Live stats

# Copyright (c) 2009, Yoan Blanc <yoan@dosimple.ch>
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright
#       notice, this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#     * Neither the name of the <organization> nor the
#       names of its contributors may be used to endorse or promote products
#       derived from this software without specific prior written permission.
# 
# THIS SOFTWARE IS PROVIDED BY <copyright holder> ''AS IS'' AND ANY
# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL <copyright holder> BE LIABLE FOR ANY
# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


require 'memcache'

class LiveStats
  
  def initialize(app, cache, options={})
    @app = app
    @cache = cache
    @period = options[:period] || 3600
    @precision = options[:precision] || 10
  end

  def inc(key, value=1, timeout=nil)
    if @cache.incr(key, value).nil?
      @cache.add(key, value, timeout || @period)
    end
  end

  def call(env) 
    env["rack.livestats.track"] = true
    now = Time::now
    
    response = @app.call(env)
    
    if env["rack.livestats.track"]
      ts = ((Time::now - now) * 1000).to_i # in ms
      key = Time::now.to_i / @precision
      
      # time spent
      inc("t"+key.to_s, ts)
      # visits
      inc("v"+key.to_s)
    end

    response
  end
end


class MyApplication

  def initialize(cache, args={})
    @cache = cache
    @period = args[:period] || 3600
    @precision = args[:precision] || 10
  end

  def prepare_data(keys, prefix)
    keys = keys.map do |key|
      prefix + key
    end

    values = @cache.get(*keys).reverse!.map do |value|
      value || 0
    end

    max = values.max
    div = [max, 1].max.to_f / @precision
    values.map! do |value|
      (value / @precision.to_f / div * 100).to_i
    end

    return values, max
  end

  def stats(env)
    now = Time::now.to_i / @precision

    keys = (0..(@period / @precision)).map do |i|
      (now - i).to_s
    end
    
    views, vmax = prepare_data(keys, "v")
    times, tmax = prepare_data(keys, "t")

    
    [200,
     {'Content-Type' => 'text/html; charset=utf-8'},
     ['<!DOCTYPE html>',
      '<html>',
        '<meta charset=utf-8>',
        '<title>live stats</title>',
        '<h1>Live stats</h1>',
        '<h2>Visits in the last hour</h2>',
        '<img src="http://chart.apis.google.com/chart?cht=ls&chs=1000x200&chd=t:%s|%s&chxt=x,y,r&chxr=0,-%d,0|1,0,%d|2,0,%d&chdl=Views+[req/s]|Time+[ms]&chco=ff0000,00ff00">' %
          [views.join(','),
           times.join(','),
           @period / 60, # in minutes
           vmax,
           tmax
          ],
      '</html>'
     ]
    ]
  end

  def default(env)
    [200,
     {"Content-Type", "text/plain; charset=utf-8"},
     ["You've been counted.\n"]
    ]
  end

  def call(env)
    if env["PATH_INFO"] == "/stats"
      # do not track the views on this page
      env["rack.livestats.track"] = false
      stats(env)
    else
      default(env)
    end
  end
end

cache = MemCache.new("127.0.0.1:11211")
args = {:period => 3600, :precision => 10}

use Rack::CommonLogger
use LiveStats, cache, args

run MyApplication.new(cache, args)