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/shutdown.go

@@ -0,0 +1,83 @@
+package app
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+)
+
+type killer struct{}
+
+func (k killer) Signal() {}
+func (k killer) String() string {
+	return "0"
+}
+
+type ShutdownHandler interface {
+	WatchForShutdown(server *http.Server)
+	shutdownHandler(w http.ResponseWriter, r *http.Request)
+}
+
+type shutdown struct {
+	sigCh chan os.Signal
+}
+
+func (s shutdown) WatchForShutdown(server *http.Server) {
+	/* Handles shutdown requests */
+	<-s.sigCh
+	err := server.Shutdown(context.Background())
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Server could not shut down gracefully: %s\n", err)
+		os.Exit(1)
+	} else {
+		os.Exit(0)
+	}
+}
+
+type ShutdownRequest struct {
+	Restart bool `json:"restart"`
+}
+
+/* shutdownHandler will shutdown the HTTP server and exit the process by signaling to the shutdown channel */
+func (s shutdown) shutdownHandler(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		w.Header().Set("Allow", http.MethodPost)
+		handleError(w, errors.New("Invalid request type"), "That request type is not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		handleError(w, err, "Could not read request body", http.StatusBadRequest)
+		return
+	}
+
+	var shutdownRequest ShutdownRequest
+	err = json.Unmarshal(body, &shutdownRequest)
+	if err != nil {
+		handleError(w, err, "Could not unmarshal data from request body", http.StatusBadRequest)
+		return
+	}
+
+	var text = "Shut down server"
+	if shutdownRequest.Restart {
+		text = "Restarted server"
+	}
+
+	w.WriteHeader(http.StatusOK)
+	response := SuccessResponse{
+		Message: text,
+		Status:  http.StatusOK,
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	} else {
+		s.sigCh <- killer{}
+	}
+}