require 'date'

module ValidatesTimeliness

  # A date and time parsing library which allows you to add custom formats using
  # simple predefined tokens. This makes it much easier to catalogue and customize
  # the formats rather than dealing directly with regular expressions.
  #
  # Formats can be added or removed to customize the set of valid date or time
  # string values.
  #
  class Parser
    cattr_reader :time_expressions, :date_expressions, :datetime_expressions

    # Set the threshold value for a two digit year to be considered last century
    #
    # Default: 30
    #
    #   Example:
    #     year = '29' is considered 2029
    #     year = '30' is considered 1930
    #
    cattr_accessor :ambiguous_year_threshold
    self.ambiguous_year_threshold = 30

    # Set the dummy date part for a time type value. Should be an array of 3 values
    # being year, month and day in that order.
    #
    # Default: [ 2000, 1, 1 ] same as ActiveRecord
    #
    cattr_accessor :dummy_date_for_time_type
    self.dummy_date_for_time_type = [ 2000, 1, 1 ]

    # Format tokens:
    #       y = year
    #       m = month
    #       d = day
    #       h = hour
    #       n = minute
    #       s = second
    #       u = micro-seconds
    #    ampm = meridian (am or pm) with or without dots (e.g. am, a.m, or a.m.)
    #       _ = optional space
    #      tz = Timezone abbreviation (e.g. UTC, GMT, PST, EST)
    #      zo = Timezone offset (e.g. +10:00, -08:00, +1000)
    #
    #   All other characters are considered literal. You can embed regexp in the
    #   format but no gurantees that it will remain intact. If you avoid the use
    #   of any token characters and regexp dots or backslashes as special characters
    #   in the regexp, it may well work as expected. For special characters use
    #   POSIX character clsses for safety.
    #
    # Repeating tokens:
    #       x = 1 or 2 digits for unit (e.g. 'h' means an hour can be '9' or '09')
    #      xx = 2 digits exactly for unit (e.g. 'hh' means an hour can only be '09')
    #
    # Special Cases:
    #      yy = 2 or 4 digit year
    #    yyyy = exactly 4 digit year
    #     mmm = month long name (e.g. 'Jul' or 'July')
    #     ddd = Day name of 3 to 9 letters (e.g. Wed or Wednesday)
    #       u = microseconds matches 1 to 6 digits
    #
    #   Any other invalid combination of repeating tokens will be swallowed up
    #   by the next lowest length valid repeating token (e.g. yyy will be
    #   replaced with yy)

    cattr_accessor :time_formats
    @@time_formats = [
      'hh:nn:ss',
      'hh-nn-ss',
      'h:nn',
      'h.nn',
      'h nn',
      'h-nn',
      'h:nn_ampm',
      'h.nn_ampm',
      'h nn_ampm',
      'h-nn_ampm',
      'h_ampm'
    ]

    cattr_accessor :date_formats
    @@date_formats = [
      'yyyy-mm-dd',
      'yyyy/mm/dd',
      'yyyy.mm.dd',
      'm/d/yy',
      'd/m/yy',
      'm\d\yy',
      'd\m\yy',
      'd-m-yy',
      'dd-mm-yyyy',
      'd.m.yy',
      'd mmm yy'
    ]

    cattr_accessor :datetime_formats
    @@datetime_formats = [
      'yyyy-mm-dd hh:nn:ss',
      'yyyy-mm-dd h:nn',
      'yyyy-mm-dd h:nn_ampm',
      'yyyy-mm-dd hh:nn:ss.u',
      'm/d/yy h:nn:ss',
      'm/d/yy h:nn_ampm',
      'm/d/yy h:nn',
      'd/m/yy hh:nn:ss',
      'd/m/yy h:nn_ampm',
      'd/m/yy h:nn',
      'dd-mm-yyyy hh:nn:ss',
      'dd-mm-yyyy h:nn_ampm',
      'dd-mm-yyyy h:nn',
      'ddd, dd mmm yyyy hh:nn:ss (zo|tz)', # RFC 822
      'ddd mmm d hh:nn:ss zo yyyy', # Ruby time string
      'yyyy-mm-ddThh:nn:ssZ', # iso 8601 without zone offset
      'yyyy-mm-ddThh:nn:sszo' # iso 8601 with zone offset
    ]


