daemon, store: switch to new store APIs in snapd (#2036)

* respond to Gustavo's review comments

- rename order->orderResult
- rename purchased->bought
- rename map ordersByID->bought

* respond to John's review comments

- Re-order case statements.
- Minimise scope of resp / err variables.
- Add FIXME to ReadyToBuy call.

daemon/api.go

@@ -1787,6 +1787,44 @@ func postCreateUser(c *Command, r *http.Request, user *auth.UserState) Response
 	}, nil)
 }
 
+func convertBuyError(err error) Response {
+	switch err {
+	case nil:
+		return nil
+	case store.ErrInvalidCredentials:
+		return Unauthorized(err.Error())
+	case store.ErrUnauthenticated:
+		return SyncResponse(&resp{
+			Type: ResponseTypeError,
+			Result: &errorResult{
+				Message: err.Error(),
+				Kind:    errorKindLoginRequired,
+			},
+			Status: http.StatusBadRequest,
+		}, nil)
+	case store.ErrTOSNotAccepted:
+		return SyncResponse(&resp{
+			Type: ResponseTypeError,
+			Result: &errorResult{
+				Message: err.Error(),
+				Kind:    errorKindTermsNotAccepted,
+			},
+			Status: http.StatusBadRequest,
+		}, nil)
+	case store.ErrNoPaymentMethods:
+		return SyncResponse(&resp{
+			Type: ResponseTypeError,
+			Result: &errorResult{
+				Message: err.Error(),
+				Kind:    errorKindNoPaymentMethods,
+			},
+			Status: http.StatusBadRequest,
+		}, nil)
+	default:
+		return InternalError("%v", err)
+	}
+}
+
 func postBuy(c *Command, r *http.Request, user *auth.UserState) Response {
 	var opts store.BuyOptions
 
@@ -1800,13 +1838,8 @@ func postBuy(c *Command, r *http.Request, user *auth.UserState) Response {
 
 	buyResult, err := s.Buy(&opts, user)
 
-	switch err {
-	default:
-		return InternalError("%v", err)
-	case store.ErrInvalidCredentials:
-		return Unauthorized(err.Error())
-	case nil:
-		// continue
+	if resp := convertBuyError(err); resp != nil {
+		return resp
 	}
 
 	return SyncResponse(buyResult, nil)
@@ -1823,6 +1856,15 @@ func getPaymentMethods(c *Command, r *http.Request, user *auth.UserState) Respon
 		return InternalError("%v", err)
 	case store.ErrInvalidCredentials:
 		return Unauthorized(err.Error())
+	case store.ErrUnauthenticated:
+		return SyncResponse(&resp{
+			Type: ResponseTypeError,
+			Result: &errorResult{
+				Message: err.Error(),
+				Kind:    errorKindLoginRequired,
+			},
+			Status: http.StatusBadRequest,
+		}, nil)
 	case nil:
 		// continue
 	}
@@ -1833,33 +1875,8 @@ func getPaymentMethods(c *Command, r *http.Request, user *auth.UserState) Respon
 func readyToBuy(c *Command, r *http.Request, user *auth.UserState) Response {
 	s := getStore(c)
 
-	err := s.ReadyToBuy(user)
-
-	switch err {
-	default:
-		return InternalError("%v", err)
-	case store.ErrInvalidCredentials:
-		return Unauthorized(err.Error())
-	case store.ErrTOSNotAccepted:
-		return SyncResponse(&resp{
-			Type: ResponseTypeError,
-			Result: &errorResult{
-				Message: err.Error(),
-				Kind:    errorKindTermsNotAccepted,
-			},
-			Status: http.StatusBadRequest,
-		}, nil)
-	case store.ErrNoPaymentMethods:
-		return SyncResponse(&resp{
-			Type: ResponseTypeError,
-			Result: &errorResult{
-				Message: err.Error(),
-				Kind:    errorKindNoPaymentMethods,
-			},
-			Status: http.StatusBadRequest,
-		}, nil)
-	case nil:
-		// continue
+	if resp := convertBuyError(s.ReadyToBuy(user)); resp != nil {
+		return resp
 	}
 
 	return SyncResponse(true, nil)