Property Partner - Coding exercise 2018

exercise.md

Config Challenge

Using Scala and a parser combinator library of your choice, please spend 3 hours on:

Every large software project has its share of configuration files to control settings, execution, etc. Let’s contemplate a config file format that looks a lot like standard PHP .ini files, but with a few tweaks.

A config file will appear as follows:

[common] 

basic_size_limit = 26214400 

student_size_limit = 52428800

paid_users_size_limit = 2147483648

path = /srv/var/tmp/ 

path<itscript> = /srv/tmp/


[ftp] 

name = "hello there, ftp uploading" 

path = /tmp/ 

path<production> = /srv/var/tmp/ 

path<staging> = /srv/uploads/ 

path<ubuntu> = /etc/var/uploads 

enabled = no

; This is a comment 


[http] 

name = "http uploading" 

path = /tmp/ 

path<production> = /srv/var/tmp/ 

path<staging> = /srv/uploads/; This is another comment 

params = array,of,values

Where "[group]" denotes the start of a group of related config options, setting = value denotes a standard setting name and associated default value, and setting<override> = value2 denotes the value for the setting if the given override is enabled. If multiple enabled overrides are defined on a setting, the one defined last will have priority.

Assignment

Your task is to write a Scala function: def loadConfig(filePath: String, overrides: List[(String, String)]) that parses this format and returns an object that can be queried as follows. Example method call with overrides: val config = loadConfig("/srv/settings.conf", List("ubuntu" -> "production"))

>>> config("common.paid_users_size_limit")

# returns 2147483648

> config("ftp.name")

# returns "hello there, ftp uploading"

>>> config("http.params")

# returns ["array", "of", "values"]

> config("ftp.lastname")

# returns None

> config("ftp.enabled")

# returns false (permitted bool values are "yes", "no", "true", "false", 1, 0)

> config("ftp[‘path’]") # returns "/etc/var/uploads"

> config("ftp")

# returns a map: # { # ‘name’ => "hello there, ftp uploading", # ‘path’ => "/etc/var/uploads", # ‘enabled’ => False # }

We expect a full Scala solution with the appropiate amount of tests included as well.

Design Considerations

• loadConfig() will be called at boot time, and thus should be as fast as possible. Conf files can get quite lengthy - there can be an arbitrary number of groups and number of settings within each group.

• config will be queried throughout the program’s execution, so each query should be very fast as well.

• Certain queries will be made very often (thousands of times), others pretty rarely.

• If the conf file is not well-formed, it is acceptable to print an error and exit from within loadConfig(). Once the object is returned, however, it is not permissible to exit or crash no matter what the query is. Returning None is acceptable, however.

• Extra points awarded for declarative config access. config.ftp.path would validly compile and return the same as config("ftp.path").