import 'package:flutter/material.dart';
import '../../services/call_session.dart';

/// Settings / key-management screen.
///
/// Allows the user to enter a shared passphrase and derive the AES-256 key.
/// The passphrase is never stored — only a non-reversible fingerprint is kept
/// via [CallSession.getSavedFingerprint].
class SettingsScreen extends StatefulWidget {
  final CallSession session;
  const SettingsScreen({super.key, required this.session});

  @override
  State<SettingsScreen> createState() => _SettingsScreenState();
}

class _SettingsScreenState extends State<SettingsScreen> {
  final _ctrl   = TextEditingController();
  final _formKey = GlobalKey<FormState>();

  bool   _loading     = false;
  bool   _obscure     = true;
  String? _fingerprint;
  String? _errorMsg;

  @override
  void initState() {
    super.initState();
    _loadFingerprint();
  }

  Future<void> _loadFingerprint() async {
    final fp = await widget.session.getSavedFingerprint();
    if (mounted) setState(() => _fingerprint = fp);
  }

  Future<void> _deriveKey() async {
    if (!(_formKey.currentState?.validate() ?? false)) return;
    setState(() { _loading = true; _errorMsg = null; });

    // Capture messenger before async gap to avoid BuildContext-across-await lint.
    final messenger = ScaffoldMessenger.of(context);

    final ok = await widget.session.loadPassphrase(_ctrl.text.trim());

    if (!mounted) return;
    if (ok) {
      await _loadFingerprint();
      messenger.showSnackBar(
        const SnackBar(
          content: Text('Key derived successfully'),
          backgroundColor: Color(0xFF00C853),
        ),
      );
    } else {
      setState(() => _errorMsg = widget.session.lastError);
    }
    setState(() => _loading = false);
  }

  Future<void> _clearKey() async {
    await widget.session.clearKey();
    _ctrl.clear();
    if (mounted) {
      setState(() => _fingerprint = null);
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Key cleared')),
      );
    }
  }

  @override
  void dispose() {
    _ctrl.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: const Color(0xFF0D0D1A),
      appBar: AppBar(
        backgroundColor: const Color(0xFF0D0D1A),
        title: const Text('Encryption Key',
            style: TextStyle(color: Colors.white, letterSpacing: 1.5)),
        iconTheme: const IconThemeData(color: Colors.white),
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(24),
        child: Form(
          key: _formKey,
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              // ── Info card ─────────────────────────────────────────
              Container(
                padding: const EdgeInsets.all(16),
                decoration: BoxDecoration(
                  color: const Color(0xFF1A1A2E),
                  borderRadius: BorderRadius.circular(12),
                  border: Border.all(color: Colors.blueAccent.withValues(alpha: 0.3)),
                ),
                child: const Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Row(children: [
                      Icon(Icons.lock_outline, color: Colors.blueAccent, size: 18),
                      SizedBox(width: 8),
                      Text('Pre-shared key setup',
                          style: TextStyle(
                              color: Colors.blueAccent,
                              fontWeight: FontWeight.bold)),
                    ]),
                    SizedBox(height: 8),
                    Text(
                      'Both devices must use the SAME passphrase before '
                      'starting a call. The passphrase is converted to a '
                      '256-bit AES key using PBKDF2-HMAC-SHA256 '
                      '(100 000 iterations).\n\n'
                      'Exchange the passphrase over a separate secure channel '
                      '(in person, encrypted message, etc.).',
                      style: TextStyle(color: Colors.white60, height: 1.5, fontSize: 13),
                    ),
                  ],
                ),
              ),

              const SizedBox(height: 28),

              // ── Passphrase field ──────────────────────────────────
              TextFormField(
                controller: _ctrl,
                obscureText: _obscure,
                style: const TextStyle(color: Colors.white, letterSpacing: 1.2),
                decoration: InputDecoration(
                  labelText: 'Shared passphrase',
                  labelStyle: const TextStyle(color: Colors.white54),
                  filled: true,
                  fillColor: const Color(0xFF1A1A2E),
                  border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(10),
                      borderSide: BorderSide.none),
                  suffixIcon: IconButton(
                    icon: Icon(
                        _obscure ? Icons.visibility_off : Icons.visibility,
                        color: Colors.white38),
                    onPressed: () => setState(() => _obscure = !_obscure),
                  ),
                ),
                validator: (v) {
                  if (v == null || v.trim().isEmpty) return 'Enter a passphrase';
                  if (v.trim().length < 8) return 'Minimum 8 characters';
                  return null;
                },
              ),

