require 'mongo/types/objectid'
require 'mongo/util/ordered_hash'
require 'mongo/gridfs/chunk'

module XGen
  module Mongo
    module GridFS

      # GridStore is an IO-like object that provides input and output for
      # streams of data to Mongo. See Mongo's documentation about GridFS for
      # storage implementation details.
      #
      # Example code:
      #
      #   require 'mongo/gridfs'
      #   GridStore.open(database, 'filename', 'w') { |f|
      #     f.puts "Hello, world!"
      #   }
      #   GridStore.open(database, 'filename, 'r') { |f|
      #     puts f.read         # => Hello, world!\n
      #   }
      #   GridStore.open(database, 'filename', 'w+') { |f|
      #     f.puts "But wait, there's more!"
      #   }
      #   GridStore.open(database, 'filename, 'r') { |f|
      #     puts f.read         # => Hello, world!\nBut wait, there's more!\n
      #   }
      class GridStore

        DEFAULT_ROOT_COLLECTION = 'gridfs'
        DEFAULT_CONTENT_TYPE = 'text/plain'

        include Enumerable

        attr_accessor :filename

        # Array of strings; may be +nil+
        attr_accessor :aliases

        # Default is DEFAULT_CONTENT_TYPE
        attr_accessor :content_type

        attr_accessor :metadata

        attr_reader :files_id

        # Time that the file was first saved.
        attr_reader :upload_date

        attr_reader :chunk_size

        attr_accessor :lineno

        class << self

          def exist?(db, name, root_collection=DEFAULT_ROOT_COLLECTION)
            db.collection("#{root_collection}.files").find({'filename' => name}).next_object != nil
          end

          def open(db, name, mode, options={})
            gs = self.new(db, name, mode, options)
            result = nil
            begin
              result = yield gs if block_given?
            ensure
              gs.close
            end
            result
          end

          def read(db, name, length=nil, offset=nil)
            GridStore.open(db, name, 'r') { |gs|
              gs.seek(offset) if offset
              gs.read(length)
            }
          end

          def readlines(db, name, separator=$/)
            GridStore.open(db, name, 'r') { |gs|
              gs.readlines(separator)
            }
          end

          def unlink(db, *names)
            names.each { |name|
              gs = GridStore.new(db, name)
              gs.send(:delete_chunks)
              gs.collection.remove('_id' => gs.files_id)
            }
          end
          alias_method :delete, :unlink

        end

        #---
        # ================================================================
        #+++

        # Mode may only be 'r', 'w', or 'w+'.
        #
        # Options. Descriptions start with a list of the modes for which that
        # option is legitimate.
        #
        # :root :: (r, w, w+) Name of root collection to use, instead of
        #          DEFAULT_ROOT_COLLECTION.
        #
        # :metadata:: (w, w+) A hash containing any data you want persisted as
        #                     this file's metadata. See also metadata=
        #
        # :chunk_size :: (w) Sets chunk size for files opened for writing
        #                See also chunk_size= which may only be called before
        #                any data is written.
        #
        # :content_type :: (w) Default value is DEFAULT_CONTENT_TYPE. See
        #                  also #content_type=
        def initialize(db, name, mode='r', options={})
          @db, @filename, @mode = db, name, mode
          @root = options[:root] || DEFAULT_ROOT_COLLECTION

          doc = collection.find({'filename' => @filename}).next_object
          if doc
            @files_id = doc['_id']
            @content_type = doc['contentType']
            @chunk_size = doc['chunkSize']
            @upload_date = doc['uploadDate']
            @aliases = doc['aliases']
            @length = doc['length']
            @metadata = doc['metadata']
          else
            @files_id = XGen::Mongo::Driver::ObjectID.new
            @content_type = DEFAULT_CONTENT_TYPE
            @chunk_size = Chunk::DEFAULT_CHUNK_SIZE
            @length = 0
          end

          case mode
          when 'r'
            @curr_chunk = nth_chunk(0)
            @position = 0
          when 'w'
            chunk_collection.create_index("chunk_index", ['files_id', 'n'])
            delete_chunks
            @curr_chunk = Chunk.new(self, 'n' => 0)
            @content_type = options[:content_type] if options[:content_type]
            @chunk_size = options[:chunk_size] if options[:chunk_size]
            @metadata = options[:metadata] if options[:metadata]
            @position = 0
          when 'w+'
            chunk_collection.create_index("chunk_index", ['files_id', 'n'])
            @curr_chunk = nth_chunk(last_chunk_number) || Chunk.new(self, 'n' => 0) # might be empty
            @curr_chunk.pos = @curr_chunk.data.length if @curr_chunk
            @metadata = options[:metadata] if options[:metadata]
            @position = @length
          else
            raise "error: illegal mode #{mode}"
          end

          @lineno = 0
          @pushback_byte = nil
        end

        def collection
          @db.collection("#{@root}.files")
        end

        # Returns collection used for storing chunks. Depends on value of
        # @root.
        def chunk_collection
          @db.collection("#{@root}.chunks")
        end

        # Change chunk size. Can only change if the file is opened for write
        # and no data has yet been written.
        def chunk_size=(size)
          unless @mode[0] == ?w && @position == 0 && @upload_date == nil
            raise "error: can only change chunk size if open for write and no data written."
          end
          @chunk_size = size
        end

