-----------------------------------------------------------------------------
-- Provides support for color manipulation in HSL color space.
--
-- http://sputnik.freewisdom.org/lib/colors/
--
-- License: MIT/X
-- 
-- (c) 2008 Yuri Takhteyev (yuri@freewisdom.org) *
--
-- * rgb_to_hsl() implementation was contributed by Markus Fleck-Graffe.
-----------------------------------------------------------------------------

module(..., package.seeall)

local Color = {}
local Color_mt = {__metatable = {}, __index = Color}

-----------------------------------------------------------------------------
-- Instantiates a new "color".
--
-- @param H              hue (0-360) _or_ an RGB string ("#930219")
-- @param S              saturation (0.0-1.0)
-- @param L              lightness (0.0-1.0)
-- @return               an instance of Color
-----------------------------------------------------------------------------
function new(H, S, L)
   if type(H) == "string" and H:sub(1,1)=="#" and H:len() == 7 then
      H, S, L = rgb_string_to_hsl(H)
   end
   assert(Color_mt)
   return setmetatable({H = H, S = S, L = L}, Color_mt)
end

-----------------------------------------------------------------------------
-- Converts an HSL triplet to RGB
-- (see http://homepages.cwi.nl/~steven/css/hsl.html).
-- 
-- @param h              hue (0-360)
-- @param s              saturation (0.0-1.0)
-- @param L              lightness (0.0-1.0)
-- @return               an R, G, and B component of RGB
-----------------------------------------------------------------------------

function hsl_to_rgb(h, s, L)
   h = h/360
   local m1, m2
   if L<=0.5 then 
      m2 = L*(s+1)
   else 
      m2 = L+s-L*s
   end
   m1 = L*2-m2

   local function _h2rgb(m1, m2, h)
      if h<0 then h = h+1 end
      if h>1 then h = h-1 end
      if h*6<1 then 
         return m1+(m2-m1)*h*6
      elseif h*2<1 then 
         return m2 
      elseif h*3<2 then 
         return m1+(m2-m1)*(2/3-h)*6
      else
         return m1
      end
   end

   return _h2rgb(m1, m2, h+1/3), _h2rgb(m1, m2, h), _h2rgb(m1, m2, h-1/3)
end

-----------------------------------------------------------------------------
-- Converts an RGB triplet to HSL.
-- (see http://easyrgb.com)
-- 
-- @param r              red (0.0-1.0)
-- @param g              green (0.0-1.0)
-- @param b              blue (0.0-1.0)
-- @return               corresponding H, S and L components
-----------------------------------------------------------------------------

function rgb_to_hsl(r, g, b)
   --r, g, b = r/255, g/255, b/255
   local min = math.min(r, g, b)
   local max = math.max(r, g, b)
   local delta = max - min

   local h, s, l = 0, 0, ((min+max)/2)

   if l > 0 and l < 0.5 then s = delta/(max+min) end
   if l >= 0.5 and l < 1 then s = delta/(2-max-min) end

   if delta > 0 then
      if max == r and max ~= g then h = h + (g-b)/delta end
      if max == g and max ~= b then h = h + 2 + (b-r)/delta end
      if max == b and max ~= r then h = h + 4 + (r-g)/delta end
      h = h / 6;
   end

   if h < 0 then h = h + 1 end
   if h > 1 then h = h - 1 end

   return h * 360, s, l
end

function rgb_string_to_hsl(rgb)
   return rgb_to_hsl(tonumber(rgb:sub(2,3), 16)/256, 
                     tonumber(rgb:sub(4,5), 16)/256,
                     tonumber(rgb:sub(6,7), 16)/256)
end

-----------------------------------------------------------------------------
-- Converts the color to an RGB string.
--
-- @return               a 6-digit RGB representation of the color prefixed
--                       with "#" (suitable for inclusion in HTML)
-----------------------------------------------------------------------------

function Color:to_rgb()
   local r, g, b = hsl_to_rgb(self.H, self.S, self.L)
   local rgb = {hsl_to_rgb(self.H, self.S, self.L)}
   local buffer = "#"
   for i,v in ipairs(rgb) do
	  buffer = buffer..string.format("%02x",math.floor(v*256+0.5))
   end
   return buffer
end

