package main

import (
	"context"
	"crypto/ecdh"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"sort"
	"strings"

	"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"
)

// The core's own credentials, sealed by the vault (novox/hq ADR 0349 §16, issue 755; the lead's decision on issue 755,
// notes 4 and 5).
//
// For a machine whose engine opens the vault's box (link.VaultBoxContract), each own secret of a module on the core's
// list (catalogue.CoreCredentialModules) travels as the vault sealed it to that machine's key, which the controller
// asks for on the send path (`get`, answered to the controller alone and sealed only to the key that machine's engine
// stated: mesh-vault's core.go) and carries without being able to open it. A machine below that contract is sent the
// controller's own sealed value, exactly as before.
//
// **The vault seals every answer afresh**, so the box last got is kept (inventory.CoreBox) and carried again while the
// vault's generation and the machine's key are the same: a declaration that changed with every answer would never be
// current. Every question but a send reads the kept box and asks nothing.
//
// **When the vault does not answer, the controller never falls back to its own seal.** A credential with a kept box
// keeps it — the machine keeps the file it has — and one with none leaves its module out of the declaration (the
// machine keeps what it holds of it, and a module not there yet is not placed). Either way the send raises a
// condition naming the vault and the machine, cleared by the first send the vault answers whole.

// engineOpensVaultBox says whether a machine's node-engine opens the vault's box, by its own newest statement.
func engineOpensVaultBox(ctx context.Context, inv *inventory.Inventory, node string) (bool, error) {
	stated, had, err := inv.HealthOf(ctx, node)
	if err != nil {
		return false, err
	}
	return had && stated.Contract >= link.VaultBoxContract, nil
}

// coreAnswer is the vault's `get` answer as the controller reads it: the name, the generation and the box, never
// opened.
type coreAnswer struct {
	Name       string          `json:"name"`
	Generation int             `json:"generation"`
	Sealed     json.RawMessage `json:"sealed"`
}

// coreAsk asks the vault for one secret sealed to the given key.
type coreAsk func(name, publicKey string) (coreAnswer, error)

// coreBoxes is what the vault's boxes make of one machine's composition.
type coreBoxes struct {
	// sealed is each core credential's box, by module and name (catalogue.Rendering.VaultSealed).
	sealed map[string]map[string]json.RawMessage
	// notPlaced is each core module left out, with why (catalogue.Rendering.NotPlaced).
	notPlaced map[string]string
	// keep is each box newly answered, to keep.
	keep []inventory.CoreBox
	// held is each credential the vault did not answer for whose kept box is carried again; silent is why the vault
	// did not answer, per credential.
	held, silent []string
}

// coreModulesOf is every module of the plan on the core's list whose own secrets this machine's declaration carries,
// with their plain own secret names, sorted: one handed to the provisioner has its secrets from the vault through the
// client, and one issued outside the mesh is never the vault's to seal here.
func coreModulesOf(modules []catalogue.Manifest, handed func(catalogue.Manifest) bool) map[string][]string {
	out := map[string][]string{}
	for _, m := range modules {
		if !catalogue.CarriesVaultSealed(m.Module) || (handed != nil && handed(m)) {
			continue
		}
		var names []string
		for name, own := range m.OwnSecrets.Plain() {
			if own.IssuedBy != catalogue.IssuedOutside {
				names = append(names, name)
			}
		}
		if len(names) > 0 {
			sort.Strings(names)
			out[m.Module] = names
		}
	}
	return out
}

// sealingKeyPEM is a machine's sealing key, recorded raw in base64, as the SPKI PEM the vault seals to.
func sealingKeyPEM(raw string) (string, error) {
	b, err := base64.StdEncoding.DecodeString(strings.TrimSpace(raw))
	if err != nil || len(b) != 32 {
		return "", errors.New("the machine's sealing key is not a raw X25519 key")
	}
	pub, err := ecdh.X25519().NewPublicKey(b)
	if err != nil {
		return "", err
	}
	der, err := x509.MarshalPKIXPublicKey(pub)
	if err != nil {
		return "", err
	}
	return string(pem.EncodeToMemory(&pem.Block{Type: "PUBLIC KEY", Bytes: der})), nil
}

