package oidc

import (
	"context"
	"fmt"
	"slices"
	"sync"
	"sync/atomic"
	"time"

	"github.com/go-jose/go-jose/v4"
	"github.com/jonboulle/clockwork"
	"github.com/zitadel/oidc/v3/pkg/op"

	"github.com/zitadel/zitadel/internal/api/authz"
	http_util "github.com/zitadel/zitadel/internal/api/http"
	"github.com/zitadel/zitadel/internal/crypto"
	"github.com/zitadel/zitadel/internal/query"
	"github.com/zitadel/zitadel/internal/telemetry/tracing"
	"github.com/zitadel/zitadel/internal/zerrors"
)

var supportedWebKeyAlgs = []string{
	string(jose.EdDSA),
	string(jose.RS256),
	string(jose.RS384),
	string(jose.RS512),
	string(jose.ES256),
	string(jose.ES384),
	string(jose.ES512),
}

func supportedSigningAlgs() []string {
	return supportedWebKeyAlgs
}

type cachedPublicKey struct {
	lastUse atomic.Int64 // unix micro time.
	expiry  *time.Time   // expiry may be nil if the key does not expire.
	webKey  *jose.JSONWebKey
}

func newCachedPublicKey(key *jose.JSONWebKey, expiry *time.Time, now time.Time) *cachedPublicKey {
	cachedKey := &cachedPublicKey{
		expiry: expiry,
		webKey: key,
	}
	cachedKey.setLastUse(now)
	return cachedKey
}

func (c *cachedPublicKey) setLastUse(now time.Time) {
	c.lastUse.Store(now.UnixMicro())
}

func (c *cachedPublicKey) getLastUse() time.Time {
	return time.UnixMicro(c.lastUse.Load())
}

func (c *cachedPublicKey) expired(now time.Time, validity time.Duration) bool {
	return c.getLastUse().Add(validity).Before(now)
}

// publicKeyCache caches public keys in a 2-dimensional map of Instance ID and Key ID.
// When a key is not present the queryKey function is called to obtain the key
// from the database.
type publicKeyCache struct {
	mtx          sync.RWMutex
	instanceKeys map[string]map[string]*cachedPublicKey

	// queryKey returns a public web key.
	// If the key does not have expiry, Time may be nil.
	queryKey func(ctx context.Context, keyID string) (*jose.JSONWebKey, *time.Time, error)
	clock    clockwork.Clock
}

// newPublicKeyCache initializes a keySetCache starts a purging Go routine.
// The purge routine deletes all public keys that are older than maxAge.
// When the passed context is done, the purge routine will terminate.
func newPublicKeyCache(background context.Context, maxAge time.Duration, queryKey func(ctx context.Context, keyID string) (*jose.JSONWebKey, *time.Time, error)) *publicKeyCache {
	k := &publicKeyCache{
		instanceKeys: make(map[string]map[string]*cachedPublicKey),
		queryKey:     queryKey,
		clock:        clockwork.FromContext(background), // defaults to real clock
	}
	go k.purgeOnInterval(background, k.clock.NewTicker(maxAge/5), maxAge)
	return k
}

func (k *publicKeyCache) purgeOnInterval(background context.Context, ticker clockwork.Ticker, maxAge time.Duration) {
	defer ticker.Stop()
	for {
		select {
		case <-background.Done():
			return
		case <-ticker.Chan():
		}

		// do the actual purging
		k.mtx.Lock()
		for instanceID, keys := range k.instanceKeys {
			for keyID, key := range keys {
				if key.expired(k.clock.Now(), maxAge) {
					delete(keys, keyID)
				}
			}
			if len(keys) == 0 {
				delete(k.instanceKeys, instanceID)
			}
		}
		k.mtx.Unlock()
	}
}

func (k *publicKeyCache) setKey(instanceID, keyID string, cachedKey *cachedPublicKey) {
	k.mtx.Lock()
	defer k.mtx.Unlock()

	if keys, ok := k.instanceKeys[instanceID]; ok {
		keys[keyID] = cachedKey
		return
	}
	k.instanceKeys[instanceID] = map[string]*cachedPublicKey{keyID: cachedKey}
}

func (k *publicKeyCache) getKey(ctx context.Context, keyID string) (_ *cachedPublicKey, err error) {
	ctx, span := tracing.NewSpan(ctx)
	defer func() { span.EndWithError(err) }()

	instanceID := authz.GetInstance(ctx).InstanceID()

	k.mtx.RLock()
	key, ok := k.instanceKeys[instanceID][keyID]
	k.mtx.RUnlock()

	if ok {
		key.setLastUse(k.clock.Now())
	} else {
		newKey, expiry, err := k.queryKey(ctx, keyID)
		if err != nil {
			return nil, err
		}
		key = newCachedPublicKey(newKey, expiry, k.clock.Now())
		k.setKey(instanceID, keyID, key)
	}

	return key, nil
}

func (k *publicKeyCache) verifySignature(ctx context.Context, jws *jose.JSONWebSignature, checkKeyExpiry bool) (_ []byte, err error) {
	ctx, span := tracing.NewSpan(ctx)
	defer func() {
		err = oidcError(err)
		span.EndWithError(err)
	}()

	if len(jws.Signatures) != 1 {
		return nil, zerrors.ThrowInvalidArgument(nil, "OIDC-Gid9s", "Errors.Token.Invalid")
	}
	key, err := k.getKey(ctx, jws.Signatures[0].Header.KeyID)
	if err != nil {
		return nil, err
	}
	if checkKeyExpiry && key.expiry != nil && key.expiry.Before(k.clock.Now()) {
		return nil, zerrors.ThrowInvalidArgument(err, "QUERY-ciF4k", "Errors.Key.ExpireBeforeNow")
	}
	return jws.Verify(key.webKey)
}

type oidcKeySet struct {
	*publicKeyCache

	keyExpiryCheck bool
}

// newOidcKeySet returns an oidc.KeySet implementation around the passed cache.
// It is advised to reuse the same cache if different key set configurations are required.
func newOidcKeySet(cache *publicKeyCache, opts ...keySetOption) *oidcKeySet {
	k := &oidcKeySet{
		publicKeyCache: cache,
	}
	for _, opt := range opts {
		opt(k)
	}
	return k
}

