CRFv3.1 Modem Emulator

-- Modem Emulation Protocol over CRFv3.1, using multicast

local fake_modems = {}

local open_channels = {}

local peripheral_old = {}

local listen_all = false -- Should we emit *all* fake modem messages, no matter if we even have a fake modem open to the sending channel?

for i,v in pairs(peripheral) do
    peripheral_old[i] = v
end

if not LANClient then
    error("The LAN Client API has not loaded yet!")
end

LANClient.join_group(2)

peripheral.isPresent = function(side)
    if fake_modems[side] ~= nil then
        return true
    end
    return peripheral_old.isPresent(side)
end

peripheral.getType = function(side)
    if fake_modems[side] ~= nil then
        return "modem"
    end
    return peripheral_old.getType(side)
end

peripheral.getMethods = function(side)
    if fake_modems[side] ~= nil then
        return {"isOpen", "open", "close", "closeAll", "transmit", "isWireless"}
    end
    return peripheral_old.getMethods(side)
end

peripheral.call = function(side, method, ...)
    local args = {...}
    if fake_modems[side] ~= nil then
        if fake_modems[side][method] then
            return fake_modems[side][method](unpack(args))
        end
    end
    return peripheral_old.call(side, method, unpack(args))
end

peripheral.getNames = function()
    local names = peripheral_old.getNames()
    for i,v in pairs(fake_modems) do
        table.insert(names, i)
    end
    return names
end

peripheral.wrap = function(side)
    if fake_modems[side] ~= nil then
        return fake_modems[side] -- we're trusting the caller to not screw with the modem object
    end
    return peripheral_old.wrap(side)
end

function backgroundListener()
    while true do
        local sender, msg = LANClient.receive()
        local data = textutils.unserialize(msg)
        if type(data) == "table" then
            --print("Got a message from "..sender)
            if data[1] == "ModemEmulator" then
                local sCh = tonumber(data[2])
                local rCh = tonumber(data[3])
                local modemData = data[4]
                --[[
                print("Got a fake modem message from "..sender)
                print("sch: "..sCh.." type: "..type(sCh))
                print("rch: "..rCh.." type: "..type(rCh))
                print("data: "..modemData)
                local foundSide = false
                ]]
                if open_channels[sCh] then
                    local side = next(fake_modems) -- Get the first modem we find
                    os.queueEvent("modem_message", side, sCh, rCh, modemData, 0)
                    --print("side: "..side)
                elseif listen_all then -- fuck it, emit as an obviously fake event
                    os.queueEvent("modem_message", "listen_all", sCh, rCh, modemData, 0)
                    --print("side: listen_all")
                end
            end
        end
    end
end

local function create_fake_modem()
    local modem = {
        channels = {},
        isWireless = function() return true end,
        isFake = function() return true end,
    }
    modem.transmit = function(channel, replyChannel, data)
        LANClient.send(-2, textutils.serialize({"ModemEmulator", channel, replyChannel, data}))
    end
    modem.isOpen = function(channel)
        if open_channels[channel] then
            --print("open_channels["..channel.."] :"..open_channels[channel])
            return true
        end
        return false
    end
    modem.open = function(channel)
        --print("ch: "..channel.." type: "..type(channel))
        if open_channels[channel] then
            open_channels[channel] = open_channels[channel]+1
        else
            open_channels[channel] = 1
        end
        --print("open_channels["..channel.."] :"..open_channels[channel])
        modem.channels[channel] = true
    end
    modem.close = function(channel)
        if open_channels[channel] then
            open_channels[channel] = open_channels[channel]-1
            if open_channels[channel] <= 0 then
                open_channels[channel] = nil
            end
            modem.channels[channel] = nil
        end
    end
    modem.closeAll = function()
        local copy = {}
        for i,v in pairs(modem.channels) do
            copy[i] = v
        end
        for i,v in pairs(copy) do
            modem.close(i)
        end
    end
    return modem
end

function register_modem(side)
    if peripheral.isPresent(side) then
        return false
    end
    fake_modems[side] = create_fake_modem()
    return true
end

function unregister_modem(side)
    if fake_modems[side] then
        fake_modems[side] = nil
    else
        return false
    end
    return true
end

function get_all_listen()
    return listen_all
end

function toggle_all_listen()
    listen_all = not listen_all
    return listen_all
end

function get_open_channels()
    return open_channels
end

if shell then
    local file = fs.open(shell.getRunningProgram(), "r")
    if file then
        local l = file.readLine()
        file.close()
        if string.match(l, "Modem Emulation Protocol") then
            if not modem_emulator then -- The API's useless if the background function isn't running
                error("The modem_emulator API has not loaded yet!")
            end
            local args = {...}
            if #args == 2 then
                if args[1] == "register" then
                    if register_modem(args[2]) then
                        print("Virtual modem successfully created.")
                    else
                        print("A peripheral already exists there.")
                    end
                elseif args[1] == "unregister" then
                    if unregister_modem(args[2]) then
                        print("Virtual modem successfully deleted.")
                    else
                        print("No peripheral exists there.")
                    end
                end
            elseif (#args == 1) and (args[1] == "listen_all") then
                if toggle_all_listen() then
                    print("All-Listen enabled.")
                else
                    print("All-Listen disabled.")
                end
            else
                print("modem_emulator -- Modem emulator API and interface")
                print(string.rep("-", term.getSize()))
                print("Usage: modem_emulator [action] [side]")
                print("Actions:")
                print("register (\"modem_emulator register [side]\"): Create a new virtual modem.")
                print("unregister (\"modem_emulator unregister [side]\"): Delete a virtual modem.")
                print("listen_all (\"modem_emulator listen_all\"): Toggle listen state; when on, then we emit all events regardless of whether we have a modem opened to the sending channel.")
            end
        end
    end
end