# --
# Copyright (C) 2008-2010 10gen Inc.
#
# 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 'digest/md5'

module Mongo

  # GridIO objects represent files in the GridFS specification. This class
  # manages the reading and writing of file chunks and metadata.
  class GridIO
    DEFAULT_CHUNK_SIZE   = 256 * 1024
    DEFAULT_CONTENT_TYPE = 'binary/octet-stream'

    attr_reader :content_type, :chunk_size, :upload_date, :files_id, :filename,
      :metadata, :server_md5, :client_md5

    # Create a new GridIO object. Note that most users will not need to use this class directly;
    # the Grid and GridFileSystem classes will instantiate this class
    #
    # @param [Mongo::Collection] files a collection for storing file metadata.
    # @param [Mongo::Collection] chunks a collection for storing file chunks.
    # @param [String] filename the name of the file to open or write.
    # @param [String] mode 'r' or 'w' or reading or creating a file.
    #
    # @option opts [Hash] :query a query selector used when opening the file in 'r' mode.
    # @option opts [Hash] :query_opts any query options to be used when opening the file in 'r' mode.
    # @option opts [String] :fs_name the file system prefix. Defaults to 'fs'
    def initialize(files, chunks, filename, mode, opts={})
      @files      = files
      @chunks     = chunks
      @filename   = filename
      @mode       = mode
      @query      = opts[:query] || {}
      @query_opts = opts[:query_opts] || {}
      @fs_name    = opts[:fs_name] || Grid::DEFAULT_FS_NAME
      @safe       = opts[:safe] || false
      @local_md5  = Digest::MD5.new if @safe

      case @mode
        when 'r' then init_read
        when 'w' then init_write(opts)
        else
          raise GridError, "Invalid file mode #{@mode}. Mode should be 'r' or 'w'."
      end
    end

    # Read the data from the file. If a length if specified, will read from the
    # current file position.
    #
    # @param [Integer] length
    #
    # @return [String]
    #   the data in the file
    def read(length=nil)
      if length == 0
        return ''
      elsif length.nil? && @file_position.zero?
        read_all
      else
        read_length(length)
      end
    end
    alias_method :data, :read

    # Write the given string (binary) data to the file.
    #
    # @param [String] string
    #   the data to write
    #
    # @return [Integer]
    #   the number of bytes written.
    def write(io)
      raise GridError, "file not opened for write" unless @mode[0] == ?w
      if io.is_a? String
        if @safe
          @local_md5.update(io)
        end
        write_string(io)
      else
        length = 0
        if @safe
          while(string = io.read(@chunk_size))
            @local_md5.update(string)
            length += write_string(string)
          end
        else
          while(string = io.read(@chunk_size))
            length += write_string(string)
          end
        end
        length
      end
    end

    # Position the file pointer at the provided location.
    #
    # @param [Integer] pos
    #   the number of bytes to advance the file pointer. this can be a negative
    #   number.
    # @param [Integer] whence
    #   one of IO::SEEK_CUR, IO::SEEK_END, or IO::SEEK_SET
    #
    # @return [Integer] the new file position
    def seek(pos, whence=IO::SEEK_SET)
      raise GridError, "Seek is only allowed in read mode." unless @mode == 'r'
      target_pos = case whence
                   when IO::SEEK_CUR
                     @file_position + pos
                   when IO::SEEK_END
                     @file_length + pos
                   when IO::SEEK_SET
                     pos
                   end

      new_chunk_number = (target_pos / @chunk_size).to_i
      if new_chunk_number != @current_chunk['n']
        save_chunk(@current_chunk) if @mode[0] == ?w
        @current_chunk = get_chunk(new_chunk_number)
      end
      @file_position  = target_pos
      @chunk_position = @file_position % @chunk_size
      @file_position
    end

    # The current position of the file.
    #
    # @return [Integer]
    def tell
      @file_position
    end

    # Creates or updates the document from the files collection that
    # stores the chunks' metadata. The file becomes available only after
    # this method has been called.
    #
    # This method will be invoked automatically when
    # on GridIO#open is passed a block. Otherwise, it must be called manually.
    #
    # @return [True]
    def close
      if @mode[0] == ?w
        @upload_date = Time.now.utc
        @files.insert(to_mongo_object)
      end
      true
    end

    def inspect
      "#<GridIO _id: #{@files_id}>"
    end

    private

    def create_chunk(n)
      chunk = OrderedHash.new
      chunk['_id']      = Mongo::ObjectID.new
      chunk['n']        = n
      chunk['files_id'] = @files_id
      chunk['data']     = ''
      @chunk_position   = 0
      chunk
    end

    def save_chunk(chunk)
      @chunks.insert(chunk)
    end

    def get_chunk(n)
      chunk = @chunks.find({'files_id' => @files_id, 'n' => n}).next_document
      @chunk_position = 0
      chunk
    end

    def last_chunk_number
      (@file_length / @chunk_size).to_i
    end

    # Read a file in its entirety.
    def read_all
      buf = ''
      while true
        buf << @current_chunk['data'].to_s
        @current_chunk = get_chunk(@current_chunk['n'] + 1)
        break unless @current_chunk
      end
      buf
    end

