Before moving on to the details of the project I'd like to highlight a few key, from my perspective, things that I hope allow to better understand this implementation, decisions I made here and in general this project as a whole.

I consider this project in its current shape to be a quickly written Proof of Concept rather than a production ready service. Given time limitations I've done my best to deliver good enough thing. My main focus was on providing something that works end to end at the cost of polishing every little detail.

Key things to keep in mind when looking at this project:

• function specs and documentation is missing,
• not enough tests, especially for corner cases,
• mnesia is used as a storage (in a dirty way) and that's not the best choice for production but good enough for PoC (I was looking for something quick and easy to use),
• the module with algorithm implementation should be better tested, not only based on fixtures,
• web layer should be spread across router and controller abstractions instead of being packed into a single module

What's more, I left some comments in the code explaining it's certain parts.

I hope you'll like my app!

The service exposes an HTTP API that allows to:

• create a canvas
• apply drawings to a canvas
• render a canvas

1. Create a canvas

• path: /api/canvas
• method: POST
• response codes:
  • 201 - canvas created successfully (canvas id is returned)

2. Get a canvas

• path: /api/canvas/{canvas_id} - replace {canvas_id} with your canvas id (returned by the above endpoint)
• method: GET
• response codes:
  • 200 - canvas returned successfully
  • 404 - canvas does not exist

3. Apply a drawing to a canvas

• path: /api/canvas/{canvas_id}/drawings - replace {canvas_id} with your canvas id (returned by the endpoint from point no 1)
• method: POST
• exemplary body parameters:

  • rectangle drawing

    {
      "type": "rectangle",
      "init_point":  [3, 2],
      "width": 5,
      "height": 8,
      "outline_char": "@",
      "fill_char": null
    }

    NOTE: null value for outline_char or fill_char means this field will not be used e.g. a rectangle will not be filled.

    NOTE: One of either outline_char or fill_char MUST always be set to value different than null.

  • flood fill drawing

    {
      "type": "flood_fill",
      "init_point":  [3, 2],
      "fill_char": "-"
    }

• response codes:
  • 201 - drawing successfully added
  • 400 - bad request
  • 404 - canvas not found

• Elixir 1.11.2
• Erlang 23.2.3

Go with one of the ways described below to have the application up and running on port 4000.

Run the below commands:

cd $PROJECT_ROOT_DIR # go to the project root directory
docker build -t canvas . # tested with docker 20.10.5
docker run -p 4000:4000 -d canvas

NOTE: When running on Ubuntu docker commands will most probably require to be called as a root user.

Run the below commands:

cd $PROJECT_ROOT_DIR # go to the project root directory
mix deps.get
mix release
_build/dev/rel/canvas/bin/canvas start

Run the below commands in the specified order to "draw" such a picture:

--------------......------------
--------------......------------
--------------......------------
OOOOOOOO------......------------
O      O------......------------
O    XXXXX----......------------
OOOOOXXXXX----------------------
-----XXXXX----------------------
--------------------------------
--------------------------------

1. Create a canvas:

curl -i -XPOST -H "Content-Type: application/json" http://localhost:4000/api/canvas
# Response:
# Canvas id: 56043694
CANVAS=your-canvas-id # assign canvas id to a variable

2. Create drawings:

curl -i -H "Content-Type: application/json" \
-d '{"type":"rectangle", "init_point": [14,0], "width": 7, "height": 6, "outline_char": null, "fill_char": "."}' \
http://localhost:4000/api/canvas/$CANVAS/drawings

curl -i -H "Content-Type: application/json" \
-d '{"type":"rectangle", "init_point": [0,3], "width": 8, "height": 4, "outline_char": "O", "fill_char": null}' \
http://localhost:4000/api/canvas/$CANVAS/drawings

curl -i -H "Content-Type: application/json" \
-d '{"type":"rectangle", "init_point": [5,5], "width": 5, "height": 3, "outline_char": "X", "fill_char": "X"}' \
http://localhost:4000/api/canvas/$CANVAS/drawings

curl -i -H "Content-Type: application/json" \
-d '{"type":"flood_fill", "init_point": [0,0], "fill_char": "-"}' \
http://localhost:4000/api/canvas/$CANVAS/drawings

3. Render the canvas:

curl -i -XGET -H "Content-Type: application/json" http://localhost:4000/api/canvas/$CANVAS