require 'strscan'

module Haml
  # This module contains functionality that's shared between Haml and Sass.
  module Shared
    extend self

    # Scans through a string looking for the interoplation-opening `#{`
    # and, when it's found, yields the scanner to the calling code
    # so it can handle it properly.
    #
    # The scanner will have any backslashes immediately in front of the `#{`
    # as the second capture group (`scan[2]`),
    # and the text prior to that as the first (`scan[1]`).
    #
    # @yieldparam scan [StringScanner] The scanner scanning through the string
    # @return [String] The text remaining in the scanner after all `#{`s have been processed
    def handle_interpolation(str)
      scan = StringScanner.new(str)
      yield scan while scan.scan(/(.*?)(\\*)\#\{/)
      scan.rest
    end

    # Moves a scanner through a balanced pair of characters.
    # For example:
    #
    #     Foo (Bar (Baz bang) bop) (Bang (bop bip))
    #     ^                       ^
    #     from                    to
    #
    # @param scanner [StringScanner] The string scanner to move
    # @param start [Character] The character opening the balanced pair.
    #   A `Fixnum` in 1.8, a `String` in 1.9
    # @param finish [Character] The character closing the balanced pair.
    #   A `Fixnum` in 1.8, a `String` in 1.9
    # @param count [Fixnum] The number of opening characters matched
    #   before calling this method
    # @return [(String, String)] The string matched within the balanced pair
    #   and the rest of the string.
    #   `["Foo (Bar (Baz bang) bop)", " (Bang (bop bip))"]` in the example above.
    def balance(scanner, start, finish, count = 0)
      str = ''
      scanner = StringScanner.new(scanner) unless scanner.is_a? StringScanner
      regexp = Regexp.new("(.*?)[\\#{start.chr}\\#{finish.chr}]", Regexp::MULTILINE)
      while scanner.scan(regexp)
        str << scanner.matched
        count += 1 if scanner.matched[-1] == start
        count -= 1 if scanner.matched[-1] == finish
        return [str.strip, scanner.rest] if count == 0
      end
    end

    # Formats a string for use in error messages about indentation.
    #
    # @param indentation [String] The string used for indentation
    # @param was [Boolean] Whether or not to add `"was"` or `"were"`
    #   (depending on how many characters were in `indentation`)
    # @return [String] The name of the indentation (e.g. `"12 spaces"`, `"1 tab"`)
    def human_indentation(indentation, was = false)
      if !indentation.include?(?\t)
        noun = 'space'
      elsif !indentation.include?(?\s)
        noun = 'tab'
      else
        return indentation.inspect + (was ? ' was' : '')
      end

      singular = indentation.length == 1
      if was
        was = singular ? ' was' : ' were'
      else
        was = ''
      end

      "#{indentation.length} #{noun}#{'s' unless singular}#{was}"
    end
  end
end