#!/usr/bin/env ruby
# Walks up and down revisions in a git repo.
# Usage:
#   git walk next
#   git walk prev
case ARGV[0]
when "next"
  rev_list = `git rev-list --children --all`
  refs = rev_list.scan(/[a-z0-9]{40}(?= )/)
  refs.unshift(rev_list[/[a-z0-9]{40}/])
  refs.reverse!

  head = `git rev-parse HEAD`.chomp
  ref_for_next_commit = refs[refs.index(head) + 1]

  if ref_for_next_commit
    puts `git checkout #{ref_for_next_commit}`
  else
    puts "You're already on the latest commit."
  end
when "prev"
  puts `git checkout HEAD^`
else
  puts "Usage: git-walk next|prev"
end