package console

// The mesh's tools found by address, not announced whole (novox/hq ADR 0195, to-be 34 §3a).
//
// The console announces six tools — five to find and call, and mesh_runtimes to say which runtimes
// discovery heard. Everything the mesh answers is reached through them by one address per layer:
//
//	<seat>.<verb>              a seat held once for the mesh — its holder answers
//	<node>/<seat>.<verb>       a seat held once per machine — that machine's holder answers
//	<node>/<module>.<tool>     a module assigned to a machine — that assignment answers
//	<module>.<tool>            also, for a module whose instances are interchangeable (ADR 0160)
//
// A module that is not interchangeable is called with its machine or refused, naming the machines
// it runs on: "whichever answers" is no answer for state a machine holds.
//
// Every discovery verb asks the mesh when it is called — kept a few seconds at most, never for a
// session — so a tool that arrived a minute ago is found without the client reconnecting.

import (
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/novox/mesh-tools/node-tools/internal/announce"
	"github.com/novox/mesh-tools/node-tools/internal/bus"
)

// IndexKept is how long what the mesh answered is kept before it is asked again: long enough that
// one agent turn's search, describe and call ask once, short enough that nothing goes stale.
var IndexKept = 5 * time.Second

// The six tools the console announces. Names of the API's kind — letters, digits, `_`, `-`.
const (
	verbOverview = "mesh_overview"
	verbMachine  = "mesh_machine"
	verbSearch   = "mesh_search"
	verbDescribe = "mesh_describe"
	verbCall     = "mesh_call"
	verbRuntimes = "mesh_runtimes"
)

// searchCap is how many matches a search answers before it says how many more there were.
const searchCap = 25

const grammar = "Addresses: `<seat>.<verb>` for a seat held once for the mesh (e.g. `mesh-controller.nodes`); " +
	"`<node>/<seat>.<verb>` for a seat every machine holds (e.g. `ace/node-packet-filter.rules`); " +
	"`<node>/<module>.<tool>` for a module on one machine (e.g. `novox/postgres.postgres_list_databases`); " +
	"and `<module>.<tool>` also for a module whose instances are interchangeable."

// discovery is the six tools as tools/list announces them.
func discovery() []map[string]any {
	str := func(desc string) map[string]any { return map[string]any{"type": "string", "description": desc} }
	obj := func(props map[string]any, required ...string) map[string]any {
		s := map[string]any{"type": "object", "properties": props}
		if len(required) > 0 {
			s["required"] = required
		}
		return s
	}
	return []map[string]any{
		{"name": verbOverview, "inputSchema": obj(map[string]any{}),
			"description": "The mesh at a glance: the seats it holds once for the whole mesh with their verbs, the seats " +
				"every machine holds, and its machines. Start here, then `mesh_machine` for one machine. " + grammar},
		{"name": verbMachine, "inputSchema": obj(map[string]any{"node": str("the machine, as mesh_overview names it")}, "node"),
			"description": "One machine: the seats it holds with their verbs, and the modules assigned to it with their tools — " +
				"each with the address to describe or call it by. " + grammar},
		{"name": verbSearch, "inputSchema": obj(map[string]any{"query": str("words to find in tool names and descriptions, e.g. `postgres databases`")}, "query"),
			"description": "Find tools anywhere in the mesh by words: every match's address and a line of what it does, across the " +
				"mesh's seats, the machines' seats and every module on every machine. " + grammar},
		{"name": verbDescribe, "inputSchema": obj(map[string]any{"address": str("the tool's address")}, "address"),
			"description": "What one tool does and the arguments it takes, as a JSON schema. The machine is in the address, " +
				"never an argument. " + grammar},
		{"name": verbCall, "inputSchema": obj(map[string]any{
			"address":   str("the tool's address"),
			"arguments": map[string]any{"type": "object", "description": "the tool's arguments, as mesh_describe gives its schema"},
		}, "address"),
			"description": "Call one tool by its address with its arguments; the answer says which machine gave it. " + grammar},
		{"name": verbRuntimes, "inputSchema": obj(map[string]any{}),
			"description": "Which runtimes answered discovery, asked now: for each, its machine, how long its answer took to " +
				"arrive, its size in bytes, how many modules and tools it announced, whether it was shortened to fit the " +
				"bus, and when it was last heard — and every runtime or machine expected that was not heard. Read-only; " +
				"for when an address is said to be missing or on another machine."},
	}
}

func isDiscovery(name string) bool {
	switch name {
	case verbOverview, verbMachine, verbSearch, verbDescribe, verbCall, verbRuntimes:
		return true
	}
	return false
}

