package auth

import (
	"context"
	"crypto/rand"
	"database/sql"
	"errors"
	"fmt"
	"log"
	"time"

	"golang.org/x/crypto/bcrypt"
)

// Errors returned by the auth service.
var (
	ErrInvalidPIN     = errors.New("auth: invalid PIN")
	ErrTooManyAttempts = errors.New("auth: too many failed attempts, please wait")
	ErrOperatorLocked = errors.New("auth: operator account locked")
	ErrOperatorExists = errors.New("auth: operator already exists")
)

// Operator represents an authenticated operator in the system.
type Operator struct {
	ID        string `json:"id"`
	Name      string `json:"name"`
	Role      string `json:"role"`
	CreatedAt int64  `json:"created_at"`
	UpdatedAt int64  `json:"updated_at"`
}

// AuditRecorder is called by the auth service to log audit events.
// This breaks the import cycle between auth and audit packages.
type AuditRecorder func(ctx context.Context, action, targetType, targetID string, metadata map[string]interface{}) error

// AuthService handles PIN-based authentication with rate limiting.
type AuthService struct {
	db       *sql.DB
	jwt      *JWTService
	recorder AuditRecorder // optional, for audit logging
}

// NewAuthService creates a new authentication service.
func NewAuthService(db *sql.DB, jwt *JWTService) *AuthService {
	return &AuthService{
		db:  db,
		jwt: jwt,
	}
}

// SetAuditRecorder sets the audit recorder for logging auth events.
// Called after the audit trail is initialized to break the init cycle.
func (s *AuthService) SetAuditRecorder(recorder AuditRecorder) {
	s.recorder = recorder
}

// initRateLimiter ensures the login_attempts table exists.
func (s *AuthService) initRateLimiter() error {
	_, err := s.db.Exec(`CREATE TABLE IF NOT EXISTS login_attempts (
		operator_id TEXT PRIMARY KEY,
		consecutive_failures INTEGER NOT NULL DEFAULT 0,
		last_failure_at INTEGER NOT NULL DEFAULT 0,
		locked_until INTEGER NOT NULL DEFAULT 0
	)`)
	return err
}

// Login authenticates an operator by PIN and returns a JWT token.
// It checks rate limiting before attempting authentication.
func (s *AuthService) Login(ctx context.Context, pin string) (token string, operator Operator, err error) {
	if pin == "" {
		return "", Operator{}, ErrInvalidPIN
	}

	// Ensure rate limiter table exists
	if err := s.initRateLimiter(); err != nil {
		return "", Operator{}, fmt.Errorf("auth: init rate limiter: %w", err)
	}

	// Load all operators from DB
	operators, err := s.loadOperators(ctx)
	if err != nil {
		return "", Operator{}, fmt.Errorf("auth: load operators: %w", err)
	}

	// Try to match PIN against each operator
	for _, op := range operators {
		if err := s.checkRateLimit(ctx, op.id); err != nil {
			// Skip rate-limited operators silently during scan
			continue
		}

		if err := bcrypt.CompareHashAndPassword([]byte(op.pinHash), []byte(pin)); err == nil {
			// Match found - reset failure counter and issue JWT
			s.resetFailures(ctx, op.id)

			operator = Operator{
				ID:        op.id,
				Name:      op.name,
				Role:      op.role,
				CreatedAt: op.createdAt,
				UpdatedAt: op.updatedAt,
			}

			token, err = s.jwt.NewToken(op.id, op.role)
			if err != nil {
				return "", Operator{}, fmt.Errorf("auth: issue token: %w", err)
			}

			// Log successful login
			if s.recorder != nil {
				_ = s.recorder(ctx, "operator.login", "operator", op.id, map[string]interface{}{
					"operator_name": op.name,
					"role":          op.role,
				})
			}

			return token, operator, nil
		}
	}

	// No match found - record failure for ALL operators (since PIN is global, not per-operator)
	// But we track per-operator to prevent brute-force enumeration
	// Actually, since the PIN is compared against all operators, we can't know
	// which operator was targeted. Record a global failure counter instead.
	// However, the spec says "keyed by operator ID" - this makes more sense
	// when PINs are unique per operator (which they should be in practice).
	// We'll record failure against a sentinel "global" key.
	s.recordFailure(ctx, "_global")
	globalLimited, _ := s.isRateLimited(ctx, "_global")
	if globalLimited {
		// Check if hard locked
		locked, _ := s.isLockedOut(ctx, "_global")
		if locked {
			return "", Operator{}, ErrOperatorLocked
		}
		return "", Operator{}, ErrTooManyAttempts
	}

	return "", Operator{}, ErrInvalidPIN
}

// operatorRow holds a full operator row for internal use during login.
type operatorRow struct {
	id        string
	name      string
	pinHash   string
	role      string
	createdAt int64
	updatedAt int64
}

