using System;

namespace Swan.Configuration {
  /// <summary>
  /// Base class for objects whose configuration may be locked,
  /// thus becoming read-only, at a certain moment in their lifetime.
  /// </summary>
  public abstract class ConfiguredObject {
    private readonly Object _syncRoot = new Object();
    private Boolean _configurationLocked;

    /// <summary>
    /// Gets a value indicating whether s configuration has already been locked
    /// and has therefore become read-only.
    /// </summary>
    /// <value>
    /// <see langword="true"/> if the configuration is locked; otherwise, <see langword="false"/>.
    /// </value>
    /// <seealso cref="EnsureConfigurationNotLocked"/>
    protected Boolean ConfigurationLocked {
      get {
        lock(this._syncRoot) {
          return this._configurationLocked;
        }
      }
    }

    /// <summary>
    /// <para>Locks this instance's configuration, preventing further modifications.</para>
    /// </summary>
    /// <remarks>
    /// <para>Configuration locking must be enforced by derived classes
    /// by calling <see cref="EnsureConfigurationNotLocked"/> at the start
    /// of methods and property setters that could change the object's
    /// configuration.</para>
    /// <para>Immediately before locking the configuration, this method calls <see cref="OnBeforeLockConfiguration"/>
    /// as a last chance to validate configuration data, and to lock the configuration of contained objects.</para>
    /// </remarks>
    /// <seealso cref="OnBeforeLockConfiguration"/>
    protected void LockConfiguration() {
      lock(this._syncRoot) {
        if(this._configurationLocked) {
          return;
        }

        this.OnBeforeLockConfiguration();
        this._configurationLocked = true;
      }
    }

    /// <summary>
    /// Called immediately before locking the configuration.
    /// </summary>
    /// <seealso cref="LockConfiguration"/>
    protected virtual void OnBeforeLockConfiguration() {
    }

    /// <summary>
    /// Checks whether a module's configuration has become read-only
    /// and, if so, throws an <see cref="InvalidOperationException"/>.
    /// </summary>
    /// <exception cref="InvalidOperationException">The configuration is locked.</exception>
    /// <seealso cref="ConfigurationLocked"/>
    protected void EnsureConfigurationNotLocked() {
      if(this.ConfigurationLocked) {
        throw new InvalidOperationException($"Configuration of this {this.GetType().Name} instance is locked.");
      }
    }
  }
}