/// <overloads>
/// Starts an interactive replay.</overloads>
/// <summary>
/// Replays all commands present in the specified <see cref="WorldState"/> but missing from
/// the current <see cref="WorldState"/>.</summary>
/// <param name="worldState">
/// The <see cref="WorldState"/> containing the new commands to show in an interactive
/// replay.</param>
/// <param name="isComputer">
/// The new value for the <see cref="IsComputerTurn"/> property while the replay is active.
/// </param>
/// <exception cref="ArgumentException">
/// One of the conditions described in <see cref="History.AddCommands"/>.</exception>
/// <exception cref="ArgumentNullException">
/// <paramref name="worldState"/> is a null reference.</exception>
/// <exception cref="PropertyValueException">
/// The current session <see cref="Session.State"/> is neither <see
/// cref="SessionState.Closed"/>, <see cref="SessionState.Computer"/>, nor <see
/// cref="SessionState.Human"/>.</exception>
/// <remarks><para>
/// <b>Start</b> sets the session <see cref="Session.State"/> to <see
/// cref="SessionState.Replay"/> and <see cref="CurrentState"/> to <see
/// cref="ReplayState.Play"/>, and begins an interactive replay of all history commands
/// stored in the specified <paramref name="worldState"/> that are not present in the <see
/// cref="WorldState.History"/> of the current session's <see cref="Session.WorldState"/>.
/// </para><para>
/// When the replay ends or is aborted, the current session's <see
/// cref="Session.WorldState"/> will be set to the specified <paramref name="worldState"/>,
/// and its previous value will be discarded. The session's original <see
/// cref="Graphics.MapView.SelectedSite"/> is likewise discarded and replaced with <see
/// cref="Site.InvalidLocation"/>.
/// </para><para>
/// The specified <paramref name="worldState"/> may contain the same number of commands as
/// that of the current <see cref="Session"/>. In this case, <b>Start</b> briefly highlights
/// the home site of the active faction but does nothing else.</para></remarks>
public void Start(WorldState worldState, bool isComputer)
{
CheckStartState();
// store computer turn flag
IsComputerTurn = isComputer;
// store current history command count
History history = Session.Instance.WorldState.History;
int index = history.Commands.Count;
// append new history commands, if any
history.AddCommands(worldState.History);
// set restore point to new world state
this._originalWorldState = worldState;
// save current session state
this._originalState = Session.State;
// ignore current site selection
this._originalSelected = Site.InvalidLocation;
// start replay with first new command
Debug.Assert(index <= history.Commands.Count);
this._commandIndex = index;
// switch session to Replay state
Session.State = SessionState.Replay;
MainWindow.Instance.StatusMessage.Push(Global.Strings.StatusReplay);
// show active faction's home site
ShowFaction(Session.Instance.WorldState.ActiveFaction);
// enter Play state
CurrentState = ReplayState.Play;
AsyncAction.Run(PlayCommands);
}