// seatInfo is a seat as the mesh's records define it, and who holds it where.
type seatInfo struct {
	Seat    string
	Scope   string // "mesh" or "node"
	Verbs   []Tool
	Holders []holder
}

type holder struct {
	Module string `json:"module"`
	Node   string `json:"node"`
}

// moduleInfo is a module that answers tools: where it runs, whether any instance will do, and its
// tools as one of its instances described them.
type moduleInfo struct {
	Module          string
	On              []string
	Interchangeable bool
	Tools           []Tool
}

// index is what the mesh answered about itself, at one moment.
type index struct {
	Seats        []seatInfo
	Machines     []string
	Modules      map[string]*moduleInfo
	NotAnswering []string
	Listing      *Listing // the flat catalogue the call path resolves subjects with
	Discovery    announce.Discovery
	// Recorded is where the controller's records place each module that declares tools.
	Recorded map[string][]string
	// Unheard is every runtime whose answer this index lacks: it said it was there and did not say
	// what it serves in time, or it answered before and not now. An address it might answer is never
	// called missing while it is here (2026-10-05).
	Unheard []unheard
}

// unheard is one runtime discovery did not hear in full, and why.
type unheard struct {
	Runtime string `json:"runtime"`
	Machine string `json:"machine,omitempty"`
	Why     string `json:"why"`
}

// unheardOn is what is unheard on one machine; with no machine, everything unheard.
func (x *index) unheardOn(node string) []unheard {
	var out []unheard
	for _, u := range x.Unheard {
		if node == "" || u.Machine == node || u.Machine == "" {
			out = append(out, u)
		}
	}
	return out
}

// sayUnheard is the unheard, as a sentence's end.
func sayUnheard(us []unheard) string {
	var parts []string
	for _, u := range us {
		who := u.Runtime
		if u.Machine != "" {
			who += " on " + u.Machine
		}
		parts = append(parts, who+" ("+u.Why+")")
	}
	return strings.Join(parts, "; ")
}

func (x *index) seat(name string) *seatInfo {
	for i := range x.Seats {
		if x.Seats[i].Seat == name {
			return &x.Seats[i]
		}
	}
	return nil
}

func findTool(tools []Tool, name string) *Tool {
	for i := range tools {
		if tools[i].Name == name {
			return &tools[i]
		}
	}
	return nil
}

// controllerOutput is a controller seat verb's answer: the command's printed output.
func controllerOutput(conn *bus.Conn, verb string) (string, error) {
	got, err := conn.Ask("seat:mesh-controller."+verb, map[string]any{}, "")
	if err != nil {
		return "", err
	}
	var r struct {
		Output string `json:"output"`
		OK     *bool  `json:"ok"`
	}
	if json.Unmarshal(got.Result, &r) != nil {
		return "", fmt.Errorf("mesh-controller.%s answered something that is not its output", verb)
	}
	if r.OK != nil && !*r.OK {
		return "", fmt.Errorf("mesh-controller.%s: %s", verb, strings.TrimSpace(r.Output))
	}
	return r.Output, nil
}

// jsonIn is the JSON document a command printed, after any lines it said first: a seat verb runs
// the controller's command, and a command may warn before it answers.
func jsonIn(output string) string {
	t := strings.TrimSpace(output)
	if strings.HasPrefix(t, "{") || strings.HasPrefix(t, "[") {
		return t
	}
	for _, open := range []string{"\n{", "\n["} {
		if i := strings.Index(output, open); i >= 0 {
			return strings.TrimSpace(output[i+1:])
		}
	}
	return ""
}

// recordedModule is a module as the controller's records hold it (`module list --json`): where the
// mesh assigned it, and whether it declares tools — what should announce itself, and where.
type recordedModule struct {
	Module string   `json:"module"`
	On     []string `json:"on"`
	Tools  bool     `json:"tools"`
}

// recordedMachine is a machine as the controller's records hold it (`node list --json`).
type recordedMachine struct {
	Name string `json:"name"`
}

