TF2 achievements: CBaseAchievement and event-driven tracking

// game/shared/tf/achievements_tf.h
class CBaseTFAchievementSimple : public CBaseAchievement
{
public:
    virtual bool LocalPlayerCanEarn();        // blocks MvM achievements in normal play, etc.
    virtual void FireGameEvent( IGameEvent *event );
};

class CBaseTFAchievement : public CBaseTFAchievementSimple
{
public:
    virtual bool LocalPlayerCanEarn();        // adds class check
};

// For achievements requiring a full round
class CTFAchievementFullRound : public CBaseTFAchievement
{
public:
    virtual void ListenForEvents();
    virtual void Event_OnRoundComplete( float flRoundTime, IGameEvent *event ) = 0;
};

// Example: tracking kills with a specific weapon
class CAchievement_TF_Soldier_KillWithDirectHit : public CBaseTFAchievement
{
    void Init()
    {
        SetFlags( ACH_SAVE_GLOBAL );
        SetGoal( 3 );   // need 3 direct hits
    }
    void ListenForEvents()
    {
        ListenForGameEvent( "player_death" );
    }
    void FireGameEvent( IGameEvent *event )
    {
        if ( !IsLocalTFPlayerClass( TF_CLASS_SOLDIER ) ) return;
        // check attacker == local player, weapon == direct hit rocket
        // then IncrementCount();
    }
};