// Package service wires the approval pipeline components (sessions,
// content binding, webauthn, DSSE signing, Transparency Log) into one
// Confirm orchestrator. Keeping it HTTP-free lets unit tests drive the
// whole flow without an httptest server.
package service

import (
	"context"
	"errors"
	"fmt"
	"time"

	"basicstack.de/proofedmesh/services/approval-service/internal/content"
	"basicstack.de/proofedmesh/services/approval-service/internal/sessions"
	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
	"basicstack.de/proofedmesh/services/approval-service/internal/store"
	"basicstack.de/proofedmesh/services/approval-service/internal/tlog"
	"basicstack.de/proofedmesh/services/approval-service/internal/webauthn"
)

// Signer is the signing-service client the orchestrator depends on.
type Signer interface {
	SignDSSE(ctx context.Context, keyRef string, stmt signer.Statement) (signer.Envelope, string, error)
}

// Submitter is the transparency-log client the orchestrator depends on.
type Submitter interface {
	Submit(ctx context.Context, env signer.Envelope, contentHash string) (tlog.Receipt, error)
}

// Orchestrator holds everything a Confirm needs. Fields are populated
// from main.go; the HTTP handler just calls Confirm.
type Orchestrator struct {
	Store         store.Store
	Sessions      *sessions.Manager
	Webauthn      *webauthn.Store
	WebauthnCfg   webauthn.VerifyConfig
	Signer        Signer
	Submitter     Submitter
	SigningKeyRef string
	// AttestationIssuer is embedded as predicate.performed_by.iss so
	// verifiers can match the approval against our Pocket-ID issuer.
	AttestationIssuer string
	Now               func() time.Time
	GenID             sessions.IDGenerator
}

// ErrContentHashMismatch is surfaced by Confirm when the preview's
// stored canonical content no longer hashes to its stored content_hash
// (store corruption) OR when the webauthn challenge the browser signed
// does not match the challenge we expected for this preview. In both
// cases the HTTP layer returns 400 per DEV-608.
var ErrContentHashMismatch = errors.New("service: content hash mismatch")

// ErrChallengeExpired is surfaced by Confirm when the preview's
// expires_at is in the past. The HTTP layer returns 403.
var ErrChallengeExpired = errors.New("service: challenge expired")

// ConfirmResult is what Confirm returns to the HTTP handler.
type ConfirmResult struct {
	ApprovalID     string
	AttestationRef string
	LogIndex       *int64
	TLogStatus     store.TLogStatus
}

// Confirm runs the full end-of-pipeline sequence:
//
//  1. Load the preview (must exist, must not be consumed, must still be
//     within expires_at).
//  2. Re-derive the WebAuthn challenge from the stored (nonce,
//     canonical) and verify the assertion against it.
//  3. Build the DSSE Statement with H_content as the subject digest.
//  4. Call the signing-service.
//  5. Persist the Approval row (status = attestation-pending).
//  6. Submit to the Transparency Log. On success, flip status to
//     "logged" and attach log_index. On TLog failure, leave the row at
//     attestation-pending so the reconciler can retry; the HTTP response
//     still returns ApprovalID + attestation_ref so the UI can carry on.
//
// The order (persist → submit) is deliberate: we never return a
// log_index to the caller for an approval that was not durably stored,
// and we never lose a signed envelope because we failed to log it.
func (o *Orchestrator) Confirm(ctx context.Context, previewID string, assertion webauthn.Assertion, userSub string) (ConfirmResult, error) {
	if previewID == "" {
		return ConfirmResult{}, errors.New("service: previewID is empty")
	}
	if userSub == "" {
		return ConfirmResult{}, errors.New("service: userSub is empty")
	}
	now := o.now()

	pv, err := o.Store.GetPreview(ctx, previewID)
	if err != nil {
		return ConfirmResult{}, err
	}
	if pv.UserSub != userSub {
		return ConfirmResult{}, store.ErrNotFound
	}
	if pv.ConsumedAt != nil {
		return ConfirmResult{}, store.ErrAlreadyConsumed
	}
	if !now.Before(pv.ExpiresAt) {
		return ConfirmResult{}, ErrChallengeExpired
	}

