//! 802.1D MAC Learning Bridge — mirrors Linux 7.1's `net/bridge/`.
//!
//! Reference files:
//! - `net/bridge/br.c` — bridge core (`br_add_bridge`, `br_del_bridge`)
//! - `net/bridge/br_fdb.c` — forwarding database (MAC learning + aging)
//! - `net/bridge/br_forward.c` — frame forwarding logic
//! - `net/bridge/br_input.c` — ingress frame handling
//! - `net/bridge/br_device.c` — bridge as a `net_device`
//!
//! The bridge composes multiple link-layer devices and forwards Ethernet
//! frames between them based on a dynamically-learned MAC→port table.
//! Unknown destinations are flooded to all other ports, mirroring Linux's
//! `br_flood()` in `br_forward.c`.

use std::cell::RefCell;
use std::collections::BTreeMap;
use std::rc::Rc;

use smoltcp::time::{Duration, Instant};
use smoltcp::wire::{
    EthernetAddress, EthernetFrame, EthernetProtocol, EthernetRepr, IpAddress, IpCidr,
};

use super::stp::{self, BPDU_MAC, PortState, StpState};
use super::LinkDevice;
use super::Stats;

const MAC_AGE_TIMEOUT: Duration = Duration::from_secs(300);

struct MacEntry {
    port: usize,
    last_seen: Instant,
}

pub struct BridgeDevice {
    name: Rc<str>,
    ports: RefCell<Vec<Box<dyn LinkDevice>>>,
    mac_table: RefCell<BTreeMap<EthernetAddress, MacEntry>>,
    stp: RefCell<Option<StpState>>,
    recv_buffer: Vec<u8>,
    ip_address: Option<IpCidr>,
}

impl BridgeDevice {
    pub fn new(name: &str) -> Self {
        Self {
            name: name.into(),
            ports: RefCell::new(Vec::new()),
            mac_table: RefCell::new(BTreeMap::new()),
            stp: RefCell::new(None),
            recv_buffer: Vec::with_capacity(1500),
            ip_address: None,
        }
    }

    pub fn add_port<T: LinkDevice + 'static>(&self, dev: T) {
        let mac = dev.mac_address();
        self.ports.borrow_mut().push(Box::new(dev));
        if let Some(stp) = self.stp.borrow_mut().as_mut() {
            stp.port_states.push(PortState::Forwarding);
        }
        let _ = mac;
    }

    /// Enable STP with the given bridge priority and MAC.
    /// Must be called after all ports are added.
    pub fn enable_stp(&self, priority: u16, bridge_mac: EthernetAddress) {
        let port_count = self.ports.borrow().len();
        *self.stp.borrow_mut() = Some(StpState::new(priority, bridge_mac, port_count));
    }

    fn learn(&self, mac: EthernetAddress, port: usize, now: Instant) {
        if !mac.is_unicast() {
            return;
        }
        self.mac_table.borrow_mut().insert(
            mac,
            MacEntry {
                port,
                last_seen: now,
            },
        );
    }

    fn age_entries(&self, now: Instant) {
        self.mac_table
            .borrow_mut()
            .retain(|_, e| now < e.last_seen + MAC_AGE_TIMEOUT);
    }

    fn lookup(&self, mac: EthernetAddress) -> Option<usize> {
        self.mac_table.borrow().get(&mac).map(|e| e.port)
    }

    fn flood(&self, packet: &[u8], now: Instant, except_port: Option<usize>) {
        for (idx, port) in self.ports.borrow_mut().iter_mut().enumerate() {
            if Some(idx) == except_port {
                continue;
            }
            if self.stp.borrow().as_ref().is_some_and(|s| s.is_blocked(idx)) {
                continue;
            }
            port.send(IpAddress::Ipv4(smoltcp::wire::Ipv4Address::UNSPECIFIED), packet, now);
        }
    }
}

impl LinkDevice for BridgeDevice {
    fn send(&mut self, _next_hop: IpAddress, packet: &[u8], now: Instant) {
        if packet.len() < 14 {
            return;
        }
        let frame = EthernetFrame::new_unchecked(packet);
        let Ok(repr) = EthernetRepr::parse(&frame) else {
            return;
        };
        let dst_mac = repr.dst_addr;
        if repr.dst_addr.is_broadcast() || repr.dst_addr.is_multicast() {
            self.flood(packet, now, None);
        } else if let Some(port_idx) = self.lookup(dst_mac) {
            if self.stp.borrow().as_ref().is_some_and(|s| s.is_blocked(port_idx)) {
                return;
            }
            if let Some(port) = self.ports.borrow_mut().get_mut(port_idx) {
                port.send(IpAddress::Ipv4(smoltcp::wire::Ipv4Address::UNSPECIFIED), packet, now);
            }
        } else {
            self.flood(packet, now, None);
        }
    }

    fn recv(&mut self, now: Instant) -> Option<&[u8]> {
        self.age_entries(now);

