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/summary.go

@@ -0,0 +1,80 @@
+package app
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type SummaryUpdateRequest struct {
+	Description string `json:"description"`
+	Title       string `json:"title"`
+}
+
+type SummaryUpdateResponse struct {
+	SuccessResponse
+	MergeRequest *gitlab.MergeRequest `json:"mr"`
+}
+
+type summaryService struct {
+	data
+	client MergeRequestUpdater
+}
+
+func (a summaryService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+
+	if r.Method != http.MethodPut {
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodPut)
+		handleError(w, InvalidRequestError{}, "Expected PUT", http.StatusMethodNotAllowed)
+		return
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		handleError(w, err, "Could not read request body", http.StatusBadRequest)
+		return
+	}
+
+	defer r.Body.Close()
+	var SummaryUpdateRequest SummaryUpdateRequest
+	err = json.Unmarshal(body, &SummaryUpdateRequest)
+
+	if err != nil {
+		handleError(w, err, "Could not read JSON from request", http.StatusBadRequest)
+		return
+	}
+
+	mr, res, err := a.client.UpdateMergeRequest(a.projectInfo.ProjectId, a.projectInfo.MergeId, &gitlab.UpdateMergeRequestOptions{
+		Description: &SummaryUpdateRequest.Description,
+		Title:       &SummaryUpdateRequest.Title,
+	})
+
+	if err != nil {
+		handleError(w, err, "Could not edit merge request summary", http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/summary"}, "Could not edit merge request summary", res.StatusCode)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+
+	response := SummaryUpdateResponse{
+		SuccessResponse: SuccessResponse{
+			Message: "Summary updated",
+			Status:  http.StatusOK,
+		},
+		MergeRequest: mr,
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+
+}