package main

// The asker on the bus: its asks in the controller's bucket `asked`, its asks and cancels published on the
// seat under the controller's name, the verbs a warrant chooses called with the controller's grant, and the
// router's record of its asks read under its name (novox/hq ADR 0259).

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

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

	"git.novox.be/novox/mesh-sdk/go/asks"

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

// askerFrom is the serving controller's asker; nil in any other process.
var askerFrom *asker

// askWithin is how long a verb a warrant chose is given to answer.
const askWithin = time.Minute

type busAsked struct{ conn *nats.Conn }

func (b busAsked) kv(ctx context.Context) (jetstream.KeyValue, error) {
	js, err := jetstream.New(b.conn)
	if err != nil {
		return nil, err
	}
	return js.KeyValue(ctx, broker.AskedBucket)
}

func (b busAsked) Get(ctx context.Context, id string) (*asked, error) {
	kv, err := b.kv(ctx)
	if err != nil {
		return nil, err
	}
	e, err := kv.Get(ctx, id)
	if errors.Is(err, jetstream.ErrKeyNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	var r asked
	return &r, json.Unmarshal(e.Value(), &r)
}

// Create keeps a new ask under its id, and only where none is kept: never over another.
func (b busAsked) Create(ctx context.Context, r asked) error {
	kv, err := b.kv(ctx)
	if err != nil {
		return err
	}
	body, err := json.Marshal(r)
	if err != nil {
		return err
	}
	_, err = kv.Create(ctx, r.ID, body)
	return err
}

// Change applies change to the ask kept under id by compare-and-set on its key's revision (the review of
// 2026-10-09, L2): read, changed, and written only over the revision read; when another write came between,
// read again and asked again, at most askChangeTries times. change says whether to write at all.
func (b busAsked) Change(ctx context.Context, id string, change func(*asked) bool) (bool, error) {
	kv, err := b.kv(ctx)
	if err != nil {
		return false, err
	}
	for try := 0; try < askChangeTries; try++ {
		e, err := kv.Get(ctx, id)
		if errors.Is(err, jetstream.ErrKeyNotFound) {
			return false, nil
		}
		if err != nil {
			return false, err
		}
		var r asked
		if err := json.Unmarshal(e.Value(), &r); err != nil {
			return false, err
		}
		if !change(&r) {
			return false, nil
		}
		body, err := json.Marshal(r)
		if err != nil {
			return false, err
		}
		if _, err := kv.Update(ctx, id, body, e.Revision()); err != nil {
			var api *jetstream.APIError
			if errors.Is(err, jetstream.ErrKeyExists) || (errors.As(err, &api) && api.ErrorCode == jetstream.JSErrCodeStreamWrongLastSequence) {
				continue
			}
			return false, err
		}
		return true, nil
	}
	return false, fmt.Errorf("the ask %s changed under every one of %d tries", id, askChangeTries)
}

func (b busAsked) All(ctx context.Context) ([]asked, error) {
	kv, err := b.kv(ctx)
	if err != nil {
		return nil, err
	}
	lister, err := kv.ListKeys(ctx)
	if err != nil {
		return nil, err
	}
	defer func() { _ = lister.Stop() }()
	var out []asked
	for k := range lister.Keys() {
		e, err := kv.Get(ctx, k)
		if err != nil {
			continue
		}
		var r asked
		if json.Unmarshal(e.Value(), &r) == nil {
			out = append(out, r)
		}
	}
	return out, nil
}

// callAction performs an action's verb as the controller, through the grant that names it.
func callAction(conn *nats.Conn) func(ctx context.Context, a conditions.Action, args map[string]string) error {
	return func(ctx context.Context, a conditions.Action, args map[string]string) error {
		seat, verb, ok := strings.Cut(a.Verb, ".")
		if !ok {
			return fmt.Errorf("%q names no seat and verb", a.Verb)
		}
		body := map[string]any{}
		for k, v := range args {
			body[k] = v
		}
		if seat == catalogue.DeliverySeat {
			_, err := askDeliveryOwner(ctx, conn, verb, body)
			return err
		}
		granted := false
		for _, v := range broker.VerbsTheControllerActsOnAWarrant {
			granted = granted || (v.Seat == seat && v.Verb == verb)
		}
		if !granted {
			return fmt.Errorf("%s: %w", a.Verb, errNotGranted)
		}
		var answer link.Answer
		var err error
		if a.Machine != "" {
			answer, err = link.AskSeatTool(ctx, conn, seat, verb, a.Machine, body, askWithin)
		} else {
			answer, err = link.AskMeshSeatTool(ctx, conn, seat, verb, body, askWithin)
		}
		if err != nil {
			return err
		}
		if answer.Error != "" {
			return fmt.Errorf("%s refused: %s", a.Verb, answer.Error)
		}
		return nil
	}
}

// routerRecordOf reads the router's record of one of the controller's asks, under its name, and answers
// how it ended when it did: the bucket is the one the asks seat's declarer names as its records.
func routerRecordOf(conn *nats.Conn, inv *inventory.Inventory) func(ctx context.Context, id string) (*asks.Warrant, error) {
	return func(ctx context.Context, id string) (*asks.Warrant, error) {
		bucket, err := asksRecords(ctx, inv)
		if err != nil || bucket == "" {
			return nil, err
		}
		reply, err := conn.RequestWithContext(ctx, "$JS.API.DIRECT.GET.KV_"+bucket+".$KV."+bucket+"."+askerName+"."+id, nil)
		if err != nil {
			return nil, err
		}
		if reply.Header.Get("Status") != "" {
			return nil, nil // none, or not readable: the event says it
		}
		var rec struct {
			State   string        `json:"state"`
			Warrant *asks.Warrant `json:"warrant"`
		}
		if json.Unmarshal(reply.Data, &rec) != nil || rec.State == "open" || rec.Warrant == nil {
			return nil, nil
		}
		return rec.Warrant, nil
	}
}

