class LetterAvatar

  # BUMP UP if avatar algorithm changes
  VERSION = 3

  # Largest avatar generated, one day when pixel ratio hit 3
  # we will need to change this
  FULLSIZE = 240

  class<<self

    class Identity
      attr_accessor :color, :letter

      def self.from_username(username)
        identity = new
        identity.color = LetterAvatar::COLORS[
          Digest::MD5.hexdigest(username)[0...15].to_i(16) % LetterAvatar::COLORS.length
        ]
        identity.letter = username[0].upcase
        identity
      end
    end

    def version
      "#{VERSION}_#{image_magick_version}"
    end

    def cache_path
      "tmp/letter_avatars/#{version}"
    end

    def generate(username, size, opts = nil)
      DistributedMutex.synchronize("letter_avatar_#{version}_#{username}_#{size}") do
        identity = Identity.from_username(username)

        cache = true
        cache = false if opts && opts[:cache] == false

        size = FULLSIZE if size > FULLSIZE
        filename = cached_path(identity, size)

        return filename if cache && File.exists?(filename)

        fullsize = fullsize_path(identity)
        generate_fullsize(identity) if !cache || !File.exists?(fullsize)

        OptimizedImage.resize(fullsize, filename, size, size)
        filename
      end
    end

    def cached_path(identity, size)
      dir = "#{cache_path}/#{identity.letter}/#{identity.color.join("_")}"
      FileUtils.mkdir_p(dir)

      "#{dir}/#{size}.png"
    end

    def fullsize_path(identity)
      cached_path(identity, FULLSIZE)
    end

    def generate_fullsize(identity)
      color = identity.color
      letter = identity.letter

      filename = fullsize_path(identity)
      stroke = darken(color, 0.8)

      instructions = %W{
        -size #{FULLSIZE}x#{FULLSIZE}
        xc:#{to_rgb(color)}
        -pointsize 180
        -fill white
        -gravity Center
        -font 'Helvetica'
        -stroke #{to_rgb(stroke)}
        -strokewidth 2
        -annotate -0+20 '#{letter}'
        -depth 8
        '#{filename}'
      }

      `convert #{instructions.join(" ")}`

      ImageOptim.new.optimize_image!(filename) rescue nil

      filename
    end

    def darken(color,pct)
      color.map do |n|
        (n.to_f * pct).to_i
      end
    end

    def to_rgb(color)
      r,g,b = color
      "'rgb(#{r},#{g},#{b})'"
    end

    def image_magick_version
      @image_magick_version ||=
        begin
          Thread.new do
            sleep 2
            cleanup_old
          end
          Digest::MD5.hexdigest(`convert --version` << `convert -list font`)
        end
    end

    def cleanup_old
      skip = File.basename(cache_path)
      parent_path = File.dirname(cache_path)
      Dir.entries(parent_path).each do |path|
        unless ['.','..'].include?(path) || path == skip
          FileUtils.rm_rf(parent_path + "/" + path)
        end
      end
    end
  end

