Crystal Shards bootstrap (Ruby)

shards_bootstrap.rb

#! /usr/bin/env ruby
#
# A bootstrap to install locked Crystal Shards dependencies. Written in Ruby so
# it doesn't need Crystal. This coul be useful to extract stdlib as distinct
# shards from the main crystal-lang/crystal repository, while still allowing to
# install and distribute them to build crystal, avoiding the crystal <-> shards
# requirement loop.
require "yaml"

# helpers:

def fatal(message)
  STDERR.puts "fatal: #{message}"
  exit 1
end

def execute(command)
  puts "+ #{command}"
  system(command)
end

def installed_version(name)
  return unless Dir.exists?(name)

  specfile = File.join(name, "shard.yml")
  return unless File.exists?(File.join(specfile))

  spec = YAML.load(File.read(specfile))
  spec["version"]
end

# configuration:
LIB_DIR = File.join(Dir.pwd, "lib")
lockfile = "shard.lock"

# validation:
unless File.exists?(lockfile)
  fatal "No shard.lock file in the current directory"
end

locked = YAML.load(File.read(lockfile))

unless (version = locked["version"].to_s) == "1.0"
  fatal "Unsupported lock version: #{version}"
end

# installation:
Dir.mkdir(LIB_DIR) unless Dir.exists?(LIB_DIR)
Dir.chdir(LIB_DIR)

locked["shards"].each do |name, dependency|
  repo =
    if dependency.has_key?("git")
      dependency["git"]
    elsif dependency.has_key?("github")
      "https://github.com/#{dependency["github"]}.git"
    elsif dependency.has_key?("bitbucket")
      "https://bitbucket.org/#{dependency["bitbucket"]}.git"
    elsif dependency.has_key?("gitlab")
      "https://gitlab.com/#{dependency["gitlab"]}.git"
    end

  refs =
    if dependency.has_key?("version")
      if installed_version(name) == dependency["version"]
        STDERR.puts "Using #{name} (#{dependency["version"]})"
        next
      end
      "v" + dependency["version"]
    else
      if File.exists?("#{name}.sha1") && File.read("#{name}.sha1") == dependency["commit"]
        STDERR.puts "Using #{name} (#{installed_version(name)} at #{commit})"
        next
      end
      dependency["commit"]
    end

  STDERR.puts "Installing #{name} at #{refs}"
  execute "rm -rf #{name} #{name}.sha1"

  # should use git archive, but it's not supported by Git HTTP protocol :(
  unless execute "git clone -q --depth=1 --branch=#{refs} --single-branch --no-checkout #{repo} #{name}"
    fatal "failed to install #{name} at #{refs}"
  end
  execute "cd #{name} && git checkout #{refs} 2> /dev/null"
  execute "rm -rf #{name}/.git"

  if refs == dependency["commit"]
    File.write("#{name}.sha1", refs)
  end
end