// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Common types for dealing with ip table entries.

use core::{
    convert::Infallible as Never,
    fmt::{Debug, Display, Formatter},
    hash::Hash,
};

use net_types::{
    ip::{GenericOverIp, Ip, IpAddress, Ipv4, Ipv4Addr, Ipv6, Ipv6Addr, Subnet, SubnetEither},
    SpecifiedAddr,
};

use crate::socket::address::SocketIpAddr;

/// The priority of a forwarding entry. Lower metrics are preferred.
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, PartialOrd, Ord)]
pub struct RawMetric(pub u32);

impl Display for RawMetric {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
        let RawMetric(metric) = self;
        write!(f, "{}", metric)
    }
}

impl From<RawMetric> for u32 {
    fn from(RawMetric(metric): RawMetric) -> u32 {
        metric
    }
}

impl From<RawMetric> for u64 {
    fn from(RawMetric(metric): RawMetric) -> u64 {
        u64::from(metric)
    }
}

/// The metric for an [`AddableEntry`].
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
pub enum AddableMetric {
    /// The entry's metric is unspecified, and shall defer to the routing metric
    /// of its interface.
    MetricTracksInterface,
    /// The entry's metric shall be the following explicit value.
    ExplicitMetric(RawMetric),
}

impl From<Metric> for AddableMetric {
    fn from(metric: Metric) -> AddableMetric {
        match metric {
            Metric::MetricTracksInterface(_) => AddableMetric::MetricTracksInterface,
            Metric::ExplicitMetric(metric) => AddableMetric::ExplicitMetric(metric),
        }
    }
}

/// `AddableEntry` is a routing entry that may be used to add a new entry to the
/// forwarding table.
///
/// See [`Entry`] for the type used to represent a route in the forwarding
/// table.
#[derive(Debug, Copy, Clone, Eq, GenericOverIp, PartialEq, Hash)]
#[generic_over_ip(A, IpAddress)]
pub struct AddableEntry<A: IpAddress, D> {
    /// The destination subnet.
    pub subnet: Subnet<A>,
    /// The outgoing interface.
    pub device: D,
    /// Next hop.
    pub gateway: Option<SpecifiedAddr<A>>,
    /// Route metric.
    pub metric: AddableMetric,
}

impl<D, A: IpAddress> AddableEntry<A, D> {
    /// Creates a new [`AddableEntry`] with a specified gateway.
    pub fn with_gateway(
        subnet: Subnet<A>,
        device: D,
        gateway: SpecifiedAddr<A>,
        metric: AddableMetric,
    ) -> Self {
        Self { subnet, device, gateway: Some(gateway), metric }
    }

    /// Creates a new [`AddableEntry`] with a specified device.
    pub fn without_gateway(subnet: Subnet<A>, device: D, metric: AddableMetric) -> Self {
        Self { subnet, device, gateway: None, metric }
    }

    /// Converts the `AddableEntry` to an `Entry`.
    pub fn resolve_metric(self, device_metric: RawMetric) -> Entry<A, D> {
        let Self { subnet, device, gateway, metric } = self;
        let metric = match metric {
            AddableMetric::MetricTracksInterface => Metric::MetricTracksInterface(device_metric),
            AddableMetric::ExplicitMetric(metric) => Metric::ExplicitMetric(metric),
        };
        Entry { subnet, device, gateway, metric }
    }

    /// Maps the device ID held by this `AddableEntry`.
    pub fn map_device_id<D2>(self, f: impl FnOnce(D) -> D2) -> AddableEntry<A, D2> {
        let Self { subnet, device, gateway, metric } = self;
        AddableEntry { subnet, device: f(device), gateway, metric }
    }

    /// Fallibly maps the device ID held by this `AddableEntry`.
    pub fn try_map_device_id<D2, E>(
        self,
        f: impl FnOnce(D) -> Result<D2, E>,
    ) -> Result<AddableEntry<A, D2>, E> {
        let Self { subnet, device, gateway, metric } = self;
        Ok(AddableEntry { subnet, device: f(device)?, gateway, metric })
    }

    /// Sets the generation on an entry.
    pub fn with_generation(self, generation: Generation) -> AddableEntryAndGeneration<A, D> {
        AddableEntryAndGeneration { entry: self, generation }
    }
}

