From 5a00a896236495842c3db214743fbde0375277ab Mon Sep 17 00:00:00 2001
From: Artjoms Nemiro <nemtjom@hotmail.com>
Date: Thu, 15 Jun 2017 23:25:47 +0300
Subject: [PATCH] Small improvement of proxy example

---
 structural/proxy/main.go | 57 +++++++++++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 13 deletions(-)

diff --git a/structural/proxy/main.go b/structural/proxy/main.go
index ed14406..f9242fe 100644
--- a/structural/proxy/main.go
+++ b/structural/proxy/main.go
@@ -11,19 +11,17 @@ func main() {
 	var excErr error   // error of executing command
 
 	// Create new instance of Proxy terminal
-	t := new(Terminal)
-
-	// Try execute command with invalid user
-	if excResp, excErr = t.ExecuteCommand("badGopher", "capture_land"); excErr != nil {
-		fmt.Printf("%s\n", excErr.Error()) // Prints: You are not allowed to execute commands
+	t, err := NewTerminal("gopher")
+	if err != nil {
+		panic(err.Error())
 	}
 
-	// Try execute incorrect command
-	if excResp, excErr = t.ExecuteCommand("gopher", "doJob"); excErr != nil {
+	// Execute user command
+	if excResp, excErr = t.Execute("gopher", "say_hi"); excErr != nil {
 		fmt.Printf("%s\n", excErr.Error()) // Prints: I know only how to say hello (command: say_hi)
 	}
 
-	// Show correct result of execution
+	// Show execution response
 	fmt.Println(excResp) // Prints: Hi gopher
 }
 
@@ -31,6 +29,11 @@ func main() {
 	From that it's can be different terminals realizations with different methods, propertys, yda yda...
 */
 
+// First we must declare interface with public method its will be implemented in GopherTerminal and Terminal(Proxy)
+type ITerminal interface {
+	Execute(cmd string) (resp string, err error)
+}
+
 // GopherTerminal for example:
 // Its a "huge" structure with different public methods
 type GopherTerminal struct {
@@ -43,6 +46,7 @@ func (gt *GopherTerminal) Execute(cmd string) (resp string, err error) {
 
 	if cmd != "say_hi" {
 		err = fmt.Errorf("Unknown command")
+		return
 	}
 
 	resp = fmt.Sprintf("Hi %s", gt.user)
@@ -57,24 +61,38 @@ func (gt *GopherTerminal) Execute(cmd string) (resp string, err error) {
 // Terminal is a implementation of Proxy, it's  validates and sends data to GopherTerminal
 // As example before send commands, user must be authorized
 type Terminal struct {
+	currentUser string
 	gopherTerminal *GopherTerminal
 }
 
+// NewTerminal creates new instance of terminal
+func NewTerminal(user string) (t *Terminal, err error)  {
+	// Check user if given correctly
+	if user == "" {
+		err = fmt.Errorf("User cant be empty")
+		return
+	}
+
+	t = &Terminal{currentUser: user}
+
+	return
+}
+
 // ExecuteCommand intercepts execution of command, implements authorizing user, validates it and
 // poxing command to real terminal (gopherTerminal) method
-func (t *Terminal) ExecuteCommand(user, command string) (resp string, err error) {
-	// As we use terminal like proxy, then
-	// we will intercept user name to validate if it's allowed to execute commands
-	if user != "gopher" {
+func (t *Terminal) Execute(user, command string) (resp string, err error) {
+	// Before we execute user commands, we validate current user, if he have rights to do it
+	if authErr := t.authorizeUser(); authErr != nil {
 		err = fmt.Errorf("You are not allowed to execute commands")
 		return
 	}
 
-	// if user allowed to execute send commands then, for example we can decide which terminal can be used, remote or local etc..
+	// If user allowed to execute send commands then, for example we can decide which terminal can be used, remote or local etc..
 	// but for example we just creating new instance of terminal,
 	// set current user and send user command to execution in terminal
 	t.gopherTerminal = new(GopherTerminal)
 	t.gopherTerminal.user = user
+
 	if resp, err = t.gopherTerminal.Execute(command); err != nil {
 		err = fmt.Errorf("I know only how to say hello (command: say_hi)")
 		return
@@ -82,3 +100,16 @@ func (t *Terminal) ExecuteCommand(user, command string) (resp string, err error)
 
 	return
 }
+
+// authorize validates user right to execute commands
+func (t *Terminal) authorizeUser() (err error) {
+	// As we use terminal like proxy, then
+	// we will intercept user name to validate if it's allowed to execute commands
+	if t.currentUser != "gopher" {
+		// Do some logs, notifications etc...
+		err = fmt.Errorf("User %s in black list", t.currentUser)
+		return
+	}
+
+	return
+}