        #---
        # ================ reading ================
        #+++

        def getc
          if @pushback_byte
            byte = @pushback_byte
            @pushback_byte = nil
            @position += 1
            byte
          elsif eof?
            nil
          else
            if @curr_chunk.eof?
              @curr_chunk = nth_chunk(@curr_chunk.chunk_number + 1)
            end
            @position += 1
            @curr_chunk.getc
          end
        end

        def gets(separator=$/)
          str = ''
          byte = self.getc
          return nil if byte == nil # EOF
          while byte != nil
            s = byte.chr
            str << s
            break if s == separator
            byte = self.getc
          end
          @lineno += 1
          str
        end

        def read(len=nil, buf=nil)
          buf ||= ''
          byte = self.getc
          while byte != nil && (len == nil || len > 0)
            buf << byte.chr
            len -= 1 if len
            byte = self.getc if (len == nil || len > 0)
          end
          buf
        end

        def readchar
          byte = self.getc
          raise EOFError.new if byte == nil
          byte
        end

        def readline(separator=$/)
          line = gets
          raise EOFError.new if line == nil
          line
        end

        def readlines(separator=$/)
          read.split(separator).collect { |line| "#{line}#{separator}" }
        end

        def each
          line = gets
          while line
            yield line
            line = gets
          end
        end
        alias_method :each_line, :each

        def each_byte
          byte = self.getc
          while byte
            yield byte
            byte = self.getc
          end
        end

        def ungetc(byte)
          @pushback_byte = byte
          @position -= 1
        end

        #---
        # ================ writing ================
        #+++

        def putc(byte)
          if @curr_chunk.pos == @chunk_size
            prev_chunk_number = @curr_chunk.chunk_number
            @curr_chunk.save
            @curr_chunk = Chunk.new(self, 'n' => prev_chunk_number + 1)
          end
          @position += 1
          @curr_chunk.putc(byte)
        end

        def print(*objs)
          objs = [$_] if objs == nil || objs.empty?
          objs.each { |obj|
            str = obj.to_s
            str.each_byte { |byte| self.putc(byte) }
          }
          nil
        end

        def puts(*objs)
          if objs == nil || objs.empty?
            self.putc(10)
          else
            print(*objs.collect{ |obj|
                    str = obj.to_s
                    str << "\n" unless str =~ /\n$/
                    str
                  })
          end
          nil
        end

        def <<(obj)
          write(obj.to_s)
        end

        # Writes +string+ as bytes and returns the number of bytes written.
        def write(string)
          raise "#@filename not opened for write" unless @mode[0] == ?w
          count = 0
          string.each_byte { |byte|
            self.putc byte
            count += 1
          }
          count
        end

        # A no-op.
        def flush
        end

        #---
        # ================ status ================
        #+++

        def eof
          raise IOError.new("stream not open for reading") unless @mode[0] == ?r
          @position >= @length
        end
        alias_method :eof?, :eof

        #---
        # ================ positioning ================
        #+++

        def rewind
          if @curr_chunk.chunk_number != 0
            if @mode[0] == ?w
              delete_chunks
              @curr_chunk = Chunk.new(self, 'n' => 0)
            else
              @curr_chunk == nth_chunk(0)
            end
          end
          @curr_chunk.pos = 0
          @lineno = 0
          @position = 0
        end

        def seek(pos, whence=IO::SEEK_SET)
          target_pos = case whence
                       when IO::SEEK_CUR
                         @position + pos
                       when IO::SEEK_END
                         @length + pos
                       when IO::SEEK_SET
                         pos
                       end
                         
          new_chunk_number = (target_pos / @chunk_size).to_i
          if new_chunk_number != @curr_chunk.chunk_number
            @curr_chunk.save if @mode[0] == ?w
            @curr_chunk = nth_chunk(new_chunk_number)
          end
          @position = target_pos
          @curr_chunk.pos = @position % @chunk_size
          0
        end

        def tell
          @position
         end

        #---
        # ================ closing ================
        #+++

        def close
          if @mode[0] == ?w
            if @curr_chunk
              @curr_chunk.truncate
              @curr_chunk.save if @curr_chunk.pos > 0
            end
            files = collection
            if @upload_date
              files.remove('_id' => @files_id)
            else
              @upload_date = Time.now
            end
            files.insert(to_mongo_object)
          end
          @db = nil
        end
          
        def closed?
          @db == nil
        end

        #---
        # ================ protected ================
        #+++

        protected

        def to_mongo_object
          h = OrderedHash.new
          h['_id'] = @files_id
          h['filename'] = @filename
          h['contentType'] = @content_type
          h['length'] = @curr_chunk ? @curr_chunk.chunk_number * @chunk_size + @curr_chunk.pos : 0
          h['chunkSize'] = @chunk_size
          h['uploadDate'] = @upload_date
          h['aliases'] = @aliases
          h['metadata'] = @metadata
          h
        end

        def delete_chunks
          chunk_collection.remove({'files_id' => @files_id}) if @files_id
          @curr_chunk = nil
        end

        def nth_chunk(n)
          mongo_chunk = chunk_collection.find({'files_id' => @files_id, 'n' => n}).next_object
          Chunk.new(self, mongo_chunk || {})
        end

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

      end
    end
  end
end