package broker

import (
	"regexp"
	"strings"
)

// A tool call names its caller (novox/hq issue 365, by ADR 0259 §3's precedent for asks).
//
//	mesh.mod.<module>.call.<tool>[.<node>].<caller>
//	mesh.seat.<seat>.call.<verb>[.<node>].<caller>
//
// The last token is the bus user that published the call, and each user is granted these subjects with its own
// name there and no other — the caller is a fact the server enforces, and the tool runtime hands it to the
// module from the subject a call arrived on (mesh-tools node-tools internal/bus caller.go holds the same shape).
//
// **A kind of its own, `call`, not the `tool` subject with a token appended.** Every grant to call a tool is a
// wildcard over the `tool` kind — `.tool.<t>.*` for the instance on any machine, `mesh.mod.*.tool.>` for every
// tool — and either would match a `tool` subject with any caller appended, so a caller could name another.
// Under `call` nothing is granted but the caller-named subjects. No stream's filter covers it: a tool call is
// never persisted (design 25 §3).
//
// **Derived from the `tool` grants, in one place** (callerNamed): wherever a principal may call or answer a
// tool, it may call it in its own name, or answer it naming any caller — so no kind of principal is left
// unable to call in its own name, and a new grant to call is one in both shapes by construction.
//
// The `tool` grants stay beside these for one release, so every caller and every runtime moves without a gap:
// their retirement is hq issue 464.
const CallKind = "call"

var userName = regexp.MustCompile(`^[A-Za-z0-9_-]+(\.[A-Za-z0-9_-]+)*$`)

// CallerToken is a bus user's name as the last token of a call it publishes: each dot written `~`, which no part
// of a user's name may hold (safeSubject), so the token names that user and no other. "" for a name that is not
// a user's.
func CallerToken(user string) string {
	if !userName.MatchString(user) {
		return ""
	}
	return strings.ReplaceAll(user, ".", "~")
}

// toolGrant splits a grant on the `tool` kind — `mesh.mod.<m>.tool.<rest>` or `mesh.seat.<s>.tool.<rest>`, any
// part possibly a wildcard — at the kind; ok is false for any other subject.
func toolGrant(subject string) (head, rest string, ok bool) {
	parts := strings.SplitN(subject, ".", 5)
	if len(parts) != 5 || parts[0] != "mesh" || (parts[1] != "mod" && parts[1] != "seat") || parts[3] != "tool" ||
		parts[2] == "" || parts[4] == "" {
		return "", "", false
	}
	return parts[0] + "." + parts[1] + "." + parts[2], parts[4], true
}

// CalledSubject is where a call to a tool subject goes naming its caller; "" when the subject is not a tool's
// or the user is not a bus user.
func CalledSubject(subject, user string) string {
	head, rest, ok := toolGrant(subject)
	token := CallerToken(user)
	if !ok || token == "" || strings.ContainsAny(rest, "*>") {
		return ""
	}
	return head + "." + CallKind + "." + rest + "." + token
}

// CalledPattern is what a holder answering a tool subject also subscribes, to hear the calls that name their
// caller: the same address under the `call` kind, any caller last. "" for a subject that is not a tool's.
func CalledPattern(subject string) string {
	head, rest, ok := toolGrant(subject)
	if !ok || strings.ContainsAny(rest, "*>") {
		return ""
	}
	return head + "." + CallKind + "." + rest + ".*"
}

// calledPublish is a grant to call on the `tool` kind, as the same grant in the caller's own name: its last
// token the caller's, and nothing that reaches past it. A `>` is every tail a call carries — the tool alone or
// the tool and the machine — so it becomes both, each ending in the caller.
func calledPublish(grant, token string) []string {
	head, rest, ok := toolGrant(grant)
	if !ok || token == "" {
		return nil
	}
	base := head + "." + CallKind + "."
	switch {
	case rest == ">":
		return []string{base + "*." + token, base + "*.*." + token}
	case strings.HasSuffix(rest, ".>"):
		return []string{base + strings.TrimSuffix(rest, ">") + "*." + token}
	}
	return []string{base + rest + "." + token}
}

// calledSubscribe is a grant to answer on the `tool` kind, as the same grant for the calls naming any caller.
func calledSubscribe(grant string) []string {
	head, rest, ok := toolGrant(grant)
	if !ok {
		return nil
	}
	base := head + "." + CallKind + "."
	if strings.HasSuffix(rest, ">") {
		return []string{base + rest}
	}
	return []string{base + rest + ".*"}
}

// callerNamed adds, beside a principal's grants on the `tool` kind, the same grants under `call`: to publish in
// its own name, to subscribe naming anybody.
func callerNamed(user string, pub, sub []string) ([]string, []string) {
	token := CallerToken(user)
	for _, g := range pub {
		pub = append(pub, calledPublish(g, token)...)
	}
	for _, g := range sub {
		sub = append(sub, calledSubscribe(g)...)
	}
	return unique(pub), unique(sub)
}