Essential Feed App – Image Feed Feature

BDD Specs

Story: Customer requests to see their image feed

Narrative #1

As an online customer
I want the app to automatically load my latest image feed
So I can always enjoy the newest images of my friends

Scenarios (Acceptance criteria)

Given the customer has connectivity
 When the customer requests to see their 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 doesn't have connectivity
 And there’s a cached version of the feed
 And the cache is less than seven days old
When the customer requests to see the feed
Then the app should display the latest feed saved

Given the customer doesn't have connectivity
 And the cache is empty
When the customer requests to see the feed
Then the app should display an error message

Use Cases

Load Feed From Remote Use Case

Data:

• URL

Primary course (happy path):

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

Invalid data – error course (sad path):

1. System delivers invalid data error.

No connectivity – error course (sad path):

1. System delivers connectivity error.

Load Feed Fallback (Cache) Use Case

Load Feed From Cache Use Case

Primary course:

1. Execute "Load Image Feed" command with above data.
2. System retrieves feed data from cache.
3. System validates cache is less than seven days old.
4. System creates image feed from cached data.
5. System delivers image feed.

Retrieval Error course (sad path):

1. System delivers error.

Expired cache course (sad path):

1. System delivers no feed images.

Empty cache course (sad path):

1. System delivers no feed images.

Validate Feed Cache Use Case

Primary course:

1. Execute "Validate Cache" command with above data.
2. System retrieves feed data from cache.
3. System validates cache is less than seven days old.

Retrieval error course (sad path):

1. System deletes cache.

Expired cache course (sad path):

1. System deletes cache.

Cache Feed Use Case

Data:

• Image Feed

Primary course (happy path):

1. Execute "Save Image Feed" command with above data.
2. System deletes old cache data.
3. System encodes image feed.
4. System timestamps the new cache.
5. System saves new cache data.
6. System delivers success message.

Deleting error course (sad path):

1. System delivers error.

Saving error course (sad path):

1. System delivers error.

Flowchart

Architecture

Model Specs

Feed Image

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

Payload contract

GET *url* (TBD)

200 RESPONSE

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