// loadOperators loads all operators from the database.
func (s *AuthService) loadOperators(ctx context.Context) ([]operatorRow, error) {
	rows, err := s.db.QueryContext(ctx,
		"SELECT id, name, pin_hash, role, created_at, updated_at FROM operators")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var operators []operatorRow
	for rows.Next() {
		var op operatorRow
		if err := rows.Scan(&op.id, &op.name, &op.pinHash, &op.role, &op.createdAt, &op.updatedAt); err != nil {
			return nil, err
		}
		operators = append(operators, op)
	}
	return operators, rows.Err()
}

// checkRateLimit checks if the operator is currently rate-limited.
func (s *AuthService) checkRateLimit(ctx context.Context, operatorID string) error {
	limited, err := s.isRateLimited(ctx, operatorID)
	if err != nil {
		return err
	}
	if limited {
		locked, _ := s.isLockedOut(ctx, operatorID)
		if locked {
			return ErrOperatorLocked
		}
		return ErrTooManyAttempts
	}
	return nil
}

// isRateLimited returns true if the operator has exceeded the failure threshold.
func (s *AuthService) isRateLimited(ctx context.Context, operatorID string) (bool, error) {
	var failures int
	var lockedUntil int64
	err := s.db.QueryRowContext(ctx,
		"SELECT consecutive_failures, locked_until FROM login_attempts WHERE operator_id = ?",
		operatorID).Scan(&failures, &lockedUntil)
	if errors.Is(err, sql.ErrNoRows) {
		return false, nil
	}
	if err != nil {
		return false, err
	}

	now := time.Now().Unix()

	// Check lockout
	if lockedUntil > now {
		return true, nil
	}

	return false, nil
}

// isLockedOut returns true if the operator is in a hard lockout (10+ failures).
func (s *AuthService) isLockedOut(ctx context.Context, operatorID string) (bool, error) {
	var failures int
	var lockedUntil int64
	err := s.db.QueryRowContext(ctx,
		"SELECT consecutive_failures, locked_until FROM login_attempts WHERE operator_id = ?",
		operatorID).Scan(&failures, &lockedUntil)
	if errors.Is(err, sql.ErrNoRows) {
		return false, nil
	}
	if err != nil {
		return false, err
	}

	now := time.Now().Unix()
	return failures >= 10 && lockedUntil > now, nil
}

// recordFailure increments the failure counter and applies rate limiting.
func (s *AuthService) recordFailure(ctx context.Context, operatorID string) {
	now := time.Now().Unix()

	// Upsert the failure record
	_, err := s.db.ExecContext(ctx, `
		INSERT INTO login_attempts (operator_id, consecutive_failures, last_failure_at, locked_until)
		VALUES (?, 1, ?, 0)
		ON CONFLICT(operator_id) DO UPDATE SET
			consecutive_failures = consecutive_failures + 1,
			last_failure_at = ?
	`, operatorID, now, now)
	if err != nil {
		log.Printf("auth: record failure error: %v", err)
		return
	}

	// Get current failure count to apply rate limiting
	var failures int
	err = s.db.QueryRowContext(ctx,
		"SELECT consecutive_failures FROM login_attempts WHERE operator_id = ?",
		operatorID).Scan(&failures)
	if err != nil {
		log.Printf("auth: get failure count error: %v", err)
		return
	}

	// Apply rate limiting thresholds
	var lockDuration time.Duration
	switch {
	case failures >= 10:
		lockDuration = 30 * time.Minute
	case failures >= 8:
		lockDuration = 5 * time.Minute
	case failures >= 5:
		lockDuration = 30 * time.Second
	default:
		return
	}

	lockedUntil := now + int64(lockDuration.Seconds())
	_, err = s.db.ExecContext(ctx,
		"UPDATE login_attempts SET locked_until = ? WHERE operator_id = ?",
		lockedUntil, operatorID)
	if err != nil {
		log.Printf("auth: set lockout error: %v", err)
		return
	}

	log.Printf("auth: rate limiting activated for %s (failures=%d, locked_for=%s)",
		operatorID, failures, lockDuration)

	// Emit audit entry on 5+ failures
	if s.recorder != nil && failures >= 5 {
		_ = s.recorder(ctx, "operator.login_rate_limited", "operator", operatorID, map[string]interface{}{
			"failures":     failures,
			"locked_until": lockedUntil,
		})
	}
}

