Add colors utilities

Local function get_base_color(), conversions hex <=> rgb, rgb color mixer, and global function get_color()

util/colors.lua

@@ -0,0 +1,53 @@
+local function get_base_color(id)
+    local colors = {
+		h = "#999", -- header
+		s = "#72FF63", -- selected
+		i = "#FFD700", -- important
+		a = "#CCCCDD", -- additional
+		H = "#608631", -- highlighted
+		n = "#00F529" -- new
+	}
+	return colors[id]
+end
+
+local function hex2rgb(hex)
+    hex = hex:gsub("#","")
+    return {
+        r = tonumber("0x" .. hex:sub(1,2)),
+        g = tonumber("0x" .. hex:sub(3,4)),
+        b = tonumber("0x" .. hex:sub(5,6))
+    }
+end
+
+local function rgb2hex(rgb)
+    return "#" .. string.format("%x", rgb.r) .. string.format("%x", rgb.g) .. string.format("%x", rgb.b)
+end
+
+local function rgbColorsMix(colors)
+    local R = 0
+    local G = 0
+    local B = 0
+    for _, c in ipairs(colors) do
+        R = R + c.r
+        G = G + c.g
+        B = B + c.b
+    end
+    R = R / #colors
+    G = G / #colors
+    B = B / #colors
+    return {r=R,g=G,b=B}
+end
+
+function mail.get_color(mix)
+    if #mix == 1 then
+        return get_base_color(mix)
+    else
+        local colors = {}
+        for i = 1, #mix do
+            local c = mix:sub(i,i)
+            colors[#colors+1] = hex2rgb(get_base_color(c))
+        end
+        local mixed_color = rgbColorsMix(colors)
+        return rgb2hex(mixed_color)
+    end
+end

util/init.lua

@@ -1,6 +1,7 @@
 -- sub files
 local MP = minetest.get_modpath(minetest.get_current_modname())
 dofile(MP .. "/util/normalize.lua")
+dofile(MP .. "/util/colors.lua")
 dofile(MP .. "/util/contact.lua")
 dofile(MP .. "/util/uuid.lua")
 dofile(MP .. "/util/time_ago.lua")