// Package ownresync hands the vault the value of this machine's own secret that runs, where the vault holds another
// (novox/hq issue 1126, cause C4).
//
// The vault's `move-in` never replaces a value it holds, so its first import of an own secret stays fixed; where the
// controller later made that secret anew (a rotation at start, a re-issue), the new value runs and the vault keeps the
// old one. The node's shadow composer sees it: composing from the vault's value, it opens both seals with this
// machine's key and its answer's shown body says delivery.MaskedAnotherValue. After each shadow answer this step asks the
// vault's `move-in` with replace_running: true and what runs, for each own secret so masked, once per running value, and
// says what it asked and what the vault answered. It is move-in's, the verb this node may ask already, so no seat and no
// bus grant changes for it.
//
// **Only while this node applies the controller's compositions**, and only for a module whose composition that runs is
// the one its want names: then the controller's value is what runs, and what runs is the truth the vault lacks. Once the
// node composes its own, the vault's value is the source and nothing is handed. **The switch** is the vault's
// (`own_take_switch`, a person's act): while it is off the vault refuses every ask, and this step says so once per value.
// The vault also refuses any value it changed in the last 15 minutes, so a re-issue the node has not applied yet is
// never put back.
package ownresync

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"sort"
	"sync"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/delivery"

	"github.com/novox/mesh-host/internal/selfcompose"
)

// Verb is the vault's verb this step asks, with ReplaceRunning true in both steps.
const Verb = "move-in"

// ReplaceRunning is move-in's argument that makes it take the running value over the one the vault holds.
const ReplaceRunning = "replace_running"

// Env is what the step reads and asks.
type Env struct {
	Node string
	// Composes is whose compositions the node applies now: delivery.ComposesController, delivery.ComposesOwn, or ""
	// while its agent has not decided. The step hands nothing but for ComposesController.
	Composes func() string
	// Running is what the node runs now (agent.Everything).
	Running func() []delivery.Composed
	// Get reads one key's latest value; nil and no error when there is none.
	Get func(ctx context.Context, bucket, key string) ([]byte, error)
	// Unseal opens a value sealed to this machine; Seal seals a value to a raw X25519 key in base64 (identity.Seal).
	Unseal func(sealed string) ([]byte, error)
	Seal   func(to string, value []byte) (string, error)
	// Ask asks one of the vault's verbs in this engine's own name (link.Session.AskVault).
	Ask func(ctx context.Context, verb string, args map[string]any) (json.RawMessage, error)
	Say func(string)
}

// Outcome is what the step did for one own secret: asked or not, and what was said.
type Outcome struct {
	Module string
	Name   string
	Asked  bool
	Said   string
	// Retry says a read or an ask the bus did not answer stopped it: no answer, kept as none, and the step is to be
	// taken again after a bound (issue 1126, 2026-10-28: "want.shanks.brother could not be read ... no responders").
	Retry bool
}

// Resync is the step of one node agent's run.
type Resync struct {
	env Env

	mu sync.Mutex
	// done is, by module/name, the running value's fingerprint the vault was asked with or why it was not: each is
	// asked, and each reason said, once.
	done map[string]string
}

// New is the step for one node.
func New(env Env) *Resync {
	if env.Say == nil {
		env.Say = func(string) {}
	}
	return &Resync{env: env, done: map[string]string{}}
}

// Take reads the node's shadow answers and hands the vault what runs of each own secret they say another value of.
func (r *Resync) Take(ctx context.Context, answers map[string]delivery.CandidateAnswer) []Outcome {
	seen := map[delivery.OwnValueDiffers]bool{}
	var drift []delivery.OwnValueDiffers
	proposals := make([]string, 0, len(answers))
	for g := range answers {
		proposals = append(proposals, g)
	}
	sort.Strings(proposals)
	for _, g := range proposals {
		for _, o := range delivery.OwnValuesDiffer(answers[g]) {
			if !seen[o] {
				seen[o] = true
				drift = append(drift, o)
			}
		}
	}
	if len(drift) == 0 {
		return nil
	}
	composes := ""
	if r.env.Composes != nil {
		composes = r.env.Composes()
	}
	var out []Outcome
	for _, o := range drift {
		res := r.one(ctx, composes, o)
		if res.Said != "" || res.Retry {
			out = append(out, res)
		}
	}
	return out
}

