class LetterAvatar
  class<<self

    FULLSIZE = 240

    def cache_path
      'tmp/letter_avatars'
    end

    def generate(username, size)

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

      if File.exists?(filename)
        return filename
      end

      fullsize = fullsize_path(username)
      if !File.exists?(fullsize)
        generate_fullsize(username)
      end

      resize(fullsize, filename, size)
    end

    def cached_path(username, size)
      dir = "#{cache_path}/#{username}"
      FileUtils.mkdir_p(dir)

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

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

    def resize(from, to, size)
      `convert #{from} -resize #{size}x#{size} #{to}`
      to
    end

    def generate_fullsize(username)

      filename = fullsize_path(username)
      color = colors[Digest::MD5.hexdigest(username)[0...15].to_i(16) % 216]
      stroke = darken(color, 0.8)

      instructions = %W{
        -size 240x240
        xc:#{to_rgb(color)}
        -pointsize 240
        -fill white
        -gravity Center
        -font 'Helvetica-Bold'
        -stroke #{to_rgb(stroke)}
        -strokewidth 2
        -annotate -5+25 '#{username[0].upcase}'
        '#{filename}'
      }

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

      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

    # palette of 216 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
    def colors
       [[198,125,40],
        [61,155,243],
        [74,243,75],
        [238,89,166],
        [52,240,224],
        [177,156,155],
        [247,242,53],
        [111,154,78],
        [237,179,245],
        [237,101,95],
        [89,239,155],
        [242,233,158],
        [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],
        [226,235,237],
        [183,119,118],
        [192,247,192],
        [113,196,122],
        [197,115,70],
        [80,175,187],
        [103,231,238],
        [240,72,133],
        [228,149,241],
        [180,188,159],
        [172,132,85],
        [221,236,102],
        [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],
        [219,229,175],
        [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],
        [222,234,142],
        [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],
        [226,226,75],
        [198,139,81],
        [115,171,32],
        [101,181,67],
        [149,137,119],
        [222,245,86],
        [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],
        [234,235,219],
        [166,152,185],
        [159,194,159],
        [222,242,47],
        [202,176,161],
        [95,140,229],
        [156,246,80],
        [93,170,203],
        [159,142,54],
        [185,237,230],
        [94,150,149],
        [187,206,136],
        [157,224,166],
        [235,158,208],
        [109,232,216],
        [141,201,87],
        [208,124,118],
        [142,125,214],
        [226,234,123],
        [72,219,41],
        [234,102,111],
        [168,142,79],
        [188,135,35],
        [214,233,195],
        [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],
        [224,244,174],
        [233,161,64],
        [130,221,137],
        [81,191,129],
        [169,162,140],
        [174,177,222],
        [236,174,47],
        [196,240,159],
        [69,222,172],
        [71,232,93],
        [118,211,238],
        [157,224,83],
        [218,105,73],
        [165,241,221]]
    end
  end
end