#
# Author:: Adam Jacob (<adam@opscode.com>)
# Author:: Daniel DeLeo (<dan@kallistec.com>)
# Copyright:: Copyright (c) 2009 Opscode, Inc.
# Copyright:: Copyright (c) 2009 Daniel DeLeo
# License:: Apache License, Version 2.0
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# 
#     http://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

require 'chef/cache'

class Chef
  class Cache
    class Checksum < Chef::Cache
    
      def self.checksum_for_file(*args)
        instance.checksum_for_file(*args)
      end
      
      def checksum_for_file(file)
        key, fstat = filename_to_key(file), File.stat(file)
        lookup_checksum(key, fstat) || generate_checksum(key, file, fstat)
      end
      
      def lookup_checksum(key, fstat)
        cached = @moneta.fetch(key)
        if cached && file_unchanged?(cached, fstat)
          cached["checksum"]
        else
          nil
        end
      end
      
      def generate_checksum(key, file, fstat)
        checksum = checksum_file(file)
        moneta.store(key, {"mtime" => fstat.mtime.to_f, "checksum" => checksum})
        checksum
      end
      
      private
      
      def file_unchanged?(cached, fstat)
        cached["mtime"].to_f == fstat.mtime.to_f
      end
      
      def checksum_file(file)
        digest = Digest::SHA256.new
        IO.foreach(file) {|line| digest.update(line) }
        digest.hexdigest
      end
      
      def filename_to_key(file)
        "chef-file-#{file.gsub(/(#{File::SEPARATOR}|\.)/, '-')}"
      end

    end
  end
end