              if (_errorMsg != null) ...[
                const SizedBox(height: 10),
                Text(_errorMsg!,
                    style: const TextStyle(color: Colors.redAccent, fontSize: 13)),
              ],

              const SizedBox(height: 20),

              // ── Derive button ─────────────────────────────────────
              ElevatedButton.icon(
                onPressed: _loading ? null : _deriveKey,
                icon: _loading
                    ? const SizedBox(
                        width: 18, height: 18,
                        child: CircularProgressIndicator(strokeWidth: 2,
                            color: Colors.white))
                    : const Icon(Icons.vpn_key_rounded),
                label: const Text('DERIVE KEY',
                    style: TextStyle(letterSpacing: 1.5)),
                style: ElevatedButton.styleFrom(
                  backgroundColor: Colors.blueAccent,
                  padding: const EdgeInsets.symmetric(vertical: 14),
                  shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(10)),
                ),
              ),

              const SizedBox(height: 32),

              // ── Key fingerprint ───────────────────────────────────
              if (_fingerprint != null) ...[
                const Text('ACTIVE KEY FINGERPRINT',
                    style: TextStyle(
                        color: Colors.white38, fontSize: 11, letterSpacing: 1.5)),
                const SizedBox(height: 8),
                Container(
                  padding:
                      const EdgeInsets.symmetric(horizontal: 16, vertical: 12),
                  decoration: BoxDecoration(
                    color: const Color(0xFF1A1A2E),
                    borderRadius: BorderRadius.circular(10),
                    border: Border.all(color: const Color(0xFF00C853).withValues(alpha: 0.4)),
                  ),
                  child: Row(
                    children: [
                      const Icon(Icons.fingerprint,
                          color: Color(0xFF00C853), size: 20),
                      const SizedBox(width: 12),
                      Text(
                        _fingerprint!,
                        style: const TextStyle(
                          color: Color(0xFF00C853),
                          fontFamily: 'monospace',
                          fontSize: 18,
                          letterSpacing: 4,
                        ),
                      ),
                    ],
                  ),
                ),
                const SizedBox(height: 8),
                const Text(
                  'Show this fingerprint to your peer — it must match on both devices.',
                  style: TextStyle(color: Colors.white38, fontSize: 12, height: 1.4),
                ),
                const SizedBox(height: 24),
                OutlinedButton.icon(
                  onPressed: _clearKey,
                  icon: const Icon(Icons.delete_outline, color: Colors.redAccent),
                  label: const Text('CLEAR KEY',
                      style: TextStyle(color: Colors.redAccent, letterSpacing: 1.5)),
                  style: OutlinedButton.styleFrom(
                    side: const BorderSide(color: Colors.redAccent),
                    padding: const EdgeInsets.symmetric(vertical: 12),
                    shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(10)),
                  ),
                ),
              ],

              const SizedBox(height: 40),

              // ── Technical info ────────────────────────────────────
              const Divider(color: Colors.white12),
              const SizedBox(height: 16),
              const Text('SYSTEM PARAMETERS',
                  style: TextStyle(
                      color: Colors.white24, fontSize: 11, letterSpacing: 1.5)),
              const SizedBox(height: 12),
              _paramRow('Cipher',     'AES-256-CTR'),
              _paramRow('KDF',        'PBKDF2-HMAC-SHA256 (100k iter)'),
              _paramRow('FEC',        'Reed-Solomon RS(15,11) GF(16)'),
              _paramRow('Modulation', '4-FSK  600 baud  1200 bps'),
              _paramRow('Voice',      'LPC-10  ~360 bps  200 ms frames'),
              _paramRow('Channel',    'Acoustic FSK over SIM call'),
            ],
          ),
        ),
      ),
    );
  }

  static Widget _paramRow(String label, String value) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 4),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            Text(label,
                style:
                    const TextStyle(color: Colors.white38, fontSize: 12)),
            Text(value,
                style: const TextStyle(
                    color: Colors.white60,
                    fontSize: 12,
                    fontFamily: 'monospace')),
          ],
        ),
      );
}