# Service Exposure — typed declarative surface for how a component is reached.
# Sibling of ServiceConcerns (concerns.ncl): where concerns answer "what does
# this service do about tls/dns/backup", exposure answers "from where is it
# reachable, over which datapath, on which ports, terminating TLS where".
#
# It unifies the six exposure idioms that today live in parallel scalar fields
# (gateway_fip · nested gateway{} · gateway_enabled/gateway_ip · private_lb_ip ·
# routes[] · fip_name/external_addr) into one closed record so a misspelled key
# blames at `nickel export` instead of silently deriving.
#
# Records are CLOSED (no `..`): extra/misspelled fields are a contract error.
# The Reachability variants are the exact kinds `prvng net map` classifies, so
# the runtime view and the static schema share one taxonomy.
#
# `Exposure` carries invariants (from_validator) that fail at `nickel export`.
# Each one encodes a real failure this session produced.

let _gateway_l7_kinds = [ 'gateway_l7_public, 'gateway_l7_private, 'gateway_l7_nested ] in
let _public_kinds     = [ 'gateway_l7_public, 'l4_lb_public, 'fip_hostnet ] in
let _member = fun x xs => std.array.any (fun e => e == x) xs in

# Invariants forced when an Exposure is evaluated. Runs after the record shape
# (defaults filled), so `ports`/`strict_chain_clients` are always present.
let _valid_exposure = std.contract.from_validator (fun exp =>
  let k = exp.binding.kind in
  # 1. reg-class bug: a VPN/private hostname must not ride a Cilium Gateway VIP —
  #    the eBPF TPROXY redirect never fires for WireGuard host-netns traffic.
  if (exp.surface == 'vpn || exp.surface == 'private) && (_member k _gateway_l7_kinds) then
    'Error { message = "vpn/private surface cannot use a gateway_l7 binding: Cilium Gateway VIPs are unreachable from the WireGuard datapath (the reg bug). Use 'l4_host_router or 'l4_lb." }
  # 2. a public hostname must land on a public path.
  else if exp.surface == 'public && !(_member k _public_kinds) then
    'Error { message = "public surface must bind via 'gateway_l7_public, 'l4_lb_public or 'fip_hostnet." }
  # 2b. a shared-FIP gateway binding must name the FIP it rides.
  else if k == 'gateway_l7_public && !(std.record.has_field "fip_name" exp.binding) then
    'Error { message = "'gateway_l7_public binding must declare binding.fip_name." }
  # 3. Sozu/lian-build failure: strict-chain clients must terminate on a hop we
  #    control the chain on ('pod_terminate), never at the shared Gateway.
  else if exp.strict_chain_clients && !(std.array.all (fun p => p.tls != 'gateway_terminate) exp.ports) then
    'Error { message = "strict_chain_clients forbids tls='gateway_terminate: the terminating hop must serve the full chain (Sozu leaf-only broke lian-build pushes to reg). Use tls='pod_terminate." }
  else 'Ok
) in

{
  # === Enums ================================================================

  # Intended audience / datapath the hostnames must be reachable from. This is
  # the axis that no existing field captures: `vpn` = reachable over WireGuard.
  # Distinct from security.posture (public/private/internal), which states intent
  # but not the datapath that actually carries the traffic.
  Surface = [| 'cluster, 'private, 'vpn, 'public |],

  # How entry traffic lands on the workload. One variant per idiom found in the
  # census; the two Cilium-Gateway variants are split public/private because they
  # sit on different VLANs with different WireGuard reachability (the reg-class bug
  # lives entirely in the gateway_l7_* variants).
  Reachability = [|
    'gateway_l7_public,   # shared-FIP Cilium Gateway on the public VLAN VIP (gateway_fip / gateway_enabled)
    'gateway_l7_private,  # private Cilium Gateway (private_gateway_*): unreachable from WireGuard datapath
    'gateway_l7_nested,   # nested gateway{}/tcp_gateway{} block (radicle)
    'l4_host_router,      # Sozu private_ingress routes[]: L4 LB DNAT, WireGuard-reachable
    'l4_lb,               # per-service private LoadBalancer (private_lb_ip)
    'l4_lb_public,        # public LoadBalancer via LB-IPAM (lb_ipam_ip)
    'fip_hostnet,         # dedicated FIP / hostNetwork (fip_name / external_addr / host_network)
    'cluster,             # ClusterIP only — flat wuwei, no external entry
  |],

  # Where the TLS session terminates. Only modes observed in the current census
  # are variants; `gateway_mode` is always "terminate" today, no passthrough
  # exists. `'passthrough` is intentionally absent until a component declares it —
  # adding a speculative variant would let invariants pass on unobserved states.
  TlsMode = [|
    'gateway_terminate,   # Cilium Gateway/Envoy terminates (gateway_mode = "terminate")
    'pod_terminate,       # the workload pod terminates (pod_tls, sozu sidecar)
    'sidecar_reload,      # a reloader sidecar rotates the cert in place (tls_rotation = 'reloader)
    'none,                # no TLS at this hop (plain HTTP / cluster-internal)
  |],

