class Container {
  constructor() {
    this._services = new Map();
    this._singletons = new Map();
    this._resolving = new Set();
  }

  register(name, factory, isSingleton = true) {
    if (typeof name !== 'string' || name.trim() === '') {
      throw new Error('Service name must be a non-empty string');
    }
    if (typeof factory !== 'function') {
      throw new Error('Factory must be a function');
    }
    if (this._services.has(name)) {
      throw new Error(`Service "${name}" is already registered`);
    }

    this._services.set(name, { factory, isSingleton });
    return this;
  }

  resolve(name) {
    if (!this._services.has(name)) {
      throw new Error(`Service "${name}" is not registered`);
    }

    if (this._resolving.has(name)) {
      const chain = Array.from(this._resolving).join(' -> ');
      throw new Error(
        `Circular dependency detected: ${chain} -> ${name}. ` +
        `This creates a circular reference that cannot be resolved.`
      );
    }

    const service = this._services.get(name);

    if (service.isSingleton && this._singletons.has(name)) {
      return this._singletons.get(name);
    }

    this._resolving.add(name);

    try {
      const instance = service.factory(this);

      if (service.isSingleton) {
        this._singletons.set(name, instance);
      }

      return instance;
    } finally {
      this._resolving.delete(name);
    }
  }

  has(name) {
    return this._services.has(name);
  }

  unregister(name) {
    if (!this._services.has(name)) {
      return false;
    }
    this._services.delete(name);
    this._singletons.delete(name);
    return true;
  }

  clear() {
    this._services.clear();
    this._singletons.clear();
    this._resolving.clear();
  }
}

module.exports = Container;