    # Read a file incrementally.
    def read_length(length)
      cache_chunk_data
      remaining  = (@file_length - @file_position)
      to_read    = length > remaining ? remaining : length
      return nil unless remaining > 0

      buf        =  ''
      while to_read > 0
        if @chunk_position == @chunk_data_length
          @current_chunk = get_chunk(@current_chunk['n'] + 1)
          cache_chunk_data
        end
        chunk_remainder = @chunk_data_length - @chunk_position
        size = (to_read >= chunk_remainder) ? chunk_remainder : to_read
        buf << @current_chunk_data[@chunk_position, size]
        to_read         -= size
        @chunk_position += size
        @file_position  += size
      end
      buf
    end

    def cache_chunk_data
      @current_chunk_data = @current_chunk['data'].to_s
      if @current_chunk_data.respond_to?(:force_encoding)
        @current_chunk_data.force_encoding("binary")
      end
      @chunk_data_length  = @current_chunk['data'].length
    end

    def write_string(string)
      # Since Ruby 1.9.1 doesn't necessarily store one character per byte.
      if string.respond_to?(:force_encoding)
        string.force_encoding("binary")
      end

      to_write = string.length
      while (to_write > 0) do
        if @current_chunk && @chunk_position == @chunk_size
          next_chunk_number = @current_chunk['n'] + 1
          @current_chunk    = create_chunk(next_chunk_number)
        end
        chunk_available = @chunk_size - @chunk_position
        step_size = (to_write > chunk_available) ? chunk_available : to_write
        @current_chunk['data'] = Binary.new((@current_chunk['data'].to_s << string[-to_write, step_size]).unpack("c*"))
        @chunk_position += step_size
        to_write -= step_size
        save_chunk(@current_chunk)
      end
      string.length - to_write
    end

    # Initialize the class for reading a file.
    def init_read
      doc = @files.find(@query, @query_opts).next_document
      raise GridError, "Could not open file matching #{@query.inspect} #{@query_opts.inspect}" unless doc

      @files_id     = doc['_id']
      @content_type = doc['contentType']
      @chunk_size   = doc['chunkSize']
      @upload_date  = doc['uploadDate']
      @aliases      = doc['aliases']
      @file_length  = doc['length']
      @metadata     = doc['metadata']
      @md5          = doc['md5']
      @filename     = doc['filename']

      @current_chunk = get_chunk(0)
      @file_position = 0
    end

    # Initialize the class for writing a file.
    def init_write(opts)
      @files_id      = opts[:_id] || Mongo::ObjectID.new
      @content_type  = opts[:content_type] || @content_type || DEFAULT_CONTENT_TYPE
      @chunk_size    = opts[:chunk_size]   || @chunk_size || DEFAULT_CHUNK_SIZE
      @file_length   = 0
      @metadata      = opts[:metadata] if opts[:metadata]

      @current_chunk = create_chunk(0)
      @file_position = 0
    end

    def to_mongo_object
      h                = OrderedHash.new
      h['_id']         = @files_id
      h['filename']    = @filename
      h['contentType'] = @content_type
      h['length']      = @current_chunk ? @current_chunk['n'] * @chunk_size + @chunk_position : 0
      h['chunkSize']   = @chunk_size
      h['uploadDate']  = @upload_date
      h['aliases']     = @aliases
      h['metadata']    = @metadata
      h['md5']         = get_md5
      h
    end

    # Get a server-side md5 and validate against the client if running in safe mode.
    def get_md5
      md5_command            = OrderedHash.new
      md5_command['filemd5'] = @files_id
      md5_command['root']    = @fs_name
      @server_md5 = @files.db.command(md5_command)['md5']
      if @safe
        @client_md5 = @local_md5.hexdigest
        if @local_md5 != @server_md5
          raise @local_md5 != @server_md5GridError, "File on server failed MD5 check"
        end
      else
        @server_md5
      end
    end
  end
end