// Copyright (C) 2022 WYATT GROUP
// Please see the AUTHORS file for details.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

part of 'pipeline.dart';

class MiddlewareNode {
  final Pipeline pipeline;

  Middleware? middleware;

  late MiddlewareNode _parent;
  late MiddlewareNode _child;
  final bool _isEnd;

  /// Reference to the previous [MiddlewareNode] in the [Pipeline]
  MiddlewareNode get parent => _parent;

  /// Reference to the next [MiddlewareNode] in the [Pipeline]
  MiddlewareNode get child => _child;

  /// Whether this is the begin [MiddlewareNode]
  bool get isBegin => _parent == this;

  /// Whether this is the end [MiddlewareNode]
  bool get isEnd => _child == this;

  /// Whether this is the first [MiddlewareNode]
  bool get isFirst => !isBegin && _parent == pipeline.begin;

  /// Whether this is the last [MiddlewareNode]
  bool get isLast => !isEnd && _child == pipeline.end;

  MiddlewareNode._(
    this.pipeline,
    this.middleware, {
    MiddlewareNode? parent,
    MiddlewareNode? child,
  }) : _isEnd = false {
    _parent = parent ?? this;
    _child = child ?? this;
  }

  MiddlewareNode._end(this.pipeline) : _isEnd = true {
    _child = this;
  }

  MiddlewareNode._begin(this.pipeline) : _isEnd = true {
    _parent = this;
  }

  /// Creates a new [MiddlewareNode] right **before** this in [pipeline]
  MiddlewareNode insertBefore(Middleware middleware) {
    if (isBegin) {
      throw StateError(
        'A MiddlewareNode cannot be inserted '
        'before begin MiddlewareNode',
      );
    }
    final newMiddlewareNode =
        MiddlewareNode._(pipeline, middleware, parent: _parent, child: this);
    _parent._child = newMiddlewareNode;
    _parent = newMiddlewareNode;
    pipeline._length++;
    return newMiddlewareNode;
  }

  /// Creates a new [MiddlewareNode] right **after** this in [pipeline]
  MiddlewareNode insertAfter(Middleware middleware) {
    if (isEnd) {
      throw StateError(
        'A MiddlewareNode cannot be inserted '
        'after end MiddlewareNode',
      );
    }
    final newMiddlewareNode =
        MiddlewareNode._(pipeline, middleware, parent: this, child: _child);
    _child._parent = newMiddlewareNode;
    _child = newMiddlewareNode;
    pipeline._length++;
    return newMiddlewareNode;
  }

  MiddlewareNode remove() {
    if (_isEnd) throw StateError('Cannot remove end MiddlewareNode');
    _child._parent = _parent;
    _parent._child = _child;
    pipeline._length--;
    return child;
  }
}