HostPC.lua

function save(table, filename)
    file = fs.open(filename,"w")
    file.write(textutils.serialize(table))
    file.close()
end

function load(filename)
    file = fs.open(filename,"r")
    data = file.readAll()
    file.close()
    return textutils.unserialize(data)
end

function newAcc(FromPort)
    I = #LogInTable
    unable = false
    event, side, x,y, ID = os.pullEvent("modem_message")
    print(ID)
    event, side, x,y, Pass = os.pullEvent("modem_message")
    print(Pass)

    for J = 1, #LogInTable, 2 do
        if LogInTable[J] == ID then
            unable = true
            modem.transmit(FromPort, 12345, "Used")
            print("Account "..ID.." already in use.")
        end
    end
    if not unable then
        modem.transmit(FromPort, 12345, "Unused")
        print("Created account for ID: "..ID)
        LogInTable[I + 1] = ID
        LogInTable[I + 2] = Pass
        J = #CurrencyTable
        CurrencyTable[J + 1] = ID
        CurrencyTable[J + 2] = 0
    end
end

function LogIn(FromPort)
    login = false
    print(FromPort.." is attempting to login.")
    event, side, x, y, ID = os.pullEvent("modem_message")
    print(ID)
    sleep(0.1)
    event, side, x, y, Pass = os.pullEvent("modem_message")
    print(Pass)

    for I = 1, #LogInTable, 2 do
        if ID == LogInTable[I] then
            if Pass == LogInTable[I + 1] then
                login = true
                loginCreds = LogInTable[I]
            end
        end
    end

    modem.transmit(FromPort, 12345, tostring(login))
    print("Sent "..tostring(login).." to "..FromPort)
end

function Transfer(FromPort)
    Owner = false
    request = false
    event, side, x,y, ID = os.pullEvent("modem_message")
    event, side, x,y, ToID = os.pullEvent("modem_message")
    event, side, x,y, Amount = os.pullEvent("modem_message")
    for I = 1, #LogInTable, 2 do
        if LogInTable[I] == tonumber(ID) then
            Currency = CurrencyTable[I + 1]
            Owner = true
        elseif LogInTable[I] == tonumber(ToID) then
            OtherCurrency = CurrencyTable[I + 1]
            request = true
        end
    end

    if not Owner or not request then
        modem.transmit(FromPort, 12345, "InvalidUser")
    elseif tonumber(Amount) > Currency or tonumber(Amount) < 0 then
        modem.transmit(FromPort, 12345, "NotEnough")
    else
        OtherCurrency = OtherCurrency + Amount
        Currency = Currency - Amount
        print(ID.." sent "..Amount.." to "..ToID)
        modem.transmit(FromPort, 12345, "Transfer Successful.")
    end

    for I = 1, #CurrencyTable, 2 do
        if CurrencyTable[I] == tonumber(ID) then
            CurrencyTable[I + 1] = Currency
        elseif CurrencyTable[I] == tonumber(ToID) then
            CurrencyTable[I + 1] = OtherCurrency
        end
    end
end

function init()

    if fs.exists("Currency") then
        CurrencyTable = load("Currency")
    else
        CurrencyTable = {}
    end

    if fs.exists("LogIn") then
        LogInTable = load("LogIn")
    else
        LogInTable = {}
    end

    modem = peripheral.wrap("back")
    modem.open(12345)
end

function getCurrency(FromPort)
    event, side, x, y, ID = os.pullEvent("modem_message")
    for I = 1, #CurrencyTable, 2 do
        if CurrencyTable[I] == tonumber(ID) then
            Currency = CurrencyTable[I + 1]
        end
    end
    modem.transmit(FromPort, 12345, Currency)
    print("Currency for "..ID..": "..Currency)
end

function main()
    print("Init complete.")
    while true do
        CurrencyTable = load("Currency")
        LogInTable = load("LogIn")
        event, side, x, FromUser, message = os.pullEvent("modem_message")
        if message == "LogIn" then
            LogIn(FromUser)
        elseif message == "CreateNew" then
            newAcc(FromUser)
        elseif message == "getCurrency" then
            getCurrency(FromUser)
        elseif message == "Transfer" then
            Transfer(FromUser)
        end
        save(CurrencyTable, "Currency")
        save(LogInTable, "LogIn")
    end
end

init()
main()