codeMnky01 / essential-feed

Essential Feed case study

Essential Feed case study

Story: Customer requests to see their image feed

Narative #1

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

Scenarios (Acceptance criteria)

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

Narative #2

As offline customer 
I want app to automatically load cached image feed
So i can always enjoy cached images while offline

Scenarios (Acceptance criteria)

 Given the customer doesn't have connectivity
   And there is a cached version of the image feed 
   And the cache is less then 7 days old
  When the customer request to show the image feed
  Then the app displays cache image feed

 Given the customer doesn't have connectivity
   And there is a cached version of the image feed 
   And the cache is 7 days old or more
  When the customer request to show the image feed
  Then the app displays error message
  
 Given the customer doesn't have connectivity
   And the cache is empty
  When the customer request to show the image feed
  Then the app displays 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 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 connection - error course (sad path):

1. System delivers connectivity error

Load Feed Image Data from Remote - Use Case

Data:

• URL

Primary course (happy path):

1. Execute "Load Image Data" command with above data
2. System downloads data from URL
3. System validates downloaded data
4. System delivers image

Cancel course:

1. System does not deliver image data nor error

Invalid data - error course (sad path):

1. System delivers invalid data error

No connection - error course (sad path):

1. System delivers connectivity error

Load Feed from Cache - Use Case

Data:

• URL

Primary course (happy path):

1. Execute "Load Image Feed" command with above data
2. System retrieves image feed data from cache
3. System validates cache is less then 7 days old
4. System creates image feed from valid data
5. System delivers image feed

Retrieval error course (sad path):

1. System delivers retrieval error

Expired cache course (sad path):

1. System delivers no feed images

Empty cache course (sad path):

1. System delivers no feed images

Load Feed Image Data from Cache - Use Case

Data:

• URL

Primary course (happy path):

1. Execute "Load Image Data" command with above data
2. System retrieves image data from cache
3. System delivers image feed

Cancel course:

1. System does not deliver image data nor error

Retrieval error course (sad path):

1. System delivers retrieval error

Empty cache course (sad path):

1. System delivers not found error

Validate Feed Cache - Use Case

Primary course (happy path):

1. Execute "Validate Feed Cache" command
2. System retrieves image feed data from cache
3. System validates cache is less then 7 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
3. System encodes new image feed
4. System timestamps encoded image feed
5. System saves new cached data
6. System delivers susccess message

Deleting error course (sad path):

1. System delivers error

Saving error course (sad path):

1. System deletes cache

Flowchart

Model Specs

Feed Image

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

Payload Contract

GET /feed

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"
		}
		...
	]
}