package auth

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"

	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/audit"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/auth/webauthn"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/store"
)

// Credentials is the WebAuthn credential store contract (SPEC-004 §4
// `webauthn_credentials`). Credentials hang off an IDENTITY, never a user
// (D-008): identity rotation destroys them.
type Credentials interface {
	// PutWebAuthnCredential stores a credential for an identity (upsert by
	// credential id).
	PutWebAuthnCredential(ctx context.Context, identityID int64, c webauthn.Credential) error

	// WebAuthnCredentials returns every credential of an identity.
	WebAuthnCredentials(ctx context.Context, identityID int64) ([]webauthn.Credential, error)

	// UpdateWebAuthnSignCount records an authenticator's advanced counter after
	// a successful assertion (clone detection).
	UpdateWebAuthnSignCount(ctx context.Context, identityID int64, credentialID []byte, signCount uint32) error

	// HasWebAuthnCredential reports whether an identity has at least one
	// registered passkey — the enrollment two-factor check (SPEC-006 §4 AC-2).
	HasWebAuthnCredential(ctx context.Context, identityID int64) (bool, error)
}

var _ Credentials = (*IdentitiesService)(nil)

// PutWebAuthnCredential implements Credentials.
func (s *IdentitiesService) PutWebAuthnCredential(ctx context.Context, identityID int64, c webauthn.Credential) error {
	if len(c.ID) == 0 {
		return errors.New("auth: webauthn credential id is empty")
	}
	if _, err := s.identityByID(identityID); err != nil {
		return err
	}
	if _, err := s.db.Exec(
		`INSERT INTO webauthn_credentials
			(credential_id, identity_id, public_key, sign_count, transports, aaguid, created_at)
		 VALUES (?, ?, ?, ?, ?, ?, ?)
		 ON CONFLICT(credential_id) DO UPDATE SET
			public_key = excluded.public_key,
			sign_count = excluded.sign_count,
			transports = excluded.transports,
			aaguid     = excluded.aaguid`,
		c.ID, identityID, c.PublicKey, int64(c.SignCount),
		strings.Join(c.Transports, ","), nullBytes(c.AAGUID),
		store.FormatTime(s.clock()),
	); err != nil {
		return fmt.Errorf("auth: store webauthn credential: %w", err)
	}

	// No key material in the trail — identifiers only (A9).
	s.record(ctx, audit.Event{
		Action:  "webauthn.credential.put",
		Subject: fmt.Sprintf("identity:%d", identityID),
		Detail:  fmt.Sprintf("credential_id=%s", fingerprint(c.ID)),
	})
	return nil
}

// WebAuthnCredentials implements Credentials.
func (s *IdentitiesService) WebAuthnCredentials(ctx context.Context, identityID int64) ([]webauthn.Credential, error) {
	rows, err := s.db.Query(
		`SELECT credential_id, public_key, sign_count, transports, aaguid
		   FROM webauthn_credentials WHERE identity_id = ? ORDER BY created_at`, identityID,
	)
	if err != nil {
		return nil, fmt.Errorf("auth: load webauthn credentials: %w", err)
	}
	defer rows.Close()

	var out []webauthn.Credential
	for rows.Next() {
		var (
			c          webauthn.Credential
			signCount  int64
			transports string
			aaguid     []byte
		)
		if err := rows.Scan(&c.ID, &c.PublicKey, &signCount, &transports, &aaguid); err != nil {
			return nil, fmt.Errorf("auth: scan webauthn credential: %w", err)
		}
		c.SignCount = uint32(signCount)
		c.AAGUID = aaguid
		if transports != "" {
			c.Transports = strings.Split(transports, ",")
		}
		out = append(out, c)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("auth: iterate webauthn credentials: %w", err)
	}
	return out, nil
}

// UpdateWebAuthnSignCount implements Credentials. It is a no-op when the
// credential is unknown — sign-count tracking is best-effort, never a gate.
func (s *IdentitiesService) UpdateWebAuthnSignCount(ctx context.Context, identityID int64, credentialID []byte, signCount uint32) error {
	if _, err := s.db.Exec(
		`UPDATE webauthn_credentials SET sign_count = ?
		  WHERE credential_id = ? AND identity_id = ?`,
		int64(signCount), credentialID, identityID,
	); err != nil {
		return fmt.Errorf("auth: update sign count: %w", err)
	}
	return nil
}

// HasWebAuthnCredential implements Credentials.
func (s *IdentitiesService) HasWebAuthnCredential(ctx context.Context, identityID int64) (bool, error) {
	var one int
	err := s.db.QueryRow(
		`SELECT 1 FROM webauthn_credentials WHERE identity_id = ? LIMIT 1`, identityID,
	).Scan(&one)
	switch {
	case errors.Is(err, sql.ErrNoRows):
		return false, nil
	case err != nil:
		return false, fmt.Errorf("auth: webauthn credential lookup: %w", err)
	}
	return true, nil
}

// nullBytes maps an empty blob to NULL.
func nullBytes(b []byte) any {
	if len(b) == 0 {
		return nil
	}
	return b
}

// fingerprint is a short label for an opaque credential id, for the audit trail
// only — the credential id is public, but the trail keeps just a prefix.
func fingerprint(id []byte) string {
	if len(id) == 0 {
		return ""
	}
	if len(id) > 8 {
		id = id[:8]
	}
	return fmt.Sprintf("%x", id)
}