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#!/usr/bin/env ruby

require 'rubygems'
require 'fileutils'
require 'word_salad'

def decorate_log_with_branch(log, branch_name, root_sha, origin=[])
  cursor = root_sha

  log[root_sha][:branch] = branch_name

  while prev = log[cursor][:parents][0] do
    # Break if we are following a branch and we reach the common ancestor.
    break if origin.include?(prev)

    log[prev][:branch] = branch_name
    cursor = prev
  end
end


def random_branch_name
  candidate = 2.words.join("_")

  while @_names_used.include?(candidate)
    candidate = 2.words.join("_")
  end

  @_names_used << candidate

  return candidate
end

@_names_used = []

repo = ARGV[0]
mainline_branch = ARGV[1]
replay_depth = ARGV[2]

# R.I.P. memory
puts "Parsing git-log..."
commits_array = `/usr/bin/env GIT_DIR=#{repo} git log --branches --format="%H%x09%P%x09%s"`.lines.collect do |log_line|
  sha, parents, subject = log_line.split("\t")
  [sha, {parents: parents.split(" "), subject: subject}]
end
log = Hash[commits_array]


puts "Finding main branch history..."
mainline_head = `/usr/bin/env GIT_DIR=#{repo} git rev-parse #{mainline_branch}`.strip
decorate_log_with_branch(log, mainline_branch, mainline_head)
mainline_history = log.map { |sha, commit| sha if commit[:branch] == mainline_branch }.compact!


puts "Finding unmerged branches..."
head_refs_array = `/usr/bin/env GIT_DIR=#{repo} git show-ref --heads`.lines.collect do |ref_line|
  sha, branch = ref_line.split(" ")
  branch.gsub!(/refs\/heads\//, '')
  @_names_used << branch
  [branch, sha]
end
head_refs = Hash[head_refs_array]

head_refs.delete(mainline_branch) # We already walked mainline branch
head_refs.each do |branch, sha|
  decorate_log_with_branch(log, branch, sha, mainline_history)
end

if depth = replay_depth.to_i
  puts "Trimming to last #{depth} commits..."
  trimmed_log = log.take(depth)
else
  trimmed_log = log
end

puts "Finding merged branches..."
trimmed_log.each do |sha, commit|
  if mainline_history.include?(sha) && commit[:parents].size == 2
    new_branch = random_branch_name

    log[sha][:ends_branch] = new_branch

    decorate_log_with_branch(log, new_branch, commit[:parents][1], mainline_history)
  end
end


puts "Pruning orphan commits..."
trimmed_log.reject! { |sha, commit| !commit[:branch] }


puts "Replaying commits in original order, send USR1 to PID #{Process.pid} to advance..."
trimmed_log.reverse_each do |sha, commit|
  @next = false
  Signal.trap("USR1") { @next = true }
  sleep(0.5) until @next

  log_line = "  #{commit[:branch]} -> #{sha}"

  File.open("#{repo}/refs/heads/#{commit[:branch]}", "w") do |f|
    f.puts(sha)
  end

  if commit[:ends_branch] && File.exists?("#{repo}/refs/heads/#{commit[:ends_branch]}")
    FileUtils.rm("#{repo}/refs/heads/#{commit[:ends_branch]}", force: true)
    log_line << " (Deleted branch #{commit[:ends_branch]})"
  end

  puts log_line
end

puts "Done!"