package main

import (
	"context"
	"fmt"
	"slices"
	"sort"
	"strings"
	"time"

	"github.com/nats-io/nats.go"

	"github.com/novox/mesh-controller/internal/catalogue"
	"github.com/novox/mesh-controller/internal/conditions"
	"github.com/novox/mesh-controller/internal/inventory"
)

// Who can become root where the trusted parties run (novox/hq ADR 0259 §8, as reviewed on 2026-10-09).
//
// The router and every channel proving its sender run as accounts of their own, so that no agent reads what
// they hold or speaks as them. **Root on their machine undoes all of it**, and so does an agent running as the
// operator's account there. A machine is **root-free** — an answer proven there may authorise — only when all
// of these are measured, now, and hold:
//
//  1. the machine names an account agents run as (novox/hq ADR 0266), so no agent runs as the operator's
//     account, which may become root;
//  2. its node-engine — running as root, which no agent controls — judged that account unable to become root
//     without a person, in a statement heard within the last 15 minutes (agentConfined, judgedConfined). The
//     engine gives that verdict only from a complete search for setuid programs younger than mesh-host's
//     rootsearch.FreshFor; before one, it says "not judged yet", which is no pass (novox/hq issue 361);
//  3. the login shell's `execute` is not served there (novox/hq ADR 0268): its holder's setting withholds it
//     **and** the bus was asked and heard no `execute` answered there. `execute` runs commands as the machine's
//     runtime account, which the mesh's acting tools give passwordless sudo; that account is taken to become
//     root, always, so no measure of it is asked.
//
// **Nothing else is a pass.** A machine that names no agent account, an unknown machine, a store or bus that
// could not be read, a verdict stale or absent — each is not root-free, and says why. The sudo module's own
// measure is no longer part of this judgement: it ran in the machine's runtime, as the very account an agent
// could become, so it could not be believed.
//
// The one judgement (judgeRoot) is read two ways: the self-check raises `root-not-free` on every machine where
// the router or a module of its own account runs and the judgement fails; and the `root-free` verb answers it
// live, to the router, which honours a verified sender only on its pass. A machine holding the operator's
// graphical session, where a messaging client's desktop app may run, is not judged here: the operator accepted
// that gap for now (hq issue 344).

// kindRootNotFree is the condition a trusted party's machine that is not root-free raises. Its own key, apart
// from ADR 0266's agent-can-become-root (Token agent-root, from DA): the two judge different things — DA the
// agent account alone, this the whole of root-free — and one key from two probes flapped between them (the
// confirmation review of 2026-10-09).
const kindRootNotFree = "root-not-free"

// routerSeat is the seat the router holds: where it runs counts as a trusted party's machine.
const routerSeat = "operator-channel"

const (
	loginShellSeat = "node-login-shell"
	// loginShellVerb is the seat's verb that runs a command, and the name of the setting its holder withholds
	// it by (novox/hq ADR 0268).
	loginShellVerb = "execute"
	// executeServes is the one value of that setting that serves the verb; anything else withholds it.
	executeServes = "serve"
)

// loginShellServed judges whether the login shell's execute is served on a machine, failing closed (novox/hq
// ADR 0268): served while the holder's setting there is `serve` (or the holder has no such setting and claims
// the verb), or while the bus heard the verb answered there, or while the bus could not be asked. why says
// which, in words.
func loginShellServed(holder string, claims bool, setting *any, heard, asked bool) (bool, string) {
	var why []string
	switch {
	case setting != nil:
		if v, _ := (*setting).(string); v == executeServes {
			why = append(why, holder+"'s execute setting there is "+executeServes)
		}
	case claims:
		why = append(why, holder+" claims execute and has no setting that withholds it")
	}
	if heard {
		why = append(why, "the bus hears execute answered there")
	} else if !asked {
		why = append(why, "the bus could not be asked whether execute is answered there")
	}
	return len(why) > 0, strings.Join(why, "; ")
}