// one is the step for one own secret: Said is empty when it was done before for the same value and reason.
func (r *Resync) one(ctx context.Context, composes string, o delivery.OwnValueDiffers) Outcome {
	res := Outcome{Module: o.Module, Name: o.Name}
	key := o.Module + "/" + o.Name
	if composes == "" {
		return res // the agent has not decided whose compositions it applies: taken again once it has
	}
	if composes != delivery.ComposesController {
		return r.said(key, "not:composes", res, fmt.Sprintf("%s holds another value in the vault than runs here, and "+
			"nothing is handed: this node composes its own (%q), so the vault's value is the source", key, composes))
	}
	sealed, why, failed := r.running(ctx, o)
	if failed != nil {
		// The bus did not answer: no reason to keep, and taken again (Retry); said once per reason.
		res.Retry = true
		return r.said(key, "retry:"+why, res, fmt.Sprintf("%s holds another value in the vault than runs here, and "+
			"nothing is handed yet: %s; asked again", key, why))
	}
	if why != "" {
		return r.said(key, "not:"+why, res, fmt.Sprintf("%s holds another value in the vault than runs here, and "+
			"nothing is handed: %s", key, why))
	}
	sum := sha256.Sum256([]byte(sealed))
	fp := hex.EncodeToString(sum[:])
	r.mu.Lock()
	asked := r.done[key] == fp
	r.mu.Unlock()
	if asked {
		return res
	}
	value, err := r.env.Unseal(sealed)
	if err != nil {
		return r.said(key, "not:unseal:"+fp, res, fmt.Sprintf("%s: what runs does not open with this machine's key, so "+
			"nothing is handed: %v", key, err))
	}
	defer wipe(value)
	said, err := r.hand(ctx, o, value)
	if err != nil {
		if ctx.Err() != nil {
			return res // the run ended: asked again in the next
		}
		if selfcompose.BusFailed(err) {
			// The vault did not answer on the bus: no word of the vault's, so not kept as asked (Retry).
			res.Retry = true
			return r.said(key, "retry:ask", res, fmt.Sprintf("%s: the vault's %s with replace_running did not answer, "+
				"and is asked again: %v", key, Verb, err))
		}
		said = fmt.Sprintf("%s: the vault's %s with replace_running refused: %v", key, Verb, err)
	}
	// Once per running value, whatever the vault answered: a refusal is the vault's word, said once, and a new value
	// that runs asks again.
	r.mu.Lock()
	r.done[key] = fp
	r.mu.Unlock()
	res.Asked, res.Said = true, said
	r.env.Say(said)
	return res
}

// said says why once per reason, and keeps the reason as done.
func (r *Resync) said(key, reason string, res Outcome, why string) Outcome {
	r.mu.Lock()
	again := r.done[key] == reason
	r.done[key] = reason
	r.mu.Unlock()
	if again {
		return res
	}
	res.Said = why
	r.env.Say(why)
	return res
}

