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/job.go

@@ -0,0 +1,85 @@
+package app
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type JobTraceRequest struct {
+	JobId int `json:"job_id"`
+}
+
+type JobTraceResponse struct {
+	SuccessResponse
+	File string `json:"file"`
+}
+
+type TraceFileGetter interface {
+	GetTraceFile(pid interface{}, jobID int, options ...gitlab.RequestOptionFunc) (*bytes.Reader, *gitlab.Response, error)
+}
+
+type traceFileService struct {
+	data
+	client TraceFileGetter
+}
+
+/* jobHandler returns a string that shows the output of a specific job run in a Gitlab pipeline */
+func (a traceFileService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	if r.Method != http.MethodGet {
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodGet)
+		handleError(w, InvalidRequestError{}, "Expected GET", 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 jobTraceRequest JobTraceRequest
+	err = json.Unmarshal(body, &jobTraceRequest)
+	if err != nil {
+		handleError(w, err, "Could not unmarshal data from request body", http.StatusBadRequest)
+		return
+	}
+
+	reader, res, err := a.client.GetTraceFile(a.projectInfo.ProjectId, jobTraceRequest.JobId)
+
+	if err != nil {
+		handleError(w, err, "Could not get trace file for job", http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/job"}, "Could not get trace file for job", res.StatusCode)
+		return
+	}
+
+	file, err := io.ReadAll(reader)
+
+	if err != nil {
+		handleError(w, err, "Could not read job trace file", http.StatusBadRequest)
+		return
+	}
+
+	response := JobTraceResponse{
+		SuccessResponse: SuccessResponse{
+			Status:  http.StatusOK,
+			Message: "Log file read",
+		},
+		File: string(file),
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+}