require "date"
require "active_support/core_ext/time/calculations"

class String
  # Converts a string to a Time value.
  # The +form+ can be either :utc or :local (default :local).
  #
  # The time is parsed using Time.parse method.
  # If +form+ is :local, then the time is in the system timezone.
  # If the date part is missing then the current date is used and if
  # the time part is missing then it is assumed to be 00:00:00.
  #
  #   "13-12-2012".to_time               # => 2012-12-13 00:00:00 +0100
  #   "06:12".to_time                    # => 2012-12-13 06:12:00 +0100
  #   "2012-12-13 06:12".to_time         # => 2012-12-13 06:12:00 +0100
  #   "2012-12-13T06:12".to_time         # => 2012-12-13 06:12:00 +0100
  #   "2012-12-13T06:12".to_time(:utc)   # => 2012-12-13 06:12:00 UTC
  #   "12/13/2012".to_time               # => ArgumentError: argument out of range
  def to_time(form = :local)
    parts = Date._parse(self, false)
    used_keys = %i(year mon mday hour min sec sec_fraction offset)
    return if (parts.keys & used_keys).empty?

    now = Time.now
    time = Time.new(
      parts.fetch(:year, now.year),
      parts.fetch(:mon, now.month),
      parts.fetch(:mday, now.day),
      parts.fetch(:hour, 0),
      parts.fetch(:min, 0),
      parts.fetch(:sec, 0) + parts.fetch(:sec_fraction, 0),
      parts.fetch(:offset, form == :utc ? 0 : nil)
    )

    form == :utc ? time.utc : time.to_time
  end

  # Converts a string to a Date value.
  #
  #   "1-1-2012".to_date   # => Sun, 01 Jan 2012
  #   "01/01/2012".to_date # => Sun, 01 Jan 2012
  #   "2012-12-13".to_date # => Thu, 13 Dec 2012
  #   "12/13/2012".to_date # => ArgumentError: invalid date
  def to_date
    ::Date.parse(self, false) unless blank?
  end

  # Converts a string to a DateTime value.
  #
  #   "1-1-2012".to_datetime            # => Sun, 01 Jan 2012 00:00:00 +0000
  #   "01/01/2012 23:59:59".to_datetime # => Sun, 01 Jan 2012 23:59:59 +0000
  #   "2012-12-13 12:50".to_datetime    # => Thu, 13 Dec 2012 12:50:00 +0000
  #   "12/13/2012".to_datetime          # => ArgumentError: invalid date
  def to_datetime
    ::DateTime.parse(self, false) unless blank?
  end
end