// indexOn asks the mesh what it holds (novox/hq ADR 0197): what answers, from every runtime's own
// announcement on the bus — one `$SRV.INFO` request — and what should, from the controller's records
// read as JSON. Nothing is inferred from a roster and nothing is parsed from print.
func indexOn(conn *bus.Conn) (*index, error) {
	var wg sync.WaitGroup
	var nodesOut, modulesOut string
	wg.Add(2)
	go func() { defer wg.Done(); nodesOut, _ = controllerOutput(conn, "nodes") }()
	go func() { defer wg.Done(); modulesOut, _ = controllerOutput(conn, "modules") }()
	d, err := announce.Gather(conn)
	wg.Wait()
	if err != nil {
		return nil, err
	}

	var endpoints []announce.Endpoint
	for _, h := range d.Heard {
		endpoints = append(endpoints, announce.Endpoints(h.Info)...)
	}
	x, announced, machines := indexOfEndpoints(endpoints)
	l := x.Listing
	x.Discovery = d
	for _, s := range d.Silent {
		x.Unheard = append(x.Unheard, unheard{Runtime: s.Name, Machine: s.Machine,
			Why: fmt.Sprintf("it answered PING; what it serves did not arrive within %s", announce.Patience)})
	}

	// What should have answered: every assignment of a module that declares tools. Silence is named;
	// a module with no tools is never a name here.
	var recorded []recordedModule
	if json.Unmarshal([]byte(jsonIn(modulesOut)), &recorded) == nil {
		for _, m := range recorded {
			if !m.Tools {
				continue
			}
			x.Recorded[m.Module] = append([]string{}, m.On...)
			for _, n := range m.On {
				// A holder of a seat held once for the mesh announces no machine — the seat is the mesh's,
				// not a machine's — so what it announced without one answers for wherever it is assigned.
				if !announced[m.Module][n] && !announced[m.Module][""] {
					l.NotAnswering = append(l.NotAnswering, m.Module+" on "+n)
				}
			}
		}
	} else {
		l.NotAnswering = append(l.NotAnswering, "mesh-controller (its records of the modules did not answer, so what is missing cannot be said)")
	}
	for _, u := range x.Unheard {
		l.NotAnswering = append(l.NotAnswering, "the runtime "+sayUnheard([]unheard{u}))
	}
	sort.Strings(l.NotAnswering)
	x.NotAnswering = l.NotAnswering

	var known []recordedMachine
	if json.Unmarshal([]byte(jsonIn(nodesOut)), &known) == nil {
		for _, n := range known {
			if n.Name != "" {
				machines[n.Name] = true
			}
		}
	}
	for n := range machines {
		x.Machines = append(x.Machines, n)
	}
	sort.Strings(x.Machines)
	return x, nil
}

func containsHolder(hs []holder, h holder) bool {
	for _, x := range hs {
		if x == h {
			return true
		}
	}
	return false
}

func (s *Surface) index() (*index, error) { return s.indexAsked(false) }

// indexAsked is what the mesh answered, asked again when `fresh` or when the kept answer is old.
func (s *Surface) indexAsked(fresh bool) (*index, error) {
	s.mu.Lock()
	if !fresh && s.idx != nil && time.Since(s.idxAt) <= IndexKept {
		x := s.idx
		s.mu.Unlock()
		return x, nil
	}
	s.mu.Unlock()
	x, err := indexOn(s.conn)
	if err != nil {
		return nil, err
	}
	s.mu.Lock()
	s.remember(x)
	s.idx, s.idxAt = x, time.Now()
	s.mu.Unlock()
	return x, nil
}

