp in the context object
@@ -31,30 +33,43 @@
 
 type contextKey string
 
-// Proxy holds the information for a specific location with the data model
-type Proxy struct {
+// Path holds the information for a specific location within the data model
+type Path struct {
 	kvStore *db.Backend
 	path    string
 }
 
-// NewProxy instantiates a new proxy to a specific location
-func NewProxy(kvStore *db.Backend, path string) *Proxy {
-	if path == "/" {
-		path = ""
-	}
-	return &Proxy{
-		kvStore: kvStore,
-		path:    path,
+// NewDBPath returns a path to the default db location
+func NewDBPath(kvStore *db.Backend) *Path {
+	return &Path{kvStore: kvStore}
+}
+
+// SubPath returns a path which points to a more specific db location
+func (p *Path) SubPath(path string) *Path {
+	path = strings.TrimRight(strings.TrimLeft(path, "/"), "/")
+	return &Path{
+		kvStore: p.kvStore,
+		path:    p.path + path + "/",
 	}
 }
 
-// List will retrieve information from the data model at the specified path location, and write it to the target slice
-// target must be a type of the form *[]<proto.Message Type>  For example: *[]*voltha.Device
-func (p *Proxy) List(ctx context.Context, path string, target interface{}) error {
-	completePath := p.path + path
+// Proxy contains all the information needed to reference a specific resource within the kv
+type Proxy Path
 
+// Proxy returns a new proxy which references the specified resource
+func (p *Path) Proxy(resource string) *Proxy {
+	resource = strings.TrimRight(strings.TrimLeft(resource, "/"), "/")
+	return &Proxy{
+		kvStore: p.kvStore,
+		path:    p.path + resource + "/",
+	}
+}
+
+// List will retrieve information from the data model at the proxy's path location, and write it to the target slice
+// target must be a type of the form *[]<proto.Message Type>  For example: *[]*voltha.Device
+func (p *Proxy) List(ctx context.Context, target interface{}) error {
 	logger.Debugw("proxy-list", log.Fields{
-		"path": completePath,
+		"path": p.path,
 	})
 
 	// verify type of target is *[]*<type>
@@ -72,13 +87,13 @@
 	}
 	dataType := elemType.Elem() // type
 
-	blobs, err := p.kvStore.List(ctx, completePath)
+	blobs, err := p.kvStore.List(ctx, p.path)
 	if err != nil {
-		return fmt.Errorf("failed to retrieve %s from kvstore: %s", path, err)
+		return fmt.Errorf("failed to retrieve %s from kvstore: %s", p.path, err)
 	}
 
 	logger.Debugw("parsing-data-blobs", log.Fields{
-		"path": path,
+		"path": p.path,
 		"size": len(blobs),
 	})
 
@@ -96,9 +111,9 @@
 	return nil
 }
 
-// Get will retrieve information from the data model at the specified path location, and write it to target
-func (p *Proxy) Get(ctx context.Context, path string, target proto.Message) (bool, error) {
-	completePath := p.path + path
+// Get will retrieve information from the data model at the proxy's path location, and write it to target
+func (p *Proxy) Get(ctx context.Context, id string, target proto.Message) (bool, error) {
+	completePath := p.path + id
 
 	logger.Debugw("proxy-get", log.Fields{
 		"path": completePath,
@@ -106,13 +121,13 @@
 
 	blob, err := p.kvStore.Get(ctx, completePath)
 	if err != nil {
-		return false, fmt.Errorf("failed to retrieve %s from kvstore: %s", path, err)
+		return false, fmt.Errorf("failed to retrieve %s from kvstore: %s", completePath, err)
 	} else if blob == nil {
 		return false, nil // this blob does not exist
 	}
 
 	logger.Debugw("parsing-data-blobs", log.Fields{
-		"path": path,
+		"path": completePath,
 	})
 
 	if err := proto.Unmarshal(blob.Value.([]byte), target); err != nil {
@@ -121,20 +136,9 @@
 	return true, nil
 }
 
-// Update will modify information in the data model at the specified location with the provided data
-func (p *Proxy) Update(ctx context.Context, path string, data proto.Message) error {
-	return p.add(ctx, path, data)
-}
-
-// AddWithID will insert new data at specified location.
-// This method also allows the user to specify the ID.
-func (p *Proxy) AddWithID(ctx context.Context, path string, id string, data proto.Message) error {
-	return p.add(ctx, path+"/"+id, data)
-}
-
-// add will insert new data at specified location.
-func (p *Proxy) add(ctx context.Context, path string, data proto.Message) error {
-	completePath := p.path + path
+// Set will add new or update existing entry at the proxy's path location
+func (p *Proxy) Set(ctx context.Context, id string, data proto.Message) error {
+	completePath := p.path + id
 
 	logger.Debugw("proxy-add", log.Fields{
 		"path": completePath,
@@ -151,9 +155,9 @@
 	return nil
 }
 
-// Remove will delete an entry at the specified location
-func (p *Proxy) Remove(ctx context.Context, path string) error {
-	completePath := p.path + path
+// Remove will delete an entry at the proxy's path location
+func (p *Proxy) Remove(ctx context.Context, id string) error {
+	completePath := p.path + id
 
 	logger.Debugw("proxy-remove", log.Fields{
 		"path": completePath,