  # palette of optimally disctinct colors
  # cf. http://tools.medialab.sciences-po.fr/iwanthue/index.php
  # parameters used:
  #   - H: 0 - 360
  #   - C: 0 - 2
  #   - L: 0.75 - 1.5
  COLORS = [[198,125,40],
      [61,155,243],
      [74,243,75],
      [238,89,166],
      [52,240,224],
      [177,156,155],
      [240,120,145],
      [111,154,78],
      [237,179,245],
      [237,101,95],
      [89,239,155],
      [43,254,70],
      [163,212,245],
      [65,152,142],
      [165,135,246],
      [181,166,38],
      [187,229,206],
      [77,164,25],
      [179,246,101],
      [234,93,37],
      [225,155,115],
      [142,140,188],
      [223,120,140],
      [249,174,27],
      [244,117,225],
      [137,141,102],
      [75,191,146],
      [188,239,142],
      [164,199,145],
      [173,120,149],
      [59,195,89],
      [222,198,220],
      [68,145,187],
      [236,204,179],
      [159,195,72],
      [188,121,189],
      [166,160,85],
      [181,233,37],
      [236,177,85],
      [121,147,160],
      [234,218,110],
      [241,157,191],
      [62,200,234],
      [133,243,34],
      [88,149,110],
      [59,228,248],
      [183,119,118],
      [251,195,45],
      [113,196,122],
      [197,115,70],
      [80,175,187],
      [103,231,238],
      [240,72,133],
      [228,149,241],
      [180,188,159],
      [172,132,85],
      [180,135,251],
      [236,194,58],
      [217,176,109],
      [88,244,199],
      [186,157,239],
      [113,230,96],
      [206,115,165],
      [244,178,163],
      [230,139,26],
      [241,125,89],
      [83,160,66],
      [107,190,166],
      [197,161,210],
      [198,203,245],
      [238,117,19],
      [228,119,116],
      [131,156,41],
      [145,178,168],
      [139,170,220],
      [233,95,125],
      [87,178,230],
      [157,200,119],
      [237,140,76],
      [229,185,186],
      [144,206,212],
      [236,209,158],
      [185,189,79],
      [34,208,66],
      [84,238,129],
      [133,140,134],
      [67,157,94],
      [168,179,25],
      [140,145,240],
      [151,241,125],
      [67,162,107],
      [200,156,21],
      [169,173,189],
      [226,116,189],
      [133,231,191],
      [194,161,63],
      [241,77,99],
      [241,217,53],
      [123,204,105],
      [210,201,119],
      [229,108,155],
      [240,91,72],
      [187,115,210],
      [240,163,100],
      [178,217,57],
      [179,135,116],
      [204,211,24],
      [186,135,57],
      [223,176,135],
      [204,148,151],
      [116,223,50],
      [95,195,46],
      [123,160,236],
      [181,172,131],
      [142,220,202],
      [240,140,112],
      [172,145,164],
      [228,124,45],
      [135,151,243],
      [42,205,125],
      [192,233,116],
      [119,170,114],
      [158,138,26],
      [73,190,183],
      [185,229,243],
      [227,107,55],
      [196,205,202],
      [132,143,60],
      [233,192,237],
      [62,150,220],
      [205,201,141],
      [106,140,190],
      [161,131,205],
      [135,134,158],
      [198,139,81],
      [115,171,32],
      [101,181,67],
      [149,137,119],
      [37,142,183],
      [183,130,175],
      [168,125,133],
      [124,142,87],
      [236,156,171],
      [232,194,91],
      [219,200,69],
      [144,219,34],
      [219,95,187],
      [145,154,217],
      [165,185,100],
      [127,238,163],
      [224,178,198],
      [119,153,120],
      [124,212,92],
      [172,161,105],
      [231,155,135],
      [157,132,101],
      [122,185,146],
      [53,166,51],
      [70,163,90],
      [150,190,213],
      [210,107,60],
      [166,152,185],
      [159,194,159],
      [39,141,222],
      [202,176,161],
      [95,140,229],
      [168,142,87],
      [93,170,203],
      [159,142,54],
      [14,168,39],
      [94,150,149],
      [187,206,136],
      [157,224,166],
      [235,158,208],
      [109,232,216],
      [141,201,87],
      [208,124,118],
      [142,125,214],
      [19,237,174],
      [72,219,41],
      [234,102,111],
      [168,142,79],
      [188,135,35],
      [95,155,143],
      [148,173,116],
      [223,112,95],
      [228,128,236],
      [206,114,54],
      [195,119,88],
      [235,140,94],
      [235,202,125],
      [233,155,153],
      [214,214,238],
      [246,200,35],
      [151,125,171],
      [132,145,172],
      [131,142,118],
      [199,126,150],
      [61,162,123],
      [58,176,151],
      [215,141,69],
      [225,154,220],
      [220,77,167],
      [233,161,64],
      [130,221,137],
      [81,191,129],
      [169,162,140],
      [174,177,222],
      [236,174,47],
      [233,188,180],
      [69,222,172],
      [71,232,93],
      [118,211,238],
      [157,224,83],
      [218,105,73],
      [126,169,36]]
end