require 'colored'
require 'grit'

class GitUp
  def run
    system('git', 'fetch', '--multiple', *remotes)
    raise GitError, "`git fetch` failed" unless $? == 0
    @remote_map = nil # flush cache after fetch

    with_stash do
      returning_to_current_branch do
        col_width = branches.map { |b| b.name.length }.max + 1

        branches.each do |branch|
          remote = remote_map[branch.name]

          print branch.name.ljust(col_width)

          if remote.commit.sha == branch.commit.sha
            puts "up to date".green
            next
          end

          base = merge_base(branch.name, remote.name)

          if base == remote.commit.sha
            puts "ahead of upstream".green
            next
          end

          if base == branch.commit.sha
            puts "fast-forwarding...".yellow
          else
            puts "rebasing...".yellow
          end

          checkout(branch.name)
          rebase(remote)
        end
      end
    end

    check_bundler
  rescue GitError => e
    puts e.message
    exit 1
  end

  def repo
    @repo ||= get_repo
  end

  def get_repo
    git_dir = `git rev-parse --git-dir`

    if $? == 0
      @repo = Grit::Repo.new(File.dirname(git_dir))
    else
      raise GitError, "We don't seem to be in a git repository."
    end
  end

  def branches
    @branches ||= repo.branches.select { |b| remote_map.has_key?(b.name) }
  end

  def remotes
    @remotes ||= remote_map.values.map { |r| r.name.split('/', 2).first }.uniq
  end

  def remote_map
    @remote_map ||= repo.branches.inject({}) { |map, branch|
      if remote = remote_for_branch(branch)
        map[branch.name] = remote
      end

      map
    }
  end

  def remote_for_branch(branch)
    remote_name   = repo.config["branch.#{branch.name}.remote"] || "origin"
    remote_branch = repo.config["branch.#{branch.name}.merge"] || branch.name
    remote_branch.sub!(%r{^refs/heads/}, '')
    repo.remotes.find { |r| r.name == "#{remote_name}/#{remote_branch}" }
  end

  def with_stash
    stashed = false

    status = repo.status
    change_count = status.added.length + status.changed.length + status.deleted.length

    if change_count > 0
      puts "stashing #{change_count} changes".magenta
      repo.git.stash
      stashed = true
    end

    yield

    if stashed
      puts "unstashing".magenta
      repo.git.stash({}, "pop")
    end
  end

  def returning_to_current_branch
    unless repo.head.respond_to?(:name)
      puts "You're not currently on a branch. I'm exiting in case you're in the middle of something.".red
      return
    end

    branch_name = repo.head.name

    yield

    unless on_branch?(branch_name)
      puts "returning to #{branch_name}".magenta
      checkout(branch_name)
    end
  end

  def checkout(branch_name)
    output = repo.git.checkout({}, branch_name)

    unless on_branch?(branch_name)
      raise GitError.new("Failed to checkout #{branch_name}", output)
    end
  end

  def rebase(target_branch)
    current_branch = repo.head

    output, err = repo.git.sh("#{Grit::Git.git_binary} rebase #{target_branch.name}")

    unless on_branch?(current_branch.name) and is_fast_forward?(current_branch, target_branch)
      raise GitError.new("Failed to rebase #{current_branch.name} onto #{target_branch.name}", output+err)
    end
  end

  def check_bundler
    return unless use_bundler?

    begin
      require 'bundler'
      ENV['BUNDLE_GEMFILE'] ||= File.expand_path('Gemfile')
      Bundler.setup
    rescue Bundler::GemNotFound, Bundler::GitError
      puts 'Gems are missing.  You should `bundle install`.'.yellow
    end
  end

  def is_fast_forward?(a, b)
    merge_base(a.name, b.name) == b.commit.sha
  end

  def merge_base(a, b)
    repo.git.send("merge-base", {}, a, b).strip
  end

  def on_branch?(branch_name=nil)
    repo.head.respond_to?(:name) and repo.head.name == branch_name
  end

  class GitError < StandardError
    def initialize(message, output=nil)
      @msg = "#{message.red}"

      if output
        @msg << "\n"
        @msg << "Here's what Git said:".red
        @msg << "\n"
        @msg << output
      end
    end

    def message
      @msg
    end
  end

private

  def use_bundler?
    ENV['GIT_UP_BUNDLER_CHECK'] == 'true' and File.exists? 'Gemfile'
  end
end