// VerifySignature implements the oidc.KeySet interface.
func (k *oidcKeySet) VerifySignature(ctx context.Context, jws *jose.JSONWebSignature) (_ []byte, err error) {
	return k.verifySignature(ctx, jws, k.keyExpiryCheck)
}

type keySetOption func(*oidcKeySet)

// withKeyExpiryCheck forces VerifySignature to check the expiry of the public key.
// Note that public key expiry is not part of the standard,
// but is currently established behavior of zitadel.
// We might want to remove this check in the future.
func withKeyExpiryCheck(check bool) keySetOption {
	return func(k *oidcKeySet) {
		k.keyExpiryCheck = check
	}
}

// keySetMap is a mapping of key IDs to public key data.
type keySetMap map[string][]byte

// getKey finds the keyID and parses the public key data
// into a JSONWebKey.
func (k keySetMap) getKey(keyID string) (*jose.JSONWebKey, error) {
	pubKey, err := crypto.BytesToPublicKey(k[keyID])
	if err != nil {
		return nil, err
	}
	return &jose.JSONWebKey{
		Key:   pubKey,
		KeyID: keyID,
		Use:   crypto.KeyUsageSigning.String(),
	}, nil
}

// VerifySignature implements the oidc.KeySet interface.
func (k keySetMap) VerifySignature(ctx context.Context, jws *jose.JSONWebSignature) ([]byte, error) {
	if len(jws.Signatures) != 1 {
		return nil, zerrors.ThrowInvalidArgument(nil, "OIDC-Eeth6", "Errors.Token.Invalid")
	}
	key, err := k.getKey(jws.Signatures[0].Header.KeyID)
	if err != nil {
		return nil, err
	}
	return jws.Verify(key)
}

const (
	signingKey = "signing_key"
	oidcUser   = "OIDC"

	retryBackoff   = 500 * time.Millisecond
	retryCount     = 3
	lockDuration   = retryCount * retryBackoff * 5
	gracefulPeriod = 10 * time.Minute
)

// SigningKey wraps the query.PrivateKey to implement the op.SigningKey interface
type SigningKey struct {
	algorithm jose.SignatureAlgorithm
	id        string
	key       interface{}
}

func (s *SigningKey) SignatureAlgorithm() jose.SignatureAlgorithm {
	return s.algorithm
}

func (s *SigningKey) Key() interface{} {
	return s.key
}

func (s *SigningKey) ID() string {
	return s.id
}

// KeySet implements the op.Storage interface
func (o *OPStorage) KeySet(ctx context.Context) (keys []op.Key, err error) {
	panic(o.panicErr("KeySet"))
}

// SignatureAlgorithms implements the op.Storage interface
func (o *OPStorage) SignatureAlgorithms(ctx context.Context) ([]jose.SignatureAlgorithm, error) {
	panic(o.panicErr("SignatureAlgorithms"))
}

// SigningKey implements the op.Storage interface
func (o *OPStorage) SigningKey(ctx context.Context) (key op.SigningKey, err error) {
	panic(o.panicErr("SigningKey"))
}

func (s *Server) Keys(ctx context.Context, r *op.Request[struct{}]) (_ *op.Response, err error) {
	ctx, span := tracing.NewSpan(ctx)
	defer func() { span.EndWithError(err) }()

	keyset, err := s.query.GetWebKeySet(ctx)
	if err != nil {
		return nil, err
	}

	resp := op.NewResponse(keyset)
	if s.jwksCacheControlMaxAge != 0 {
		resp.Header.Set(http_util.CacheControl,
			fmt.Sprintf("max-age=%d, must-revalidate", int(s.jwksCacheControlMaxAge/time.Second)),
		)
	}
	return resp, nil
}

func appendPublicKeysToWebKeySet(keyset *jose.JSONWebKeySet, pubkeys *query.PublicKeys) {
	if pubkeys == nil || len(pubkeys.Keys) == 0 {
		return
	}
	keyset.Keys = slices.Grow(keyset.Keys, len(pubkeys.Keys))

	for _, key := range pubkeys.Keys {
		keyset.Keys = append(keyset.Keys, jose.JSONWebKey{
			Key:       key.Key(),
			KeyID:     key.ID(),
			Algorithm: key.Algorithm(),
			Use:       key.Use().String(),
		})
	}
}

func queryKeyFunc(q *query.Queries) func(ctx context.Context, keyID string) (*jose.JSONWebKey, *time.Time, error) {
	return func(ctx context.Context, keyID string) (*jose.JSONWebKey, *time.Time, error) {
		webKey, err := q.GetPublicWebKeyByID(ctx, keyID)
		if err != nil {
			return nil, nil, err
		}
		return webKey, nil, nil
	}
}