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// Package tracking provides the use-case of tracking a cargo. Used by views
// facing the end-user.
package tracking
import (
// ErrInvalidArgument is returned when one or more arguments are invalid.
var ErrInvalidArgument = errors.New("invalid argument")
// Service is the interface that provides the basic Track method.
type Service interface {
// Track returns a cargo matching a tracking ID.
Track(id string) (Cargo, error)
type service struct {
cargos cargo.Repository
handlingEvents cargo.HandlingEventRepository
func (s *service) Track(id string) (Cargo, error) {
if id == "" {
return Cargo{}, ErrInvalidArgument
c, err := s.cargos.Find(cargo.TrackingID(id))
if err != nil {
return Cargo{}, err
return assemble(c, s.handlingEvents), nil
// NewService returns a new instance of the default Service.
func NewService(cargos cargo.Repository, events cargo.HandlingEventRepository) Service {
return &service{
cargos: cargos,
handlingEvents: events,
// Cargo is a read model for tracking views.
type Cargo struct {
TrackingID string `json:"tracking_id"`
StatusText string `json:"status_text"`
Origin string `json:"origin"`
Destination string `json:"destination"`
ETA time.Time `json:"eta"`
NextExpectedActivity string `json:"next_expected_activity"`
ArrivalDeadline time.Time `json:"arrival_deadline"`
Events []Event `json:"events"`
// Leg is a read model for booking views.
type Leg struct {
VoyageNumber string `json:"voyage_number"`
From string `json:"from"`
To string `json:"to"`
LoadTime time.Time `json:"load_time"`
UnloadTime time.Time `json:"unload_time"`
// Event is a read model for tracking views.
type Event struct {
Description string `json:"description"`
Expected bool `json:"expected"`
func assemble(c *cargo.Cargo, events cargo.HandlingEventRepository) Cargo {
return Cargo{
TrackingID: string(c.TrackingID),
Origin: string(c.Origin),
Destination: string(c.RouteSpecification.Destination),
ETA: c.Delivery.ETA,
NextExpectedActivity: nextExpectedActivity(c),
ArrivalDeadline: c.RouteSpecification.ArrivalDeadline,
StatusText: assembleStatusText(c),
Events: assembleEvents(c, events),
func assembleLegs(c cargo.Cargo) []Leg {
var legs []Leg
for _, l := range c.Itinerary.Legs {
legs = append(legs, Leg{
VoyageNumber: string(l.VoyageNumber),
From: string(l.LoadLocation),
To: string(l.UnloadLocation),
LoadTime: l.LoadTime,
UnloadTime: l.UnloadTime,
return legs
func nextExpectedActivity(c *cargo.Cargo) string {
a := c.Delivery.NextExpectedActivity
prefix := "Next expected activity is to"
switch a.Type {
case cargo.Load:
return fmt.Sprintf("%s %s cargo onto voyage %s in %s.", prefix, strings.ToLower(a.Type.String()), a.VoyageNumber, a.Location)
case cargo.Unload:
return fmt.Sprintf("%s %s cargo off of voyage %s in %s.", prefix, strings.ToLower(a.Type.String()), a.VoyageNumber, a.Location)
case cargo.NotHandled:
return "There are currently no expected activities for this cargo."
return fmt.Sprintf("%s %s cargo in %s.", prefix, strings.ToLower(a.Type.String()), a.Location)
func assembleStatusText(c *cargo.Cargo) string {
switch c.Delivery.TransportStatus {
case cargo.NotReceived:
return "Not received"
case cargo.InPort:
return fmt.Sprintf("In port %s", c.Delivery.LastKnownLocation)
case cargo.OnboardCarrier:
return fmt.Sprintf("Onboard voyage %s", c.Delivery.CurrentVoyage)
case cargo.Claimed:
return "Claimed"
return "Unknown"
func assembleEvents(c *cargo.Cargo, handlingEvents cargo.HandlingEventRepository) []Event {
h := handlingEvents.QueryHandlingHistory(c.TrackingID)
var events []Event
for _, e := range h.HandlingEvents {
var description string
switch e.Activity.Type {
case cargo.NotHandled:
description = "Cargo has not yet been received."
case cargo.Receive:
description = fmt.Sprintf("Received in %s, at %s", e.Activity.Location, time.Now().Format(time.RFC3339))
case cargo.Load:
description = fmt.Sprintf("Loaded onto voyage %s in %s, at %s.", e.Activity.VoyageNumber, e.Activity.Location, time.Now().Format(time.RFC3339))
case cargo.Unload:
description = fmt.Sprintf("Unloaded off voyage %s in %s, at %s.", e.Activity.VoyageNumber, e.Activity.Location, time.Now().Format(time.RFC3339))
case cargo.Claim:
description = fmt.Sprintf("Claimed in %s, at %s.", e.Activity.Location, time.Now().Format(time.RFC3339))
case cargo.Customs:
description = fmt.Sprintf("Cleared customs in %s, at %s.", e.Activity.Location, time.Now().Format(time.RFC3339))
description = "[Unknown status]"
events = append(events, Event{
Description: description,
Expected: c.Itinerary.IsExpected(e),
return events
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