// resetFailures clears the failure counter for an operator.
func (s *AuthService) resetFailures(ctx context.Context, operatorID string) {
	_, err := s.db.ExecContext(ctx,
		"DELETE FROM login_attempts WHERE operator_id = ?", operatorID)
	if err != nil {
		log.Printf("auth: reset failures error: %v", err)
	}

	// Also reset global counter on any successful login
	_, err = s.db.ExecContext(ctx,
		"DELETE FROM login_attempts WHERE operator_id = '_global'")
	if err != nil {
		log.Printf("auth: reset global failures error: %v", err)
	}
}

// GetFailureCount returns the current consecutive failure count for rate limiting tests.
func (s *AuthService) GetFailureCount(ctx context.Context, operatorID string) (int, error) {
	var failures int
	err := s.db.QueryRowContext(ctx,
		"SELECT consecutive_failures FROM login_attempts WHERE operator_id = ?",
		operatorID).Scan(&failures)
	if errors.Is(err, sql.ErrNoRows) {
		return 0, nil
	}
	return failures, err
}

// HashPIN hashes a PIN using bcrypt with cost 12.
func HashPIN(pin string) (string, error) {
	hash, err := bcrypt.GenerateFromPassword([]byte(pin), 12)
	if err != nil {
		return "", fmt.Errorf("auth: hash PIN: %w", err)
	}
	return string(hash), nil
}

// CreateOperator creates a new operator with a hashed PIN.
func (s *AuthService) CreateOperator(ctx context.Context, name, pin, role string) (Operator, error) {
	if name == "" {
		return Operator{}, fmt.Errorf("auth: empty operator name")
	}
	if pin == "" {
		return Operator{}, fmt.Errorf("auth: empty PIN")
	}
	if role != "admin" && role != "floor" && role != "viewer" {
		return Operator{}, fmt.Errorf("auth: invalid role %q (must be admin, floor, or viewer)", role)
	}

	hash, err := HashPIN(pin)
	if err != nil {
		return Operator{}, err
	}

	id := generateUUID()
	now := time.Now().Unix()

	_, err = s.db.ExecContext(ctx,
		"INSERT INTO operators (id, name, pin_hash, role, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?)",
		id, name, hash, role, now, now)
	if err != nil {
		return Operator{}, fmt.Errorf("auth: create operator: %w", err)
	}

	return Operator{
		ID:        id,
		Name:      name,
		Role:      role,
		CreatedAt: now,
		UpdatedAt: now,
	}, nil
}

// ListOperators returns all operators (without PIN hashes).
func (s *AuthService) ListOperators(ctx context.Context) ([]Operator, error) {
	rows, err := s.db.QueryContext(ctx,
		"SELECT id, name, role, created_at, updated_at FROM operators ORDER BY name")
	if err != nil {
		return nil, fmt.Errorf("auth: list operators: %w", err)
	}
	defer rows.Close()

	var operators []Operator
	for rows.Next() {
		var op Operator
		if err := rows.Scan(&op.ID, &op.Name, &op.Role, &op.CreatedAt, &op.UpdatedAt); err != nil {
			return nil, err
		}
		operators = append(operators, op)
	}
	return operators, rows.Err()
}

// UpdateOperator updates an operator's name, PIN (optional), and/or role.
// If pin is empty, the PIN is not changed.
func (s *AuthService) UpdateOperator(ctx context.Context, id, name, pin, role string) error {
	if id == "" {
		return fmt.Errorf("auth: empty operator ID")
	}
	if role != "" && role != "admin" && role != "floor" && role != "viewer" {
		return fmt.Errorf("auth: invalid role %q", role)
	}

	now := time.Now().Unix()

	if pin != "" {
		hash, err := HashPIN(pin)
		if err != nil {
			return err
		}
		_, err = s.db.ExecContext(ctx,
			"UPDATE operators SET name = ?, pin_hash = ?, role = ?, updated_at = ? WHERE id = ?",
			name, hash, role, now, id)
		if err != nil {
			return fmt.Errorf("auth: update operator: %w", err)
		}
	} else {
		_, err := s.db.ExecContext(ctx,
			"UPDATE operators SET name = ?, role = ?, updated_at = ? WHERE id = ?",
			name, role, now, id)
		if err != nil {
			return fmt.Errorf("auth: update operator: %w", err)
		}
	}

	return nil
}

// generateUUID generates a v4 UUID.
func generateUUID() string {
	b := make([]byte, 16)
	_, _ = rand.Read(b)
	b[6] = (b[6] & 0x0f) | 0x40 // Version 4
	b[8] = (b[8] & 0x3f) | 0x80 // Variant 1
	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
		b[0:4], b[4:6], b[6:8], b[8:10], b[10:16])
}