EssentialFeed

Implementing the example project for the iOS Lead Essentials course

Specification (User Stories)

---

Give some assistive rules on how to write good stories and narratives.

Story: Customer requests to see the feed

Narrative #1

As an online customer
I want the app to load the feed
So I can see the feed

Scenarios (Acceptance Criteria)

Given the customer has connectivity
When the customer requests to see the feed
Then the app should display the latest feed from remote
And replace the cache with the new feed  

Narrative #2

As an offline customer
I want the app to show the latest saved version of my image feed
So I can always enjoy images of my friends

Scenarios (Acceptance Criteria)

Given the customer has no connectivity
When the customer requests to see the feed
Then the app should display the latest saved feed 

Given the customer has no connectivity
And the cache is empty
When the customer requests to see the feed
Then the app should display an error message  

Use Cases

---

Use Case #1: Load Feed

Data:

• URL

Primary course (happy path):

1. Execute "Load Feed Items" command with above data
2. System downloads data from the URL.
3. System validates downloaded data.
4. System creates feed items from valid data.
5. System delivers feed items.

Invalid data - error course (sad path):

1. System delivers error.

No connectivity - error course (sad path):

1. System delivers error.

Use Case #2: Load Feed Fallback (Cache)

Data:

• Max age

Primary course (happy path):

1. Execute "Retrieve Feed Items" command with above data
2. System fetches feed data from cache.
3. System creates feed items from cached data.
4. System delivers feed items.

Empty Cache (sad path)

1. System delivers error.

Use Case #3: Save Feed Items

Data:

• Feed items

Primary course (happy path):

1. Execute "Save Feed Items" command with above data
2. System encodes feed items.
3. System timestamps the new cache.
4. System replaces the cache with new data.
5. System delivers success message.

Empty Cache (sad path)

1. System delivers error.

Flowchart

Architecture

Model Specs

Feed Item

Property	Type
id	UUID
description	String (optional)
location	String (optional)
imageURL	URL

Payload contract

GET *url* (TBD)

200 RESPONSE

{
	"items": [
		{
			"id": "a UUID",
			"description": "a description",
			"location": "a location",
			"image": "https://a-image.url"
		},
		{
			"id": "a UUID",
			"description": "a description",
			"image": "https://a-image.url"
		},
		{
			"id": "a UUID",
			"location": "a location",
			"image": "https://a-image.url"
		},
		{
			"id": "a UUID",
			"image": "https://a-image.url"
		}
	]
}