// An example policy script; see "Policy scripts" in bin/bgp/README.md for
// everything a function can read and change.
//
// A function is given a route and the peer it comes from (or goes to). It
// may change the route, and returns whether the route is taken (or
// announced). Which function is for which peer is said in the
// configuration: import { function: "from_peer" }.
//
// Constants defined here are for every function below.

// Where a route was learned: what the rules for announcing it go by.
const LEARNED_FROM = #{
    customer: "65000:1000",
    peer: "65000:2000",
    provider: "65000:3000",
    route_server: "65000:2000",
};

// A customer's route is preferred to a peer's, and that to a provider's:
// the first earns money, the last costs it.
const PREFERENCE = #{ customer: 300, peer: 200, route_server: 200, provider: 100 };

const BLACKHOLE = "65535:666";
const NO_EXPORT = "65535:65281";

// Routes on their way in.
fn from_peer(route, peer) {
    // Not ours to act on, from just anyone.
    if route.has_community(BLACKHOLE) { return false; }

    // Marks in our own range mean something here: nobody else's word for
    // them is taken.
    route.remove_community("65000:*");
    if peer.role in LEARNED_FROM {
        route.add_community(LEARNED_FROM[peer.role]);
        route.local_pref = PREFERENCE[peer.role];
    }

    // A peer can ask to be a last resort: 65000:80 on a route of its own.
    if route.has_community(peer.asn % 65536, 80) {
        route.local_pref = 80;
    }
    true
}

// Routes on their way out.
fn to_peer(route, peer) {
    if route.has_community(NO_EXPORT) { return false; }

    // Only customers are told what we learned from peers and providers.
    let from_above = route.has_community("65000:2000") || route.has_community("65000:3000");
    if from_above && peer.role != "customer" { return false; }

    // Our marks are our own business.
    route.remove_community("65000:*");

    // Traffic from this one is wanted by another way: the path looks
    // longer to it.
    if peer.name == "backup-transit" { route.prepend(2); }
    true
}