class GitHubPages::Configuration

Sets and manages Jekyll configuration defaults and overrides

def configure_plugins(config)

Requires default plugins and configures whitelist in development 
def configure_plugins(config)
  # Ensure we have those gems we want.
  config["plugins"] = Array(config["plugins"]) | DEFAULT_PLUGINS
  # To minimize errors, lazy-require jekyll-remote-theme if requested by the user
  config["plugins"].push("jekyll-remote-theme") if config.key? "remote_theme"
  return unless development?
  if disable_whitelist?
    config["whitelist"] = config["whitelist"] | config["plugins"]
  end
  config["whitelist"] = config["whitelist"] | DEVELOPMENT_PLUGINS
end

def debug_print_versions

stream for debugging purposes. See by running Jekyll with '--verbose'
Print the versions for github-pages and jekyll to the debug 
def debug_print_versions
  Jekyll.logger.debug "GitHub Pages:", "github-pages v#{GitHubPages::VERSION}"
  Jekyll.logger.debug "GitHub Pages:", "jekyll v#{Jekyll::VERSION}"
end

def defaults_for_env 

def defaults_for_env
  defaults = development? ? DEFAULTS : PRODUCTION_DEFAULTS
  Jekyll::Utils.deep_merge_hashes Jekyll::Configuration::DEFAULTS, defaults
end

def development? 

def development?
  Jekyll.env == "development"
end

def disable_whitelist? 

def disable_whitelist?
  development? && !ENV["DISABLE_WHITELIST"].to_s.empty?
end

def effective_config(user_config)

Note: this is a highly modified version of Jekyll#configuration

Returns the effective Configuration

values which themselves override our defaults.
configuration sandwhich with our overrides overriding the user's specified
Given a user's config, determines the effective configuration by building a user 
def effective_config(user_config)
  # Merge user config into defaults
  config = Jekyll::Utils.deep_merge_hashes(defaults_for_env, user_config)
    .fix_common_issues
    .add_default_collections
  # Allow theme to be explicitly disabled via "theme: null"
  config["theme"] = user_config["theme"] if user_config.key?("theme")
  exclude_cname(config)
  # Merge overwrites into user config
  config = Jekyll::Utils.deep_merge_hashes config, OVERRIDES
  restrict_and_config_markdown_processor(config)
  configure_plugins(config)
  config
end

def exclude_cname(config)

If the user's 'exclude' config is the default, also exclude the CNAME 
def exclude_cname(config)
  return unless config["exclude"].eql? Jekyll::Configuration::DEFAULTS["exclude"]
  config["exclude"].concat(DEFAULTS["exclude"])
end

def processed(site) 

def processed(site)
  site.instance_variable_set :@_github_pages_processed, true
end

def processed?(site) 

def processed?(site)
  site.instance_variable_get(:@_github_pages_processed) == true
end

def restrict_and_config_markdown_processor(config)

be idempotentish.
This can get called multiply on the same config, so try to

neither of these.
Ensure we're using Kramdown or GFM. Force to Kramdown if 
def restrict_and_config_markdown_processor(config)
  config["markdown"] = "kramdown" unless \
    %w(kramdown gfm commonmarkghpages).include?(config["markdown"].to_s.downcase)
  return unless config["markdown"].to_s.casecmp("gfm").zero?
  config["markdown"] = "CommonMarkGhPages"
  config["commonmark"] = {
    "extensions" => %w(table strikethrough autolink tagfilter),
    "options" => %w(footnotes),
  }
end

def set(site)

guards against double-processing via the value in #processed.
Equivalent #set! function contains the code of interest. This function
Set the site's configuration. Implemented as an `after_reset` hook. 
def set(site)
  return if processed? site
  debug_print_versions
  set!(site)
  processed(site)
end

def set!(site)

Should be called by #set to protect against multiple processings.
Set the site's configuration with all the proper defaults and overrides. 
def set!(site)
  site.config = effective_config(site.config)
end