/// An IPv4 forwarding entry or an IPv6 forwarding entry.
#[allow(missing_docs)]
#[derive(Debug, Copy, Clone, Eq, GenericOverIp, PartialEq, Hash)]
#[generic_over_ip()]
pub enum AddableEntryEither<D> {
    V4(AddableEntry<Ipv4Addr, D>),
    V6(AddableEntry<Ipv6Addr, D>),
}

impl<D> AddableEntryEither<D> {
    /// Creates a new [`AddableEntryEither`] with the specified device as the
    /// next hop.
    pub fn without_gateway(subnet: SubnetEither, device: D, metric: AddableMetric) -> Self {
        match subnet {
            SubnetEither::V4(subnet) => {
                AddableEntry::without_gateway(subnet, device, metric).into()
            }
            SubnetEither::V6(subnet) => {
                AddableEntry::without_gateway(subnet, device, metric).into()
            }
        }
    }
}

impl<A: IpAddress, D> From<AddableEntry<A, D>> for AddableEntryEither<D> {
    fn from(entry: AddableEntry<A, D>) -> AddableEntryEither<D> {
        A::Version::map_ip(entry, AddableEntryEither::V4, AddableEntryEither::V6)
    }
}

/// A routing table entry together with the generation it was created in.
#[derive(Debug, Copy, Clone, GenericOverIp)]
#[generic_over_ip(A, IpAddress)]
pub struct AddableEntryAndGeneration<A: IpAddress, D> {
    /// The entry.
    pub entry: AddableEntry<A, D>,
    /// The generation in which it was created.
    pub generation: Generation,
}

/// Wraps a callback to upgrade a "stored" entry to a "live" entry.
#[derive(GenericOverIp)]
#[generic_over_ip(A, IpAddress)]
pub struct EntryUpgrader<'a, A: IpAddress, DeviceId, WeakDeviceId>(
    // TODO(https://fxbug.dev/42148629): Remove or explain #[allow(dead_code)].
    #[allow(dead_code)]
    pub  &'a mut dyn FnMut(
        AddableEntryAndGeneration<A, WeakDeviceId>,
    ) -> Option<EntryAndGeneration<A, DeviceId>>,
);

impl<A: IpAddress, D> From<Entry<A, D>> for AddableEntry<A, D> {
    fn from(Entry { subnet, device, gateway, metric }: Entry<A, D>) -> Self {
        Self { subnet: subnet, device: device, gateway: gateway, metric: metric.into() }
    }
}

/// The metric for an [`Entry`].
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
pub enum Metric {
    /// The entry's metric tracks its interface's routing metric and has the
    /// included value.
    MetricTracksInterface(RawMetric),
    /// The entry's metric was explicitly set to the included value.
    ExplicitMetric(RawMetric),
}

impl Metric {
    /// Returns the underlying value of the `Metric`.
    pub fn value(&self) -> RawMetric {
        match self {
            Self::MetricTracksInterface(value) => *value,
            Self::ExplicitMetric(value) => *value,
        }
    }
}

/// A forwarding entry.
///
/// `Entry` is a `Subnet` with an egress device and optional gateway.
#[derive(Debug, Copy, Clone, Eq, GenericOverIp, PartialEq, Hash)]
#[generic_over_ip(A, IpAddress)]
pub struct Entry<A: IpAddress, D> {
    /// The matching subnet.
    pub subnet: Subnet<A>,
    /// The destination device.
    pub device: D,
    /// An optional gateway if the subnet is not on link.
    // TODO(https://fxbug.dev/42074188): Restrict `gateway` to `UnicastAddr`.
    pub gateway: Option<SpecifiedAddr<A>>,
    /// The metric of the entry.
    pub metric: Metric,
}

/// A forwarding entry with the generation it was created in.
#[derive(Debug, Copy, Clone, GenericOverIp, PartialEq, Eq)]
#[generic_over_ip(A, IpAddress)]
pub struct EntryAndGeneration<A: IpAddress, D> {
    /// The entry.
    pub entry: Entry<A, D>,
    /// The generation.
    pub generation: Generation,
}

impl<A: IpAddress, D: Debug> Display for EntryAndGeneration<A, D> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
        let EntryAndGeneration { entry, generation: Generation(generation) } = self;
        write!(f, "{} (generation = {})", entry, generation)
    }
}

