Take control of NPC followers

src/avatar.cpp

@@ -145,6 +145,43 @@ avatar::avatar( avatar && ) = default;
 // NOLINTNEXTLINE(performance-noexcept-move-constructor)
 avatar &avatar::operator=( avatar && ) = default;
 
+static void swap_npc( npc &one, npc &two, npc &tmp )
+{
+    tmp = std::move( one );
+    one = std::move( two );
+    two = std::move( tmp );
+}
+
+void avatar::control_npc( npc &np )
+{
+    if( !np.is_player_ally() ) {
+        debugmsg( "control_npc() called on non-allied npc %s", np.name );
+        return;
+    }
+    if( !shadow_npc ) {
+        shadow_npc = std::make_unique<npc>();
+        shadow_npc->op_of_u.trust = 10;
+        shadow_npc->op_of_u.value = 10;
+        shadow_npc->set_attitude( NPCATT_FOLLOW );
+    }
+    npc tmp;
+    // move avatar character data into shadow npc
+    swap_character( *shadow_npc, tmp );
+    // swap target npc with shadow npc
+    swap_npc( *shadow_npc, np, tmp );
+    // move shadow npc character data into avatar
+    swap_character( *shadow_npc, tmp );
+    // the avatar character is no longer a follower NPC
+    g->remove_npc_follower( getID() );
+    // the previous avatar character is now a follower
+    g->add_npc_follower( np.getID() );
+    np.set_fac( faction_id( "your_followers" ) );
+    // perception and mutations may have changed, so reset light level caches
+    g->reset_light_level();
+    // center the map on the new avatar character
+    g->update_map( *this );
+}
+
 void avatar::toggle_map_memory()
 {
     show_map_memory = !show_map_memory;

src/avatar.h

@@ -103,6 +103,11 @@ class avatar : public Character
             return this;
         }
 
+        /**
+         * Makes the avatar "take over" the given NPC, while the current avatar character
+         * becomes an NPC.
+         */
+        void control_npc( npc & );
         using Character::query_yn;
         bool query_yn( const std::string &mes ) const override;
 
@@ -316,6 +321,7 @@ class avatar : public Character
 
         vproto_id starting_vehicle;
         std::vector<mtype_id> starting_pets;
+        std::set<character_id> follower_ids;
 
     private:
         // the encumbrance on your limbs reducing your dodging ability
@@ -361,6 +367,12 @@ class avatar : public Character
         int per_upgrade = 0;
 
         monster_visible_info mon_visible;
+
+        /**
+         * The NPC that would control the avatar's character in the avatar's absence.
+         * The Character data in this object is not relevant/used.
+         */
+        std::unique_ptr<npc> shadow_npc;
 };
 
 avatar &get_avatar();

src/character.cpp

@@ -507,6 +507,13 @@ character_id Character::getID() const
     return this->id;
 }
 
+void Character::swap_character( Character &other, Character &tmp )
+{
+    tmp = std::move( other );
+    other = std::move( *this );
+    *this = std::move( tmp );
+}
+
 void Character::randomize_height()
 {
     // Height distribution data is taken from CDC distributes statistics for the US population

src/character.h

@@ -2247,7 +2247,6 @@ class Character : public Creature, public visitable
         int focus_pool = 0;
     public:
         int cash = 0;
-        std::set<character_id> follower_ids;
         weak_ptr_fast<Creature> last_target;
         cata::optional<tripoint> last_target_pos;
         // Save favorite ammo location
@@ -3066,6 +3065,9 @@ class Character : public Creature, public visitable
         Character();
         Character( Character && ) noexcept( map_is_noexcept );
         Character &operator=( Character && ) noexcept( list_is_noexcept );
+        // Swaps the data of this Character and "other" using "tmp" for temporary storage.
+        // Leaves "tmp" in an undefined state.
+        void swap_character( Character &other, Character &tmp );
     public:
         struct trait_data {
             /** Whether the mutation is activated. */

