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/server.go

@@ -0,0 +1,199 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/harrisoncramer/gitlab.nvim/cmd/app/git"
+	"github.com/xanzy/go-gitlab"
+)
+
+/*
+startSever starts the server and runs concurrent goroutines
+to handle potential shutdown requests and incoming HTTP requests.
+*/
+func StartServer(client *Client, projectInfo *ProjectInfo, GitInfo git.GitData) {
+
+	s := shutdown{
+		sigCh: make(chan os.Signal, 1),
+	}
+
+	fr := attachmentReader{}
+	r := CreateRouter(
+		client,
+		projectInfo,
+		s,
+		func(a *data) error { a.projectInfo = projectInfo; return nil },
+		func(a *data) error { a.gitInfo = &GitInfo; return nil },
+		func(a *data) error { err := attachEmojis(a, fr); return err },
+	)
+	l := createListener()
+
+	server := &http.Server{Handler: r}
+
+	/* Starts the Go server */
+	go func() {
+		err := server.Serve(l)
+		if err != nil {
+			if errors.Is(err, http.ErrServerClosed) {
+				os.Exit(0)
+			} else {
+				fmt.Fprintf(os.Stderr, "Server did not respond: %s\n", err)
+				os.Exit(1)
+			}
+		}
+	}()
+
+	port := l.Addr().(*net.TCPAddr).Port
+	err := checkServer(port)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Server did not respond: %s\n", err)
+		os.Exit(1)
+	}
+
+	/* This print is detected by the Lua code */
+	fmt.Println("Server started on port: ", port)
+
+	/* Handles shutdown requests */
+	s.WatchForShutdown(server)
+}
+
+/*
+CreateRouterAndApi wires up the router and attaches all handlers to their respective routes. It also
+iterates over all option functions to configure API fields such as the project information and default
+file reader functionality
+*/
+
+type data struct {
+	projectInfo *ProjectInfo
+	gitInfo     *git.GitData
+	emojiMap    EmojiMap
+}
+
+type optFunc func(a *data) error
+
+func CreateRouter(gitlabClient *Client, projectInfo *ProjectInfo, s ShutdownHandler, optFuncs ...optFunc) *http.ServeMux {
+	m := http.NewServeMux()
+
+	d := data{
+		projectInfo: &ProjectInfo{},
+		gitInfo:     &git.GitData{},
+	}
+
+	/* Mutates the API struct as necessary with configuration functions */
+	for _, optFunc := range optFuncs {
+		err := optFunc(&d)
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	m.HandleFunc("/mr/approve", withMr(mergeRequestApproverService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/comment", withMr(commentService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/merge", withMr(mergeRequestAccepterService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/discussions/list", withMr(discussionsListerService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/discussions/resolve", withMr(discussionsResolutionService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/info", withMr(infoService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/assignee", withMr(assigneesService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/summary", withMr(summaryService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/reviewer", withMr(reviewerService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/revisions", withMr(revisionsService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/reply", withMr(replyService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/label", withMr(labelService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/revoke", withMr(mergeRequestRevokerService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/awardable/note/", withMr(emojiService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/draft_notes/", withMr(draftNoteService{d, gitlabClient}, d, gitlabClient))
+	m.HandleFunc("/mr/draft_notes/publish", withMr(draftNotePublisherService{d, gitlabClient}, d, gitlabClient))
+
+	m.HandleFunc("/pipeline", pipelineService{d, gitlabClient, git.Git{}}.handler)
+	m.HandleFunc("/pipeline/trigger/", pipelineService{d, gitlabClient, git.Git{}}.handler)
+	m.HandleFunc("/users/me", meService{d, gitlabClient}.handler)
+	m.HandleFunc("/attachment", attachmentService{data: d, client: gitlabClient, fileReader: attachmentReader{}}.handler)
+	m.HandleFunc("/create_mr", mergeRequestCreatorService{d, gitlabClient}.handler)
+	m.HandleFunc("/job", traceFileService{d, gitlabClient}.handler)
+	m.HandleFunc("/project/members", projectMemberService{d, gitlabClient}.handler)
+	m.HandleFunc("/merge_requests", mergeRequestListerService{d, gitlabClient}.handler)
+	m.HandleFunc("/merge_requests_by_username", mergeRequestListerByUsernameService{d, gitlabClient}.handler)
+
+	m.HandleFunc("/shutdown", s.shutdownHandler)
+	m.Handle("/ping", http.HandlerFunc(pingHandler))
+
+	return m
+}
+
+/* Used to check whether the server has started yet */
+func pingHandler(w http.ResponseWriter, _ *http.Request) {
+	w.WriteHeader(http.StatusOK)
+	fmt.Fprintln(w, "pong")
+}
+
+/* checkServer pings the server repeatedly for 1 full second after startup in order to notify the plugin that the server is ready */
+func checkServer(port int) error {
+	for i := 0; i < 10; i++ {
+		resp, err := http.Get("http://localhost:" + fmt.Sprintf("%d", port) + "/ping")
+		if resp.StatusCode == 200 && err == nil {
+			return nil
+		}
+		time.Sleep(100 * time.Microsecond)
+	}
+
+	return errors.New("Could not start server!")
+}
+
+/* Creates a TCP listener on the port specified by the user or a random port */
+func createListener() (l net.Listener) {
+	addr := fmt.Sprintf("localhost:%d", pluginOptions.Port)
+	l, err := net.Listen("tcp", addr)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error starting server: %s\n", err)
+		os.Exit(1)
+	}
+
+	return l
+}
+
+type ServiceWithHandler interface {
+	handler(http.ResponseWriter, *http.Request)
+}
+
+/* withMr is a Middlware that gets the current merge request ID and attaches it to the projectInfo */
+func withMr(svc ServiceWithHandler, c data, client MergeRequestLister) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		// If the merge request is already attached, skip the middleware logic
+		if c.projectInfo.MergeId == 0 {
+			options := gitlab.ListProjectMergeRequestsOptions{
+				Scope:        gitlab.Ptr("all"),
+				SourceBranch: &c.gitInfo.BranchName,
+				TargetBranch: pluginOptions.ChosenTargetBranch,
+			}
+
+			mergeRequests, _, err := client.ListProjectMergeRequests(c.projectInfo.ProjectId, &options)
+			if err != nil {
+				handleError(w, fmt.Errorf("Failed to list merge requests: %w", err), "Failed to list merge requests", http.StatusInternalServerError)
+				return
+			}
+
+			if len(mergeRequests) == 0 {
+				err := fmt.Errorf("No merge requests found for branch '%s'", c.gitInfo.BranchName)
+				handleError(w, err, "No merge requests found", http.StatusBadRequest)
+				return
+			}
+
+			if len(mergeRequests) > 1 {
+				err := errors.New("Please call gitlab.choose_merge_request()")
+				handleError(w, err, "Multiple MRs found", http.StatusBadRequest)
+				return
+			}
+
+			mergeIdInt := mergeRequests[0].IID
+			c.projectInfo.MergeId = mergeIdInt
+		}
+
+		// Call the next handler if middleware succeeds
+		svc.handler(w, r)
+	}
+}