Master Server

-- GLOBALS

local routers = {}
local servers = {}
local side = "top"
local myID = os.getComputerID()
local w, h = term.getSize()

-- Functions & Stuff

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 addConnector(newid, parentid, connections)
    -- If there are no connectors there is nothing to add to.
    if #connections == 0 then return false end

    for i = 1, #connections, 1 do
        local child = connections[i]

        -- Removing new connector if it already exists.
        for j = 1, #child.children, 1 do
            if child.children[j].id == newid then
                table.remove(child.children, j)
            end
        end

        -- If parent connector is found, add new connector to children.
        if child.id == parentid then
            table.insert(child.children, {
                id = newid,
                children = {}
            })

            return true
        end

        -- If no parent connector is found, use recursion to go through all children of the the current connector.
        addConnector(newid, parentid, child.children)
    end

    -- If no parent connector is found, return false.
    return false
end

function removeConnector(oldid, connections)
    -- If there are no connections we can't remove any.
    if #connections == 0 then return false end

    -- Looping over connections to find target id.
    for i = 1, #connections, 1 do
        local child = connections[i]

        -- If current router's id matches the one we're looking for, remove it and return true.
        if child.id == oldid then
            table.remove(connections, i)
            return true
        end

        -- Using recursion to search all children of the current router for the id we're looking for.
        if removeConnector(oldid, child.children) then return true end
    end

    -- Returning false if we don't find the id we're looking for.
    return false
end

function findConnector(id, connections)
    -- If no connections are found we have nothing to search for.
    if #connections == 0 then return "" end

    -- Loop through all connections to find the id we're searching for.
    for i = 1, #connections, 1 do
        local child = connections[i]

        -- If the current router's id matches the one we're searching for we return that.
        if child.id == id then return child.id end

        -- Using recursion to search routers' childs.
        local path = findConnector(id, child.children)

        -- If a path is found to the id we're searching for, we'll return the current router's id and that path.
        if path ~= "" then return child.id.."-"..path end
    end

    return ""
end

function findTopConnector(id)
    -- Loop over all top routers and check id's.
    for i = 1, #routers, 1 do
        local route = routers[i]
        -- If top router is the one we're searching for we don't return a path.
        if route.id == id then
            return route.id, ""
        end

        -- Trying to find the id we're searching for in current routers children.
        local path = findConnector(id, route.children)

        -- If a path is found to the id we're searching for, return the current router id and that path.
        if path ~= "" then return route.id, path end
    end

    -- If no path at all is found, error.
    print("A network error has occured.")
    return -1, ""
end

function printNetworkTree(connections, index)
    -- If no connections, we can't print the network tree.
    if #connections == 0 then return end

    for i = 1, #connections, 1 do
        local child = connections[i]
        print(string.rep(" ", index)..child.id)
        printNetworkTree(child.children, index + 1)
    end
end

function processRequest(request, senderId)
    -- Same in routers, simple responds to messages.
    if request == "$HELLO" then
        -- If we receive a network discovery message, we'll respond with $HELLO
        rednet.send(senderId, "$HELLO")
        return

    elseif request == "$ADDME" then
        -- If we receive an add me request, we'll instantly add this router to the network.
        table.insert(routers, {
            id = senderId,
            children = {}
        })
        local file =
        rednet.send(senderId, "$ACK")

        printNetworkTree(routers, 0)
        return
    end

    -- If it's a client request, we'll funnel it down to the next router close to the target router.
    if string.find(request, "$CLIENT") then
        request = string.gsub(request, "$CLIENT", "")
        local values = split(request, "-")

        -- Finding the path to the target router, to send it to the closest one.
        local routeId, dest = findTopConnector(tonumber(values[1]))
        if dest ~= "" then
            request = dest.."-"..values[2]
        else
            request = values[2]
        end

        rednet.send(routeId, request)

    -- If it's a server request, we'll send it to the right server.
    elseif string.find(request, "$SERVER") then
        local sent = false

        request = string.gsub(request, "$SERVER", "")

        -- Finding the server to forward the request to.
        for i = 1, #servers, 1 do
            local s, e = string.find(request, servers[i].name)
            if s == 2 then
                request = string.sub(request, e + 1)
                rednet.send(servers[i].id, request)
                sent = true
                break
            end
        end

        -- If no server is found, we ignore it.
        if not sent then print("No server with the requested name is registered on the network. Requested server: "..request) end

    -- If it's meant for the master server we'll process it ourselves.
    elseif string.find(request, "$MASTER") then
        request = string.gsub(request, "$MASTER", "")

        -- If we receive an add router request, this means the request has been through more than just the original router.
        if string.find(request, "$ADDROUTER") then
            request = string.gsub(request, "$ADDROUTER", "")
            local values = split(request, "-")

            -- We'll add the router to the children of the router we received the message from.
            addConnector(tonumber(values[1]), tonumber(values[2]), routers)
            print("Added new router.")

            printNetworkTree(routers, 0)

            -- We'll find the nearest router on the path to the newly added router, and send an ackowledged message back.
            local routeId, dest = findTopConnector(tonumber(values[1]))
            rednet.send(routeId, dest.."-$ACK")

        -- Adding a new server when receiving this request.
        elseif string.find(request, "$ADDSERVER") then
            request = string.gsub(request, "$ADDSERVER", "")
            local values = split(request, "-")

            table.insert(servers, {
                id = tonumber(values[1]),
                name = values[2]
            })

            print("Added new server: "..values[2])

            rednet.send(senderId, "$ACK")
        end

    -- If the message isn't recognized we'll ignore it.
    else
        print("Unrecognizable message received.")
    end
end

function printHeader()
    term.setCursorPos(1, 1)
    print(string.rep("-", w))
    term.setCursorPos(w/2 - #"MASTER SERVER"/2, 2)
    print("MASTER SERVER")
    term.setCursorPos(1, 3)
    print(string.rep("-", w))
    print("Open on ID "..myID)
    print("")
end

-- Main Logic

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

local pref = textutils.unserialise(readFromFile("gravinet/master/pref"))
side = pref.side

if fs.exists("gravinet/master/routers") then
    routers = textutils.unserialise(readFromFile("gravinet/master/routers"))
end

if fs.exists("gravinet/master/servers") then
    servers = textutils.unserialise(readFromFile("gravinet/master/servers"))
end

term.clear()
rednet.open(side)

printHeader()

while true do
    local cx, cy = term.getCursorPos()
    printHeader()
    term.setCursorPos(cx, cy)
    print("Listening for request...")
    local requestID, request = rednet.receive()
    processRequest(request, requestID)
end
rednet.close()