#!/usr/bin/env ruby
#
# the_long_tail
#
# A histogram view on contributor stats
#
# notes
#
# Since this script does not track file-renames in the git history, the
# dependence of Casks upon occasional contributors/non-maintainers can
# only be expressed as a range or lower bound.
#

###
### dependencies
###

require "open3"
require "set"

###
### configurable constants
###

BINS = [
         (1..10).to_a,
         100,
         1000,
       ].flatten

OCCASIONAL_CUTOFF = 5

CASK_PATH = "Casks".freeze

# all maintainers, past and present
MAINTAINERS = %w[
                paul.t.hinze@gmail.com
                fanquake@users.noreply.github.com
                fanquake@gmail.com
                kevin@suttle.io
                leoj3n@gmail.com
                nano@fdp.io
                nanoid.xd@gmail.com
                me@passcod.name
                walker@pobox.com
                info@vitorgalvao.com
                calebcenter@live.com
                ndr@qef.io
                josh@joshbutts.com
                goxberry@gmail.com
                radek.simko@gmail.com
                federicobond@gmail.com
                claui@users.noreply.github.com
                amorymeltzer@gmail.com
                hagins.josh@gmail.com
                dragon.vctr@gmail.com
                mail@sebastianroeder.de
                github@adityadalal.com
                adityadalal924@users.noreply.github.com
              ].freeze

###
### git methods
###

def cd_to_project_root
  Dir.chdir File.dirname(File.expand_path(__FILE__))
  @git_root ||= Open3.popen3(*%w[
                                git rev-parse --show-toplevel
                              ]) do |_stdin, stdout, _stderr|
    begin
      stdout.gets.chomp
    rescue
    end
  end
  Dir.chdir @git_root
  @git_root
end

def authors
  @authors ||= Open3.popen3(*%w[
                               git log --no-merges --format=%ae --
                             ]) do |_stdin, stdout, _stderr|
    h = {}
    stdout.each_line do |line|
      line.chomp!
      h[line] ||= 0
      h[line]  += 1
    end
    h
  end
end

def casks_by_author
  @casks_by_author ||= Open3.popen3(*%w[
                                       git log --no-merges --name-only --format=%ae --
                                     ],
                                    CASK_PATH) do |_stdin, stdout, _stderr|
    email = nil
    h = {}
    stdout.each_line.to_a.join("").split("\n\n").each do |paragraph|
      if paragraph.include?("Casks/")
        lines = paragraph.split("\n")
        email = lines.pop
        h[email] ||= Set.new
        h[email].merge(lines.compact)
      else
        email = paragraph.chomp
      end
    end
    h
  end
end

###
### filesystem methods
###

def all_casks
  @all_casks ||= Open3.popen2("/usr/bin/find",
                              CASK_PATH,
                              *%w[-type f -name *.rb]) do |_stdin, stdout|
    stdout.each_line.map(&:chomp)
  end
end

###
### analysis and report methods
###

def histogram
  if @histogram.nil?
    @histogram = Hash[*BINS.map { |elt| [elt, 0] }.flatten]
    authors.each do |_name, num_commits|
      bottom = 0
      BINS.each do |top|
        @histogram[bottom] += 1 if num_commits >= bottom && num_commits < top
        bottom = top
      end
    end
  end
  @histogram
end

def historic_occasional_cask_set
  @historic_occasional_cask_set = authors.each.collect do |name, num_commits|
    if num_commits > OCCASIONAL_CUTOFF
      nil
    elsif !casks_by_author.key?(name)
      nil
    else
      casks_by_author[name].to_a
    end
  end.flatten.compact.to_set
end

def extant_occasional_cask_count
  # avoid double-counting renames by intersecting with extant Casks
  historic_occasional_cask_set.intersection(all_casks).count
end

def historic_nonmaintainer_cask_set
  @historic_nonmaintainer_cask_set = authors.each.collect do |name, _num_commits|
    if MAINTAINERS.include?(name)
      nil
    else
      casks_by_author[name].to_a
    end
  end.flatten.compact.to_set
end

def extant_nonmaintainer_cask_count
  # avoid double-counting renames by intersecting with extant Casks
  historic_nonmaintainer_cask_set.intersection(all_casks).count
end

def extant_occasional_cask_percentage
  @extant_occasional_cask_percentage ||= (100 * extant_occasional_cask_count / all_casks.count).to_i
end

def historic_occasional_cask_percentage
  @historic_occasional_cask_percentage ||= (100 * historic_occasional_cask_set.count / all_casks.count).to_i
end

def extant_nonmaintainer_cask_percentage
  @extant_nonmaintainer_cask_percentage ||= (100 * extant_nonmaintainer_cask_count / all_casks.count).to_i
end

def historic_nonmaintainer_cask_percentage
  # this is so large, it might cross 100%
  @historic_nonmaintainer_cask_percentage ||= [100, (100 * historic_nonmaintainer_cask_set.count / all_casks.count).to_i].min
end

def onetime_author_percentage
  @onetime_author_percentage ||= (100 *
                                  histogram[1] /
                                  authors.length).to_i
end

def occasional_author_percentage
  # why is it so hard to slice a hash?
  @occasional_author_percentage ||= (100 *
                                 (1..OCCASIONAL_CUTOFF).to_a.collect { |bin| histogram[bin] }.reduce(:+) /
                                 authors.length).to_i
end

def graph_width
  if @graph_width.nil?
    @graph_width  = `/bin/stty size 2>/dev/null`.chomp.split(" ").last.to_i
    @graph_width  = 80 if @graph_width <= 0
    @graph_width -= 20 if @graph_width > 20
  end
  @graph_width
end

def graph_normalization
  @graph_normalization ||= histogram.values.max.to_f
end

def print_header
  puts "Commits\tContributors"
  puts "---------------------"
end

def print_table
  BINS.each do |bin|
    plural = (bin % 10) == 0 ? "'s" : ""
    graph = "." * ((histogram[bin] / graph_normalization) * graph_width)
    puts "#{bin}#{plural}\t#{histogram[bin]}\t#{graph}"
  end
end

def print_footer
  puts %Q{\n#{occasional_author_percentage}% of contributors are "occasional" (with <= #{OCCASIONAL_CUTOFF} commits)}
  puts "\n#{onetime_author_percentage}% of contributors commit only once"
  puts "\n#{extant_occasional_cask_percentage}% - #{historic_occasional_cask_percentage}% of Casks depend on an occasional contributor"
  puts "\n#{extant_nonmaintainer_cask_percentage}% - #{historic_nonmaintainer_cask_percentage}% of Casks depend on a contributor who is not a maintainer"
  puts "\n"
end

def generate_report
  print_header
  print_table
  print_footer
end

###
### main
###

cd_to_project_root
generate_report