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/merge_mr.go

@@ -0,0 +1,80 @@
+package app
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type AcceptMergeRequestRequest struct {
+	Squash        bool   `json:"squash"`
+	SquashMessage string `json:"squash_message"`
+	DeleteBranch  bool   `json:"delete_branch"`
+}
+
+type MergeRequestAccepter interface {
+	AcceptMergeRequest(pid interface{}, mergeRequest int, opt *gitlab.AcceptMergeRequestOptions, options ...gitlab.RequestOptionFunc) (*gitlab.MergeRequest, *gitlab.Response, error)
+}
+
+type mergeRequestAccepterService struct {
+	data
+	client MergeRequestAccepter
+}
+
+/* acceptAndMergeHandler merges a given merge request into the target branch */
+func (a mergeRequestAccepterService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Access-Control-Allow-Methods", http.MethodGet)
+	if r.Method != http.MethodPost {
+		handleError(w, InvalidRequestError{}, "Expected POST", http.StatusMethodNotAllowed)
+		return
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		handleError(w, err, "Could not read request body", http.StatusBadRequest)
+		return
+	}
+
+	var acceptAndMergeRequest AcceptMergeRequestRequest
+	err = json.Unmarshal(body, &acceptAndMergeRequest)
+	if err != nil {
+		handleError(w, err, "Could not unmarshal request body", http.StatusBadRequest)
+		return
+	}
+
+	opts := gitlab.AcceptMergeRequestOptions{
+		Squash:                   &acceptAndMergeRequest.Squash,
+		ShouldRemoveSourceBranch: &acceptAndMergeRequest.DeleteBranch,
+	}
+
+	if acceptAndMergeRequest.SquashMessage != "" {
+		opts.SquashCommitMessage = &acceptAndMergeRequest.SquashMessage
+	}
+
+	_, res, err := a.client.AcceptMergeRequest(a.projectInfo.ProjectId, a.projectInfo.MergeId, &opts)
+
+	if err != nil {
+		handleError(w, err, "Could not merge MR", http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/mr/merge"}, "Could not merge MR", res.StatusCode)
+		return
+	}
+
+	response := SuccessResponse{
+		Status:  http.StatusOK,
+		Message: "MR merged successfully",
+	}
+
+	w.WriteHeader(http.StatusOK)
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+}