-----------------------------------------------------------------------------
-- Creates a new color with hue different by delta.
--
-- @param delta          a delta for hue.
-- @return               a new instance of Color.
-----------------------------------------------------------------------------
function Color:hue_offset(delta)
   return new((self.H + delta) % 360, self.S, self.L)
end

-----------------------------------------------------------------------------
-- Creates a complementary color.
--
-- @return               a new instance of Color
-----------------------------------------------------------------------------
function Color:complementary() 
   return self:hue_offset(180)
end

-----------------------------------------------------------------------------
-- Creates two neighboring colors (by hue), offset by "angle".
--
-- @param angle          the difference in hue between this color and the 
--                       neighbors
-- @return               two new instances of Color
-----------------------------------------------------------------------------
function Color:neighbors(angle)
   local angle = angle or 30
   return self:hue_offset(angle), self:hue_offset(360-angle)
end

-----------------------------------------------------------------------------
-- Creates two new colors to make a triadic color scheme.
--
-- @return               two new instances of Color
-----------------------------------------------------------------------------
function Color:triadic() 
   return self:neighbors(120)
end

-----------------------------------------------------------------------------
-- Creates two new colors, offset by angle from this colors complementary.
--
-- @param angle          the difference in hue between the complementary and
--                       the returned colors
-- @return               two new instances of Color
-----------------------------------------------------------------------------
function Color:split_complementary(angle)
   return self:neighbors(180-(angle or 30))
end

-----------------------------------------------------------------------------
-- Creates a new color with saturation set to a new value.
--
-- @param saturation     the new saturation value (0.0 - 1.0)
-- @return               a new instance of Color
-----------------------------------------------------------------------------
function Color:desaturate_to(saturation)
   return new(self.H, saturation, self.L)
end

-----------------------------------------------------------------------------
-- Creates a new color with saturation set to a old saturation times r.
--
-- @param r              the multiplier for the new saturation
-- @return               a new instance of Color
-----------------------------------------------------------------------------
function Color:desaturate_by(r)
   return new(self.H, self.S*r, self.L)
end	      

-----------------------------------------------------------------------------
-- Creates a new color with lightness set to a new value.
--
-- @param lightness      the new lightness value (0.0 - 1.0)
-- @return               a new instance of Color
-----------------------------------------------------------------------------
function Color:lighten_to(lightness)
   return new(self.H, self.S, lightness)
end

-----------------------------------------------------------------------------
-- Creates a new color with lightness set to a old lightness times r.
--
-- @param r              the multiplier for the new lightness
-- @return               a new instance of Color
-----------------------------------------------------------------------------
function Color:lighten_by(r)
   return new(self.H, self.S, self.L*r)
end

-----------------------------------------------------------------------------
-- Creates n variations of this color using supplied function and returns
-- them as a table.
--
-- @param f              the function to create variations
-- @param n              the number of variations
-- @return               a table with n values containing the new colors
-----------------------------------------------------------------------------
function Color:variations(f, n)
   n = n or 5
   local results = {}
   for i=1,n do
	  table.insert(results, f(self, i, n))
   end
   return results
end

-----------------------------------------------------------------------------
-- Creates n tints of this color and returns them as a table
--
-- @param n              the number of tints
-- @return               a table with n values containing the new colors
-----------------------------------------------------------------------------
function Color:tints(n)
   local f = function (color, i, n) 
                return color:lighten_to(color.L + (1-color.L)/n*i)
             end
   return self:variations(f, n)
end

-----------------------------------------------------------------------------
-- Creates n shades of this color and returns them as a table
--
-- @param n              the number of shades
-- @return               a table with n values containing the new colors
-----------------------------------------------------------------------------
function Color:shades(n)
   local f = function (color, i, n) 
                return color:lighten_to(color.L - (color.L)/n*i)
             end
   return self:variations(f, n)
end

function Color:tint(r)
      return self:lighten_to(self.L + (1-self.L)*r)
end

function Color:shade(r)
      return self:lighten_to(self.L - self.L*r)
end

Color_mt.__tostring = Color.to_rgb