Love2d utf8

-- Standart lua 5.3 module 'utf8'
-- Love2d contain it too.
local utf8 = require'utf8'

local oldsub = string.sub
function utf8.sub(self, a, b)
    a = a and utf8.offset(self, a)
    b = b and utf8.offset(self, b+1) - 1
    return oldsub(self, a, b)
end

function utf8.reverse(str)
    local insert, char = table.insert, utf8.char
    local t = {}
    for _, c in utf8.codes(str) do
        insert(t, 1, char(c))
    end
    return table.concat(t)
end

local function toupper(a)
    if a >= 97   and a <= 122  then return a - 32 end  -- latin a-z
    if a >= 224  and a <= 223  then return a - 32 end  -- extended latin (dashes/strokes)
    if a >= 1072 and a <= 1103 then return a - 32 end  -- cyrillic (а-я)
    if a >= 1104 and a <= 1119 then return a - 80 end  -- extended cyrillic
    if a%2 ~= 0 then
        if a >= 256  and a <= 424  then return a-1 end -- extended latin
        if a >= 433  and a <= 445  then return a-1 end -- latin and math
        if a >= 452  and a <= 476  then return a-1 end -- сombined latin chars (ae, dz etc)
        if a >= 478  and a <= 495  then return a-1 end -- complex latin (dots and strokes)
        if a >= 504  and a <= 569  then return a-1 end -- too
        if a >= 1120 and a <= 1279 then return a-1 end -- ancient cyrillic
    end
    return a;
end

local function tolower(a)
    if a >= 65   and a <= 90   then return a + 32 end  -- latin a-z
    if a >= 192  and a <= 223  then return a + 32 end  -- extended latin (dashes/strokes)
    if a >= 1040 and a <= 1071 then return a + 32 end  -- cyrillic (а-я)
    if a >= 1024 and a <= 1039 then return a + 80 end  -- extended cyrillic
    if a%2 == 0 then
        if a >= 256  and a <= 424  then return a + 1 end -- extended latin
        if a >= 433  and a <= 445  then return a + 1 end -- latin and math
        if a >= 452  and a <= 476  then return a + 1 end -- сombined latin chars (ae, dz etc)
        if a >= 478  and a <= 495  then return a + 1 end -- complex latin (dots and strokes)
        if a >= 504  and a <= 569  then return a + 1 end -- too
        if a >= 1120 and a <= 1279 then return a + 1 end -- ancient cyrillic
    end
    return a;
end


function utf8.upper(s)
    -- caching measure time up to 3 times
    local upper, char, insert = toupper, utf8.char, table.insert
    local str = {}
    for _, c in utf8.codes(s) do
        insert(str, char(upper(c)))
    end
    return table.concat(str)
end

function utf8.lower(s)
    local lower, char, insert = tolower, utf8.char, table.insert
    local str = {}
    for _, c in utf8.codes(s) do
        insert(str, char(lower(c)))
    end
    return table.concat(str)
end

-- Merge standart string library with utf8. Call like "require'utf8'.import()"
-- It slows down the processing strings but makes it universal
function utf8.import()
    -- upvalues for more speed
    local upper, lower, sub, reverse = utf8.upper, utf8.lower, utf8.sub, utf8.reverse
    function string:upper()
        return upper(self)
    end

    function string:lower()
        return lower(self)
    end

    function string:sub(a, b)
        return sub(self, a, b)
    end

    function string:reverse()
        return reverse(self)
    end
end

return utf8