  # === Records (all closed) =================================================

  PortMap = {
    name     | String | optional | doc "Human label (e.g. \"https\", \"ssh\", \"smtp\")",
    listen   | Number | doc "Port the entry point listens on",
    target   | Number | doc "Container/service port traffic is forwarded to",
    protocol | [| 'TCP, 'UDP |] | default = 'TCP,
    tls      | TlsMode | doc "TLS termination for this port" | default = 'none,
  },

  # The entry point: which datapath, and the statically-known address/name when
  # there is one. entry_ip is optional because FIP-backed entries only resolve
  # to a concrete IP at the cluster (surfaced by `prvng net map --live`).
  Binding = {
    kind     | Reachability,
    entry_ip | String | optional | doc "VIP / LoadBalancer IP when known at eval time",
    fip_name | String | optional | doc "Hetzner FIP resource name (gateway_l7_public, fip_hostnet)",
    node     | String | optional | doc "Pinned node for hostNetwork / FIP-follows-pod",
  },

  # One reachability path for a set of hostnames. A service with both a public
  # gateway path and a VPN L4 path declares two Exposure entries.
  ExposureShape = {
    hostnames | Array String | doc "FQDNs that resolve to this binding",
    surface   | Surface,
    binding   | Binding,
    ports     | Array PortMap | default = [],
    strict_chain_clients | Bool
      | doc "Clients require the full cert chain (not just the leaf) — forbids terminating on a hop that serves an incomplete chain"
      | default = false,
    ingress_restrictions | Array String
      | doc "Source constraints (CIDRs, NetworkPolicy refs) applied at the entry point"
      | default = [],
    dns_zone | String
      | doc "Explicit split-DNS zone for these hostnames; defaults to the hostname minus its first label (apex domains must set it)"
      | optional,
  },

  # The public contract: shape + invariants. `Array Exposure` in ServiceExposure
  # forces every entry through both, so a bad surface/kind pair fails export.
  Exposure = std.contract.Sequence [ ExposureShape, _valid_exposure ],

  ServiceExposure = {
    service    | String,
    namespace  | String,
    exposures  | Array Exposure,
  },

  # === Builders =============================================================
  # Mirror concerns.ncl's builder style: components/migrations construct entries
  # without repeating the Binding plumbing.

  gateway_public = fun fip hostnames ports => {
    surface = 'public,
    binding = { kind = 'gateway_l7_public, fip_name = fip },
    ports   = ports,
  },

  gateway_private = fun entry hostnames ports => {
    surface = 'vpn,
    binding = { kind = 'gateway_l7_private, entry_ip = entry },
    ports   = ports,
  },

  l4_private = fun entry hostnames ports => {
    surface = 'vpn,
    binding = { kind = 'l4_lb, entry_ip = entry },
    ports   = ports,
  },

  host_router = fun entry hostnames ports => {
    surface = 'vpn,
    binding = { kind = 'l4_host_router, entry_ip = entry },
    ports   = ports,
  },

  cluster_only = fun hostnames ports => {
    surface = 'cluster,
    binding = { kind = 'cluster },
    ports   = ports,
  },

  # Build a host-router ServiceExposure from a list of hostnames served by one
  # L4 entry point (e.g. the Sozu private_ingress at .6). One vpn exposure per
  # host; used as the single source that both routes[] and dns_internal follow,
  # so a fresh deploy cannot drift between the router config and the split DNS.
  host_router_exposure = fun svc ns ip hs =>
    {
      service   = svc,
      namespace = ns,
      exposures =
        std.array.map
          (fun h => {
            hostnames = [h],
            surface   = 'vpn,
            binding   = { kind = 'l4_host_router, entry_ip = ip },
            ports     = [{ name = "https", listen = 443, target = 443, tls = 'pod_terminate }],
          })
          hs,
    } | ServiceExposure,

  # === Derivation ===========================================================
  # Split-DNS routes derived from the exposure surface, so `dns_internal` stops
  # being a hand-maintained parallel field. Emits { host, zone, target, ttl } —
  # the exact shape dns_private.make_route produces — for every hostname of every
  # exposure that has a statically-known entry_ip. Zone = explicit dns_zone, or
  # the hostname minus its first label. Exposures with no entry_ip (pure-FIP,
  # resolved at the cluster) contribute nothing.
  derive_dns_internal = fun svc_exp =>
    std.array.flat_map
      (fun exp =>
        if std.record.has_field "entry_ip" exp.binding then
          let zone_of = fun h =>
            if std.record.has_field "dns_zone" exp then exp.dns_zone
            else
              let parts = std.string.split "." h in
              std.string.join "." (std.array.slice 1 (std.array.length parts) parts)
          in
          std.array.map
            (fun h => { host = h, zone = zone_of h, target = exp.binding.entry_ip, ttl = 300 })
            exp.hostnames
        else [])
      svc_exp.exposures,
}