// asksRecords is the bucket the asks seat's declarer keeps its record of asks in.
func asksRecords(ctx context.Context, inv *inventory.Inventory) (string, error) {
	declared, err := inv.Catalogue(ctx)
	if err != nil {
		return "", err
	}
	for _, m := range declared {
		for _, s := range m.DefinesSeats {
			if s.Name == broker.AsksSeat && len(s.Records) > 0 {
				return broker.BucketName(m.Module, s.Records[0]), nil
			}
		}
	}
	return "", nil
}

// routerHereIn says whether a module declaring the asks seat, with its ask named by its caller, is assigned:
// without it nothing takes an ask, and asking would only fill a queue nobody reads.
func routerHereIn(inv *inventory.Inventory) func(ctx context.Context) (bool, error) {
	return func(ctx context.Context) (bool, error) {
		entries, err := inv.Catalogued(ctx)
		if err != nil {
			return false, err
		}
		for _, e := range entries {
			for _, s := range e.Manifest.DefinesSeats {
				if s.Name == broker.AsksSeat && s.NamedByCaller("ask") && len(e.On) > 0 {
					return true, nil
				}
			}
		}
		return false, nil
	}
}

// grantHeldIn says whether the bus holds the controller's grant to ask (novox/hq issue 353): the user list the
// machine holding the bus was last sent is the one the mesh composes now (brokerBehind, the same judgement a
// push makes to send that machine first). While it is behind, the controller's ask is refused by the bus,
// whatever the record says of the router, so nothing is asked and the operator is told to push that machine.
// Judged at most every grantLookEvery: composing the list resolves the bus's machine whole.
func grantHeldIn(open *stores) func(ctx context.Context) (bool, string, error) {
	var mu sync.Mutex
	var at time.Time
	var held bool
	var why string
	return func(ctx context.Context) (bool, string, error) {
		mu.Lock()
		defer mu.Unlock()
		if !at.IsZero() && time.Since(at) < grantLookEvery {
			return held, why, nil
		}
		machine, behind, err := brokerBehind(ctx, open, nil)
		if err != nil {
			return false, "", err
		}
		at, held, why = time.Now(), !behind, ""
		if behind {
			why = fmt.Sprintf("the bus's user list on %s is behind what the mesh composes, so the bus has not been "+
				"given the controller's grant to ask; `push %s` carries it", machine, machine)
		}
		return held, why, nil
	}
}

// grantLookEvery is how often the bus's user list is judged against the one its machine was last sent.
const grantLookEvery = 30 * time.Second

// channelsIn is what the channels are now, as a fingerprint: each module claiming a kind of the channel
// bench, where, promising what, and whether of its own account. An ask the router refused is asked again
// once this changes.
func channelsIn(inv *inventory.Inventory) func(ctx context.Context) string {
	return func(ctx context.Context) string {
		entries, err := inv.Catalogued(ctx)
		if err != nil {
			return ""
		}
		var parts []string
		for _, e := range entries {
			for _, c := range e.Manifest.Claims {
				if c.Kind == "" || !catalogue.KindedBenches[c.Name] {
					continue
				}
				on := append([]string(nil), e.On...)
				sort.Strings(on)
				caps := append([]string(nil), c.Capabilities...)
				sort.Strings(caps)
				parts = append(parts, fmt.Sprintf("%s/%s=%s@%s[%s]own:%t", c.Name, c.Kind, e.Manifest.Module,
					strings.Join(on, ","), strings.Join(caps, ","), e.Manifest.RunsAs != ""))
			}
		}
		sort.Strings(parts)
		return strings.Join(parts, ";")
	}
}

// startAsking makes the serving controller's asker and hands it the router's words.
func startAsking(ctx context.Context, open *stores, server *link.Server, conn *nats.Conn, keeper *conditions.Keeper) {
	js, err := jetstream.New(conn)
	if err != nil {
		fmt.Printf("the operator cannot be asked: %v\n", err)
		return
	}
	a := &asker{
		open: keeper.Open,
		silence: func(ctx context.Context, key string, d time.Duration, by, why string) error {
			_, err := keeper.Silence(ctx, key, d, by, why)
			return err
		},
		store: busAsked{conn: conn},
		publish: func(ctx context.Context, subject string, body []byte, id string) error {
			_, err := js.Publish(ctx, subject, body, jetstream.WithMsgID(id))
			return err
		},
		call: callAction(conn),
		// A proposed settings layer is set by this controller itself on the warrant (novox/hq ADR 0277).
		setLayer: setLayerIn(open),
		record: func(ctx context.Context, act link.HandAct) error {
			_, err := link.RecordHandAct(ctx, conn, act)
			return err
		},
		routerRecord: routerRecordOf(conn, open.inventory),
		routerHere:   routerHereIn(open.inventory),
		grantHeld:    grantHeldIn(open),
		channels:     channelsIn(open.inventory),
		raise: func(ctx context.Context, obs []conditions.Observation) error {
			return keeper.Reconcile(ctx, sourceAsker, obs)
		},
		now:  time.Now,
		logf: func(format string, args ...any) { fmt.Printf(format+"\n", args...) },
	}
	if err := server.Decides(a); err != nil {
		fmt.Printf("the operator's answers cannot be heard, so nothing is asked: %v\n", err)
		return
	}
	askerFrom = a
	go a.keep(ctx)
}