GridLock

local conv = {}

local lastn = 0
local function getNumber(key, mx)
    local n = 0
    for i=1,string.len(key) do
        n = n + (string.byte(key:sub(i, i))*key:len())
    end
    n = (n + lastn) % mx
    if n == 0 then n = 1 end
    lastn = n
    return n
end

local chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!£$%^&*()-=_+[];'#,./{}:@~<>?\\| "..'"'
local function getIndex(char)
    local i = 1
    for j=1,chars:len() do if chars:sub(j,j) == char then i = j end end
    --print("i="..i..", char="..char)
    return i
end

local function genConv(password)
    local curc = chars
    local n = 1
    --print(string.len(curc)..":"..#conv)
    while string.len(curc) > 0 do
        local i = getNumber(password, string.len(curc))
        --term.write(":"..i..","..curc:len())
        conv[curc:sub(i, i)] = n
        n = n + 1
        local bef = ""
        if i > 1 then bef = curc:sub(1, i-1) end
        local aft = ""
        if i < string.len(curc) then aft = curc:sub(i+1, -1) end
        curc = bef..aft
    end
    --print("")
    --print(string.len(curc)..":"..#conv)
    lastn = 0
end

local function getCoord(a, b)
    local cood = {conv[a], conv[b]}
    return cood
end

local function getIs(c1, c2)
    local ci1 = {c1[1], c2[2]}
    local ci2 = {c2[1], c1[2]}
    --print("c1: "..type(ci1).." c2: "..type(ci2).." c1; "..type(ci1[1])..","..type(ci1[2]).." c2; "..type(ci2[1])..","..type(ci2[2]))
    return ci1, ci2
end

local function getCoordI(i1, i2)
    local p1 = {i1[1], i2[2]}
    local p2 = {i2[1], i1[2]}
    return p1, p2
end

local function getLetter(number)
    --print("n: "..number)
    --[[
    for k,v in pairs(conv) do
        if v == number then return k end
    end
    ]]
    --print("no pair found for "..number)
    number = number%chars:len()
    if number == 0 then number = 1 end
    return chars:sub(number, number)
end

local function getCLetter(number)
    for k,v in pairs(conv) do
        if v == number then return k end
    end
end

local function getAB(c)
    local a = getCLetter(c[1])
    local b = getCLetter(c[2])
    if a ~= nil and b ~= nil then
        return a..b
    else
        error("Something went wrong! Grid match up returned nil value.. letter invalid? WORKING")
    end
end

local function encode(str)
    while string.len(str)%4 ~= 0 do
        str = str.." "
    end
    local estr = ""
    for i=1,str:len(),4 do
        local a1 = str:sub(i, i)
        local b1 = str:sub(i+1, i+1)
        local a2 = str:sub(i+2, i+2)
        local b2 = str:sub(i+3, i+3)
        local co1 = getCoord(a1, b1)
        local co2 = getCoord(a2, b2)
        local i1, i2 = getIs(co1, co2)
        if i == 1 then
            --print("c1: "..co1[1]..","..co1[2].." c2: "..co2[1]..","..co2[2])
            --print("i1: "..i1[1]..","..i1[2].." i2: "..i2[1]..","..i2[2])
        end
        local letters = {getLetter(i1[1]), getLetter(i1[2]), getLetter(i2[1]), getLetter(i2[2])}
        local ok = true
        for i=1,#letters do if letters[i] == nil then ok = false end end
        if #letters < 4 then ok = false error("letters have reduced in size? ("..#letters..")") end
        if ok then
            for i=1,#letters do
                estr = estr..letters[i]
            end
        else
            error("Something went wrong! Grid match up returned nil value.. letter invalid? (ENCODING)")
        end
    end
    return estr
end

local function decode(str)
    local dstr = ""
    for i=1,str:len(),4 do
        --local i1 = {char[str:sub(i, i)], conv[str:sub(i+1, i+1)]}
        --local i2 = {conv[str:sub(i+2, i+2)], conv[str:sub(i+3, i+3)]}
        local i1 = {getIndex(str:sub(i, i)), getIndex(str:sub(i+1, i+1))}
        local i2 = {getIndex(str:sub(i+2, i+2)), getIndex(str:sub(i+3, i+3))}

        local p1, p2 = getCoordI(i1, i2)
        if i == 1 then
            --print("i1: "..i1[1]..","..i1[2].." i2: "..i2[1]..","..i2[2])
            --print("c1: "..p1[1]..","..p1[2].." c2: "..p2[1]..","..p2[2])
        end
        local ab1 = getAB(p1)
        local ab2 = getAB(p2)
        if ab1 ~= nil and ab2 ~= nil then
            dstr = dstr..ab1..ab2
        else
            error("Something went wrong! No idea what!")
        end
    end
    return dstr
end


print("E/D-crypt?")
local cmd = read()
if cmd:lower() == "e" then
    print("password?")
    local pass = read()
    print("text?")
    local text = read()
    genConv(pass)
    local estr = encode(text)
    print(estr)

    local file = fs.open("enc", "a")
    file.writeLine("PASS: "..pass.." TEXT: "..text.." ENC: "..estr)
    file.close()

elseif cmd:lower() == "d" then
    print("password?")
    local pass = read()
    print("text?")
    local text = read()
    genConv(pass)
    local dstr = decode(text)
    print(dstr)

    local file = fs.open("enc", "a")
    file.writeLine("PASS: "..pass.." TEXT: "..text.." DEC: "..dstr)
    file.close()
end