package decision

import (
	"context"
	"encoding/json"
	"github.com/netkingdom/access-engine/internal/callerauth"
	"github.com/netkingdom/access-engine/internal/sign"
	"github.com/netkingdom/access-engine/internal/taskexecution"
	"github.com/netkingdom/access-engine/pkg/api"
	"github.com/netkingdom/approval-engine/adapters/go/approvalfact"
	"time"
)

// legacyDigestProjection preserves the published PDP digest profile while the
// signed structured binding retains original numeric kinds. It is used only
// for digest material, never to reconstruct an Approval-native act.
func legacyDigestProjection(request api.CheckRequest) (api.CheckRequest, error) {
	raw, err := json.Marshal(request)
	if err != nil {
		return api.CheckRequest{}, err
	}
	var projected api.CheckRequest
	err = json.Unmarshal(raw, &projected)
	return projected, err
}
func nativeServiceAct(request api.CheckRequest) ([]byte, error) {
	purpose, ok := request.Context["purpose"].(string)
	if !ok || purpose == "" || request.Subject.ID != "secrets-engine" || request.Subject.Type != "service" {
		return nil, taskexecution.ErrServiceInput
	}
	if principal, exists := request.Subject.Attributes["principal"]; exists && principal != "secrets-engine" {
		return nil, taskexecution.ErrServiceInput
	}
	// All map numbers originate from the number-preserving request/registry
	// profile. This raw draft is canonicalized only by the Approval owner helper.
	return json.Marshal(map[string]any{"action": request.Action, "actor": request.Subject.ID, "principal": "secrets-engine", "purpose": purpose, "target": request.Resource})
}
func (e *Engine) signTaskEnvelope(envelope *api.DecisionEnvelope) error {
	e.mu.RLock()
	key, kid := e.signingKey, e.signingKID
	e.mu.RUnlock()
	if len(key) == 0 {
		return ErrServicePilotUnavailable
	}
	return sign.Sign(envelope, key, kid)
}

