Module:Color contrast

--
-- This module implements
--  {{Color contrast ratio}}
--  {{Greater color contrast ratio}}
--  {{ColorToLum}}
--  {{RGBColorToLum}}
--
local p = {}
local HTMLcolor = mw.loadData( 'Module:Color contrast/colors' )

local function sRGB (v)
 if (v <= 0.03928) then
  v = v / 12.92
 else
  v = math.pow((v+0.055)/1.055, 2.4)
 end
 return v
end

local function rgbdec2lum(R, G, B)
 if ( 0 <= R and R < 256 and 0 <= G and G < 256 and 0 <= B and B < 256 ) then
  return 0.2126 * sRGB(R/255) + 0.7152 * sRGB(G/255) + 0.0722 * sRGB(B/255)
 else
  return ''
 end
end

local function hsl2lum(h, s, l)
 if ( 0 <= h and h < 360 and 0 <= s and s <= 1 and 0 <= l and l <= 1 ) then
  local c = (1 - math.abs(2*l - 1))*s
  local x = c*(1 - math.abs( math.fmod(h/60, 2) - 1) )
  local m = l - c/2

  local r, g, b = m, m, m
  if( 0 <= h and h < 60 ) then
   r = r + c
   g = g + x
  elseif( 60 <= h and h < 120 ) then
   r = r + x
   g = g + c
  elseif( 120 <= h and h < 180 ) then
   g = g + c
   b = b + x
  elseif( 180 <= h and h < 240 ) then
   g = g + x
   b = b + c
  elseif( 240 <= h and h < 300 ) then
   r = r + x
   b = b + c
  elseif( 300 <= h and h < 360 ) then
   r = r + c
   b = b + x
  end
  return rgbdec2lum(255*r, 255*g, 255*b)
 else
  return ''
 end
end

local function color2lum(c)

 if (c == nil) then
  return ''
 end

 -- html '#' entity
 c = c:gsub("&#35;", "#")

 -- whitespace
 c = c:match( '^%s*(.-)[%s;]*$' )

 -- unstrip nowiki strip markers
 c = mw.text.unstripNoWiki(c)

 -- lowercase
 c = c:lower()

 -- first try to look it up
 local L = HTMLcolor[c]
 if (L ~= nil) then
  return L
 end

 -- convert from hsl
 if mw.ustring.match(c,'^hsl%([%s]*[0-9][0-9%.]*[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
  local h, s, l = mw.ustring.match(c,'^hsl%([%s]*([0-9][0-9%.]*)[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
  return hsl2lum(tonumber(h), tonumber(s)/100, tonumber(l)/100)
 end

 -- convert from rgb
 if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*%)$') then
  local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*%)$')
  return rgbdec2lum(tonumber(R), tonumber(G), tonumber(B))
 end

 -- convert from rgb percent
 if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
  local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
  return rgbdec2lum(255*tonumber(R)/100, 255*tonumber(G)/100, 255*tonumber(B)/100)
 end

 -- remove leading # (if there is one) and whitespace
 c = mw.ustring.match(c, '^[%s#]*([a-f0-9]*)[%s]*$')

 -- split into rgb
 local cs = mw.text.split(c or '', '')
 if( #cs == 6 ) then
  local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[2])
  local G = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[4])
  local B = 16*tonumber('0x' .. cs[5]) + tonumber('0x' .. cs[6])

  return rgbdec2lum(R, G, B)
 elseif ( #cs == 3 ) then
  local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[1])
  local G = 16*tonumber('0x' .. cs[2]) + tonumber('0x' .. cs[2])
  local B = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[3])

  return rgbdec2lum(R, G, B)
 end

 -- failure, return blank
 return ''
end

-- This exports the function for use in other modules.
-- The colour is passed as a string.
function p._lum(color)
 return color2lum(color)
end

