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/attachment.go

@@ -0,0 +1,116 @@
+package app
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type FileReader interface {
+	ReadFile(path string) (io.Reader, error)
+}
+
+type AttachmentRequest struct {
+	FilePath string `json:"file_path"`
+	FileName string `json:"file_name"`
+}
+
+type AttachmentResponse struct {
+	SuccessResponse
+	Markdown string `json:"markdown"`
+	Alt      string `json:"alt"`
+	Url      string `json:"url"`
+}
+
+type attachmentReader struct{}
+
+func (ar attachmentReader) ReadFile(path string) (io.Reader, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := io.ReadAll(file)
+	if err != nil {
+		return nil, err
+	}
+
+	defer file.Close()
+
+	reader := bytes.NewReader(data)
+
+	return reader, nil
+}
+
+type FileUploader interface {
+	UploadFile(pid interface{}, content io.Reader, filename string, options ...gitlab.RequestOptionFunc) (*gitlab.ProjectFile, *gitlab.Response, error)
+}
+
+type attachmentService struct {
+	data
+	fileReader FileReader
+	client     FileUploader
+}
+
+/* attachmentHandler uploads an attachment (file, image, etc) to Gitlab and returns metadata about the upload. */
+func (a attachmentService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	if r.Method != http.MethodPost {
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodPost)
+		handleError(w, InvalidRequestError{}, "Expected POST", http.StatusMethodNotAllowed)
+		return
+	}
+
+	var attachmentRequest AttachmentRequest
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		handleError(w, err, "Could not read request body", http.StatusBadRequest)
+		return
+	}
+
+	defer r.Body.Close()
+
+	err = json.Unmarshal(body, &attachmentRequest)
+	if err != nil {
+		handleError(w, err, "Could not unmarshal JSON", http.StatusBadRequest)
+		return
+	}
+
+	file, err := a.fileReader.ReadFile(attachmentRequest.FilePath)
+	if err != nil || file == nil {
+		handleError(w, err, fmt.Sprintf("Could not read %s file", attachmentRequest.FileName), http.StatusInternalServerError)
+		return
+	}
+
+	projectFile, res, err := a.client.UploadFile(a.projectInfo.ProjectId, file, attachmentRequest.FileName)
+	if err != nil {
+		handleError(w, err, fmt.Sprintf("Could not upload %s to Gitlab", attachmentRequest.FileName), http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/attachment"}, fmt.Sprintf("Could not upload %s to Gitlab", attachmentRequest.FileName), res.StatusCode)
+		return
+	}
+
+	response := AttachmentResponse{
+		SuccessResponse: SuccessResponse{
+			Status:  http.StatusOK,
+			Message: "File uploaded successfully",
+		},
+		Markdown: projectFile.Markdown,
+		Alt:      projectFile.Alt,
+		Url:      projectFile.URL,
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+}