    # All tokens available for format construction. The token array is made of
    # validation regexp and key for format proc mapping if any.
    # If the token needs no format proc arg then the validation regexp should
    # not have a capturing group, as all captured groups are passed to the
    # format proc.
    #
    # The token regexp should only use a capture group if 'look-behind' anchor
    # is required. The first capture group will be considered a literal and put
    # into the validation regexp string as-is. This is a hack.
    #
    cattr_accessor :format_tokens
    @@format_tokens = {
      'ddd'  => [ '\w{3,9}' ],
      'dd'   => [ '\d{2}',   :day ],
      'd'    => [ '\d{1,2}', :day ],
      'mmm'  => [ '\w{3,9}', :month ],
      'mm'   => [ '\d{2}',   :month ],
      'm'    => [ '\d{1,2}', :month ],
      'yyyy' => [ '\d{4}',   :year ],
      'yy'   => [ '\d{4}|\d{2}', :year ],
      'hh'   => [ '\d{2}',   :hour ],
      'h'    => [ '\d{1,2}', :hour ],
      'nn'   => [ '\d{2}',   :min ],
      'n'    => [ '\d{1,2}', :min ],
      'ss'   => [ '\d{2}',   :sec ],
      's'    => [ '\d{1,2}', :sec ],
      'u'    => [ '\d{1,6}', :usec ],
      'ampm' => [ '[aApP]\.?[mM]\.?', :meridian ],
      'zo'   => [ '[+-]\d{2}:?\d{2}', :offset ],
      'tz'   => [ '[A-Z]{1,4}' ],
      '_'    => [ '\s?' ]
    }

    # Arguments which will be passed to the format proc if matched in the
    # time string. The key must be the key from the format tokens. The array
    # consists of the arry position of the arg, the arg name, and the code to
    # place in the time array slot. The position can be nil which means the arg
    # won't be placed in the array.
    #
    # The code can be used to manipulate the arg value if required, otherwise
    # should just be the arg name.
    #
    cattr_accessor :format_proc_args
    @@format_proc_args = {
      :year     => [0,   'y', 'unambiguous_year(y)'],
      :month    => [1,   'm', 'month_index(m)'],
      :day      => [2,   'd', 'd'],
      :hour     => [3,   'h', 'full_hour(h, md ||= nil)'],
      :min      => [4,   'n', 'n'],
      :sec      => [5,   's', 's'],
      :usec     => [6,   'u', 'microseconds(u)'],
      :offset   => [7,   'z', 'offset_in_seconds(z)'],
      :meridian => [nil, 'md', nil]
    }

    @@type_wrapper = {
      :date     => [/\A/, nil],
      :time     => [nil , /\Z/],
      :datetime => [/\A/, /\Z/]
    }

    class << self

      def compile_format_expressions
        @@time_expressions     = compile_formats(@@time_formats)
        @@date_expressions     = compile_formats(@@date_formats)
        @@datetime_expressions = compile_formats(@@datetime_formats)
      end

      def parse(raw_value, type, options={})
        return nil if raw_value.blank?
        return raw_value if raw_value.acts_like?(:time) || raw_value.acts_like?(:date)
        
        time_array = _parse(raw_value, type, options.reverse_merge(:strict => true))
        return nil if time_array.nil?
        
        if type == :date
          Date.new(*time_array[0..2]) rescue nil
        else
          make_time(time_array[0..7], options[:timezone_aware])
        end
      end

      def make_time(time_array, timezone_aware=false)
        # Enforce strict date part validity which Time class does not
        return nil unless Date.valid_civil?(*time_array[0..2])

        if timezone_aware
          Time.zone.local(*time_array)
        else
          Time.time_with_datetime_fallback(ValidatesTimeliness.default_timezone, *time_array)
        end
      rescue ArgumentError, TypeError
        nil
      end

      # Loop through format expressions for type and call the format method on a match.
      # Allow pre or post match strings to exist if strict is false. Otherwise wrap
      # regexp in start and end anchors.
      #
      # Returns time array if matches a format, nil otherwise.
      #
      def _parse(string, type, options={})
        options.reverse_merge!(:strict => true)

        sets = if options[:format]
          options[:strict] = true
          [ send("#{type}_expressions").assoc(options[:format]) ]
        else
          expression_set(type, string)
        end

        set = sets.find do |format, regexp|
          string =~ wrap_regexp(regexp, type, options[:strict])
        end

        if set
          last   = options[:include_offset] ? 8 : 7
          values = send(:"format_#{set[0]}", *$~[1..last])
          values[0..2] = ValidatesTimeliness.dummy_date_for_time_type if type == :time
          return values
        end
      rescue
        nil
      end

      # Delete formats of specified type. Error raised if format not found.
      def remove_formats(type, *remove_formats)
        remove_formats.each do |format|
          unless self.send("#{type}_formats").delete(format)
            raise "Format #{format} not found in #{type} formats"
          end
        end
        compile_format_expressions
      end

