utils.lua

-- much help from https://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/
-- basically a lua implementation of the above link

-- Helper "round" method
local function round(x, p)
	local power = 10 ^ (p or 0)
	return (x * power + 0.5 - (x * power + 0.5) % 1) / power
end

-- Useful public methods
local function hex_to_rgba(hex)
	hex = hex:gsub("#", "")
	return
		tonumber("0x"..hex:sub(1,2)),
		tonumber("0x"..hex:sub(3,4)),
		tonumber("0x"..hex:sub(5,6)),
		--if alpha exists in hex, return it
		#hex == 8 and tonumber("0x"..hex:sub(7,8)) / 255 or nil
end

local function rgba_to_hex(obj)
	local r = obj.r or obj[1]
	local g = obj.g or obj[2]
	local b = obj.b or obj[3]
	local a = obj.a or 1
	local h = (obj.hashtag or obj[4]) and "#" or ""
	return h..string.format("%02x%02x%02x",
		math.floor(r),
		math.floor(g),
		math.floor(b))
		--this part only shows the alpha channel if it's not 1
		..(a ~= 1 and string.format("%02x", math.floor(a*255)) or "")
end

--disclaimer I have no idea what any of the math does
local function rgb_to_hsl(obj)
	local r = obj.r or obj[1]
	local g = obj.g or obj[2]
	local b = obj.b or obj[3]

	local R, G, B = r / 255, g / 255, b / 255
	local max, min = math.max(R, G, B), math.min(R, G, B)
	local l, s, h

	-- Get luminance
	l = (max + min) / 2

	-- short circuit saturation and hue if it's grey to prevent divide by 0
	if max == min then
		s = 0
		h = obj.h or obj[4] or 0
		return 0, 0, l
	end

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

	-- Get hue
	if max == R then h = (G - B) / (max - min) * 60
	elseif max == G then h = (2.0 + (B - R) / (max - min)) * 60
	else h = (4.0 + (R - G) / (max - min)) * 60
	end

	-- Make sure it goes around if it's negative (hue is a circle)
	if h ~= 360 then h = h % 360 end

	return h, s, l
end

--no clue about any of this either
local function hsl_to_rgb(obj)
	local h = obj.h or obj[1]
	local s = obj.s or obj[2]
	local l = obj.l or obj[3]

	local temp1, temp2, temp_r, temp_g, temp_b, temp_h

	-- Set the temp variables
	if l <= 0.5 then temp1 = l * (s + 1)
	else temp1 = l + s - l * s
	end

	temp2 = l * 2 - temp1

	temp_h = h / 360

	temp_r = temp_h + 1/3
	temp_g = temp_h
	temp_b = temp_h - 1/3


	-- Make sure it's between 0 and 1
	if temp_r ~= 1 then temp_r = temp_r % 1 end
	if temp_g ~= 1 then temp_g = temp_g % 1 end
	if temp_b ~= 1 then temp_b = temp_b % 1 end

	local rgb = {}

	-- Bunch of tests
	-- Once again I haven't the foggiest what any of this does
	for _, v in pairs({{temp_r, "r"}, {temp_g, "g"}, {temp_b, "b"}}) do

		if v[1] * 6 < 1 then rgb[v[2]] = temp2 + (temp1 - temp2) * v[1] * 6
		elseif v[1] * 2 < 1 then rgb[v[2]] = temp1
		elseif v[1] * 3 < 2 then rgb[v[2]] = temp2 + (temp1 - temp2) * (2/3 - v[1]) * 6
		else rgb[v[2]] = temp2
		end

	end

	return
		round(rgb.r * 255),
		round(rgb.g * 255),
		round(rgb.b * 255)
end

--check if table contains item
local function contains(obj, value)
	for _, v in pairs(obj) do if v == value then return true end end
	return false
end

return {
	hex_to_rgba = hex_to_rgba,
	rgba_to_hex = rgba_to_hex,
	rgb_to_hsl = rgb_to_hsl,
	hsl_to_rgb = hsl_to_rgb,
	contains = contains,
	copy = copy
}