package gateway

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

	"github.com/DeBrosOfficial/network/pkg/serverless"
	"github.com/DeBrosOfficial/network/pkg/serverless/registry"
	"go.uber.org/zap"
)

// Claims-provider hook (bugboard #548/#920).
//
// A namespace opts into additive, signed JWT claims by deploying a serverless
// function with the RESERVED name "auth-claims-provider". At /v1/auth/verify
// mint time the gateway invokes it (in the namespace's own context, so it can
// read the namespace's tables) with {"wallet","namespace"} and merges the
// string→string object it returns into the JWT's custom claims — e.g.
// {"account_id":"<users.user_id>"} so push devices key on the stable account
// identity rather than the authenticating wallet.
//
// Hard guarantees:
//   - FAIL-OPEN: a missing / slow / erroring / malformed provider yields NO
//     claims; authentication never breaks because a claims function is down.
//   - Reserved claims (sub/iss/aud/iat/nbf/exp/namespace/custom) can never be
//     set by the provider — the gateway controls those.
//   - Bounded: timeout, max claim count, max total size.

const (
	// claimsProviderFnName is the reserved function name a namespace deploys to
	// inject additive JWT claims at mint time.
	claimsProviderFnName = "auth-claims-provider"
	// claimsProviderTimeout bounds the provider invocation so a slow/hung
	// function never stalls the auth path past this budget (fail-open after).
	claimsProviderTimeout = 2 * time.Second
	// maxCustomClaims / maxCustomClaimsBytes cap what a provider may inject —
	// JWTs ride in headers, and an unbounded claim blob is a DoS / cost vector.
	maxCustomClaims      = 16
	maxCustomClaimsBytes = 4096
	// claimsProviderWarnInterval rate-limits the fail-open WARN so a broken
	// provider doesn't flood the log on every login.
	claimsProviderWarnInterval = 30 * time.Second
)

// reservedClaimKeys can never be injected by a namespace claims provider; the
// gateway owns these. A provider that returns any of them has them dropped.
var reservedClaimKeys = map[string]struct{}{
	"sub": {}, "iss": {}, "aud": {}, "iat": {},
	"nbf": {}, "exp": {}, "namespace": {}, "custom": {},
}

// jwtClaimsProvider implements auth.ClaimsResolver by invoking the namespace's
// reserved auth-claims-provider function.
type jwtClaimsProvider struct {
	invoker *serverless.Invoker
	logger  *zap.Logger

	mu          sync.Mutex
	lastWarnUTC time.Time
}

// newJWTClaimsProvider builds the resolver. A nil invoker disables the hook
// (ResolveClaims returns nil).
func newJWTClaimsProvider(invoker *serverless.Invoker, logger *zap.Logger) *jwtClaimsProvider {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &jwtClaimsProvider{invoker: invoker, logger: logger.Named("claims-provider")}
}

// ResolveClaims invokes the namespace's auth-claims-provider and returns the
// sanitized additive claims, or nil. Never errors (fail-open contract).
func (p *jwtClaimsProvider) ResolveClaims(ctx context.Context, wallet, namespace string) map[string]string {
	if p.invoker == nil || wallet == "" || namespace == "" {
		return nil
	}

	input, err := json.Marshal(map[string]string{"wallet": wallet, "namespace": namespace})
	if err != nil {
		return nil
	}

	callCtx, cancel := context.WithTimeout(ctx, claimsProviderTimeout)
	defer cancel()

	resp, err := p.invoker.Invoke(callCtx, &serverless.InvokeRequest{
		Namespace:    namespace,
		FunctionName: claimsProviderFnName,
		Input:        input,
		// Gateway-initiated, no end-user caller → system trigger skips the
		// per-caller authorization check.
		TriggerType: serverless.TriggerTypeInternal,
	})
	if err != nil || resp == nil {
		// The namespace simply hasn't deployed the function (registry miss) is
		// the normal no-claims case for most namespaces — stay silent. Any
		// other failure is a real problem worth a rate-limited WARN.
		if !errors.Is(err, registry.ErrFunctionNotFound) {
			p.warnRateLimited("claims provider invoke failed (minting without custom claims)",
				namespace, err)
		}
		return nil
	}
	if resp.Status != serverless.InvocationStatusSuccess {
		p.warnRateLimited("claims provider returned non-success (minting without custom claims)",
			namespace, nil)
		return nil
	}

	return sanitizeProviderClaims(resp.Output)
}

// sanitizeProviderClaims parses the provider's RAW stdout as a bare JSON object
// of additive claims (NOT an {ok,result} Ack envelope — per the #976 contract)
// and returns a safe string→string subset: string values only, reserved keys
// dropped, bounded count and total size. Any parse failure → nil (fail-open).
func sanitizeProviderClaims(raw []byte) map[string]string {
	if len(raw) == 0 || len(raw) > maxCustomClaimsBytes {
		return nil
	}
	var obj map[string]any
	if err := json.Unmarshal(raw, &obj); err != nil || len(obj) == 0 {
		return nil
	}
	// Iterate in sorted key order so an over-budget provider payload truncates
	// DETERMINISTICALLY (Go map iteration is randomized) — the same output must
	// always yield the same claims, never a per-login-varying subset.
	keys := make([]string, 0, len(obj))
	for k := range obj {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	out := make(map[string]string, len(obj))
	total := 0
	for _, k := range keys {
		if len(out) >= maxCustomClaims {
			break
		}
		if _, reserved := reservedClaimKeys[k]; reserved {
			continue
		}
		s, ok := obj[k].(string) // string→string contract; non-string values dropped
		if !ok {
			continue
		}
		total += len(k) + len(s)
		if total > maxCustomClaimsBytes {
			break
		}
		out[k] = s
	}
	if len(out) == 0 {
		return nil
	}
	return out
}

func (p *jwtClaimsProvider) warnRateLimited(msg, namespace string, err error) {
	p.mu.Lock()
	now := time.Now()
	if now.Sub(p.lastWarnUTC) < claimsProviderWarnInterval {
		p.mu.Unlock()
		return
	}
	p.lastWarnUTC = now
	p.mu.Unlock()

	fields := []zap.Field{zap.String("namespace", namespace), zap.String("function", claimsProviderFnName)}
	if err != nil {
		fields = append(fields, zap.Error(err))
	}
	p.logger.Warn(msg, fields...)
}