      # Adds new formats. Must specify format type and can specify a :before
      # option to nominate which format the new formats should be inserted in
      # front on to take higher precedence.
      # Error is raised if format already exists or if :before format is not found.
      def add_formats(type, *add_formats)
        formats = self.send("#{type}_formats")
        options = {}
        options = add_formats.pop if add_formats.last.is_a?(Hash)
        before = options[:before]
        raise "Format for :before option #{format} was not found." if before && !formats.include?(before)

        add_formats.each do |format|
          raise "Format #{format} is already included in #{type} formats" if formats.include?(format)

          index = before ? formats.index(before) : -1
          formats.insert(index, format)
        end
        compile_format_expressions
      end

      # Removes formats where the 1 or 2 digit month comes first, to eliminate
      # formats which are ambiguous with the European style of day then month.
      # The mmm token is ignored as its not ambigous.
      def remove_us_formats
        us_format_regexp = /\Am{1,2}[^m]/
        date_formats.reject! { |format| us_format_regexp =~ format }
        datetime_formats.reject! { |format| us_format_regexp =~ format }
        compile_format_expressions
      end

      def full_hour(hour, meridian)
        hour = hour.to_i
        return hour if meridian.nil?
        if meridian.delete('.').downcase == 'am'
          raise if hour == 0 || hour > 12
          hour == 12 ? 0 : hour
        else
          hour == 12 ? hour : hour + 12
        end
      end

      def unambiguous_year(year)
        if year.length <= 2
          century = Time.now.year.to_s[0..1].to_i
          century -= 1 if year.to_i >= ambiguous_year_threshold
          year = "#{century}#{year.rjust(2,'0')}"
        end
        year.to_i
      end

      def month_index(month)
        return month.to_i if month.to_i.nonzero?
        abbr_month_names.index(month.capitalize) || month_names.index(month.capitalize)
      end

      def month_names
        I18n.t('date.month_names')
      end

      def abbr_month_names
        I18n.t('date.abbr_month_names')
      end

      def microseconds(usec)
        (".#{usec}".to_f * 1_000_000).to_i
      end

      def offset_in_seconds(offset)
        sign = offset =~ /^-/ ? -1 : 1
        parts = offset.scan(/\d\d/).map {|p| p.to_f }
        parts[1] = parts[1].to_f / 60
        (parts[0] + parts[1]) * sign * 3600
      end

    private

      # Generate regular expression from format string
      def generate_format_expression(string_format)
        format = string_format.dup
        format.gsub!(/([\.\\])/, '\\\\\1') # escapes dots and backslashes
        found_tokens, token_order = [], []

        tokens = format_tokens.keys.sort {|a,b| a.size <=> b.size }.reverse
        tokens.each do |token|
          regexp_str, arg_key = *format_tokens[token]
          if format.gsub!(/#{token}/, "%<#{found_tokens.size}>")
            regexp_str = "(#{regexp_str})" if arg_key
            found_tokens << [regexp_str, arg_key]
          end
        end

        format.scan(/%<(\d)>/).each {|token_index| 
          token_index = token_index.first
          token = found_tokens[token_index.to_i]
          format.gsub!("%<#{token_index}>", token[0])
          token_order << token[1]
        }

        compile_format_method(token_order.compact, string_format)
        Regexp.new(format)
      rescue
        raise "The following format regular expression failed to compile: #{format}\n from format #{string_format}."
      end

      # Compiles a format method which maps the regexp capture groups to method 
      # arguments based on order captured. A time array is built using the values
      # in the position indicated by the first element of the proc arg array.
      #
      def compile_format_method(order, name)
        values  = [nil] * 7
        args = []
        order.each do |part|
          proc_arg = format_proc_args[part]
          args << proc_arg[1]
          values[proc_arg[0]] = proc_arg[2] if proc_arg[0]
        end
        class_eval <<-DEF
          class << self
            define_method(:"format_#{name}") do |#{args.join(',')}|
              [#{values.map {|i| i || 'nil' }.join(',')}].map {|i| i.is_a?(Float) ? i : i.to_i }
            end
          end
        DEF
      end

      def compile_formats(formats)
        formats.map { |format| [ format, generate_format_expression(format) ] }
      end

      # Pick expression set and combine date and datetimes for
      # datetime attributes to allow date string as datetime
      def expression_set(type, string)
        case type
        when :date
          date_expressions
        when :time
          time_expressions
        when :datetime
          # gives a speed-up for date string as datetime attributes
          if string.length < 11
            date_expressions + datetime_expressions
          else
            datetime_expressions + date_expressions
          end
        end
      end

      def wrap_regexp(regexp, type, strict=false)
        type = strict ? :datetime : type
        /#{@@type_wrapper[type][0]}#{regexp}#{@@type_wrapper[type][1]}/
      end

    end
  end
end

ValidatesTimeliness::Parser.compile_format_expressions