// indexOfEndpoints is what the announced endpoints say: every seat with its verbs and holders, every
// module with its tools and machines, the flat listing, and which module announced on which machine.
func indexOfEndpoints(endpoints []announce.Endpoint) (*index, map[string]map[string]bool, map[string]bool) {
	l := &Listing{Tools: []Tool{}, NotAnswering: []string{}}
	x := &index{Modules: map[string]*moduleInfo{}, Listing: l, Recorded: map[string][]string{}}
	announced := map[string]map[string]bool{} // module → node → announced something
	seats := map[string]*seatInfo{}
	// <module>.<tool>, or seat:<seat>.<verb>, → index in l.Tools. **Apart**, because a seat and a module may
	// share a name — mesh-delivery is the delivery's seat and the module holding it (novox/hq ADR 0239), and
	// the module answers the seat's verbs with tools of the same names: in one namespace the module's tool
	// took the key first, and the seat was listed with no verb at all (novox/hq issue 287).
	toolAt := map[string]int{}
	machines := map[string]bool{}
	for _, e := range endpoints {
		if e.Node != "" {
			machines[e.Node] = true
		}
		if announced[e.Module] == nil {
			announced[e.Module] = map[string]bool{}
		}
		announced[e.Module][e.Node] = true
		switch e.Kind {
		case announce.KindSeat:
			st := seats[e.Seat]
			if st == nil {
				st = &seatInfo{Seat: e.Seat, Scope: e.Scope}
				seats[e.Seat] = st
			}
			if st.Scope != "node" && e.Scope == "node" {
				st.Scope = "node"
			}
			h := holder{Module: e.Module, Node: e.Node}
			if !containsHolder(st.Holders, h) {
				st.Holders = append(st.Holders, h)
			}
			key := "seat:" + e.Seat + "." + e.Tool
			if _, have := toolAt[key]; !have {
				toolAt[key] = len(l.Tools)
				t := Tool{Module: e.Seat, Name: e.Tool, Description: e.Description, Input: e.Schema, Seat: true, Scope: st.Scope}
				l.Tools = append(l.Tools, t)
				st.Verbs = append(st.Verbs, t)
			}
		case announce.KindTool:
			m := x.Modules[e.Module]
			if m == nil {
				m = &moduleInfo{Module: e.Module}
				x.Modules[e.Module] = m
			}
			if e.Node != "" && !contains(m.On, e.Node) {
				m.On = append(m.On, e.Node)
			}
			m.Interchangeable = m.Interchangeable || e.Interchangeable
			key := e.Module + "." + e.Tool
			i, have := toolAt[key]
			if !have {
				i = len(l.Tools)
				toolAt[key] = i
				l.Tools = append(l.Tools, Tool{Module: e.Module, Name: e.Tool, Description: e.Description, Input: e.Schema})
			}
			if !contains(l.Tools[i].Subjects, e.Subject) {
				l.Tools[i].Subjects = append(l.Tools[i].Subjects, e.Subject)
			}
		}
	}
	// A tool's subjects as a call looks them up: the plain one any instance answers first, then each
	// machine's.
	for i := range l.Tools {
		t := &l.Tools[i]
		if t.Seat {
			continue
		}
		plain := "mesh.mod." + t.Module + ".tool." + t.Name
		sort.SliceStable(t.Subjects, func(a, b int) bool {
			if (t.Subjects[a] == plain) != (t.Subjects[b] == plain) {
				return t.Subjects[a] == plain
			}
			return t.Subjects[a] < t.Subjects[b]
		})
	}
	for _, t := range l.Tools {
		if !t.Seat {
			x.Modules[t.Module].Tools = append(x.Modules[t.Module].Tools, t)
		}
	}
	for _, m := range x.Modules {
		sort.Strings(m.On)
	}
	for _, st := range seats {
		sort.Slice(st.Holders, func(a, b int) bool { return st.Holders[a].Node < st.Holders[b].Node })
		x.Seats = append(x.Seats, *st)
	}
	sort.Slice(x.Seats, func(i, j int) bool { return x.Seats[i].Seat < x.Seats[j].Seat })
	sort.SliceStable(l.Tools, func(i, j int) bool {
		return l.Tools[i].Module+"."+l.Tools[i].Name < l.Tools[j].Module+"."+l.Tools[j].Name
	})
	return x, announced, machines
}

// target is what an address resolves to.
type target struct {
	Address string
	Key     string // the call key the existing path takes: seat:<s>.<v>[@node] or <m>.<t>[@node]
	Name    string // <seat>.<verb> or <module>.<tool>, for the listing's subject lookup
	Node    string
	Tool    Tool
	Seat    bool
}

// resolve turns an address into exactly one target, or says why it cannot.
func resolve(x *index, address string) (target, error) {
	address = strings.TrimSpace(address)
	node, rest, hasNode := strings.Cut(address, "/")
	if !hasNode {
		rest, node = address, ""
	}
	dot := strings.Index(rest, ".")
	if dot <= 0 || dot == len(rest)-1 || strings.Contains(rest, "/") {
		return target{}, fmt.Errorf("%q is not an address. %s", address, grammar)
	}
	prefix, name := rest[:dot], rest[dot+1:]