/// Used to compare routes for how early they were added to the table.
///
/// If two routes have the same prefix length and metric, and are both on-link
/// or are both-off-link, then the route with the earlier generation will be
/// preferred.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Generation(u64);

impl Generation {
    /// Returns the initial generation.
    pub fn initial() -> Self {
        Self(0)
    }

    /// Returns the next generation.
    pub fn next(&self) -> Generation {
        let Self(n) = self;
        Generation(n + 1)
    }
}

impl<A: IpAddress, D> Entry<A, D> {
    /// Maps the device ID held by this `Entry`.
    pub fn map_device_id<D2>(self, f: impl FnOnce(D) -> D2) -> Entry<A, D2> {
        let Self { subnet, device, gateway, metric } = self;
        Entry { subnet, device: f(device), gateway, metric }
    }

    /// Sets the generation on an entry.
    pub fn with_generation(self, generation: Generation) -> EntryAndGeneration<A, D> {
        EntryAndGeneration { entry: self, generation }
    }
}

impl<A: IpAddress, D: Debug> Display for Entry<A, D> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
        let Entry { subnet, device, gateway, metric } = self;
        match gateway {
            Some(gateway) => {
                write!(f, "{:?} (via {}) -> {} metric {}", device, gateway, subnet, metric.value())
            }
            None => write!(f, "{:?} -> {} metric {}", device, subnet, metric.value()),
        }
    }
}

/// An IPv4 forwarding entry or an IPv6 forwarding entry.
#[allow(missing_docs)]
#[derive(Debug, Copy, Clone, Eq, GenericOverIp, PartialEq)]
#[generic_over_ip()]
pub enum EntryEither<D> {
    V4(Entry<Ipv4Addr, D>),
    V6(Entry<Ipv6Addr, D>),
}

impl<A: IpAddress, D> From<Entry<A, D>> for EntryEither<D> {
    fn from(entry: Entry<A, D>) -> EntryEither<D> {
        #[derive(GenericOverIp)]
        #[generic_over_ip(I, Ip)]
        struct EntryHolder<I: Ip, D>(Entry<I::Addr, D>);
        A::Version::map_ip(entry, EntryEither::V4, EntryEither::V6)
    }
}

/// `OrderedLocality` provides an implementation of `core::cmp::PartialOrd` for
/// a route's "locality".
// Define an enum, so that `OnLink` routes are sorted before `OffLink` routes.
// See https://doc.rust-lang.org/core/cmp/trait.PartialOrd.html#derivable for
// more details.
#[derive(PartialEq, PartialOrd, Eq, Ord)]
pub(crate) enum OrderedLocality {
    // The route does not have a gateway.
    OnLink,
    // The route does have a gateway.
    OffLink,
}

// `OrderedRoute` provides an implementation of `core::cmp::PartialOrd`
// for routes. Note that the fields are consulted in the order they are
// declared. For more details, see
// https://doc.rust-lang.org/core/cmp/trait.PartialOrd.html#derivable.
#[derive(PartialEq, PartialOrd, Eq, Ord)]
pub(crate) struct OrderedEntry<'a, A: IpAddress, D> {
    // Order longer prefixes before shorter prefixes.
    prefix_len: core::cmp::Reverse<u8>,
    // Order lower metrics before larger metrics.
    metric: u32,
    // Order `OnLink` routes before `OffLink` routes.
    locality: OrderedLocality,
    // Earlier-added routes should come before later ones.
    generation: Generation,
    // To provide a consistent ordering, tiebreak using the remaining fields
    // of the entry.
    subnet_addr: A,
    device: &'a D,
    // Note that while this appears to duplicate the ordering provided by
    // `locality`, it's important that we sort above on presence of the gateway
    // and not on the actual address of the gateway. The latter is only used
    // for tiebreaking at the end to provide a total order. Duplicating it this
    // way allows us to avoid writing a manual `PartialOrd` impl.
    gateway: Option<SpecifiedAddr<A>>,
}

impl<'a, A: IpAddress, D> From<&'a EntryAndGeneration<A, D>> for OrderedEntry<'a, A, D> {
    fn from(entry: &'a EntryAndGeneration<A, D>) -> OrderedEntry<'a, A, D> {
        let EntryAndGeneration { entry: Entry { subnet, device, gateway, metric }, generation } =
            entry;
        OrderedEntry {
            prefix_len: core::cmp::Reverse(subnet.prefix()),
            metric: metric.value().into(),
            locality: gateway.map_or(OrderedLocality::OnLink, |_gateway| OrderedLocality::OffLink),
            generation: *generation,
            subnet_addr: subnet.network(),
            device: &device,
            gateway: *gateway,
        }
    }
}

