A solution for the Dev Challenge. Analyses a log file.

log_stats.rb

#!/usr/bin/env ruby

# USAGE:
# Script can be called from the command line with `./log_stats.rb`.
# Optional a log file can be specified: `./log_stats.rb path/to/file.log`.



# This function kicks off the script in case it's called from the command line
def run!
	# Optional:
	# Use the first argument as path to the log file.
	# Ignore other arguments.
	file_path = ARGV.first || 'sample.log'


	# Instantiate LogStats with the urls of interest
	# and outputs the statistics.
	puts LogStats.new.
		add_url('get', '/api/users/{user_id}/count_pending_messages').
		add_url('get', '/api/users/{user_id}/get_messages').
		add_url('get', '/api/users/{user_id}/get_friends_progress').
		add_url('get', '/api/users/{user_id}/get_friends_score').
		add_url('post', '/api/users/{user_id}').
		add_url('get', '/api/users/{user_id}').
		# Collect information from the log file.
		parse(file_path)
end



# This is the main class for the script.
# It supports multiple urls to collect statistics for.
# And it can read log files.
class LogStats

	# Each LogStats instance has its own set of urls.
	def initialize
		@urls = []
	end

	# Add a new url.
	#
	# method - The method for the url.
	# url - The url itself.
	def add_url(method, url)
		@urls << Url.new(method, url)
		self
	end

	# Parse a log file and add the collected data to the urls.
	# 
	# file_path - Path to the log file to read.
	def parse(file_path)
		File.open(file_path, 'r') do |f|
			f.each_line do |l|
				update_url Line.new(l)
			end
		end	
		self	
	end

	# Returns the formated statistics for all urls.
	def to_s
		@urls.join "\n"
	end


	private

	# Find the right url the given line and update it with the data.
	# 
	# line - The Line to add to the urls.
	def update_url(line)
		url = @urls.find { |u| u.matches? line }
		url.update(line) if url
	end

end


# A data structure containing the information of a line from a log file.
class LogStats::Line

	# Accessible data for a line.
	attr_reader :method, :url, :dyno, :time

	# Regexp to abstract the needed data from a line String.
	MATCH_PARTS = /method=(.+?) .*?path=(.+?) .*?dyno=(.+?) .*?connect=(.+?)ms.*?service=(.+?)ms/

	# Parses a log line and uses its data.
	# 
	# str - String containing a raw line from the log file.
	def initialize(str)
		parts = MATCH_PARTS.match str
		@method = parts[1].downcase
		@url = parts[2]
		@dyno = parts[3]
		@time = parts[4].to_i + parts[5].to_i
	end

end


# Collect data for a single url.
# Calculate statistics from the data and display it nicely formatted. 
class LogStats::Url

	# Placeholder String used in urls for the user id. 
	PLACEHOLDER = '{user_id}'

	# Initalized all the data field for counting.
	#
	# method - The method for the url.
	# url - The url itself. LogUrls can be identified by method + url.
	def initialize(method, url)
		@url = url
		@method = method.downcase
		@count = 0
		@dyno_counts = Hash.new(0)
		@times = []
		# Generate regex from url and placeholder to compare to actual line data later.
		@url_matcher = Regexp.new "^#{url.gsub(PLACEHOLDER, '[0-9]+?')}(\\?.*)?$"
	end

	# Checks if a Line belongs to this Url.
	# 
	# line - Line to compare the Url to.
	# 
	# Returns a Boolean indicating if the line matches or not.
	def matches?(line)
		@method == line.method && @url_matcher.match(line.url)
	end


	# Add line to data of this Url.
	# 
	# line - Line containing data to add.
	def update(line)
		@count += 1
		@times << line.time
		@dyno_counts[line.dyno] += 1
	end

	# Returns a formatted String with calculated statisics for this Url.
	def to_str
		return "#{@method.upcase} #{@url} - no calls" if @times.empty?
		"#{@method.upcase} #{@url} - calls: #{@count}, mean: #{mean}ms, " +
		"median: #{median}ms, mode: #{mode}, most used dyno: #{max_dyno}"
	end

	
	private

	# Calculate the mean response time for this url.
	# 
	# Returns an Integer with the average time in ms.
	def mean
		(@times.inject(:+) / @times.size).to_i
	end

	# Calculate the median response time for this url.
	# 
	# Returns an Integer with the median time in ms.
	def median
		sorted = @times.sort
		middle = sorted.size / 2
		if sorted.size.odd?
			sorted[middle]
		else
			(sorted[middle.floor] + sorted[middle.ceil]) / 2
		end
	end

	# Calculate the mode response time for this url.
	# If there is no unique maximum just one of them is returned.
	# 
	# Returns an Integer with the mode time in ms.
	def mode
		counts = @times.inject( Hash.new(0) ) do |counts, t| 
			counts[t] += 1 
			counts
		end
		max_val( counts )
	end

	# Find the dyno that was used the most.
	# If there is no unique maximum just one of them is returned.
	# 
	# Returns the dyno with the most counts.
	def max_dyno
		max_val( @dyno_counts )
	end

	# Find the key of an Array with the highest value.
	# 
	# Returns the found key.
	def max_val(arr)
		arr.max_by { |k, v| v }[0]
	end
end



# Run if called from command line.
run! if __FILE__ == $0