require 'open3'

# Responsible for running the `sloccount` system command and handling any resulting errors
# The SLOCCount project is at http://www.dwheeler.com/sloccount/ and can be installed on OSX using homebrew:
#     brew install sloccount
class SLOCCountScanner
  class Exception < StandardError; end
  class ArgumentError < RuntimeError; end
  class Unavailable < RuntimeError; end
  class NoInput < RuntimeError; end
  class NoDirectory < RuntimeError; end

  def initialize(system_sloccount = SystemSLOCCount.instance)
    @system_sloccount = system_sloccount
  end

  def scan(directory)
    fail ArgumentError, "directory must must be a string (or quack like a string)" unless directory.respond_to?(:to_str)
    fail Unavailable, "The 'sloccount' command is unavailable. Is it installed and in your path?" unless @system_sloccount.available?
    fail NoDirectory, "No such directory: '#{directory}'" unless Dir.exist?(directory)

    result, status = @system_sloccount.call(directory)

    if status.success?
      SLOCCount.new(result)
    else
      check_for_errors(result) { NullSLOCCount.new }
    end
  end

private

  def check_for_errors(result)
    case result
    when /SLOC total is zero, no further analysis performed/
      yield

    when /Error: You must provide a directory or directories of source code/
      # Because of the check above, it shouldn't be possible to get here
      raise NoInput, "sloccount requires a directory or directories of source code"
    else
      raise Exception, "sloccount raised an error we didn't recognise. Here's the output:\n#{result}"
    end
  end

  # Responsible for isolating the system calls to run SLOCCount
  class SystemSLOCCount
    require 'singleton'
    include Singleton

    COMMAND_NAME = "sloccount".freeze

    def available?
      _result, status = system_which_sloccount
      status.success?
    end

    def call(directory)
      # DANGER!!! calling system command
      # also: danger! not covered by specs

      # Should be safe from injection because of the `Dir.exist?` check.
      Open3.capture2("#{COMMAND_NAME} #{directory} 2> #{error_log_name}")

    ensure
      delete_empty_error_log
    end

  private

    def system_which_sloccount
      # DANGER!!! calling system command
      # also: danger! not covered by specs

      Open3.capture2("which #{COMMAND_NAME}")
    end

    def error_log_name
      "#{COMMAND_NAME}_error.log"
    end

    def delete_empty_error_log
      File.delete(error_log_name) if File.zero?(error_log_name)
    end
  end
end