/// systemd service [Type].
enum SystemdType { simple, exec, forking, oneshot, notify }

/// systemd Restart= policy.
enum RestartPolicy { onFailure, always, no }

extension RestartPolicyX on RestartPolicy {
  String get value => switch (this) {
    RestartPolicy.onFailure => 'on-failure',
    RestartPolicy.always => 'always',
    RestartPolicy.no => 'no',
  };
  String get label => switch (this) {
    RestartPolicy.onFailure => 'On failure',
    RestartPolicy.always => 'Always',
    RestartPolicy.no => 'Never',
  };
}

/// Everything needed to generate and register a `.service` unit file.
class SystemdSpec {
  String unitName; // e.g. "orders" -> orders.service
  String description;
  SystemdType type;
  String user;
  String group;
  String workingDirectory;
  String execStart;
  RestartPolicy restart;
  int restartSec;

  /// Raw "KEY=VALUE" lines.
  String environmentLines;

  /// Extra `After=`/`Wants=` targets, e.g. mariadb.service.
  List<String> afterUnits;

  /// Add `SuccessExitStatus=143` (SIGTERM) — recommended for JVM apps.
  bool javaSuccessExit;

  bool enableOnBoot;
  bool startNow;

  SystemdSpec({
    this.unitName = '',
    this.description = '',
    this.type = SystemdType.simple,
    this.user = 'root',
    this.group = '',
    this.workingDirectory = '',
    this.execStart = '',
    this.restart = RestartPolicy.onFailure,
    this.restartSec = 5,
    this.environmentLines = '',
    List<String>? afterUnits,
    this.javaSuccessExit = false,
    this.enableOnBoot = true,
    this.startNow = true,
  }) : afterUnits = afterUnits ?? ['network.target'];

  /// Sanitized unit name (no spaces / .service suffix).
  String get safeName {
    var n = unitName.trim();
    if (n.toLowerCase().endsWith('.service')) {
      n = n.substring(0, n.length - '.service'.length);
    }
    return n.replaceAll(RegExp(r'[^A-Za-z0-9_.@-]'), '-');
  }

  List<String> get envList => environmentLines
      .split('\n')
      .map((e) => e.trim())
      .where((e) => e.isNotEmpty && e.contains('='))
      .toList();

  /// Renders the unit file contents.
  String render() {
    final b = StringBuffer();
    b.writeln('# Generated by PeachDeployments');
    b.writeln('[Unit]');
    b.writeln(
      'Description=${description.trim().isEmpty ? safeName : description.trim()}',
    );
    final afters = afterUnits.where((a) => a.trim().isNotEmpty).toList();
    if (afters.isNotEmpty) {
      b.writeln('After=${afters.join(' ')}');
      // Wants only the non-core targets (don't hard-require network.target).
      final wants = afters.where((a) => a != 'network.target').toList();
      if (wants.isNotEmpty) b.writeln('Wants=${wants.join(' ')}');
    }
    b.writeln();
    b.writeln('[Service]');
    b.writeln('Type=${type.name}');
    if (user.trim().isNotEmpty) b.writeln('User=${user.trim()}');
    if (group.trim().isNotEmpty) b.writeln('Group=${group.trim()}');
    if (workingDirectory.trim().isNotEmpty) {
      b.writeln('WorkingDirectory=${workingDirectory.trim()}');
    }
    for (final e in envList) {
      b.writeln('Environment="$e"');
    }
    b.writeln('ExecStart=${execStart.trim()}');
    b.writeln('Restart=${restart.value}');
    if (restart != RestartPolicy.no) b.writeln('RestartSec=$restartSec');
    if (javaSuccessExit) b.writeln('SuccessExitStatus=143');
    b.writeln();
    b.writeln('[Install]');
    b.writeln('WantedBy=multi-user.target');
    return b.toString();
  }

  /// Human-readable list of the commands the installer will run.
  List<String> plannedCommands({required bool sudo}) {
    final p = sudo ? 'sudo ' : '';
    final target = '/etc/systemd/system/$safeName.service';
    return [
      'write $target',
      '${p}chmod 644 $target',
      '${p}systemctl daemon-reload',
      if (enableOnBoot) '${p}systemctl enable $safeName',
      if (startNow) '${p}systemctl restart $safeName',
      '${p}systemctl status $safeName',
    ];
  }
}