/// `Ip` extension trait to assist in defining [`NextHop`].
pub trait IpTypesIpExt: packet_formats::ip::IpExt {
    /// A marker type carried by the [`NextHop::Broadcast`] variant to indicate
    /// that it is uninhabited for IPv6.
    type BroadcastMarker: Debug + Copy + Clone + PartialEq + Eq;
}

impl IpTypesIpExt for Ipv4 {
    type BroadcastMarker = ();
}

impl IpTypesIpExt for Ipv6 {
    type BroadcastMarker = Never;
}

/// Wrapper struct to provide a convenient [`GenericOverIp`] impl for use
/// with [`IpTypesIpExt::BroadcastMarker`].
#[derive(GenericOverIp)]
#[generic_over_ip(I, Ip)]
pub struct WrapBroadcastMarker<I: IpTypesIpExt>(pub I::BroadcastMarker);

/// The next hop for a [`Destination`].
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum NextHop<A: IpAddress>
where
    A::Version: IpTypesIpExt,
{
    /// Indicates that the next-hop for a the packet is the remote since it is a
    /// neighboring node (on-link).
    RemoteAsNeighbor,
    /// Indicates that the next-hop is a gateway/router since the remote is not
    /// a neighboring node (off-link).
    Gateway(SpecifiedAddr<A>),
    /// Indicates that the packet should be broadcast rather than sent to a
    /// specific neighbor.
    Broadcast(<A::Version as IpTypesIpExt>::BroadcastMarker),
}

impl<A: IpAddress, NewIp: IpTypesIpExt> GenericOverIp<NewIp> for NextHop<A>
where
    A::Version: IpTypesIpExt,
{
    type Type = NextHop<NewIp::Addr>;
}

impl<A> NextHop<A>
where
    A: IpAddress,
    A::Version: IpTypesIpExt,
{
    pub(crate) fn into_next_hop_and_broadcast_marker(
        self,
        remote_ip: SpecifiedAddr<A>,
    ) -> (SpecifiedAddr<A>, Option<<A::Version as IpTypesIpExt>::BroadcastMarker>) {
        match self {
            NextHop::RemoteAsNeighbor => (remote_ip, None),
            NextHop::Gateway(gateway) => (gateway, None),
            NextHop::Broadcast(marker) => (remote_ip, Some(marker)),
        }
    }
}

/// An IP Address that witnesses properties needed to be routed.
pub type RoutableIpAddr<A> = SocketIpAddr<A>;

/// The resolved route to a destination IP address.
#[derive(Debug, Copy, Clone, PartialEq, Eq, GenericOverIp)]
#[generic_over_ip(I, Ip)]
pub struct ResolvedRoute<I: IpTypesIpExt, D> {
    /// The source address to use when forwarding packets towards the
    /// destination.
    pub src_addr: RoutableIpAddr<I::Addr>,
    /// The device over which this destination can be reached.
    pub device: D,
    /// Present when `device` is loopback with the device that the destination
    /// address is assigned to.
    ///
    /// NB: it's possible that `local_delivery_device` is itself loopback.
    pub local_delivery_device: Option<D>,
    /// The next hop via which this destination can be reached.
    pub next_hop: NextHop<I::Addr>,
}

/// The destination of an outbound IP packet.
///
/// Outbound IP packets are sent to a particular device (specified by the
/// `device` field).
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub(crate) struct Destination<A: IpAddress, D>
where
    A::Version: IpTypesIpExt,
{
    /// Indicates the next hop via which this destination can be reached.
    pub(crate) next_hop: NextHop<A>,
    /// Indicates the device over which this destination can be reached.
    pub(crate) device: D,
}