	s := x.seat(prefix)
	if s != nil && x.Modules[prefix] != nil && findTool(x.Modules[prefix].Tools, name) != nil {
		// **A seat and a module of one name** (novox/hq issue 287): mesh-delivery is the delivery's seat and
		// the module holding it. The module's tool is meant when the seat has no such verb, or when a machine
		// is named for a seat held once for the mesh — `<node>/<module>.<tool>` is a module on one machine.
		if findTool(s.Verbs, name) == nil || (node != "" && s.Scope != "node") {
			s = nil
		}
	}
	if s != nil {
		verb := findTool(s.Verbs, name)
		if verb == nil {
			if len(s.Verbs) == 0 {
				return target{}, fmt.Errorf("the seat %s has no verb %s: its holder announced none", prefix, name)
			}
			return target{}, fmt.Errorf("the seat %s has no verb %s; it has %s", prefix, name, toolNames(s.Verbs))
		}
		if s.Scope == "node" {
			if node == "" {
				return target{}, fmt.Errorf("%s is held once per machine: write <node>/%s — it is held on %s",
					prefix, rest, orNobody(nodesOf(s.Holders)))
			}
			return target{Address: node + "/" + rest, Key: "seat:" + rest + "@" + node, Name: rest, Node: node, Tool: *verb, Seat: true}, nil
		}
		if node != "" {
			return target{}, fmt.Errorf("%s is held once for the whole mesh: write %s, without a machine", prefix, rest)
		}
		return target{Address: rest, Key: "seat:" + rest, Name: rest, Tool: *verb, Seat: true}, nil
	}

	m := x.Modules[prefix]
	if m == nil {
		if on := x.Recorded[prefix]; len(on) > 0 {
			why := "it did not announce itself on the bus"
			if us := x.unheardOnAny(on); len(us) > 0 {
				why = "discovery did not hear in full from " + sayUnheard(us)
			}
			return target{}, fmt.Errorf("%s is assigned to %s in the mesh's records, but nothing that answered discovery serves it: %s. "+
				"Ask again in a moment; mesh_runtimes shows which runtimes answered", prefix, strings.Join(on, ", "), why)
		}
		if len(x.Unheard) > 0 {
			return target{}, fmt.Errorf("nothing that answered discovery is called %s, but not every runtime answered: %s — "+
				"%s may be theirs. Ask again in a moment; mesh_runtimes shows which runtimes answered", prefix, sayUnheard(x.Unheard), prefix)
		}
		return target{}, fmt.Errorf("nothing in the mesh is called %s: no seat, and no module that answers tools. "+
			"mesh_search finds a tool by words", prefix)
	}
	tool := findTool(m.Tools, name)
	if tool == nil {
		return target{}, fmt.Errorf("%s has no tool %s; it has %s", prefix, name, toolNames(m.Tools))
	}
	if node == "" {
		if !m.Interchangeable {
			return target{}, fmt.Errorf("%s keeps state on each machine it runs on, so a call names the machine: "+
				"write <node>/%s — it runs on %s", prefix, rest, orNobody(m.On))
		}
		return target{Address: rest, Key: rest, Name: rest, Tool: *tool}, nil
	}
	if len(m.On) > 0 && !contains(m.On, node) {
		if us := x.unheardOn(node); len(us) > 0 || contains(x.Recorded[prefix], node) {
			why := "it did not announce itself there"
			if len(us) > 0 {
				why = "discovery did not hear in full from " + sayUnheard(us)
			}
			return target{}, fmt.Errorf("%s on %s did not answer discovery: %s. It was heard on %s. "+
				"Ask again in a moment; mesh_runtimes shows which runtimes answered", prefix, node, why, orNobody(m.On))
		}
		return target{}, fmt.Errorf("%s does not run on %s; it runs on %s", prefix, node, orNobody(m.On))
	}
	return target{Address: node + "/" + rest, Key: rest + "@" + node, Name: rest, Node: node, Tool: *tool}, nil
}

// unheardOnAny is what is unheard on any of these machines.
func (x *index) unheardOnAny(nodes []string) []unheard {
	var out []unheard
	for _, u := range x.Unheard {
		if u.Machine == "" || contains(nodes, u.Machine) {
			out = append(out, u)
		}
	}
	return out
}

func contains(xs []string, s string) bool {
	for _, x := range xs {
		if x == s {
			return true
		}
	}
	return false
}

func toolNames(ts []Tool) string {
	names := make([]string, 0, len(ts))
	for _, t := range ts {
		names = append(names, t.Name)
	}
	sort.Strings(names)
	return strings.Join(names, ", ")
}

func nodesOf(hs []holder) []string {
	var out []string
	for _, h := range hs {
		if h.Node != "" && !contains(out, h.Node) {
			out = append(out, h.Node)
		}
	}
	sort.Strings(out)
	return out
}

func orNobody(nodes []string) string {
	if len(nodes) == 0 {
		return "no machine the mesh knows of"
	}
	return strings.Join(nodes, ", ")
}