// running is the sealed value of o in the composition that runs, when that composition is the one the module's want
// names; or why it is not handed, with the error of a read the bus did not answer, which is no answer.
func (r *Resync) running(ctx context.Context, o delivery.OwnValueDiffers) (sealed, why string, failed error) {
	var comp *delivery.Composed
	if r.env.Running != nil {
		for _, c := range r.env.Running() {
			if c.Module == o.Module {
				c := c
				comp = &c
				break
			}
		}
	}
	if comp == nil {
		return "", o.Module + " runs no composition here", nil
	}
	wantKey, err := delivery.WantKey(r.env.Node, o.Module)
	if err != nil {
		return "", err.Error(), nil
	}
	raw, err := r.env.Get(ctx, delivery.AssignerWantsBucket, wantKey)
	if err != nil {
		return "", fmt.Sprintf("its want %s could not be read (%v)", wantKey, err), err
	}
	if raw == nil {
		return "", fmt.Sprintf("it has no want %s", wantKey), nil
	}
	want, err := delivery.DecodeWant(raw)
	if err != nil {
		return "", fmt.Sprintf("its want %s is not one: %v", wantKey, err), nil
	}
	if want.Self || want.Removed || want.Composed == "" {
		return "", fmt.Sprintf("its want %s names no composition of the controller's", wantKey), nil
	}
	// What runs is the composition the want names, as the module's have says: applied and running.
	haveKey, err := delivery.HaveKey(r.env.Node, o.Module)
	if err != nil {
		return "", err.Error(), nil
	}
	raw, err = r.env.Get(ctx, delivery.HaveBucket, haveKey)
	if err != nil {
		return "", fmt.Sprintf("its have %s could not be read (%v)", haveKey, err), err
	}
	if raw == nil {
		return "", fmt.Sprintf("it has no have %s", haveKey), nil
	}
	have, err := delivery.DecodeHave(raw)
	if err != nil {
		return "", fmt.Sprintf("its have %s is not one: %v", haveKey, err), nil
	}
	if have.Composed != want.Composed || have.Phase != delivery.PhaseRunning {
		return "", fmt.Sprintf("what runs (%s, %s) is not yet the composition its want names (%s)", have.Composed,
			have.Phase, want.Composed), nil
	}
	// On a node the resource's id carries its module's name (`only-office.needs-jwt`); delivery.OwnNeedName reads it.
	id := o.Module + "." + catalogue.NeedID(o.Name)
	for _, res := range comp.Resources {
		var body struct {
			ID     string `json:"id"`
			Sealed any    `json:"sealed"`
		}
		if json.Unmarshal(res, &body) != nil {
			continue
		}
		if name, own := delivery.OwnNeedName(o.Module, body.ID); !own || name != o.Name {
			continue
		}
		if s, ok := body.Sealed.(string); ok && s != "" {
			return s, "", nil
		}
		return "", fmt.Sprintf("its resource %s carries no value sealed to this machine", id), nil
	}
	return "", fmt.Sprintf("what runs holds no resource %s", id), nil
}

// hand asks the vault's two steps with value, and checks what the vault holds after by its fingerprint.
func (r *Resync) hand(ctx context.Context, o delivery.OwnValueDiffers, value []byte) (string, error) {
	raw, err := r.env.Ask(ctx, Verb, map[string]any{ReplaceRunning: true, "module": o.Module, "name": o.Name,
		"why": "this node's shadow answer says the vault holds another value than runs here"})
	if err != nil {
		return "", err
	}
	var opened struct {
		Call   string `json:"call"`
		SealTo string `json:"seal_to"`
		Secret string `json:"secret"`
	}
	if err := json.Unmarshal(raw, &opened); err != nil || opened.Call == "" || opened.SealTo == "" {
		return "", fmt.Errorf("the vault answered no call and no key to seal to")
	}
	sealed, err := r.env.Seal(opened.SealTo, value)
	if err != nil {
		return "", fmt.Errorf("the vault's key for the call is not a sealing key: %w", err)
	}
	raw, err = r.env.Ask(ctx, Verb, map[string]any{ReplaceRunning: true, "call": opened.Call, "sealed": sealed})
	if err != nil {
		return "", err
	}
	var kept struct {
		Secret      string `json:"secret"`
		From        int    `json:"from_generation"`
		To          int    `json:"to_generation"`
		Unchanged   bool   `json:"unchanged"`
		Fingerprint string `json:"fingerprint"`
		Said        string `json:"said"`
	}
	if err := json.Unmarshal(raw, &kept); err != nil || kept.Secret == "" {
		return "", fmt.Errorf("the vault answered %s with no secret", opened.Secret)
	}
	sum := sha256.Sum256(value)
	if kept.Fingerprint != "sha256:"+hex.EncodeToString(sum[:]) {
		return "", fmt.Errorf("the vault says it holds %s at generation %d, but not the value handed in", kept.Secret, kept.To)
	}
	if kept.Unchanged {
		return fmt.Sprintf("handed the vault what runs of %s: it held that value already (generation %d)", kept.Secret, kept.To), nil
	}
	return fmt.Sprintf("handed the vault what runs of %s: generation %d replaced by %d, the value that runs", kept.Secret,
		kept.From, kept.To), nil
}

func wipe(b []byte) {
	for i := range b {
		b[i] = 0
	}
}