require 'forwardable'
require 'tempfile'

require_relative 'roles/human_readable'

class PgExport
  class Dump
    TIMESTAMP = '_%Y%m%d_%H%M%S'.freeze

    extend Forwardable
    include Roles::HumanReadable

    CHUNK_SIZE = (2**16).freeze

    def_delegators :file, :path, :read, :write, :<<, :rewind, :close, :size, :eof?

    attr_reader :name, :db_name

    def initialize(name:, db_name:)
      @name, @db_name = name, db_name
      @timestamp = Time.now.strftime(TIMESTAMP)
    end

    def ext
      ''
    end

    def open(operation_type, &block)
      case operation_type.to_sym
      when :read then File.open(path, 'r', &block)
      when :write then File.open(path, 'w', &block)
      else raise ArgumentError, 'Operation type can be only :read or :write'
      end
    end

    def each_chunk
      open(:read) do |file|
        yield file.read(CHUNK_SIZE) until file.eof?
      end
    end

    def timestamped_name
      db_name + timestamp + ext
    end

    def to_s
      "#{name} (#{size_human})"
    end

    private

    attr_reader :timestamp

    def file
      @file ||= Tempfile.new(file_name)
    end

    def file_name
      name.downcase.gsub(/[^0-9a-z]/, '_')
    end
  end
end