Created
June 13, 2021 07:31
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from the book "Learning Go"
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package main | |
import ( | |
"errors" | |
"fmt" | |
"net/http" | |
) | |
func main() { | |
l := LoggerAdaptor(LogOutput) | |
ds := NewSimpleDataStore() | |
logic := NewSimpleLogic(l, ds) | |
c := NewController(l, logic) | |
http.HandleFunc("/hello", c.SayHello) | |
http.ListenAndServe(":8080", nil) | |
} | |
func LogOutput(message string) { | |
fmt.Println(message) | |
} | |
type SimpleDataStore struct { | |
userData map[string]string | |
} | |
func (sds SimpleDataStore) UserNameForID(userID string) (string, bool) { | |
name, ok := sds.userData[userID] | |
return name, ok | |
} | |
func NewSimpleDataStore() SimpleDataStore { | |
return SimpleDataStore{ | |
userData: map[string]string{ | |
"1": "Fred", | |
"2": "Mary", | |
"3": "Pat", | |
}, | |
} | |
} | |
// We define interfaces for our actual business logic, since | |
// we may move our logger and simpledatastore to something | |
// more complex later.. | |
type DataStore interface { | |
UserNameForID(userID string) (string, bool) | |
} | |
type Logger interface { | |
Log(message string) | |
} | |
// Logoutput needs to adhere to this interface now.. | |
type LoggerAdaptor func(message string) | |
func (lg LoggerAdaptor) Log(message string) { | |
lg(message) | |
} | |
type SimpleLogic struct { | |
l Logger | |
ds DataStore | |
} | |
func (sl SimpleLogic) SayHello(userID string) (string, error) { | |
sl.l.Log("in SayHello for " + userID) | |
name, ok := sl.ds.UserNameForID(userID) | |
if !ok { | |
return "", errors.New("unknown user") | |
} | |
return "Hello, " + name, nil | |
} | |
func (sl SimpleLogic) SayGoodbye(userID string) (string, error) { | |
sl.l.Log("in SayGoodbye for " + userID) | |
name, ok := sl.ds.UserNameForID(userID) | |
if !ok { | |
return "", errors.New("unknown user") | |
} | |
return "Goodbye, " + name, nil | |
} | |
func NewSimpleLogic(l Logger, ds DataStore) SimpleLogic { | |
return SimpleLogic{ | |
l: l, | |
ds: ds, | |
} | |
} | |
// Now the API | |
type Logic interface { | |
SayHello(userID string) (string, error) | |
} | |
type Controller struct { | |
l Logger | |
logic Logic | |
} | |
func (c Controller) SayHello(w http.ResponseWriter, r *http.Request) { | |
c.l.Log("In Say Hello") | |
userID := r.URL.Query().Get("user_id") | |
message, err := c.logic.SayHello(userID) | |
if err != nil { | |
w.WriteHeader(http.StatusBadRequest) | |
w.Write([]byte(err.Error())) | |
return | |
} | |
w.Write([]byte(message)) | |
} | |
// factory function for this too.. accept interface, return | |
// structs | |
func NewController(l Logger, logic Logic) Controller { | |
return Controller{ | |
l: l, | |
logic: logic, | |
} | |
} |
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