	// Defense-in-depth: recompute H_content from the stored canonical
	// content and make sure it still equals the stored content_hash.
	if content.RehashCanonical(pv.ContentCanonical) != pv.ContentHash {
		return ConfirmResult{}, fmt.Errorf("%w: stored canonical content does not match stored content_hash", ErrContentHashMismatch)
	}

	expectedChallenge := content.ChallengeFor(pv.Nonce, pv.ContentCanonical)
	cred, err := webauthn.Verify(o.WebauthnCfg, o.Webauthn, assertion, expectedChallenge)
	if err != nil {
		if errors.Is(err, webauthn.ErrChallengeMismatch) {
			return ConfirmResult{}, fmt.Errorf("%w: %v", ErrContentHashMismatch, err)
		}
		return ConfirmResult{}, err
	}
	if cred.UserSub != userSub {
		return ConfirmResult{}, webauthn.ErrAssertionInvalid
	}

	// Atomically mark the preview consumed so a parallel confirm cannot
	// reuse the same signed envelope. If this fails ErrAlreadyConsumed
	// we lose the race and must not continue.
	if _, err := o.Store.ConsumePreview(ctx, pv.ID, now); err != nil {
		return ConfirmResult{}, err
	}

	stmt := buildStatement(pv, userSub, o.AttestationIssuer, now)
	env, envHash, err := o.Signer.SignDSSE(ctx, o.SigningKeyRef, stmt)
	if err != nil {
		return ConfirmResult{}, err
	}

	approvalID, err := o.genID("ap")
	if err != nil {
		return ConfirmResult{}, err
	}

	appr := store.Approval{
		ID:             approvalID,
		PreviewID:      pv.ID,
		SessionID:      pv.SessionID,
		UserSub:        userSub,
		ContentHash:    pv.ContentHash,
		Envelope:       env,
		AttestationRef: envHash,
		TLogStatus:     store.TLogPending,
		ConfirmedAt:    now,
	}
	if err := o.Store.SaveApproval(ctx, appr); err != nil {
		return ConfirmResult{}, err
	}

	receipt, submitErr := o.Submitter.Submit(ctx, env, envHash)
	if submitErr != nil {
		// Approval row stays at attestation-pending; record the error
		// for diagnostics but return success-with-pending to the client.
		_ = o.Store.MarkApprovalTLogError(ctx, approvalID, submitErr.Error())
		return ConfirmResult{
			ApprovalID:     approvalID,
			AttestationRef: envHash,
			TLogStatus:     store.TLogPending,
		}, nil
	}
	loggedAt := receipt.LoggedAt
	if loggedAt.IsZero() {
		loggedAt = now
	}
	if err := o.Store.MarkApprovalLogged(ctx, approvalID, receipt.LogIndex, loggedAt); err != nil {
		return ConfirmResult{}, err
	}
	idx := receipt.LogIndex
	return ConfirmResult{
		ApprovalID:     approvalID,
		AttestationRef: envHash,
		LogIndex:       &idx,
		TLogStatus:     store.TLogLogged,
	}, nil
}

func (o *Orchestrator) now() time.Time {
	if o.Now != nil {
		return o.Now()
	}
	return time.Now()
}

// NewID returns an opaque ID with the given prefix. Exposed so the HTTP
// layer can mint preview_ids with the same injectable generator.
func (o *Orchestrator) NewID(prefix string) (string, error) {
	if o.GenID != nil {
		return o.GenID(prefix)
	}
	return sessions.DefaultIDGenerator(prefix)
}

func (o *Orchestrator) genID(prefix string) (string, error) { return o.NewID(prefix) }

// buildStatement renders the in-toto v1 Statement for an approval. The
// subject.digest IS the H_content of the preview; verifiers rehash the
// stored canonical content to prove the signature covers it.
func buildStatement(pv store.Preview, userSub, issuer string, performedAt time.Time) signer.Statement {
	// Strip the "sha256:" prefix for the digest map, per in-toto convention.
	digest := pv.ContentHash
	if len(digest) > 7 && digest[:7] == "sha256:" {
		digest = digest[7:]
	}
	predicate := map[string]any{
		"approval_schema": "basicstack.de/attestations/approval/v1",
		"preview_id":      pv.ID,
		"session_id":      pv.SessionID,
		"content_hash":    pv.ContentHash,
		"performed_by": map[string]any{
			"iss":        issuer,
			"sub":        userSub,
			"session_id": pv.SessionID,
		},
		"performed_at":        performedAt.UTC().Format(time.RFC3339),
		"verification_digits": pv.VerificationDigits,
	}
	return signer.Statement{
		"_type": "https://in-toto.io/Statement/v1",
		"subject": []any{
			map[string]any{
				"name":   "approval/" + pv.ID,
				"digest": map[string]any{"sha256": digest},
			},
		},
		"predicateType": "https://basicstack.de/attestations/approval/v1",
		"predicate":     predicate,
	}
}