npctrade: rework price adjustment formula

src/item.cpp

@@ -6352,31 +6352,7 @@ int item::price( bool practical ) const
     int res = 0;
 
     visit_items( [&res, practical]( const item * e, item * ) {
-        if( e->rotten() ) {
-            // TODO: Special case things that stay useful when rotten
-            return VisitResponse::NEXT;
-        }
-
-        int child = units::to_cent( practical ? e->type->price_post : e->type->price );
-        if( e->damage() > 0 ) {
-            // maximal damage level is 4, maximal reduction is 40% of the value.
-            child -= child * static_cast<double>( e->damage_level() ) / 10;
-        }
-
-        if( e->count_by_charges() || e->made_of( phase_id::LIQUID ) ) {
-            // price from json data is for default-sized stack
-            child *= e->charges / static_cast<double>( e->type->stack_size );
-
-        } else if( e->magazine_integral() && e->ammo_remaining() && e->ammo_data() ) {
-            // items with integral magazines may contain ammunition which can affect the price
-            child += item( e->ammo_data(), calendar::turn, e->ammo_remaining() ).price( practical );
-
-        } else if( e->is_tool() && e->type->tool->max_charges != 0 ) {
-            // if tool has no ammo (e.g. spray can) reduce price proportional to remaining charges
-            child *= e->ammo_remaining() / static_cast<double>( std::max( e->type->charges_default(), 1 ) );
-        }
-
-        res += child;
+        res += e->price_no_contents( practical );
         return VisitResponse::NEXT;
     } );
 
@@ -6390,8 +6366,12 @@ int item::price_no_contents( bool practical ) const
     }
     int price = units::to_cent( practical ? type->price_post : type->price );
     if( damage() > 0 ) {
-        // maximal damage level is 4, maximal reduction is 40% of the value.
-        price -= price * static_cast< double >( damage_level() ) / 10;
+        // maximal damage level is 4, maximal reduction is 80% of the value.
+        price -= price * static_cast< double >( damage_level() ) / 5;
+    }
+
+    if( is_filthy() ) {
+        price *= 0.8;
     }
 
     if( count_by_charges() || made_of( phase_id::LIQUID ) ) {

src/npc.cpp

@@ -54,6 +54,7 @@
 #include "mtype.h"
 #include "mutation.h"
 #include "npc_class.h"
+#include "npctrade.h"
 #include "npctrade_utils.h"
 #include "npctalk.h"
 #include "options.h"
@@ -148,6 +149,7 @@ static const trait_id trait_MUTE( "MUTE" );
 static const trait_id trait_PROF_DICEMASTER( "PROF_DICEMASTER" );
 static const trait_id trait_PSYCHOPATH( "PSYCHOPATH" );
 static const trait_id trait_SAPIOVORE( "SAPIOVORE" );
+static const trait_id trait_SQUEAMISH( "SQUEAMISH" );
 static const trait_id trait_TERRIFYING( "TERRIFYING" );
 
 class monfaction;
@@ -1952,12 +1954,13 @@ bool npc::wants_to_buy( const item &it, int at_price, int /*market_price*/ ) con
         return true;
     }
 
-    if( it.has_flag( flag_TRADER_AVOID ) ) {
+    if( it.has_flag( flag_TRADER_AVOID ) or it.has_var( VAR_TRADE_IGNORE ) or
+        ( my_fac == nullptr and has_trait( trait_SQUEAMISH ) and it.is_filthy() ) ) {
         return false;
     }
 
     // TODO: Base on inventory
-    return at_price > 0;
+    return at_price >= 0;
 }
 
 // Will the NPC freely exchange items with the player?

src/npctrade.cpp

@@ -146,7 +146,7 @@ double npc_trading::net_price_adjustment( const Character &buyer, const Characte
     double adjust = 0.05 * ( seller.int_cur - buyer.int_cur ) +
                     price_adjustment( seller.get_skill_level( skill_speech ) -
                                       buyer.get_skill_level( skill_speech ) );
-    return std::max( adjust, 1.0 );
+    return seller.is_npc() ? adjust : -1 / adjust;
 }
 
 int npc_trading::bionic_install_price( Character &installer, Character &patient,
@@ -166,8 +166,7 @@ int npc_trading::adjusted_price( item const *it, int amount, Character const &bu
 
     int price = it->price_no_contents( true );
     if( it->count_by_charges() and amount >= 0 ) {
-        price /= it->charges;
-        price *= amount;
+        price *= static_cast<double>( amount ) / it->charges;
     }
     if( buyer.is_npc() ) {
         price = buyer.as_npc()->value( *it, price );
@@ -176,7 +175,7 @@ int npc_trading::adjusted_price( item const *it, int amount, Character const &bu
     }
 
     if( fac == nullptr || fac->currency != it->typeId() ) {
-        return static_cast<int>( price * adjust );
+        return static_cast<int>( price * ( 1 + 0.25 * adjust ) );
     }
 
     return price;

src/skill.cpp

@@ -585,23 +585,7 @@ bool SkillLevelMap::has_same_levels_as( const SkillLevelMap &other ) const
 // Caps at 200% when you are 5 levels ahead, int comparison is handled in npctalk.cpp
 double price_adjustment( int barter_skill )
 {
-    if( barter_skill <= 0 ) {
-        return 1.0;
-    }
-    if( barter_skill >= 5 ) {
-        return 2.0;
-    }
-    switch( barter_skill ) {
-        case 1:
-            return 1.05;
-        case 2:
-            return 1.15;
-        case 3:
-            return 1.30;
-        case 4:
-            return 1.65;
-        default:
-            // Should never occur
-            return 1.0;
-    }
+    int const skill = std::min( 5, std::abs( barter_skill ) );
+    double const val = 0.045 * std::pow( skill, 2 ) - 0.025 * skill + 1;
+    return barter_skill >= 0 ? val : 1 / val;
 }