-- lemonserver.lua -- registration & relay server for Lemonphone DM system
-- by ChatGPT (GPT-5)

local PROTOCOL = "lemonos-net"
local REGISTRY_FILE = "/lemonserver_registry.db"
local PEERS_FILE = "/lemonserver_peers.db"
local DEFAULT_TTL = 8
local HEARTBEAT_INTERVAL = 30

local function save_table(path, tbl)
    local f = fs.open(path, "w")
    if not f then return false end
    f.write(textutils.serialize(tbl))
    f.close()
    return true
end
local function load_table(path)
    if not fs.exists(path) then return {} end
    local f = fs.open(path, "r")
    if not f then return {} end
    local ok, t = pcall(textutils.unserialize, f.readAll())
    f.close()
    if ok and type(t) == "table" then return t end
    return {}
end

local registry = load_table(REGISTRY_FILE) -- phone -> { serverID, nodeID, meta, created }
local peers = load_table(PEERS_FILE)       -- nodeID string -> true
local seen = {}
local msgCounter = 0
local myID = os.getComputerID()

math.randomseed(os.time() + myID)

local function mkMsgID()
    msgCounter = msgCounter + 1
    return tostring(myID) .. "-" .. tostring(os.time()) .. "-" .. tostring(msgCounter)
end

local function cleanupSeen()
    local now = os.time()
    for k,v in pairs(seen) do if v <= now then seen[k] = nil end end
end

local function genHex(n)
    local s = ""
    for i = 1, n do s = s .. string.format("%x", math.random(0,15)) end
    return s
end

local function makePhone(serviceType)
    serviceType = tostring(serviceType or "2")
    for _ = 1, 200 do
        local a, b = genHex(4), genHex(4)
        local num = serviceType .. "-" .. a .. "-" .. b
        if not registry[num] then return num end
    end
    return nil
end

local function saveAll()
    save_table(REGISTRY_FILE, registry)
    save_table(PEERS_FILE, peers)
end

local function registerPhone(serviceType, clientNode, clientMeta)
    local num = makePhone(serviceType)
    if not num then return nil, "exhausted" end
    registry[num] = { serverID = myID, nodeID = clientNode, meta = clientMeta or {}, created = os.time() }
    saveAll()
    return num
end

local function sendRaw(node, tbl)
    local ok, s = pcall(textutils.serialize, tbl)
    if not ok then return false, "serialize" end
    rednet.send(tonumber(node), s, PROTOCOL)
    return true
end

local function broadcastToPeers(tbl)
    for k,_ in pairs(peers) do
        local nid = tonumber(k)
        if nid and nid ~= myID then pcall(sendRaw, nid, tbl) end
    end
end

local function deliverToClientLocal(localPhone, msg)
    local rec = registry[localPhone]
    if not rec then return false, "not-local" end
    local target = rec.nodeID or rec.serverID
    if target then
        pcall(sendRaw, tonumber(target), msg)
        return true
    end
    return false, "no-target"
end

local function handleRegister(req, fromNode)
    local num, err = registerPhone(req.serviceType, fromNode, req.clientInfo)
    local res = { msgType = "register_res", id = mkMsgID(), inReplyTo = req.id, assigned = num, timestamp = os.time() }
    pcall(sendRaw, fromNode, res)
    print(("Registered %s for node %d"):format(tostring(num), fromNode))
end

local function handleDM(msg, fromNode)
    if not msg.id then return end
    if seen[msg.id] then return end
    seen[msg.id] = os.time() + 60

    local rec = registry[msg.toPhone]
    if rec and rec.serverID == myID then
        local ok, err = deliverToClientLocal(msg.toPhone, msg)
        if ok then
            local ack = { msgType="ack", id=mkMsgID(), inReplyTo=msg.id, timestamp=os.time(), status="delivered" }
            pcall(sendRaw, fromNode, ack)
            print(("Delivered DM %s -> %s locally"):format(tostring(msg.fromPhone), tostring(msg.toPhone)))
            return
        end
    end

    -- known owner but remote
    if rec and rec.serverID and rec.serverID ~= myID and peers[tostring(rec.serverID)] then
        pcall(sendRaw, tonumber(rec.serverID), msg)
        return
    end

    -- relay to peers if unknown or unreachable
    if not msg.ttl then msg.ttl = DEFAULT_TTL end
    if msg.ttl <= 0 then return end
    msg.ttl = msg.ttl - 1
    msg.path = msg.path or {}
    table.insert(msg.path, myID)
    broadcastToPeers(msg)
end

local function handleIncoming(raw, sender)
    local ok, tbl = pcall(textutils.unserialize, raw)
    if not ok or type(tbl) ~= "table" then return end
    if tbl.msgType == "register_req" then handleRegister(tbl, sender); return
    elseif tbl.msgType == "dm" then handleDM(tbl, sender); return
    elseif tbl.msgType == "peer_announce" then peers[tostring(sender)] = true saveAll() return
    elseif tbl.msgType == "heartbeat" then peers[tostring(sender)] = true saveAll() return
    end
end

local function receiveLoop()
    while true do
        local sender, raw = rednet.receive(PROTOCOL)
        if sender and raw then
            local ok, err = pcall(handleIncoming, raw, sender)
            if not ok then print("Error handling: " .. tostring(err)) end
        end
    end
end

local function housekeeping()
    while true do
        cleanupSeen()
        local announce = { msgType = "peer_announce", id = mkMsgID(), timestamp = os.time(), serverID = myID }
        broadcastToPeers(announce)
        sleep(HEARTBEAT_INTERVAL)
    end
end

local function adminConsole()
    print("LemonServer admin console. Commands: peers, registry, addpeer <id>, rempeer <id>, save, quit")
    while true do
        io.write("> ")
        local line = io.read()
        if not line then break end
        local cmd, arg = line:match("^(%S+)%s*(.*)$")
        if cmd == "peers" then
            print("Peers:")
            for k,_ in pairs(peers) do print(" - " .. k) end
        elseif cmd == "registry" then
            print("Registry entries:")
            for p,v in pairs(registry) do
                print((" %s -> server %s node %s (created %s)"):format(p, tostring(v.serverID), tostring(v.nodeID), tostring(v.created)))
            end
        elseif cmd == "addpeer" and arg ~= "" then
            peers[arg] = true saveAll() print("Added " .. arg)
        elseif cmd == "rempeer" and arg ~= "" then
            peers[arg] = nil saveAll() print("Removed " .. arg)
        elseif cmd == "save" then
            saveAll() print("Saved")
        elseif cmd == "quit" then print("Exiting console.") break
        else print("Unknown command.")
        end
    end
end

-- start server
if peripheral.find("modem") then
    -- best-effort open modem on a side; prefer existing config
    -- open all modem sides to be safe if possible
    for _, side in ipairs(peripheral.getNames()) do
        if peripheral.getType(side) == "modem" then
            pcall(rednet.open, side)
        end
    end
end

print("LemonServer starting as node " .. tostring(myID))
saveAll()
parallel.waitForAny(receiveLoop, housekeeping, adminConsole)