// firstLine is a description's first line, for a list.
func firstLine(s string) string {
	s = strings.TrimSpace(s)
	if i := strings.IndexAny(s, "\n"); i >= 0 {
		s = s[:i]
	}
	if len(s) > 160 {
		s = s[:157] + "…"
	}
	return s
}

// schemaAsPassed is a tool's schema as an agent passes it at this address. Where the address names
// the machine, `node` is taken out: the machine is in the address. Where it does not — a seat held
// once for the mesh, or an interchangeable module — `node` is the tool's own argument, and is kept.
//
// **Taking it out everywhere made the mesh's own verbs lie** (novox/hq issue 244): the controller's
// `push`, `plan`, `assign`, `pin` and `settings` take the machine they act on as `node`, and were
// described without it — `push` as taking nothing at all, so a push naming one machine arrived as a
// push of every machine behind.
func schemaAsPassed(t target) map[string]any {
	if t.Node == "" {
		return asSchema(t.Tool.Input)
	}
	return schemaWithoutNode(t.Tool.Input)
}

// argumentsAsSent are a call's arguments as the tool at this address receives them, or why the call
// is refused. **Nothing given is dropped without a word** (novox/hq issue 244):
//   - where the address names the machine, a `node` naming the same machine is redundant and taken
//     out; one naming another machine is refused — which of the two was meant is not guessed;
//   - where it does not, `node` is the tool's own argument and goes to it like any other;
//   - a seat's schema is the mesh's record of the verb, so an argument a seat's verb does not
//     declare is refused here, naming it, rather than sent to be passed over.
func argumentsAsSent(t target, given map[string]any) (map[string]any, error) {
	args := map[string]any{}
	for k, v := range given {
		args[k] = v
	}
	if n, has := args["node"]; has && t.Node != "" {
		if named, _ := n.(string); strings.TrimSpace(named) != t.Node {
			return nil, fmt.Errorf("%s names the machine %s in its address and %v in its arguments: say it once, in the address",
				t.Address, t.Node, n)
		}
		delete(args, "node")
	}
	if !t.Seat {
		return args, nil
	}
	declared := map[string]bool{}
	var names []string
	if p, ok := schemaAsPassed(t)["properties"].(map[string]any); ok {
		for k := range p {
			declared[k] = true
			names = append(names, k)
		}
	}
	sort.Strings(names)
	var strangers []string
	for k := range args {
		if !declared[k] {
			strangers = append(strangers, k)
		}
	}
	if len(strangers) > 0 {
		sort.Strings(strangers)
		takes := "nothing"
		if len(names) > 0 {
			takes = strings.Join(names, ", ")
		}
		return nil, fmt.Errorf("%s takes no argument %s — it takes %s (mesh_describe %s); nothing was sent",
			t.Address, strings.Join(strangers, ", "), takes, t.Address)
	}
	return args, nil
}

// schemaWithoutNode is a tool's schema with `node` taken out, for an address that names the machine.
func schemaWithoutNode(raw json.RawMessage) map[string]any {
	schema := asSchema(raw)
	out := map[string]any{}
	for k, v := range schema {
		out[k] = v
	}
	if p, ok := schema["properties"].(map[string]any); ok {
		props := map[string]any{}
		for k, v := range p {
			if k != "node" {
				props[k] = v
			}
		}
		out["properties"] = props
	}
	if r, ok := schema["required"].([]any); ok {
		var keep []any
		for _, k := range r {
			if k != "node" {
				keep = append(keep, k)
			}
		}
		if len(keep) == 0 {
			delete(out, "required")
		} else {
			out["required"] = keep
		}
	}
	return out
}

// answerText is a discovery verb's answer as MCP content: JSON, indented.
func answerText(v any) map[string]any {
	var b strings.Builder
	enc := json.NewEncoder(&b)
	enc.SetEscapeHTML(false) // `<node>/…` is read by an agent, not embedded in a page
	enc.SetIndent("", "  ")
	_ = enc.Encode(v)
	return map[string]any{"content": []map[string]any{{"type": "text", "text": strings.TrimRight(b.String(), "\n")}}}
}

func failure(text string) map[string]any {
	return map[string]any{"content": []map[string]any{{"type": "text", "text": text}}, "isError": true}
}

