GraviMail Server

-- GLOBALS
local master = -1
local side = "top"
local myID = os.getComputerID()
local w, h = term.getSize()

local mails = {}

-- Functions & Stuff
function addLeadingZero(amount, int)
    return string.format("%"..string.rep("0", amount).."2d", tonumber(int))
end

function writeToFile(data, filename)
    local file = fs.open(filename, "w")
    file.write(textutils.serialise(data))
    file.close()
end

function readFromFile(filename)
    if not fs.exists(filename) then
        return
    end
    local file = fs.open(filename, "r")
    local data = file.readAll()
    file.close()
    return data
end

function split(str, pat)
    local t = { }
    local fpat = "(.-)"..pat
    local last_end = 1
    local s, e, cap = str:find(fpat, 1)
    while s do
      if s ~= 1 or cap ~= "" then
        table.insert(t,cap)
      end
      last_end = e+1
      s, e, cap = str:find(fpat, last_end)
    end
    if last_end <= #str then
      cap = str:sub(last_end)
      table.insert(t, cap)
    end
    return t

end

function printHeader()
    term.setCursorPos(1, 1)
    print(string.rep("-", w))
    term.setCursorPos(w/2 - #"MAIL SERVER"/2, 2)
    print("MAIL SERVER")
    term.setCursorPos(1, 3)
    print(string.rep("-", w))
    print("")
end

function addMail(mailData)
    table.insert(mails, {
        id = mailData[1],
        from = mailData[2],
        date = mailData[3].."."..mailData[4].."."..mailData[5],
        time = mailData[6]..":"..addLeadingZero(1, mailData[7]),
        body = mailData[8]
    })

    writeToFile(mails, "mailDB")
end

function requestMails(id)
    local foundMails = ""
    if #mails > 0 then
        for i, mail in pairs(mails) do
            if mail["id"] == id then
                foundMails = foundMails.."!NM!"
                foundMails = foundMails.."!ED!"..mail["id"].."!ED!"..mail["from"].."!ED!"..mail["date"].."!ED!"..mail["time"].."!ED!"..mail["body"].."!ED!"
                table.remove(mails, i)
            end
        end
    end
    local resp = "$CLIENT-"..id.."-"
    resp = resp.."$RESPONSE"..foundMails
    print(resp)
    rednet.send(master, resp)
    writeToFile(mails, "mailDB")
end

function processRequest(request, senderId)
    if string.find(request, "$EMAIL") then
        request = string.gsub(request, "$EMAIL", "")
        local values = split(request, "!ED!")
        if #values == 8 then
            addMail(values)
        end
    elseif string.find(request, "$REQUEST") then
        request = string.gsub(request, "$REQUEST", "")
        local values = split(request, "!ED!")
        if #values >= 2 and tonumber(values[1]) then
            if values[2] == "EMAILS" then
                requestMails(values[1])
            end
        end
    end
end

-- Connection Logic

mails = readFromFile("mailDB") ~= nil and textutils.unserialise(readFromFile("mailDB")) or {}

if not fs.exists("gravimail/server/pref") then
    error("GraviMail server not installed via installer, make sure to do that!")
    return
end

local pref = fs.open("gravimail/server/pref", "r").readAll()
pref = textutils.unserialise(pref)

side = pref.side
master = tonumber(pref.master)

if master == -1 then
    print("Bad ID!")
    return
end

term.clear()
printHeader()

rednet.open(side)

local id, message
while true do
    print("Requesting admission on "..master)
    rednet.send(master, "$MASTER$ADDSERVER-"..myID.."-MAIL")
    id, message = rednet.receive(5)
    if message == "$ACK" then
        print("Confirmed.")
        break
    end
end

while true do
    local cx, cy = term.getCursorPos()
    printHeader()
    term.setCursorPos(cx, cy)
    print("Listening for messages...")
    id, message = rednet.receive()
    processRequest(message, id)
end