// rootFacts is what the judgement reads of one machine.
type rootFacts struct {
	Machine string
	// Unread is every read that failed, in words: any one is a fail.
	Unread []string
	// AgentNamed is whether the machine names an agent account; Confined whether its node-engine judged it
	// unable to become root, freshly; ConfinedWhy the judgement's words either way.
	AgentNamed  bool
	Confined    bool
	ConfinedWhy string
	// Execute is whether the login shell's execute is served there; ExecuteWhy why, in words.
	Execute    bool
	ExecuteWhy string
	// SearchPending is the agent account unjudged only because the node-engine's setuid search runs, within
	// the quiet the controller gives it (searchQuietFor; ADR 0266's quiet window, issue 361).
	SearchPending bool
}

// rootVerdict is the judgement on one machine, as the root-free verb answers it.
type rootVerdict struct {
	Machine string    `json:"machine"`
	Free    bool      `json:"free"`
	Why     string    `json:"why"`
	Judged  time.Time `json:"judged"`
	// Quiet is a machine not free only because its setuid search still runs, within searchQuietFor: the
	// self-check raises nothing for it then (ADR 0266's quiet window). It is never free for it.
	Quiet bool `json:"quiet,omitempty"`
}

// judgeRoot is the one judgement: free only when nothing failed to read, an agent account is named and judged
// confined, and execute is not served.
func judgeRoot(f rootFacts, now time.Time) rootVerdict {
	v := rootVerdict{Machine: f.Machine, Judged: now.UTC()}
	var not []string
	if len(f.Unread) > 0 {
		not = append(not, "not measured: "+strings.Join(f.Unread, "; "))
	}
	switch {
	case f.ConfinedWhy == "":
		// Not read (said above), or nothing said of it: never a pass.
		if len(f.Unread) == 0 {
			not = append(not, "whether agents there can become root was not judged")
		}
	case !f.AgentNamed:
		not = append(not, "agents run as the operator's account there, which may become root ("+f.ConfinedWhy+")")
	case !f.Confined:
		not = append(not, f.ConfinedWhy)
	}
	if f.Execute {
		not = append(not, "the login shell runs any command an agent gives it as the machine's runtime account, "+
			"which can become root ("+orNoneKnown(f.ExecuteWhy)+")")
	}
	if len(not) > 0 {
		v.Why = strings.Join(not, "; ")
		// The one failure is the agent account not judged yet, because its search runs.
		v.Quiet = len(not) == 1 && f.SearchPending && f.AgentNamed && !f.Confined && len(f.Unread) == 0 && !f.Execute
		return v
	}
	v.Free = true
	v.Why = f.ConfinedWhy + "; the login shell's execute is not served there"
	return v
}

// rootReader reads the facts of machines live: the catalogue's placements, the node-engine's verdicts and the
// bus's discovery, each once per reader.
type rootReader struct {
	entries []inventory.Entry
	read    error
	heard   map[string]map[string]map[string]bool
	asked   error
	// confined is agentConfined; settings the login shell holder's settings on a machine. Replaceable in a test.
	confined func(ctx context.Context, node string, now time.Time) (named, confined bool, why string, err error)
	// quiet says the one thing keeping a machine's agent account unjudged is the node-engine's setuid
	// search, within searchQuietFor (ADR 0266, searchStillRunning). Read by the self-check alone, to raise nothing
	// then; nil reads no quiet. It never makes a machine root-free.
	quiet    func(ctx context.Context, node string, now time.Time) bool
	settings func(ctx context.Context, node, module string) ([]catalogue.Layer, error)
}

func newRootReader(ctx context.Context, inv *inventory.Inventory, conn *nats.Conn) *rootReader {
	r := &rootReader{}
	r.entries, r.read = inv.Catalogued(ctx)
	if conn == nil {
		r.asked = fmt.Errorf("this process holds no connection to the bus")
	} else {
		r.heard, r.asked = discoverSeatVerbs(ctx, conn)
	}
	r.confined = func(ctx context.Context, node string, now time.Time) (bool, bool, string, error) {
		return agentConfined(ctx, inv, node, now)
	}
	r.settings = inv.SettingsFor
	return r
}