// discover answers one of the discovery verbs.
func (s *Surface) discover(name string, args map[string]any) map[string]any {
	if name == verbRuntimes {
		return s.runtimesAnswer()
	}
	x, err := s.index()
	if err != nil {
		return failure("the mesh's discovery failed: " + err.Error())
	}
	str := func(k string) string { v, _ := args[k].(string); return strings.TrimSpace(v) }

	switch name {
	case verbOverview:
		type verbLine struct {
			Address     string `json:"address"`
			Description string `json:"description"`
		}
		var mesh, node []map[string]any
		for _, st := range x.Seats {
			var verbs []verbLine
			for _, v := range st.Verbs {
				addr := st.Seat + "." + v.Name
				if st.Scope == "node" {
					addr = "<node>/" + addr
				}
				verbs = append(verbs, verbLine{addr, firstLine(v.Description)})
			}
			entry := map[string]any{"seat": st.Seat, "verbs": verbs}
			if st.Scope == "node" {
				entry["held on"] = nodesOf(st.Holders)
				node = append(node, entry)
			} else {
				if h := nodesOf(st.Holders); len(h) > 0 {
					entry["held on"] = h
				}
				mesh = append(mesh, entry)
			}
		}
		modules := 0
		tools := 0
		for _, m := range x.Modules {
			modules++
			tools += len(m.Tools)
		}
		return answerText(map[string]any{
			"seats of the mesh":   mesh,
			"seats every machine": node,
			"machines":            x.Machines,
			"modules with tools":  fmt.Sprintf("%d modules, %d tools — mesh_machine lists a machine's, mesh_search finds one", modules, tools),
			"not answering":       x.NotAnswering,
		})

	case verbMachine:
		node := str("node")
		if node == "" {
			return failure("mesh_machine needs `node`: one of " + orNobody(x.Machines))
		}
		if !contains(x.Machines, node) {
			return failure(fmt.Sprintf("the mesh knows no machine %q; it has %s", node, orNobody(x.Machines)))
		}
		var seats []map[string]any
		for _, st := range x.Seats {
			if st.Scope != "node" || !contains(nodesOf(st.Holders), node) {
				continue
			}
			var verbs []string
			for _, v := range st.Verbs {
				verbs = append(verbs, node+"/"+st.Seat+"."+v.Name)
			}
			var by string
			for _, h := range st.Holders {
				if h.Node == node {
					by = h.Module
				}
			}
			seats = append(seats, map[string]any{"seat": st.Seat, "held by": by, "verbs": verbs})
		}
		var modules []map[string]any
		names := make([]string, 0, len(x.Modules))
		for n := range x.Modules {
			names = append(names, n)
		}
		sort.Strings(names)
		for _, n := range names {
			m := x.Modules[n]
			if !contains(m.On, node) {
				continue
			}
			var tools []map[string]string
			for _, t := range m.Tools {
				tools = append(tools, map[string]string{"address": node + "/" + m.Module + "." + t.Name, "does": firstLine(t.Description)})
			}
			entry := map[string]any{"module": m.Module, "tools": tools}
			if m.Interchangeable {
				entry["interchangeable"] = "any instance answers <module>.<tool> as well"
			}
			modules = append(modules, entry)
		}
		out := map[string]any{"machine": node, "seats": seats, "modules": modules}
		if seats == nil {
			out["seats"] = []map[string]any{}
		}
		if modules == nil {
			out["modules"] = []map[string]any{}
		}
		if us := x.unheardOn(node); len(us) > 0 {
			out["incomplete"] = "discovery did not hear in full from " + sayUnheard(us) +
				"; what is listed may be missing what it serves. Ask again in a moment; mesh_runtimes shows which runtimes answered"
		}
		return answerText(out)

