ASCII canvas

Your task is to build a client-server system to represent an ASCII art drawing canvas. The exercise involves two pieces:

• A server that will implement the drawing endpoints into a canvas.
• A read-only client that will show the canvas stored by the server with the drawings.

What we are looking for is...

• correctly functioning solution that comes with running instructions and examples.
• readable, clear code of the kind you would yourself like your team-mates to write and maintain with you.
• appropriately automatically tested, including failure scenarios.
• appropriate data structures and algorithms being applied as part of your solution.
• a version history being included with your solution.

The server should be...

• implementing the canvas behaviours described below into a web service API as you see fit.
• written in Elixir if you are applying to an Elixir position, and in Go, if you are applying to a Go position. In case this a a mixed position, please, clarify with the recruiter.
• automatically tested appropriately.
• runnable with clear running instructions.

Canvas should be...

• identifiable with a globally unique identifier.
• persisted across application launches.
• not authenticating users: authenticating or authorizing requests is out of scope.

Drawing operation

• A rectangle parameterised with...
  • Coordinates for the upper-left corner.
  • width and height.
  • an optional fill character.
  • an optional outline character.
  • One of either fill or outline should always be present.

A character can be assumed to be an ASCII encoded byte.

The canvas can be assumed to be a fixed size.

The read-only client should be...

• Non-interactive: you do not need to implement any client-side interactions. Read-only.
• simple: you can implement the drawing operations with constant-width characters.
• runnable with clear running instructions.

Test fixture 1

• Rectangle at [3,2] with width: 5, height: 3, outline character: @, fill character: X
• Rectangle at [10, 3] with width: 14, height: 6, outline character: X, fill character: O

   @@@@@
   @XXX@  XXXXXXXXXXXXXX
   @@@@@  XOOOOOOOOOOOOX
          XOOOOOOOOOOOOX
          XOOOOOOOOOOOOX
          XOOOOOOOOOOOOX
          XXXXXXXXXXXXXX

Test fixture 2

• Rectangle at [14, 0] with width 7, height 6, outline character: none, fill: .
• Rectangle at [0, 3] with width 8, height 4, outline character: O, fill: none
• Rectangle at [5, 5] with width 5, height 3, outline character: X, fill: X

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

Solution

Install

• Go
• Docker
• docker-compose

Building:

  ./dockerise.sh

API endpoints inside the container:

POST localhost:8888/canvas/add
GET localhost:8888/canvas?id={id}

POST Input example:

[
    {
       "RectangleAt" : [3,2],
       "Width": 5,
       "Height":3,
       "Outline": "@",
       "Fill": "X"
    }, 
    {
       "RectangleAt" : [10,3],
       "Width": 14,
       "Height":6,
       "Outline": "X",
       "Fill": "O"
     }
]

POST Output example:

{
    "CanvasID": "ff89e33b-4cd5-45b1-af19-5e6ad7288412",
    "Drawing": [
        "                        ",
        "                        ",
        "   @@@@@                ",
        "   @XXX@  XXXXXXXXXXXXXX",
        "   @@@@@  XOOOOOOOOOOOOX",
        "          XOOOOOOOOOOOOX",
        "          XOOOOOOOOOOOOX",
        "          XOOOOOOOOOOOOX",
        "          XXXXXXXXXXXXXX"
    ]
}

Demo