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_requests_by_username_test.go

@@ -0,0 +1,87 @@
+package app
+
+import (
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type fakeMergeRequestListerByUsername struct {
+	testBase
+	emptyResponse bool
+}
+
+func (f fakeMergeRequestListerByUsername) ListProjectMergeRequests(pid interface{}, opt *gitlab.ListProjectMergeRequestsOptions, options ...gitlab.RequestOptionFunc) ([]*gitlab.MergeRequest, *gitlab.Response, error) {
+	resp, err := f.handleGitlabError()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if f.emptyResponse {
+		return []*gitlab.MergeRequest{}, resp, err
+	}
+
+	return []*gitlab.MergeRequest{{IID: 10}}, resp, err
+}
+
+func TestListMergeRequestByUsername(t *testing.T) {
+	var testListMrsByUsernamePayload = MergeRequestByUsernameRequest{Username: "hcramer", UserId: 1234, State: "opened"}
+	t.Run("Gets merge requests by username", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", testListMrsByUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{}}
+		data := getSuccessData(t, svc, request)
+		assert(t, data.Message, "Merge requests fetched for hcramer")
+		assert(t, data.Status, http.StatusOK)
+	})
+
+	t.Run("Should handle no merge requests", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", testListMrsByUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{emptyResponse: true}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Message, "No MRs found")
+		assert(t, data.Details, "hcramer did not have any MRs")
+		assert(t, data.Status, http.StatusNotFound)
+	})
+
+	t.Run("Should require username", func(t *testing.T) {
+		missingUsernamePayload := testListMrsByUsernamePayload
+		missingUsernamePayload.Username = ""
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", missingUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Message, "username is required")
+		assert(t, data.Details, "username is a required payload field")
+		assert(t, data.Status, http.StatusBadRequest)
+	})
+
+	t.Run("Should require User ID for assignee call", func(t *testing.T) {
+		missingUsernamePayload := testListMrsByUsernamePayload
+		missingUsernamePayload.UserId = 0
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", missingUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Message, "user_id is required")
+		assert(t, data.Details, "user_id is a required payload field")
+		assert(t, data.Status, http.StatusBadRequest)
+	})
+
+	t.Run("Should handle error from Gitlab", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", testListMrsByUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{testBase: testBase{errFromGitlab: true}}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Message, "An error occurred")
+		assert(t, data.Details, strings.Repeat("Some error from Gitlab; ", 3))
+		assert(t, data.Status, http.StatusInternalServerError)
+	})
+
+	t.Run("Handles non-200 from Gitlab", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/merge_requests_by_username", testListMrsByUsernamePayload)
+		svc := mergeRequestListerByUsernameService{testProjectData, fakeMergeRequestListerByUsername{testBase: testBase{status: http.StatusSeeOther}}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Message, "An error occurred")
+		assert(t, data.Details, strings.Repeat("An error occurred on the /merge_requests_by_username endpoint; ", 3))
+		assert(t, data.Status, http.StatusInternalServerError)
+	})
+}