function p._greatercontrast(args)
 local bias = tonumber(args['bias'] or '0') or 0
 local css = (args['css'] and args['css'] ~= '') and true or false
 local v1 = color2lum(args[1] or '')
 local c2 = args[2] or '#FFFFFF'
 local v2 = color2lum(c2)
 local c3 = args[3] or '#000000'
 local v3 = color2lum(c3)
 local ratio1 = -1;
 local ratio2 = -1;
 if (type(v1) == 'number' and type(v2) == 'number') then
  ratio1 = (v2 + 0.05)/(v1 + 0.05)
  ratio1 = (ratio1 < 1) and 1/ratio1 or ratio1
 end
 if (type(v1) == 'number' and type(v3) == 'number') then
  ratio2 = (v3 + 0.05)/(v1 + 0.05)
  ratio2 = (ratio2 < 1) and 1/ratio2 or ratio2
 end

 if css then
  local c1 = args[1] or ''
  if mw.ustring.match(c1, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
   mw.ustring.match(c1, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
    c1 = '#' .. c1
  end
  if mw.ustring.match(c2, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
   mw.ustring.match(c2, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
    c2 = '#' .. c2
  end
  if mw.ustring.match(v3, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') or
   mw.ustring.match(v3, '^[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]$') then
    c3 = '#' .. c3
  end
  return 'background-color:' .. c1 .. '; color:' .. ((ratio1 > 0) and (ratio2 > 0) and ((ratio1 + bias > ratio2) and c2 or c3) or '') .. ';'
 end

 return (ratio1 > 0) and (ratio2 > 0) and ((ratio1 + bias > ratio2) and c2 or c3) or ''
end

function p._ratio(args)
 local v1 = color2lum(args[1])
 local v2 = color2lum(args[2])
 if (type(v1) == 'number' and type(v2) == 'number') then
  -- v1 should be the brighter of the two.
  if v2 > v1 then
   v1, v2 = v2, v1
  end
  return (v1 + 0.05)/(v2 + 0.05)
 else
  return args['error'] or '?'
 end
end

function p._styleratio(args)
 local style = (args[1] or ''):lower()
 local bg, fg = 'white', 'black'
 local lum_bg, lum_fg = 1, 0

 if args[2] then
  local lum = color2lum(args[2])
  if lum ~= '' then bg, lum_bg = args[2], lum end
 end
 if args[3] then
  local lum = color2lum(args[3])
  if lum ~= '' then fg, lum_fg = args[3], lum end
 end

 local slist = mw.text.split(mw.ustring.gsub(mw.ustring.gsub(style or '', '&#[Xx]23;', '#'), '&#35;', '#'), ';')
 for k = 1,#slist do
  local s = slist[k]
  local k,v = s:match( '^[%s]*([^:]-):([^:]-)[%s;]*$' )
  k = k or ''
  v = v or ''
  if (k:match('^[%s]*(background)[%s]*$') or k:match('^[%s]*(background%-color)[%s]*$')) then
   local lum = color2lum(v)
   if( lum ~= '' ) then bg, lum_bg = v, lum end
  elseif (k:match('^[%s]*(color)[%s]*$')) then
   local lum = color2lum(v)
   if( lum ~= '' ) then bg, lum_fg = v, lum end
  end
 end
 if lum_bg > lum_fg then
  return (lum_bg + 0.05)/(lum_fg + 0.05)
 else
  return (lum_fg + 0.05)/(lum_bg + 0.05)
 end
end

--[[
Use {{#invoke:Color contrast|somecolor}} directly or
{{#invoke:Color contrast}} from a wrapper template.

Parameters:
 -- |1= — required; A color to check.
--]]
function p.lum(frame)
 local color = frame.args[1] or frame:getParent().args[1]
 return p._lum(color)
end

function p.ratio(frame)
 local args = frame.args[1] and frame.args or frame:getParent().args
 return p._ratio(args)
end

function p.styleratio(frame)
 local args = frame.args[1] and frame.args or frame:getParent().args
 return p._styleratio(args)
end

function p.greatercontrast(frame)
 local args = frame.args[1] and frame.args or frame:getParent().args
 return p._greatercontrast(args)
end

return p