hannso / mars-rover

MARS ROVER CHALLENGE

Instructions

• Ruby version 2.1.5 or later should be installed
• Run bundle to install Rspec and Rake gems

To run tests

• Navigate into folder in terminal.
• rake

To submit input

• Navigate into folder in terminal
• run Rake
• Submit input
• Hold 'Ctrl' 'd' when done.

Assumptions

• Rovers can occupy the same position
• Rovers can not go over the edge of the plateau
• Input may be incorrectly submitted
• Design may be altered in the future to accommodate new commands

Approach

• This project has been developed with TDD, using both unit and feature tests.
• The example input and output is used in the feature test.

Design

This design is composed of a Grid, Orientator and Rover class. There are also Controller and Parser classes that parses the input as formatted by the brief, and tells the different classes how to interact.

Orientator class

• The responsibility of this class is to understanding bearings and directions. I saw it as an object that the rover would have - like a navigator. It is something that could be recycled and injected into a another moving object.

• I decided not to hardcode the cardinal points into the Orientator class, in order to adhere to the Open-Close Principle. The cardinal points, with their corresponding bearing, can be injected into the class in hash form. These could be stored as a constant in a separate file, which would be useful if a range of different classes depended on them within a system. This means these commands can be easily altered. You could for example add :NW, :NE etc, or change :N to :North easily.

• I decided that bearings in radians should be the primary attribute of this class, because this is something that can be mapped to a wide variety of scenarios, rather than storing the more superficial cardinal point - like :North, :East - which can now be changed(as discussed above). It also allows for a range of trig functions to be used. In other scenarios, bearings in radians is more likely to be readable to other classes.

This is in comparison to an initial draft which contained the following:

CARDINAL_POINTS = { North: [0,+1], South: [0,-1], West: [-1, 0], East: [+1,0] }

The above meant that, to add more/change the cardinal points, either: a) If the hash was injected in, a lot of logic would have to be contained within this hash, that arguably, should be part of the orientator class. The orientator would have to assume a lot about this hash - understanding how to interact with array values. b) Or it would be hard coded into the class.

There are less obvious  ways to add other cardinal points like :North_West ; the data is not as malleable.

• Turning commands: "left", "right", are injected in the same way as the cardinal_points, to adhere to the Open Close Principle. Allowing for new commands like "turn around"/"a quarter left"

Rover class

• The responsibility of the rover class is to move, turn, land and have a position. It relies on the direction_vector provided by the orientator, injected in, to know in which direction to move. It does not understand any bearings logic.

• It also has a grid injected in because it needs to be able to know the boundaries of the grid/surface it is on.

Grid class

• The grid class models the plateau (named grid for ease of spelling!). It is initialized with a 2 coordinates - the second of which defaults to [0,0] if not entered. (The controller allows this default to occur).

• There are private methods which clarify what the lower boundary and upper boundary of the x and y values. Given that the brief specifies that the inputted coordinate would be the upper-right corner, these are potentially unnecessary for an MVP. There could be a method which ensures that the positive values are inputted for the upper-right coordinate on initialization, and the other coordinate is always set to [0,0]. My approach does, however, allow for flexibility/recyclability. If the grid was part of larger grid, for example, and the second coordinate was (-5,-5), it would still function. And, there is an option to set the second coordinate.

PARSERS & CONTROLLERS

• These have been designed to respond to the exact input type specified by the brief and create the relevant rovers and grids with command.

Grid Parser

• Handles all the input and is responsible for selecting relevant lines to create grid, and returning a grid object to the Controller.

Multiple Rovers Parser

• Handles all input and is responsible for selecting relevant lines for all rovers. It identifies the correct data needed for each rover, and creates a Rover Parser for each group of this data, to handle this. It tells each Rover Parser where in the sequence the rover is, for error handling.
• Receives the rover results from the Rover Parser, so it has multiple rover results.

Rover Parser

• Uses data given by Multiple Rovers Parser to create rovers and initiate the commands on the rovers.
• Reads the results of the rover, which are then called from the rover parser.

Controller

• Receives input from user and sends this to the parsers to handle. Prints the formatted results of the all the rovers by calling on the Multiple Rover Parsers

Improvements: I would like to research design patterns to improve the Controller/Parser aspect of my design. I have focused primarily on the logic of the Orientator, Rover, and Plateau. Ideally, I would like to find an alternative to the switch statement in my Rover Parser, when the different commands are being handled, as these are commands with the corresponding command strings are hard coded in so do not adhere well to adhere to the Open Close Principle. This section could also be redesigned, so that rovers cannot land on the same coordinate.