require 'fileutils'
require 'systemu'

# File Utilities for use in transferring filesystem objects,
# decrypting a file, unpacking a targz archive, and validating checksums
# @author rnanders@stanford.edu
module LyberCore
  module Utils
    class FileUtilities


      # Executes a system command in a subprocess. 
      # The method will return stdout from the command if execution was successful.
      # The method will raise an exception if if execution fails. 
      # The exception's message will contain the explaination of the failure.
      # @param [String] command the command to be executed
      # @return [String] stdout from the command if execution was successful
      def FileUtilities.execute(command)
        status, stdout, stderr = systemu(command)
        if (status.exitstatus != 0)
          raise stderr
        end
        return stdout
      rescue
        msg = "Command failed to execute: [#{command}] caused by <STDERR = #{stderr.split($/).join('; ')}>"
        msg << " STDOUT = #{stdout.split($/).join('; ')}" if (stdout && (stdout.length > 0))
        raise msg

      end

      # Generates a dirname for storing or retrieving a file in
      # "pair tree" hierachical structure, where the path is derived
      # from segments of a barcode string
      #
      # = Input:
      # * barcode = barcode string
      #
      # = Return value:
      # * A string containing a slash-delimited dirname derived from the barcode
      def FileUtilities.pair_tree_from_barcode(barcode)
        if (barcode.class != String)
          raise "Barcode must be a String"
        end
        # figure out if this is a SUL barcode or from coordinate library
        library_prefix=barcode[0..4]
        if ( library_prefix == '36105' )
          pair_tree=barcode[5..10].gsub(/(..)/, '\1/')
        else
          library_prefix=barcode[0..2]
          pair_tree=barcode[3..8].gsub(/(..)/, '\1/')
        end
        return "#{library_prefix}/#{pair_tree}"
      end

      # Transfers a filesystem object (file or directory)
      # from a source to a target location. Uses rsync in "archive" mode
      # over an ssh connection.
      #
      # = Inputs:
      # * filename = basename of the filesystem object to be transferred
      # * source_dir = dirname of the source location from which the object is read
      # * dest_dir = dirname of the target location to which the object is written
      # If one of the locations is on a remote server, then the dirname should be
      # prefixed with  user@hosthame:
      #
      # = Return value:
      # * The method will return true if the transfer is successful.
      # * The method will raise an exception if either the rsync command fails,
      # or a test for the existence of the transferred object fails.
      # The exception's message will contain the explaination of the failure
      #
      # Network transfers will only succeed if the appropriate public key
      # authentication has been previously set up.
      def FileUtilities.transfer_object(filename, source_dir, dest_dir)
        source_path=File.join(source_dir, filename)
        rsync='rsync -a -e ssh '
        rsync_cmd = rsync + "'" + source_path + "' " +  dest_dir
        LyberCore::Log.debug("rsync command is: #{rsync_cmd}")
        self.execute(rsync_cmd)
        if not File.exists?(File.join(dest_dir, filename))
          raise "#{filename} is not found in  #{dest_dir}"
        end
        return true
      end

      # Decrypts a GPG encrypted file using the "gpg" command
      #
      # = Inputs:
      # * workspace_dir = dirname containing the file
      # * targzgpg = the filename of the GPG encrypted file
      # * targz = the filename of the unencrypted file
      # * passphrase = the string used to decrypt the file
      #
      # = Return value:
      # * The method will return true if the decryption is successful.
      # * The method will raise an exception if either the decryption command fails,
      # or a test for the existence of the decrypted file fails.
      # The exception's message will contain the explaination of the failure
      def FileUtilities.gpgdecrypt(workspace_dir, targzgpg, targz, passphrase)
        LyberCore::Log.debug("decrypting #{targzgpg}")
        gpg_cmd="/usr/bin/gpg --passphrase '#{passphrase}'  "  +
                 "--batch --no-mdc-warning --no-secmem-warning " +
                 " --output " + File.join(workspace_dir, targz)  +
                " --decrypt " + File.join(workspace_dir, targzgpg)
        self.execute(gpg_cmd)
        if not File.exists?(File.join(workspace_dir, targz))
          raise "#{targz} was not created in  #{workspace_dir}"
        end
        return true
      end

      # Unpacks a TAR-ed, GZipped archive using a "tar -xzf" command
      #
      # = Inputs:
      # * original_dir = dirname containing the archive file
      # * targz = the filename of the archive file
      # * destination_dir = the target directory into which the contents are written
      #
      # = Return value:
      # * The method will return true if the unpacking is successful.
      # * The method will raise an exception if either the unpack command fails,
      # or a test for the existence of files in the target directory fails.
      # The exception's message will contain the explaination of the failure.
      def FileUtilities.unpack(original_dir, targz, destination_dir)
        LyberCore::Log.debug("unpacking #{targz}")
        FileUtils.mkdir_p(destination_dir)
        dir_save = Dir.pwd
        Dir.chdir(destination_dir)
        unpack_cmd="tar -xzf " + File.join(original_dir, targz)
        self.execute(unpack_cmd)
        if not (Dir.entries(destination_dir).length > 0)
          raise "#{destination_dir} is empty"
        end
        return true
      ensure
        Dir.chdir(dir_save)
      end

      # Verifies MD5 checksums for the files in a directory
      # against the checksum values in the supplied file
      # (Uses md5sum command)
      #
      # = Inputs:
      # * directory = dirname containing the file to be checked
      # * checksum_file = the name of the file containing the expected checksums
      #
      # = Return value:
      # * The method will return true if the verification is successful.
      # * The method will raise an exception if either the md5sum command fails,
      # or a test of the md5sum output indicates a checksum mismatch.
      # The exception's message will contain the explaination of the failure.
      def FileUtilities.verify_checksums(directory, checksum_file)
        LyberCore::Log.debug("verifying checksums in #{directory}")
        dir_save = Dir.pwd
        Dir.chdir(directory)
        checksum_cmd = 'md5sum -c ' + checksum_file + ' | grep -v OK | wc -l'
        badcount = self.execute(checksum_cmd).to_i
        if not (badcount==0)
          raise "#{badcount} files had bad checksums"
        end
        return true
      ensure
        Dir.chdir(dir_save)
      end
    end

  end
end