Add reponse helper function for group permissions

Reponse to extract groups and their permissions was added.

Additional definitons for the avilable Bitbucket Server permission
levels were added to allow for easier usage.

Tests were added and udpated.

api_response.go

@@ -105,12 +105,61 @@ type UserWithMetadata struct {
 	Status   string        `json:"status"`
 }
 
+// PermissionGlobal are global permissions
+type PermissionGlobal string
+
+const (
+	// PermissionGlobalLicensedUser represents the ability to log into the system
+	PermissionGlobalLicensedUser PermissionGlobal = "LICENSED_USER"
+	// PermissionGlobalProjectCreate allows project creation
+	PermissionGlobalProjectCreate PermissionGlobal = "PROJECT_CREATE"
+	// PermissionGlobalAdmin represents an administrator
+	PermissionGlobalAdmin PermissionGlobal = "ADMIN"
+	// PermissionGlobalSysAdmin represents a system administrator
+	PermissionGlobalSysAdmin PermissionGlobal = "SYS_ADMIN"
+)
+
+// PermissionProject are project level permissions
+type PermissionProject string
+
+const (
+	// PermissionProjectAdmin grants admin priviledges
+	PermissionProjectAdmin PermissionProject = "PROJECT_ADMIN"
+	// PermissionProjectRead grants read priviledges
+	PermissionProjectRead PermissionProject = "PROJECT_READ"
+	// PermissionProjectWrite grants write priviledges
+	PermissionProjectWrite PermissionProject = "PROJECT_WRITE"
+)
+
+// PermissionRepository are repository level permissions
+type PermissionRepository string
+
+const (
+	// PermissionRepositoryAdmin grants admin priviledges
+	PermissionRepositoryAdmin PermissionRepository = "REPO_ADMIN"
+	// PermissionRepositoryRead grants read priviledges
+	PermissionRepositoryRead PermissionRepository = "REPO_READ"
+	// PermissionRepositoryWrite grants write priviledges
+	PermissionRepositoryWrite PermissionRepository = "REPO_WRITE"
+)
+
 // UserPermission contains a user with its permission
 type UserPermission struct {
 	User       User   `json:"user"`
 	Permission string `json:"permission"`
 }
 
+// Group represents a user group
+type Group struct {
+	Name string `json:"name"`
+}
+
+// GroupPermission contains a group with its permission
+type GroupPermission struct {
+	Group      Group  `json:"group"`
+	Permission string `json:"permission"`
+}
+
 type MergeResult struct {
 	Outcome string `json:"outcome"`
 	Current bool   `json:"current"`
@@ -323,6 +372,21 @@ type Change struct {
 	} `json:"new"`
 }
 
+// String converts global permission to its string representation
+func (p PermissionGlobal) String() string {
+	return string(p)
+}
+
+// String converts project permission to its string representation
+func (p PermissionProject) String() string {
+	return string(p)
+}
+
+// String converts repository permission to its string representation
+func (p PermissionRepository) String() string {
+	return string(p)
+}
+
 func (k *SSHKey) String() string {
 	parts := make([]string, 1, 2)
 	parts[0] = strings.TrimSpace(k.Text)
@@ -399,6 +463,13 @@ func GetUsersPermissionResponse(r *APIResponse) ([]UserPermission, error) {
 	return c, err
 }
 
+// GetGroupsPermissionResponse casts group permissions into structure
+func GetGroupsPermissionResponse(r *APIResponse) ([]GroupPermission, error) {
+	var c []GroupPermission
+	err := mapstructure.Decode(r.Values["values"], &c)
+	return c, err
+}
+
 // GetWebhooksResponse cast Webhooks into structure
 func GetWebhooksResponse(r *APIResponse) ([]Webhook, error) {
 	var h []Webhook

api_response_test.go

@@ -360,7 +360,7 @@ func TestGetUsersPermissionResponse(t *testing.T) {
 						Slug:        "jcitizen",
 						Type:        "NORMAL",
 					},
-					Permission: "REPO_ADMIN",
+					Permission: PermissionRepositoryAdmin.String(),
 				},
 			},
 			wantErr: false,
@@ -380,6 +380,75 @@ func TestGetUsersPermissionResponse(t *testing.T) {
 	}
 }
 
+func TestGetGroupsPermissionResponse(t *testing.T) {
+	type args struct {
+		r *APIResponse
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    []GroupPermission
+		wantErr bool
+	}{
+		{
+			name: "Empty list",
+			args: args{
+				r: &APIResponse{
+					Values: map[string]interface{}{"values": []interface{}{}},
+				},
+			},
+			want:    []GroupPermission{},
+			wantErr: false,
+		},
+		{
+			name: "Bad response",
+			args: args{
+				r: &APIResponse{
+					Values: map[string]interface{}{"values": "not an array"},
+				},
+			},
+			want:    nil,
+			wantErr: true,
+		},
+		{
+			name: "Single group permission",
+			args: args{
+				r: &APIResponse{
+					Values: map[string]interface{}{
+						"values": []interface{}{map[string]interface{}{
+							"group": map[string]interface{}{
+								"name": "group1",
+							},
+							"permission": "REPO_ADMIN",
+						}},
+					},
+				},
+			},
+			want: []GroupPermission{
+				GroupPermission{
+					Group: Group{
+						Name: "group1",
+					},
+					Permission: PermissionRepositoryAdmin.String(),
+				},
+			},
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := GetGroupsPermissionResponse(tt.args.r)
+			if err != nil && !tt.wantErr {
+				t.Errorf("GetGroupsPermissionResponse() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("GetGroupsPermissionResponse() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestNewAPIResponse(t *testing.T) {
 	type args struct {
 		r *http.Response