// facts reads one machine, at now.
func (r *rootReader) facts(ctx context.Context, machine string, now time.Time) rootFacts {
	f := rootFacts{Machine: machine}
	if r.read != nil {
		f.Unread = append(f.Unread, "the catalogue's placements could not be read: "+r.read.Error())
	}
	named, confined, why, err := r.confined(ctx, machine, now)
	if err != nil {
		f.Unread = append(f.Unread, "the account agents run as could not be read: "+err.Error())
	} else {
		f.AgentNamed, f.Confined, f.ConfinedWhy = named, confined, why
	}
	f.Execute, f.ExecuteWhy = r.executeServed(ctx, machine)
	if r.quiet != nil && f.AgentNamed && !f.Confined {
		f.SearchPending = r.quiet(ctx, machine, now)
	}
	return f
}

// executeServed is whether the login shell's execute is served on a machine, failing closed: the bus not
// asked, the placements not read, or a holder's setting not read, is served.
func (r *rootReader) executeServed(ctx context.Context, machine string) (bool, string) {
	heard := r.heard[loginShellSeat][loginShellVerb][machine]
	asked := r.asked == nil
	var whys []string
	served := false
	holders := 0
	for _, e := range r.entries {
		if !e.Manifest.ClaimsSeat(loginShellSeat) || !slices.Contains(e.On, machine) {
			continue
		}
		holders++
		var setting *any
		if _, declared := e.Manifest.Settings[loginShellVerb]; declared {
			layers, err := r.settings(ctx, machine, e.Manifest.Module)
			if err != nil {
				served = true
				whys = append(whys, e.Manifest.Module+"'s setting there could not be read: "+err.Error())
				continue
			}
			for _, s := range catalogue.Effective(e.Manifest, layers) {
				if s.Key == loginShellVerb {
					v := s.Value
					setting = &v
				}
			}
		}
		if s, why := loginShellServed(e.Manifest.Module, claimServes(e.Manifest, loginShellSeat, loginShellVerb),
			setting, heard, asked); s {
			served = true
			whys = append(whys, why)
		}
	}
	if holders == 0 {
		// Nobody is assigned to serve it; the bus must still hear nobody answering it.
		if s, why := loginShellServed("no holder", false, nil, heard, asked); s {
			served = true
			whys = append(whys, why)
		}
	}
	if r.read != nil {
		served = true
		whys = append(whys, "who holds the login shell there could not be read")
	}
	return served, strings.Join(whys, "; ")
}

// claimServes says whether a manifest's claim of a seat names a verb among those it serves.
func claimServes(m catalogue.Manifest, seat, verb string) bool {
	for _, c := range m.Claims {
		if c.Name == seat && slices.Contains(c.Serves, verb) {
			return true
		}
	}
	return false
}

// judgeRootFree is the root-free verb's answer: each named machine judged now. It never fails: what could not
// be read is a machine not free, saying so.
func judgeRootFree(ctx context.Context, r *rootReader, machines []string, now time.Time) []rootVerdict {
	out := make([]rootVerdict, 0, len(machines))
	for _, m := range machines {
		out = append(out, judgeRoot(r.facts(ctx, m, now), now))
	}
	return out
}

// trustedMachines are the machines where the router or a module of its own account runs, each with those
// modules.
func trustedMachines(entries []inventory.Entry) map[string][]string {
	trusted := map[string][]string{}
	for _, e := range entries {
		for _, node := range e.On {
			if e.Manifest.RunsAs != "" || e.Manifest.ClaimsSeat(routerSeat) {
				trusted[node] = append(trusted[node], e.Manifest.Module)
			}
		}
	}
	return trusted
}

