class RuboCop::Cop::Rails::TimeZone

Time.at(timestamp).in_time_zone
DateTime.strptime(str, “%Y-%m-%d %H:%M %Z”).in_time_zone
Time.current
# no offense only if style is ‘flexible’
Time.zone.parse(‘2015-03-02 19:05:37’)
Time.zone.now
# no offense
Time.parse(‘2015-03-02 19:05:37’)
Time.now
# always offense
@example
to use Time.in_time_zone.
When EnforcedStyle is ‘flexible’ then it’s also allowed
then only use of Time.zone is allowed.
Two styles are supported for this cop. When EnforcedStyle is ‘strict’
and the article danilenko.org/2012/7/6/rails_timezones/ .
Built on top of Ruby on Rails style guide (github.com/bbatsov/rails-style-guide#time)
This cop checks for the use of Time methods without zone.

def acceptable? 

def acceptable?
  style == :flexible
end

def acceptable_methods(klass, method_name, node) 

def acceptable_methods(klass, method_name, node)
  acceptable = [
    "`Time.zone.#{safe_method(method_name, node)}`",
    "`#{klass}.current`"
  ]
  ACCEPTED_METHODS.each do |am|
    acceptable << "`#{klass}.#{method_name}.#{am}`"
  end
  acceptable
end

def build_message(klass, method_name, node) 

def build_message(klass, method_name, node)
  if acceptable?
    format(MSG_ACCEPTABLE,
           "#{klass}.#{method_name}",
           acceptable_methods(klass, method_name, node).join(', '))
  elsif method_name == 'current'
    format(MSG_CURRENT,
           "#{klass}.#{method_name}")
  else
    safe_method_name = safe_method(method_name, node)
    format(MSG,
           "#{klass}.#{method_name}",
           "Time.zone.#{safe_method_name}")
  end
end

def check_localtime(node) 

def check_localtime(node)
  selector_node = node
  while node && node.send_type?
    break if extract_method(node) == :localtime
    node = node.parent
  end
  return if node.arguments?
  add_offense(selector_node, :selector, MSG_LOCALTIME)
end

def check_time_node(klass, node) 

def check_time_node(klass, node)
  chain = extract_method_chain(node)
  return if danger_chain?(chain)
  return check_localtime(node) if need_check_localtime?(chain)
  method_name = (chain & DANGEROUS_METHODS).join('.')
  return if offset_provided?(node)
  message = build_message(klass, method_name, node)
  add_offense(node, :selector, message)
end

def danger_chain?(chain) 

def danger_chain?(chain)
  (chain & DANGEROUS_METHODS).empty? || !(chain & good_methods).empty?
end

def extract_method(node) 

def extract_method(node)
  _receiver, method_name, *_args = *node
  method_name
end

def extract_method_chain(node) 

def extract_method_chain(node)
  chain = []
  while !node.nil? && node.send_type?
    chain << extract_method(node) if method_from_time_class?(node)
    node = node.parent
  end
  chain
end

def good_methods 

def good_methods
  if style == :strict
    GOOD_METHODS
  else
    GOOD_METHODS + [:current] + ACCEPTED_METHODS
  end
end

def method_from_time_class?(node)

called is part of the time class.
Only add the method to the chain if the method being 
def method_from_time_class?(node)
  receiver, method_name, *_args = *node
  if (receiver.is_a? RuboCop::AST::Node) && !receiver.cbase_type?
    method_from_time_class?(receiver)
  else
    TIMECLASS.include? method_name
  end
end

def method_send?(node)

and receiver is the given node
checks that parent node of send_type 
def method_send?(node)
  return false unless node.parent && node.parent.send_type?
  receiver, _method_name, *_args = *node.parent
  receiver == node
end

def need_check_localtime?(chain) 

def need_check_localtime?(chain)
  acceptable? && chain.include?(:localtime)
end

def offset_provided?(node)

Time.new(1988, 3, 15, 3, 0, 0, "-05:00")
Example:
When it is, that should be considered safe
Time.new can be called with a time zone offset 
def offset_provided?(node)
  node.arguments.size >= 7
end

def on_const(node) 

def on_const(node)
  mod, klass = *node
  # we should only check core class
  # (`DateTime`/`Time` or `::Date`/`::DateTime`)
  return unless (mod.nil? || mod.cbase_type?) && method_send?(node)
  check_time_node(klass, node.parent) if TIMECLASS.include?(klass)
end

def safe_method(method_name, node) 

def safe_method(method_name, node)
  return method_name unless method_name == 'new'
  if node.arguments?
    'local'
  else
    'now'
  end
end