fix: Rework spell studying and notify (#5524)

* Rework spell studying and notify

Studying a spell now tracks level gained and sends appropriate level up event on level up.

Updates notify event such that it will grant new spell if dependent spell level is equal to or greater than target level.

* Add documentation

* style(autofix.ci): automated formatting

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

doc/src/content/docs/en/mod/json/reference/creatures/magic.md

@@ -66,6 +66,7 @@ In `data/mods/Magiclysm` there is a template spell, copied here for your perusal
   "sound_ambient": true, // whether or not this is treated as an ambient sound or not
   "sound_id": "misc", // the sound id
   "sound_variant": "shockwave" // the sound variant
+  "learn_spells": { "acid_resistance_greater": 15 } // You learn the specified spell once your level in this spell is greater than or equal to the number shown.
 }
 ```
 
@@ -265,10 +266,11 @@ that use a negative 'recover' effect to cause pain or stamina damage. For exampl
 
 ### Learning Spells
 
-There are two ways of granting spells that is implemented: Mutating can grant a spell with the
-"spells_learned" field which also lets you specify the level granted. Otherwise you can learn a
-spell from an item through a use_action, which is also the only way to train a spell other than
-using it. Examples of both are shown below:
+There are three ways of granting spells that are implemented: Mutating can grant a spell with the
+"spells_learned" field which also lets you specify the level granted. Certain spells can also teach
+you spells once they reach an appropriate level via the "learn_spells" variable. Finally, You can
+learn a spell from an item through a use_action, which is also the only way to train a spell other
+than using it. Examples of all three are shown below:
 
 ```json
 {
@@ -287,6 +289,20 @@ using it. Examples of both are shown below:
 },
 ```
 
+For the below example you will learn the spell Greater Acid Resistance once Acid Resistance reaches
+level 15
+
+```json
+{
+    "id": "acid_resistance",
+    "type": "SPELL",
+    "name": { "str": "Acid Resistance" },
+    "description": "Protects the user from acid.",
+    ...
+    "learn_spells": { "acid_resistance_greater": 15 }
+}
+```
+
 You can study this spellbook for a rate of ~1 experience per turn depending on intelligence,
 spellcraft, and focus.
 

src/activity_handlers.cpp

@@ -4672,27 +4672,40 @@ void activity_handlers::study_spell_do_turn( player_activity *act, player *p )
     }
     if( act->get_str_value( 1 ) == "study" ) {
         spell &studying = p->magic->get_spell( spell_id( act->name ) );
-        if( act->get_str_value( 0 ) == "gain_level" ) {
-            if( studying.get_level() < act->get_value( 1 ) ) {
-                act->moves_left = 1000000;
-            } else {
-                act->moves_left = 0;
-            }
-        }
+        const int old_level = studying.get_level();
         const int xp = roll_remainder( studying.exp_modifier( *p ) / to_turns<float>( 6_seconds ) );
+
         act->values[0] += xp;
         studying.gain_exp( xp );
+        // Every time we use get_level the level is recalculated, this is suboptimal, so we remember it here.
+        const int new_level = studying.get_level();
+
+        if( new_level > old_level ) {
+            act->values[1] += new_level - old_level;
+            g->events().send<event_type::player_levels_spell>( studying.id(), new_level );
+            if( act->get_str_value( 0 ) == "gain_level" ) {
+                act->moves_left = 0;
+            }
+        } else if( act->get_str_value( 0 ) == "gain_level" ) {
+            act->moves_left = 1000000;
+        }
     }
 }
 
 void activity_handlers::study_spell_finish( player_activity *act, player *p )
 {
     act->set_to_null();
     const int total_exp_gained = act->get_value( 0 );
+    const int total_levels_gained = act->get_value( 1 );
 
     if( act->get_str_value( 1 ) == "study" ) {
-        p->add_msg_if_player( m_good, _( "You gained %i experience from your study session." ),
-                              total_exp_gained );
+        std::string level_string;
+        if( total_levels_gained > 0 ) {
+            level_string = string_format( vgettext( " and %d level", " and %d levels", total_levels_gained ),
+                                          total_levels_gained );
+        }
+        p->add_msg_if_player( m_good, _( "You gained %i experience%s from your study session." ),
+                              total_exp_gained, level_string );
         const spell &sp = p->magic->get_spell( spell_id( act->name ) );
         p->practice( sp.skill(), total_exp_gained, sp.get_difficulty() );
     } else if( act->get_str_value( 1 ) == "learn" && act->values[2] == 0 ) {

src/iuse_actor.cpp

@@ -2576,7 +2576,7 @@ int learn_spell_actor::use( player &p, item &, bool, const tripoint & ) const
     if( study_spell->moves_total == 10100 ) {
         study_spell->str_values[0] = "gain_level";
         study_spell->values[0] = 0; // reserved for xp
-        study_spell->values[1] = p.magic->get_spell( spell_id( spells[action] ) ).get_level() + 1;
+        study_spell->values[1] = 0; // reserved for levels
     }
     study_spell->name = spells[action];
     p.assign_activity( std::move( study_spell ), false );

src/magic.cpp

@@ -2159,13 +2159,12 @@ void spell_events::notify( const cata::event &e )
                  it != spell_cast.learn_spells.end(); ++it ) {
                 std::string learn_spell_id = it->first;
                 int learn_at_level = it->second;
-                if( learn_at_level == slvl ) {
+                if( slvl >= learn_at_level && !g->u.magic->knows_spell( learn_spell_id ) ) {
                     g->u.magic->learn_spell( learn_spell_id, g->u );
                     spell_type spell_learned = spell_factory.obj( spell_id( learn_spell_id ) );
                     add_msg(
                         _( "Your experience and knowledge in creating and manipulating magical energies to cast %s have opened your eyes to new possibilities, you can now cast %s." ),
-                        spell_cast.name,
-                        spell_learned.name );
+                        spell_cast.name, spell_learned.name );
                 }
             }
             break;