vjiki / nasa-images

NASA rover images test

This test is about creating your own API by collecting data from NASA's APIs for the Mars rovers.

Please read through these instructions carefully before you begin.

What we look at

• Focus on object oriented design, for example how the code follows SOLID and DRY principles
• General code layout
• Extensibility of the solution

It is not as important that the implementation actually works as the overall structure and design of the API.

The problem

You are requested to implement an API that can be used to display daily images from the rovers that are on Mars. For a start, your API should be able to get the navigation camera images from the curiosity rover from the last 10 days and limit the number of images to 3 per day. If there are no images for a particular day the result for that day should be empty. The entrypoint for your API should be a minimal command line script.

NASA provides a simple HTTP API that allows for querying of rover images. This is an example on how to query for the navigation camera images for a particular date:

https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/photos?earth_date=2016-4-2&camera=NAVCAM&api_key=DEMO_KEY

NASA's documentation can be found here.

You don't need to specifically add support for the other rovers nor the other kinds of cameras, but your solution should be easily extended to support multiple rovers, cameras, and other endpoints.

In order to not query the NASA API every time the navigation camera images from the last 10 days are requested, you should implement a caching layer. It is not as important where your API caches (be it files, memory, or something else), the actual cache implementation should be easily replaced with something else.

Example output

Your API should have a simple command line interface which just outputs json. You don't need to spend time on formatting the output. Example output for the last 10 days of curiosity navigation camera images (with a limit of 3 images per day).

$ php <my cli entrypoint.php>
{
    "2016-4-6": [],
    "2016-4-5": [],
    "2016-4-4": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01302/opgs/edr/ncam/NLB_513062102EDR_S0540000NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01302/opgs/edr/ncam/NLB_513062029EDR_S0540000NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01302/opgs/edr/ncam/NLB_513061956EDR_S0540000NCAM00546M_.JPG"],
    "2016-4-3": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01301/opgs/edr/ncam/NLB_512995594EDR_F0540000NCAM07753M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01301/opgs/edr/ncam/NLB_512995563EDR_F0540000NCAM07753M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01301/opgs/edr/ncam/NLB_512995472EDR_F0540000NCAM07753M_.JPG"],
    "2016-4-2": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01300/opgs/edr/ncam/NLB_512914365EDR_F0532980NCAM00320M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01300/opgs/edr/ncam/NLB_512913929EDR_F0532980NCAM00207M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01300/opgs/edr/ncam/NLB_512912740EDR_F0532980NCAM00207M_.JPG"],
    "2016-4-1": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01299/opgs/edr/ncam/NLB_512813334EDR_S0532980NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01299/opgs/edr/ncam/NLB_512813261EDR_S0532980NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01299/opgs/edr/ncam/NLB_512813188EDR_S0532980NCAM00546M_.JPG"],
    "2016-3-31": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01298/opgs/edr/ncam/NLB_512725460EDR_F0532944NCAM00385M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01298/opgs/edr/ncam/NLB_512725436EDR_F0532944NCAM00385M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01298/opgs/edr/ncam/NRB_512730078EDR_F0532980NCAM00353M_.JPG"],
    "2016-3-30": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01297/opgs/edr/ncam/NLB_512637743EDR_S0532644NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01297/opgs/edr/ncam/NLB_512637670EDR_S0532644NCAM00546M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01297/opgs/edr/ncam/NLB_512637597EDR_S0532644NCAM00546M_.JPG"],
    "2016-3-29": ["http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01296/opgs/edr/ncam/NLB_512555701EDR_F0532644NCAM00354M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01296/opgs/edr/ncam/NLB_512555670EDR_F0532644NCAM00354M_.JPG", "http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/01296/opgs/edr/ncam/NLB_512555645EDR_F0532644NCAM00354M_.JPG"],
    "2016-3-28": []
}

Implementation details

• You are free to use any programming language you like.
• You should not use any other application framework with the exception of potential test frameworks that you'd like to use (such as a unit testing framework). For PHP there's a composer.json example if you want to use it.
• It is not crucial that the API actually works, the extensibility and design of the API is more important.
• Unit tests is not a must but definitely a plus.