Generate a "Compare View" in markdown, complete with Gravatars and links to GitHub commits

git.rake

require 'digest/md5'

namespace :git do

  GITHUB_COMMIT_URL = "https://github.com/path/to/your/repo/commit/"  # <= set me
  
  # Before doing a deploy, I like to check GitHub's branch list
  # but I wanted to be able to save it in a Lighthouse message
  COMPARE_FOR = {
    'production' => 'origin/production..origin/release',
    'release' => 'origin/production..origin/release',
    'staging' => 'origin/staging..origin/master',
    'master' => 'origin/staging..origin/master'
  }

  desc "generate compare view from git log"
  task :log do
    branch = current_branch
    compare = COMPARE_FOR[branch]
    raise "Not sure what to compare '#{branch}' with." if compare.nil?
    
    today = Time.now.strftime('%Y-%m-%d')
    file = "#{today}-compare.md"
    raise "File in the way '#{file}'." if File.exists?(file)
    
    run_cmd('git fetch') # track the latest
    
    GitLog.new(file, compare)
  end
  
  # local branch currently checked out:
  def current_branch
    out = run_cmd('git branch')
    local_branch = $1 if out =~ /\* (\S+)\s/m
  end
  
  def run_cmd(cmd)
    out = `#{cmd}`
    err = $?
    raise "Running `#{cmd}' failed (#{err})." unless err == 0
    out
  end
  
  
  
  # Parse a git log and reformat it as markdown with GitHub links and Gravatars
  class GitLog
    
    def initialize(file, compare)
      @authors = {}
      
      format = "%ad|%an|%ae|%s|%h"  # date, name, email, subject, commit_hash
      
      # get the git log:
      # for options: http://www.kernel.org/pub/software/scm/git/docs/git-log.html
      raw = run_cmd(%Q{git log --pretty=format:"#{format}" --no-merges --topo-order --reverse --date=short #{compare}})
      raise "No differences found." if raw.length == 0
      
      puts "Compare View for #{compare} => #{file}"
      
      File.open(file, "w") do |file|
        file << markdown_header("Compare View #{compare}")
        
        raw.each_line do |line|
          file << parse(line.chomp) << "\n"
        end
        
        file << "\n" << author_references.join("\n")
      end
      
      raw = nil
    end
    
    def parse(line)
      date, name, email, subject, commit_hash = line.split('|')
      
      ref = add_author(name, email)
      image_ref = "![][#{ref}]"   # markdown image reference ![alt][id]
      commit = markdown_github_url(commit_hash)
      
      [date, "#{image_ref} #{name}", subject, commit].join('|')
    end
    
    def add_author(name, email)
      author = @authors[email]
      if author.nil?
        author = {:name => name, :email => email, :ref => "id#{@authors.length}"}
        @authors[email] = author
      end
      author[:ref]
    end
    
    def author_references
      @authors.map do |k, author|
        ref = author[:ref]
        gravatar = gravatar_url(author[:email])
        name = author[:name]
        %Q{[#{ref}]: #{gravatar} "#{name}"}   # markdown reference-style image
      end
    end
    
    def markdown_header(title)
      <<-MD.gsub(/^\s+/, '')
      ## #{title}
      Date|Name|Subject|Commit
      ----|----|-------|------
      MD
    end
    
    # gravatar image url
    def gravatar_url(email, size=25)
      digest = Digest::MD5.hexdigest(email.strip.downcase)
      "https://secure.gravatar.com/avatar/#{digest}?s=#{size}"
    end

    # markdown-style urls to GitHub commits
    def markdown_github_url(commit_hash)
      "[#{commit_hash}](#{GITHUB_COMMIT_URL}#{commit_hash})"
    end
  end
  
end