// coreBoxesOf decides each core credential of a machine: on a send, the vault's answer (the kept box while its
// generation and key are the same), the kept box where the vault did not answer, or the module left out where nothing
// was kept; on any other question, the kept box, or a stand-in the next send asks for. Pure: what to keep and what to
// say is answered, not done.
func coreBoxesOf(node, sealingKey string, core map[string][]string, kept map[string]map[string]inventory.CoreBox,
	choosing Choosing, ask coreAsk) coreBoxes {
	out := coreBoxes{sealed: map[string]map[string]json.RawMessage{}, notPlaced: map[string]string{}}
	modules := make([]string, 0, len(core))
	for m := range core {
		modules = append(modules, m)
	}
	sort.Strings(modules)
	for _, module := range modules {
		if sealingKey == "" {
			out.notPlaced[module] = fmt.Sprintf("%s has no sealing key, so the vault can seal %s's credentials to "+
				"nothing there (novox/hq ADR 0349 §16)", node, module)
			continue
		}
		key, err := sealingKeyPEM(sealingKey)
		if err != nil {
			out.notPlaced[module] = fmt.Sprintf("%s's credentials cannot be asked of the vault: %v", module, err)
			continue
		}
		boxes := map[string]json.RawMessage{}
		for _, name := range core[module] {
			k, has := kept[module][name]
			valid := has && k.SealedTo == sealingKey && len(k.Box) > 0
			if choosing != Allocating {
				if valid {
					boxes[name] = k.Box
				} else {
					boxes[name] = catalogue.ForeseenVaultBox
				}
				continue
			}
			secret := "own/" + node + "/" + module + "/" + name
			got, err := ask(secret, key)
			if err == nil && (got.Generation <= 0 || canonicalBox(got.Sealed) == nil) {
				err = errors.New("it answered no box")
			}
			if err != nil {
				out.silent = append(out.silent, fmt.Sprintf("%s: %v", secret, err))
				if valid {
					boxes[name] = k.Box
					out.held = append(out.held, module+"/"+name)
					continue
				}
				out.notPlaced[module] = fmt.Sprintf("the vault did not give %s's credential %s for %s (%v), and the "+
					"controller never seals it itself (novox/hq ADR 0349 §16): not placed until the vault answers",
					module, name, node, err)
				break
			}
			if valid && k.Generation == got.Generation {
				boxes[name] = k.Box
				continue
			}
			box := canonicalBox(got.Sealed)
			boxes[name] = box
			out.keep = append(out.keep, inventory.CoreBox{Module: module, Name: name, Generation: got.Generation,
				SealedTo: sealingKey, Box: box})
		}
		if _, left := out.notPlaced[module]; !left {
			out.sealed[module] = boxes
		}
	}
	return out
}

// canonicalBox is the vault's box in the one form the declaration carries — the sealed box's fields, in their order,
// and nothing else — or nil when it is not one.
func canonicalBox(raw json.RawMessage) json.RawMessage {
	var b struct {
		V   int    `json:"v"`
		Eph string `json:"eph"`
		IV  string `json:"iv"`
		Tag string `json:"tag"`
		Ct  string `json:"ct"`
	}
	if err := json.Unmarshal(raw, &b); err != nil || b.V <= 0 || b.Eph == "" || b.Ct == "" {
		return nil
	}
	out, _ := json.Marshal(b)
	return out
}

