package overlay

import (
	"os"
	"regexp"
	"strings"
)

// Names are how one node reaches another by name rather than by address.
//
// novox/hq 08-connectivity: what the host receives is the resolver's configuration, as files,
// listing every peer's internal name and overlay address. Computed centrally for the same reason
// the peer graph is — it needs every node at once.

// SuffixVar lets a mesh choose what its internal names end in.
const SuffixVar = "MESH_INTERNAL_SUFFIX"

// DefaultSuffix is `.internal`, which IANA reserved for exactly this in 2024. A name under it can
// never collide with a public one, so an internal name that leaks into a public resolver fails
// rather than reaching a stranger's machine.
const DefaultSuffix = "internal"

// HostsPath is where the names go.
//
// This is not the `/etc/hosts` floor the design removes. That floor existed because a node had to
// reach the mesh's database before its own DNS worked — a fallback for a circularity, and the
// circularity is gone. This is the mechanism itself: the complete set of names in this mesh,
// generated whole and owned by the mesh (novox/hq ADR 0011), rather than a patch written
// underneath something else.
//
// A file rather than a resolver daemon, deliberately, for now: it works on every Linux, needs no
// package, and has no failure mode of its own. A daemon becomes necessary when names are wanted
// that are not one-per-node — service names, wildcards — and that is not yet true.
const HostsPath = "/etc/hosts"

// Suffix is what internal names end in.
func Suffix() string {
	if v := strings.TrimSpace(os.Getenv(SuffixVar)); v != "" {
		return strings.TrimPrefix(v, ".")
	}
	return DefaultSuffix
}

// nodeName is what a node may be called, so that it can also be a hostname.
var nodeName = regexp.MustCompile(`^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$`)

// InternalName is a node's name inside the mesh.
func InternalName(node string) string { return node + "." + Suffix() }

// **What remains of a larger file.** The rest wrote /etc/hosts — that is the `node-names` fact now
// (catalogue.FactsInto), computed where the graph lives instead of by a module that ran nothing.
// The naming stays here, because several things compose a node's internal name and one of them
// writing the suffix differently would be a name nothing answers to.