#! /usr/bin/env ruby

require 'rubygems'
require 'optparse'

OptionParser.new do |opts|
  opts.banner = <<BANNER
Find the commit that broke the build

Usage:
    git-autobisect 'ruby test/foo_test.rb -n "/xxx/"' [options]

Options:
BANNER
  opts.on("-h", "--help","Show this.") { puts opts; exit }
  opts.on("-v", "--version","Show Version"){
    version = File.read(File.expand_path("../../VERSION", __FILE__))
    puts "git-autobisect #{version}"; exit
  }
end.parse!

command = ARGV.first
if command.to_s.empty?
  puts "Usage instructions: git-autobisect --help"
  exit
end

def run(cmd)
  all = ""
  puts cmd
  IO.popen(cmd) do |pipe|
    while str = pipe.gets
      all << str
      puts str
    end
  end
  [$?.success?, all]
end

def run!(command)
  raise "Command failed #{command}" unless run(command).first
end

def find_first_good_commit(commits, command)
  # scan backwards through commits to find a good
  i = 0
  stay_slow_until = 3

  loop do
    # pick next commit (start slow, then get faster)
    i += 1
    offset = (i <= stay_slow_until ? i-1 : (i-1)*10)
    break unless commit = commits[offset]

    # see if it works
    puts " ---> Now trying #{commit}"
    run!("git checkout #{commit}")
    return commit if run(command).first
  end
end

command = "(bundle check || bundle) && (#{command})" if File.exist?("Gemfile")
puts " ---> Initial run:"
if run(command).first
  puts " ---> Current commit is not broken"
  exit 1
end

puts " ---> Trying to find first good commit:"
max_commits = 1000
commits = `git log --pretty=format:'%h' | head -n #{max_commits}`.split("\n")
unless good = find_first_good_commit(commits[1..-1], command)
  puts " --> No good commit found"
  exit 1
end

# bisect to get exact match
bad = commits[0]
run! "git bisect reset"
run! "git bisect start"
run! "git checkout #{bad}"
run! "git bisect bad"
run! "git checkout #{good}"
run! "git bisect good"
success, output = run("git bisect run sh -c '#{command}'")
if success
  # git bisect randomly stops at a commit
  first_bad = output.match(/([\da-f]+) is the first bad commit/)[1]
  run! "git checkout #{first_bad}"
  exit 0
else
  exit 1
end