        // STP hello timer — send periodic BPDUs if we're the root bridge
        if self.stp.borrow_mut().as_mut().is_some_and(|s| s.send_hello(now)) {
            let bpdu = {
                let stp = self.stp.borrow();
                stp.as_ref().map(|s| s.build_bpdu())
            };
            if let Some(bpdu) = bpdu {
                for port in self.ports.borrow_mut().iter_mut() {
                    port.send(IpAddress::Ipv4(smoltcp::wire::Ipv4Address::UNSPECIFIED), &bpdu, now);
                }
            }
        }

        let mut received: Option<(usize, Vec<u8>, EthernetAddress, EthernetProtocol)> = None;
        {
            let mut ports = self.ports.borrow_mut();
            for (port_idx, port) in ports.iter_mut().enumerate() {
                if let Some(buf) = port.recv(now) {
                    let frame = EthernetFrame::new_unchecked(buf);
                    let Ok(repr) = EthernetRepr::parse(&frame) else {
                        continue;
                    };
                    self.learn(repr.src_addr, port_idx, now);
                    received = Some((port_idx, buf.to_vec(), repr.dst_addr, repr.ethertype));
                    break;
                }
            }
        }

        if let Some((port_idx, packet, dst_mac, ethertype)) = received {
            // BPDU: process via STP, don't forward
            if dst_mac == BPDU_MAC {
                let response = self.stp.borrow_mut().as_mut()
                    .and_then(|s| s.process_bpdu(port_idx, &packet, now));
                if let Some(rsp) = response {
                    if let Some(port) = self.ports.borrow_mut().get_mut(port_idx) {
                        port.send(IpAddress::Ipv4(smoltcp::wire::Ipv4Address::UNSPECIFIED), &rsp, now);
                    }
                }
                return None;
            }

            if ethertype == EthernetProtocol::Arp
                || ethertype == EthernetProtocol::Ipv4
                || ethertype == EthernetProtocol::Ipv6
            {
                if dst_mac.is_broadcast() || dst_mac.is_multicast() {
                    self.recv_buffer = packet.clone();
                    self.flood(&self.recv_buffer, now, Some(port_idx));
                    return Some(&self.recv_buffer);
                } else if let Some(dst_port_idx) = self.lookup(dst_mac) {
                    if dst_port_idx != port_idx
                        && !self.stp.borrow().as_ref().is_some_and(|s| s.is_blocked(dst_port_idx))
                    {
                        let mut ports = self.ports.borrow_mut();
                        if let Some(target) = ports.get_mut(dst_port_idx) {
                            target.send(IpAddress::Ipv4(smoltcp::wire::Ipv4Address::UNSPECIFIED), &packet, now);
                        }
                        return None;
                    }
                }
                self.recv_buffer = packet;
                return Some(&self.recv_buffer);
            }
        }
        None
    }

    fn name(&self) -> &Rc<str> {
        &self.name
    }

    fn can_recv(&self) -> bool {
        self.ports.borrow().iter().any(|p| p.can_recv())
    }

    fn mac_address(&self) -> Option<EthernetAddress> {
        None
    }

    fn set_mac_address(&mut self, _addr: EthernetAddress) {}

    fn ip_address(&self) -> Option<IpCidr> {
        self.ip_address
    }

    fn set_ip_address(&mut self, addr: IpCidr) {
        self.ip_address = Some(addr);
    }

    fn arp_table(&self) -> String {
        let mut out = String::from("Bridge FDB:\n");
        for (mac, entry) in self.mac_table.borrow().iter() {
            out.push_str(&format!("  {} port={} last_seen={}\n", mac, entry.port, entry.last_seen));
        }
        if self.mac_table.borrow().is_empty() {
            out.push_str("  (empty)\n");
        }
        out
    }

    fn link_state(&self) -> &'static str {
        if self.ports.borrow().is_empty() { "down" } else { "up" }
    }

    fn statistics(&self) -> Stats {
        let mut total = Stats::default();
        for port in self.ports.borrow().iter() {
            let s = port.statistics();
            total.rx_bytes += s.rx_bytes;
            total.rx_packets += s.rx_packets;
            total.tx_bytes += s.tx_bytes;
            total.tx_packets += s.tx_packets;
        }
        total
    }

    fn arp_stats(&self) -> String {
        let mut out = String::new();
        for (i, port) in self.ports.borrow().iter().enumerate() {
            let s = port.arp_stats();
            if !s.is_empty() {
                out.push_str(&format!("port{}: {}", i, s));
            }
        }
        out
    }
}