	case verbSearch:
		query := strings.ToLower(str("query"))
		if query == "" {
			return failure("mesh_search needs `query`: words to find, e.g. `postgres databases`")
		}
		words := strings.Fields(query)
		type hit struct {
			Address string `json:"address"`
			Does    string `json:"does"`
			Also    string `json:"also,omitempty"`
		}
		var hits []hit
		matches := func(parts ...string) bool {
			hay := strings.ToLower(strings.Join(parts, " "))
			for _, w := range words {
				if !strings.Contains(hay, w) {
					return false
				}
			}
			return true
		}
		for _, st := range x.Seats {
			for _, v := range st.Verbs {
				if !matches(st.Seat, v.Name, v.Description) {
					continue
				}
				if st.Scope == "node" {
					on := nodesOf(st.Holders)
					first := "<node>"
					also := ""
					if len(on) > 0 {
						first = on[0]
						if len(on) > 1 {
							also = "also on " + strings.Join(on[1:], ", ")
						}
					}
					hits = append(hits, hit{first + "/" + st.Seat + "." + v.Name, firstLine(v.Description), also})
				} else {
					hits = append(hits, hit{st.Seat + "." + v.Name, firstLine(v.Description), ""})
				}
			}
		}
		names := make([]string, 0, len(x.Modules))
		for n := range x.Modules {
			names = append(names, n)
		}
		sort.Strings(names)
		for _, n := range names {
			m := x.Modules[n]
			for _, t := range m.Tools {
				if !matches(m.Module, t.Name, t.Description) {
					continue
				}
				switch {
				case m.Interchangeable:
					hits = append(hits, hit{m.Module + "." + t.Name, firstLine(t.Description), "any instance; on " + orNobody(m.On)})
				case len(m.On) == 0:
					hits = append(hits, hit{"<node>/" + m.Module + "." + t.Name, firstLine(t.Description), "the mesh places it on no machine"})
				default:
					also := ""
					if len(m.On) > 1 {
						also = "also on " + strings.Join(m.On[1:], ", ")
					}
					hits = append(hits, hit{m.On[0] + "/" + m.Module + "." + t.Name, firstLine(t.Description), also})
				}
			}
		}
		out := map[string]any{"matches": hits}
		if len(hits) > searchCap {
			out["matches"] = hits[:searchCap]
			out["more"] = fmt.Sprintf("%d more; narrow the words", len(hits)-searchCap)
		}
		if len(hits) == 0 {
			out["matches"] = []hit{}
			out["hint"] = "nothing matched every word; try fewer words, or mesh_overview and mesh_machine to browse"
		}
		if len(x.Unheard) > 0 {
			out["incomplete"] = "discovery did not hear in full from " + sayUnheard(x.Unheard) +
				"; what they serve is not searched. mesh_runtimes shows which runtimes answered"
		}
		return answerText(out)

	case verbDescribe:
		t, err := resolve(x, str("address"))
		if err != nil {
			return failure(err.Error())
		}
		if !t.Seat && len(t.Tool.Input) == 0 {
			// Discovery carries a seat's schema, not a module tool's: asked of the runtime serving it.
			t.Tool.Input = inputOf(s.conn, t.Tool.Module, t.Tool.Name)
		}
		description := t.Tool.Description
		if description == "" {
			description = t.Name
		}
		return answerText(map[string]any{"address": t.Address, "description": description,
			"arguments": schemaAsPassed(t)})

	case verbCall:
		t, err := resolve(x, str("address"))
		if err != nil {
			return failure(err.Error())
		}
		given, _ := args["arguments"].(map[string]any)
		callArgs, err := argumentsAsSent(t, given)
		if err != nil {
			return failure(err.Error())
		}
		var got bus.Answered
		if t.Seat {
			got, err = s.conn.Ask(t.Key, callArgs, "")
		} else {
			got, err = callTool(s.conn, t.Key, callArgs, nil, x.Listing)
		}
		if err != nil {
			return failure(whyItFailed(t.Address, err))
		}
		content := []map[string]any{{"type": "text", "text": pretty(got.Result)}}
		if got.Node != "" {
			content = append(content, map[string]any{"type": "text", "text": "answered by " + got.Node})
		}
		return map[string]any{"content": content}
	}
	return failure("no discovery verb " + name)
}

// inputOf is a module tool's input schema, asked of a runtime that serves the module — its `tools` verb,
// answered on the module's plain subject by any instance — because discovery no longer carries it: every
// tool's schema made a machine's one discovery answer outgrow the bus (2026-10-04). Nil when nothing
// answers, which describes the tool as taking nothing rather than failing the description.
func inputOf(conn *bus.Conn, module, tool string) json.RawMessage {
	got, err := conn.Ask(module+".tools", map[string]any{}, "")
	if err != nil {
		return nil
	}
	var answer struct {
		Tools []struct {
			Name  string          `json:"name"`
			Input json.RawMessage `json:"input"`
		} `json:"tools"`
	}
	if json.Unmarshal(got.Result, &answer) != nil {
		return nil
	}
	for _, t := range answer.Tools {
		if t.Name == tool {
			return t.Input
		}
	}
	return nil
}