// agentRootObservation is the condition of a trusted party's machine that is not root-free.
func agentRootObservation(v rootVerdict, trusted []string) conditions.Observation {
	trusted = append([]string(nil), trusted...)
	sort.Strings(trusted)
	return conditions.Observation{Scope: conditions.ScopeMachine, ID: v.Machine, Token: kindRootNotFree,
		Machine: v.Machine, Kind: kindRootNotFree, Severity: conditions.Urgent,
		Summary: fmt.Sprintf("%s is not root-free, where %s run: until it is, the router approves nothing proven "+
			"there (novox/hq ADR 0259 §8): %s", v.Machine, strings.Join(trusted, ", "), v.Why),
		Headline: "Phone answers held on " + v.Machine,
		Needs:    "give the programs working for you on " + v.Machine + " an account that cannot become root.",
		Explanation: "The modules that prove your answers from your phone run on " + v.Machine + ", and the mesh " +
			"cannot show that a program working for you there is unable to become root or to act as you. Until " +
			"it can, answers from your phone can only acknowledge.",
		Resolved: "Answers from your phone can approve again on " + v.Machine}
}

// probeAgentRoot is the probe: every trusted party's machine, judged by the one judgement.
func probeAgentRoot(ctx context.Context, d *doctor) ([]conditions.Observation, error) {
	var conn *nats.Conn
	if d.js != nil {
		conn = d.js.Conn()
	}
	inv := d.open.inventory
	r := newRootReader(ctx, inv, conn)
	if r.read != nil {
		return nil, r.read
	}
	// The self-check alone reads ADR 0266's quiet window: nothing raised while a machine's setuid search
	// runs, within searchQuietFor. The root-free verb never reads it, so the machine still answers not free.
	r.quiet = func(ctx context.Context, node string, now time.Time) bool {
		n, err := inv.NodeByName(ctx, node)
		if err != nil || n.AgentAccount == "" {
			return false
		}
		h, had, err := inv.HealthOf(ctx, node)
		if err != nil {
			return false
		}
		quiet, err := searchStillRunning(ctx, inv, node, n.AgentAccount, h, had, now)
		return err == nil && quiet
	}
	obs := rootObservations(ctx, r, trustedMachines(r.entries), time.Now())
	// A membership that lost its verified sender to a judgement that failed at a push gets it back here, once
	// the machines pass (issue 930); the bound is one self-check.
	giveVerifiedSendersBack(ctx, d)
	return obs, nil
}

// rootObservations judges the machines and says each that fails.
func rootObservations(ctx context.Context, r *rootReader, trusted map[string][]string, now time.Time) []conditions.Observation {
	var machines []string
	for m := range trusted {
		machines = append(machines, m)
	}
	sort.Strings(machines)
	var out []conditions.Observation
	for _, v := range judgeRootFree(ctx, r, machines, now) {
		if !v.Free && !v.Quiet {
			out = append(out, agentRootObservation(v, trusted[v.Machine]))
		}
	}
	return out
}

// rootClock is the clock the root-free verb judges by.
var rootClock = time.Now

// rootFreeAnswer is the root-free verb: the named machines, each judged now by the serving controller. Only it
// answers: a process that is not serving says so, and a caller reads that as no machine free.
func rootFreeAnswer(ctx context.Context, machines string, now time.Time) (any, error) {
	d := doctorFrom
	if d == nil || d.open == nil || d.open.inventory == nil {
		return nil, fmt.Errorf("this controller is not serving, so it judges no machine root-free: ask again, and " +
			"the serving controller answers")
	}
	var names []string
	for _, m := range strings.Split(machines, ",") {
		if m = strings.TrimSpace(m); m != "" && !slices.Contains(names, m) {
			names = append(names, m)
		}
	}
	if len(names) == 0 {
		return nil, fmt.Errorf("root-free judges the machines named, and none was")
	}
	var conn *nats.Conn
	if d.js != nil {
		conn = d.js.Conn()
	}
	return map[string]any{"machines": judgeRootFree(ctx, newRootReader(ctx, d.open.inventory, conn), names, now)}, nil
}