# encoding: utf-8
require 'mail/fields/common/common_field'

module Mail
  # Provides access to an unstructured header field
  #
  # ===Per RFC 2822:
  #  2.2.1. Unstructured Header Field Bodies
  #  
  #     Some field bodies in this standard are defined simply as
  #     "unstructured" (which is specified below as any US-ASCII characters,
  #     except for CR and LF) with no further restrictions.  These are
  #     referred to as unstructured field bodies.  Semantically, unstructured
  #     field bodies are simply to be treated as a single line of characters
  #     with no further processing (except for header "folding" and
  #     "unfolding" as described in section 2.2.3).
  class UnstructuredField
    
    include Mail::CommonField
    include Mail::Utilities
    
    def initialize(name, value, charset = nil)
      self.charset = charset
      @errors = []
      if charset
        self.charset = charset
      else
        if value.to_s.respond_to?(:encoding)
          self.charset = value.to_s.encoding
        else
          self.charset = $KCODE
        end
      end
      self.name = name
      self.value = value
      self
    end
    
    def charset
      @charset
    end
    
    def charset=(val)
      @charset = val
    end

    def errors
      @errors
    end
    
    def encoded
      do_encode(self.name)
    end
    
    def decoded
      do_decode
    end

    def default
      decoded
    end
    
    def parse # An unstructured field does not parse
      self
    end

    private
    
    def do_encode(name)
      value.nil? ? '' : "#{wrapped_value}\r\n"
    end
    
    def do_decode
      value.blank? ? nil : Encodings.decode_encode(value, :decode)
    end
    
    # 2.2.3. Long Header Fields
    # 
    #  Each header field is logically a single line of characters comprising
    #  the field name, the colon, and the field body.  For convenience
    #  however, and to deal with the 998/78 character limitations per line,
    #  the field body portion of a header field can be split into a multiple
    #  line representation; this is called "folding".  The general rule is
    #  that wherever this standard allows for folding white space (not
    #  simply WSP characters), a CRLF may be inserted before any WSP.  For
    #  example, the header field:
    #  
    #          Subject: This is a test
    #  
    #  can be represented as:
    #  
    #          Subject: This
    #           is a test
    #  
    #  Note: Though structured field bodies are defined in such a way that
    #  folding can take place between many of the lexical tokens (and even
    #  within some of the lexical tokens), folding SHOULD be limited to
    #  placing the CRLF at higher-level syntactic breaks.  For instance, if
    #  a field body is defined as comma-separated values, it is recommended
    #  that folding occur after the comma separating the structured items in
    #  preference to other places where the field could be folded, even if
    #  it is allowed elsewhere.
    def wrapped_value # :nodoc:
      @folded_line = []
      @unfolded_line = decoded.to_s.clone
      fold("#{name}: ".length)
      wrap_lines(name, @folded_line)
    end

    def wrap_lines(name, folded_lines)
      result = []
      index = 0
      result[index] = "#{name}: #{folded_lines.shift}"
      folded_lines.each do |line|
        if (result[index] + line).length < 77
          result[index] << " " + line
        else
          result[index] << "\r\n\t"
          index += 1
          result[index] = line
        end
      end
      result.join
    end

    def fold(prepend = 0) # :nodoc:
      # Get the last whitespace character, OR we'll just choose 
      # 78 if there is no whitespace, or 23 for non ascii:
      # Each QP byte is 6 chars (=0A)
      # Plus 18 for the =?encoding?Q?= ... ?=
      # Plus 2 for the \r\n and 1 for the \t
      # 80 - 2 - 1 - 18 = 59 / 6 ~= 10
      @unfolded_line.ascii_only? ? (limit = 78 - prepend) : (limit = 10 - prepend)
      # find the last white space character within the limit
      if wspp = @unfolded_line.mb_chars.slice(0..limit) =~ /[ \t][^ \t]*$/
        wrap = true
        wspp = limit if wspp == 0
        @folded_line << encode(@unfolded_line.mb_chars.slice!(0...wspp).strip.to_str)
        @folded_line.flatten!
      # if no last whitespace before the limit, find the first
      elsif wspp = @unfolded_line.mb_chars =~ /[ \t][^ \t]/
        wrap = true
        wspp = limit if wspp == 0
        @folded_line << encode(@unfolded_line.mb_chars.slice!(0...wspp).strip.to_str)
        @folded_line.flatten!
      # if no whitespace, don't wrap
      else
        wrap = false
      end

      if wrap && @unfolded_line.length > limit
        fold
      else
        @folded_line << encode(@unfolded_line)
        @folded_line.flatten!
      end
    end

    def encode(value)
      value.gsub!("\r", "=0D")
      value.gsub!("\n", "=0A")
      Encodings.q_value_encode(value, @charset).split(" ")
    end

  end
end