src/debug_menu.cpp

@@ -147,6 +147,7 @@ std::string enum_to_string<debug_menu::debug_menu_index>( debug_menu::debug_menu
         case debug_menu::debug_menu_index::LEARN_MA: return "LEARN_MA";
         case debug_menu::debug_menu_index::UNLOCK_RECIPES: return "UNLOCK_RECIPES";
         case debug_menu::debug_menu_index::EDIT_PLAYER: return "EDIT_PLAYER";
+        case debug_menu::debug_menu_index::CONTROL_NPC: return "CONTROL_NPC";
         case debug_menu::debug_menu_index::SPAWN_ARTIFACT: return "SPAWN_ARTIFACT";
         case debug_menu::debug_menu_index::SPAWN_CLAIRVOYANCE: return "SPAWN_CLAIRVOYANCE";
         case debug_menu::debug_menu_index::MAP_EDITOR: return "MAP_EDITOR";
@@ -237,6 +238,7 @@ static int player_uilist()
         { uilist_entry( debug_menu_index::DAMAGE_SELF, true, 'd', _( "Damage self" ) ) },
         { uilist_entry( debug_menu_index::BLEED_SELF, true, 'b', _( "Bleed self" ) ) },
         { uilist_entry( debug_menu_index::SET_AUTOMOVE, true, 'a', _( "Set automove route" ) ) },
+        { uilist_entry( debug_menu_index::CONTROL_NPC, true, 'x', _( "Control NPC follower" ) ) },
     };
     if( !spell_type::get_all().empty() ) {
         uilist_initializer.emplace_back( uilist_entry( debug_menu_index::CHANGE_SPELLS, true, 'S',
@@ -1126,6 +1128,29 @@ static void spawn_nested_mapgen()
     }
 }
 
+static void control_npc_menu()
+{
+    std::vector<shared_ptr_fast<npc>> followers;
+    uilist charmenu;
+    int charnum = 0;
+    for( const auto &elem : g->get_follower_list() ) {
+        shared_ptr_fast<npc> follower = overmap_buffer.find_npc( elem );
+        if( follower ) {
+            followers.emplace_back( follower );
+            charmenu.addentry( charnum++, true, MENU_AUTOASSIGN, follower->get_name() );
+        }
+    }
+    if( followers.empty() ) {
+        return;
+    }
+    charmenu.w_y_setup = 0;
+    charmenu.query();
+    if( charmenu.ret < 0 || static_cast<size_t>( charmenu.ret ) >= followers.size() ) {
+        return;
+    }
+    get_avatar().control_npc( *followers.at( charmenu.ret ) );
+}
+
 static void character_edit_menu()
 {
     std::vector< tripoint > locations;
@@ -2361,7 +2386,11 @@ void debug()
         break;
 
         case debug_menu_index::EDIT_PLAYER:
-            debug_menu::character_edit_menu();
+            character_edit_menu();
+            break;
+
+        case debug_menu_index::CONTROL_NPC:
+            control_npc_menu();
             break;
 
         case debug_menu_index::SPAWN_ARTIFACT:

src/debug_menu.h

@@ -38,6 +38,7 @@ enum class debug_menu_index : int {
     LEARN_MA,
     UNLOCK_RECIPES,
     EDIT_PLAYER,
+    CONTROL_NPC,
     SPAWN_ARTIFACT,
     SPAWN_CLAIRVOYANCE,
     MAP_EDITOR,

src/savegame_json.cpp

@@ -963,7 +963,6 @@ void Character::load( const JsonObject &data )
     }
 
     data.read( "addictions", addictions );
-    data.read( "followers", follower_ids );
 
     // Add the earplugs.
     if( has_bionic( bionic_id( "bio_ears" ) ) && !has_bionic( bionic_id( "bio_earplugs" ) ) ) {
@@ -1174,7 +1173,6 @@ void Character::store( JsonOut &json ) const
 
     // "Looks like I picked the wrong week to quit smoking." - Steve McCroskey
     json.member( "addictions", addictions );
-    json.member( "followers", follower_ids );
 
     json.member( "worn", worn ); // also saves contents
     json.member( "inv" );
@@ -1257,6 +1255,7 @@ void avatar::store( JsonOut &json ) const
         json.end_array();
     }
 
+    json.member( "followers", follower_ids );
     // someday, npcs may drive
     json.member( "controlling_vehicle", controlling_vehicle );
 
@@ -1346,6 +1345,7 @@ void avatar::load( const JsonObject &data )
         hobbies.insert( hobbies.end(), &hobby.obj() );
     }
 
+    data.read( "followers", follower_ids );
     data.read( "controlling_vehicle", controlling_vehicle );
 
     data.read( "grab_point", grab_point );