// coreVault is how a send asks the vault for a core credential: its `get`, in the controller's name. A test stands
// in for it.
var coreVault = func(ctx context.Context) coreAsk {
	vault := theVault(ctx)
	return func(name, publicKey string) (coreAnswer, error) {
		raw, err := vault("get", map[string]any{"name": name, "public_key": publicKey})
		if err != nil {
			return coreAnswer{}, err
		}
		var a coreAnswer
		if err := json.Unmarshal(raw, &a); err != nil {
			return coreAnswer{}, fmt.Errorf("the vault's answer is not one: %w", err)
		}
		return a, nil
	}
}

// coreBoxesFor is coreBoxesOf for one machine, read from and kept in the store, and said on a send.
func coreBoxesFor(ctx context.Context, inv *inventory.Inventory, node string, modules []catalogue.Manifest,
	handed func(catalogue.Manifest) bool, choosing Choosing) (coreBoxes, error) {
	core := coreModulesOf(modules, handed)
	if len(core) == 0 {
		if choosing == Allocating {
			settleVaultSilent(ctx, node)
		}
		return coreBoxes{}, nil
	}
	key, err := inv.SealingKeyOf(ctx, node)
	if err != nil {
		return coreBoxes{}, err
	}
	kept, err := inv.KeptCoreBoxes(ctx, node)
	if err != nil {
		return coreBoxes{}, err
	}
	var ask coreAsk
	if choosing == Allocating {
		ask = coreVault(ctx)
	}
	out := coreBoxesOf(node, key, core, kept, choosing, ask)
	for _, b := range out.keep {
		if err := inv.KeepCoreBox(ctx, node, b); err != nil {
			return coreBoxes{}, err
		}
	}
	if choosing == Allocating {
		sayVaultSilent(ctx, node, out)
	}
	return out, nil
}

// kindVaultSilent is a send that did not have the vault's box for a core credential of a machine.
const kindVaultSilent = "vault-silent"

// vaultSilentObservation is that, as a condition: `machine.<machine>.vault-silent`.
func vaultSilentObservation(node string, b coreBoxes) conditions.Observation {
	o := conditions.Observation{Scope: conditions.ScopeMachine, ID: node, Kind: kindVaultSilent, Token: kindVaultSilent,
		Machine: node, Severity: conditions.Warning, Source: coreDowngradeSource}
	var said []string
	if len(b.notPlaced) > 0 {
		o.Severity = conditions.Urgent
		var left []string
		for m := range b.notPlaced {
			left = append(left, m)
		}
		sort.Strings(left)
		said = append(said, "not placed: "+strings.Join(left, ", "))
	}
	if len(b.held) > 0 {
		said = append(said, "kept as last sent: "+strings.Join(b.held, ", "))
	}
	o.Summary = fmt.Sprintf("the vault did not answer for the core's credentials on %s; %s", node, strings.Join(said, "; "))
	o.Said = o.Summary + " — " + strings.Join(b.silent, "; ")
	return o
}

// sayVaultSilent raises the condition for a send the vault did not answer whole, and clears it for one it did.
func sayVaultSilent(ctx context.Context, node string, b coreBoxes) {
	if len(b.silent) == 0 && len(b.notPlaced) == 0 {
		settleVaultSilent(ctx, node)
		return
	}
	fmt.Printf("HELD: %s\n", vaultSilentObservation(node, b).Said)
	if conditionsFrom == nil {
		return
	}
	if _, err := conditionsFrom.Observe(ctx, vaultSilentObservation(node, b)); err != nil {
		fmt.Printf("the condition for the vault's silence on %s could not be raised: %v\n", node, err)
	}
}

// settleVaultSilent clears the condition once a send had every core credential of the machine from the vault.
func settleVaultSilent(ctx context.Context, node string) {
	if conditionsFrom == nil {
		return
	}
	key := vaultSilentObservation(node, coreBoxes{}).Key()
	if _, err := conditionsFrom.Clear(ctx, key, "the vault answered for every core credential of "+node); err != nil {
		fmt.Printf("the condition %s could not be cleared: %v\n", key, err)
	}
}