local M = {}

-- Convert a hex color value to RGB
-- @param hex: The hex color value
-- @return r: Red (0-255)
-- @return g: Green (0-255)
-- @return b: Blue (0-255)
M.hex2rgb = function(hex)
   local hash = string.sub(hex, 1, 1) == "#"
   if string.len(hex) ~= (7 - (hash and 0 or 1)) then return nil end

   local r = tonumber(hex:sub(2 - (hash and 0 or 1), 3 - (hash and 0 or 1)), 16)
   local g = tonumber(hex:sub(4 - (hash and 0 or 1), 5 - (hash and 0 or 1)), 16)
   local b = tonumber(hex:sub(6 - (hash and 0 or 1), 7 - (hash and 0 or 1)), 16)
   return r, g, b
end

-- Convert an RGB color value to hex
-- @param r: Red (0-255)
-- @param g: Green (0-255)
-- @param b: Blue (0-255)
-- @return The hexadecimal string representation of the color
M.rgb2hex = function(r, g, b)
   return string.format("#%02x%02x%02x", math.floor(r), math.floor(g), math.floor(b))
end

-- Helper function to convert a HSL color value to RGB
-- Not to be used directly, use M.hsl2rgb instead
M.hsl2rgb_helper = function(p, q, a)
   if (a < 0) then a = a + 6 end
   if (a >= 6) then a = a - 6 end
   if (a < 1) then return (q - p) * a + p
   elseif (a < 3) then return q
   elseif (a < 4) then return (q - p) * (4 - a) + p
   else return p end
end

-- Convert a HSL color value to RGB
-- @param h: Hue (0-360)
-- @param s: Saturation (0-1)
-- @param l: Lightness (0-1)
-- @return r: Red (0-255)
-- @return g: Green (0-255)
-- @return b: Blue (0-255)
M.hsl2rgb = function(h, s, l)
   local t1, t2, r, g, b

   h = h / 60
   if (l <= 0.5) then
      t2 = l * (s + 1)
   else
      t2 = l + s - (l * s)
   end

   t1 = l * 2 - t2
   r = M.hsl2rgb_helper(t1, t2, h + 2) * 255
   g = M.hsl2rgb_helper(t1, t2, h) * 255
   b = M.hsl2rgb_helper(t1, t2, h - 2) * 255

   return r, g, b
end

-- Convert an RGB color value to HSL
-- @param r Red (0-255)
-- @param g Green (0-255)
-- @param b Blue (0-255)
-- @return h Hue (0-360)
-- @return s Saturation (0-1)
-- @return l Lightness (0-1)
M.rgb2hsl = function(r, g, b)
   local min, max, l, s, maxcolor, h
   r, g, b = r / 255, g / 255, b / 255

   min = math.min(r, g, b)
   max = math.max(r, g, b)
   maxcolor = 1 + (max == b and 2 or (max == g and 1 or 0))

   if maxcolor == 1 then h = (g - b) / (max - min)
   elseif maxcolor == 2 then h = 2 + (b - r) / (max - min)
   elseif maxcolor == 3 then h = 4 + (r - g) / (max - min) end

   if not rawequal(type(h), 'number') then h = 0 end

   h = h * 60

   if h < 0 then h = h + 360 end

   l = (min + max) / 2

   if min == max then
      s = 0
   else
      if l < 0.5 then s = (max - min) / (max + min)
      else s = (max - min) / (2 - max - min) end
   end

   return h, s, l
end

-- Convert a hex color value to HSL
-- @param hex: The hex color value
-- @param h: Hue (0-360)
-- @param s: Saturation (0-1)
-- @param l: Lightness (0-1)
M.hex2hsl = function(hex)
   local r, g, b = M.hex2rgb(hex)
   return M.rgb2hsl(r, g, b)
end

-- Convert a HSL color value to hex
-- @param h: Hue (0-360)
-- @param s: Saturation (0-1)
-- @param l: Lightness (0-1)
-- @returns hex color value
M.hsl2hex = function(h, s, l)
   local r, g, b = M.hsl2rgb(h, s, l)
   return M.rgb2hex(r, g, b)
end

-- Change the hue of a color by a given amount
-- @param hex The hex color value
-- @param amount The amount to change the hue.
--               Negative values decrease the hue, positive values increase it.
-- @return The hex color value
M.change_hex_hue = function(hex, percent)
   local h, s, l = M.hex2hsl(hex)
   h = h + (percent / 100)
   if h > 360 then h = 360 end
   if h < 0 then h = 0 end
   return M.hsl2hex(h, s, l)
end

-- Desaturate or saturate a color by a given percentage
-- @param hex The hex color value
-- @param percent The percentage to desaturate or saturate the color.
--                Negative values desaturate the color, positive values saturate it
-- @return The hex color value
M.change_hex_saturation = function(hex, percent)
   local h, s, l = M.hex2hsl(hex)
   s = s + (percent / 100)
   if s > 1 then s = 1 end
   if s < 0 then s = 0 end
   return M.hsl2hex(h, s, l)
end

-- Lighten or darken a color by a given percentage
-- @param hex The hex color value
-- @param percent The percentage to lighten or darken the color.
--                Negative values darken the color, positive values lighten it
-- @return The hex color value
M.change_hex_lightness = function(hex, percent)
   local h, s, l = M.hex2hsl(hex)
   l = l + (percent / 100)
   if l > 1 then l = 1 end
   if l < 0 then l = 0 end
   return M.hsl2hex(h, s, l)
end

-- Compute a gradient between two colors
-- @param hex1 The first hex color value
-- @param hex2 The second hex color value
-- @param steps The number of steps to compute
-- @return A table of hex color values
M.compute_gradient = function(hex1, hex2, steps)
   local h1, s1, l1 = M.hex2hsl(hex1)
   local h2, s2, l2 = M.hex2hsl(hex2)
   local h, s, l
   local h_step = (h2 - h1) / (steps - 1)
   local s_step = (s2 - s1) / (steps - 1)
   local l_step = (l2 - l1) / (steps - 1)
   local gradient = {}

   for i = 0, steps - 1 do
      h = h1 + (h_step * i)
      s = s1 + (s_step * i)
      l = l1 + (l_step * i)
      gradient[i + 1] = M.hsl2hex(h, s, l)
   end

   return gradient
end

return M