Fix MR Selection, Go Code Refactor (#358)

refactor: Refactors the Go codebase into a more modular and idiomatic approach
fix: require selection of specific MR when there are multiple targets for a given source branch
feat: Allows for the passing of Gitlab's filter options when choosing an MR, improves MR selection
feat: API to choose an MR from a list based on the provided username's involvement as an assignee/reviewer/author

This is a #MINOR release

cmd/app/user.go

@@ -0,0 +1,56 @@
+package app
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type UserResponse struct {
+	SuccessResponse
+	User *gitlab.User `json:"user"`
+}
+
+type MeGetter interface {
+	CurrentUser(options ...gitlab.RequestOptionFunc) (*gitlab.User, *gitlab.Response, error)
+}
+
+type meService struct {
+	data
+	client MeGetter
+}
+
+func (a meService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	if r.Method != http.MethodGet {
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodGet)
+		handleError(w, InvalidRequestError{}, "Expected GET", http.StatusMethodNotAllowed)
+		return
+	}
+
+	user, res, err := a.client.CurrentUser()
+
+	if err != nil {
+		handleError(w, err, "Failed to get current user", http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, err, "User API returned non-200 status", res.StatusCode)
+		return
+	}
+
+	response := UserResponse{
+		SuccessResponse: SuccessResponse{
+			Message: "User fetched successfully",
+			Status:  http.StatusOK,
+		},
+		User: user,
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+}