// CheckTrustedService is the only v2 task evaluation path. Its source reader
// and immutable service input are server-created, not HTTP validation flags.
// It never consumes an approval or causes a protected backend effect.
func (e *Engine) CheckTrustedService(ctx context.Context, input taskexecution.ServiceInput, source *taskexecution.ApprovalReader) (api.DecisionEnvelope, error) {
	if !e.IsTrustedServicePilot() || !input.NumberPreserved() || !source.Configured() {
		return api.DecisionEnvelope{}, ErrServicePilotUnavailable
	}
	now := e.now()
	submitted, err := input.RequestAt(now)
	if err != nil {
		return api.DecisionEnvelope{}, err
	}
	normalized, facts := e.normalizeRequest(submitted)
	if (facts.resourceFound || facts.subjectFound) && !e.store.NumbersPreserved() {
		return api.DecisionEnvelope{}, ErrServicePilotUnavailable
	}
	original, err := legacyDigestProjection(submitted)
	if err != nil {
		return api.DecisionEnvelope{}, err
	}
	evaluated, err := legacyDigestProjection(normalized)
	if err != nil {
		return api.DecisionEnvelope{}, err
	}
	native, err := nativeServiceAct(normalized)
	if err != nil {
		return api.DecisionEnvelope{}, err
	}
	ctx = callerauth.WithRecord(ctx, input.Caller())
	var approvalEvidence *api.ApprovalObservationProvenance
	deadline := input.Caller().NotAfter
	contract := submitted.Context["execution_contract"].(map[string]any)
	operationEnd, err := time.Parse(time.RFC3339Nano, contract["operation_deadline"].(string))
	if err != nil {
		return api.DecisionEnvelope{}, taskexecution.ErrServiceInput
	}
	if operationEnd.Before(deadline) {
		deadline = operationEnd
	}
	carried, hasClaim := submitted.Context[api.ApprovalContextKey]
	if hasClaim {
		claim, ok := carried.(map[string]any)
		if !ok {
			return api.DecisionEnvelope{}, taskexecution.ErrApprovalSource
		}
		id, ok := claim["approval_id"].(string)
		if !ok {
			return api.DecisionEnvelope{}, taskexecution.ErrApprovalSource
		}
		originalRaw, err := json.Marshal(carried)
		if err != nil {
			return api.DecisionEnvelope{}, taskexecution.ErrApprovalSource
		}
		observed, err := source.Observe(ctx, id)
		if err != nil {
			return api.DecisionEnvelope{}, err
		}
		// One validation instant AFTER network I/O; a fresh read cannot rescue the
		// original carried claim's freshness, source expiry or operation deadline.
		now = e.now()
		if _, err := input.RequestAt(now); err != nil {
			return api.DecisionEnvelope{}, err
		}
		verified, err := observed.Validate(originalRaw, approvalfact.Expected{ApprovalID: id, NativeBindingJSON: native, PDPDigest: api.ApprovalBindingDigest(evaluated)}, now)
		if err != nil {
			return api.DecisionEnvelope{}, err
		}
		factEnd, err := verified.Deadline()
		if err != nil {
			return api.DecisionEnvelope{}, err
		}
		if factEnd.Before(deadline) {
			deadline = factEnd
		}
		approvalEvidence, err = verified.Provenance()
		if err != nil {
			return api.DecisionEnvelope{}, err
		}
	}
	expectation, err := e.policy.EvaluatePreservingNumbers(ctx, normalized)
	if err != nil {
		return api.DecisionEnvelope{}, err
	}
	if !hasClaim && expectation.Effect == api.DecisionEffectAllow {
		return api.DecisionEnvelope{}, ErrServicePilotUnavailable
	}
	now = e.now()
	if _, err := input.RequestAt(now); err != nil {
		return api.DecisionEnvelope{}, err
	}
	envelope := e.envelope(ctx, normalized, submitted, expectation, facts)
	envelope.Binding.RequestDigest = api.RequestDigest(evaluated)
	envelope.Binding.SubmittedRequestDigest = api.RequestDigest(original)
	// Claim-free signed DENY is the producer-owned normalization receipt used
	// before Approval issue. It supplies facts only, never execution authority.
	envelope.Binding.ApprovalBindingDigest = api.ApprovalBindingDigest(evaluated)
	envelope.Provenance.ApprovalObservation = approvalEvidence
	if envelope.Effect == api.DecisionEffectAllow {
		if approvalEvidence == nil || envelope.Lifetime == nil {
			return api.DecisionEnvelope{}, ErrServicePilotUnavailable
		}
		lifetime, err := trustedTaskLifetime(contract, operationEnd, deadline, now, e.policy.Metadata.AllowTTL)
		if err != nil {
			return api.DecisionEnvelope{}, err
		}
		envelope.Lifetime = lifetime
	}
	if err := e.signTaskEnvelope(&envelope); err != nil {
		return api.DecisionEnvelope{}, err
	}
	if err := e.recordDecisions([]api.DecisionEnvelope{envelope}); err != nil {
		return api.DecisionEnvelope{}, err
	}
	return envelope, nil
}

// The source ceiling is deliberately no larger than the existing task-token
// ceiling. Structural backend budgets do not guarantee an executable window.
const trustedTaskMaxAuthority = 120 * time.Second
const trustedTaskCleanupReserve = 5 * time.Second

// trustedTaskLifetime authorizes the entire exact operation, not merely its
// start. It cannot extend any caller, original/fresh fact, or approval bound.
func trustedTaskLifetime(contract map[string]any, operationEnd, authorityEnd, now time.Time, declared string) (*api.DecisionLifetime, error) {
	maximum, err := api.ParseAllowTTL(declared)
	if err != nil || maximum <= 0 || maximum > trustedTaskMaxAuthority || now.IsZero() || operationEnd.After(authorityEnd) || !operationEnd.After(now) || operationEnd.Sub(now) > maximum {
		return nil, ErrServicePilotUnavailable
	}
	budget, ok := contract["backend_budget"].(map[string]any)
	if !ok {
		return nil, ErrServicePilotUnavailable
	}
	number, ok := budget["ttl_seconds"].(json.Number)
	if !ok {
		return nil, ErrServicePilotUnavailable
	}
	seconds, err := number.Int64()
	if err != nil || seconds < 30 || seconds > 120 {
		return nil, ErrServicePilotUnavailable
	}
	remaining := operationEnd.Sub(now)
	if remaining < time.Duration(seconds)*time.Second+trustedTaskCleanupReserve {
		return nil, ErrServicePilotUnavailable
	}
	return &api.DecisionLifetime{Kind: api.DecisionLifetimeTTL, TTL: remaining.String(), NotBefore: now.UTC().Format(time.RFC3339Nano), ExpiresAt: operationEnd.UTC().Format(time.RFC3339Nano)}, nil
}