mobs have a chance to drop held items on death

src/damage_system.rs

@@ -1,7 +1,9 @@
 use super::{
-    gamelog, Attributes, GrantsXP, Item, Map, Name, ParticleBuilder, Player, Pools, Position, RunState, SufferDamage,
+    gamelog, Attributes, Equipped, GrantsXP, InBackpack, Item, Map, Name, ParticleBuilder, Player, Pools, Position,
+    RunState, SufferDamage,
 };
 use crate::gamesystem::{mana_per_level, player_hp_per_level};
+use rltk::prelude::*;
 use specs::prelude::*;
 
 pub struct DamageSystem {}
@@ -153,9 +155,55 @@ pub fn delete_the_dead(ecs: &mut World) {
             }
         }
     }
+    let items_to_delete = drop_some_held_items_and_return_the_rest(ecs, &dead);
+    for item in items_to_delete {
+        ecs.delete_entity(item).expect("Unable to delete item.");
+    }
     // For everything that died, increment the event log, and delete.
     for victim in dead {
         gamelog::record_event("death_count", 1);
         ecs.delete_entity(victim).expect("Unable to delete.");
     }
 }
+
+fn drop_some_held_items_and_return_the_rest(ecs: &mut World, dead: &Vec<Entity>) -> Vec<Entity> {
+    let mut to_drop: Vec<(Entity, Position)> = Vec::new();
+    let entities = ecs.entities();
+    let mut equipped = ecs.write_storage::<Equipped>();
+    let mut carried = ecs.write_storage::<InBackpack>();
+    let mut positions = ecs.write_storage::<Position>();
+    let mut rng = ecs.write_resource::<RandomNumberGenerator>();
+    // Make list of every item in every dead thing's inv/equip
+    for victim in dead.iter() {
+        for (entity, equipped) in (&entities, &equipped).join() {
+            if equipped.owner == *victim {
+                // Push equipped item entities and positions
+                let pos = positions.get(*victim);
+                if let Some(pos) = pos {
+                    to_drop.push((entity, pos.clone()));
+                }
+            }
+        }
+        for (entity, backpack) in (&entities, &carried).join() {
+            if backpack.owner == *victim {
+                // Push backpack item entities and positions
+                let pos = positions.get(*victim);
+                if let Some(pos) = pos {
+                    to_drop.push((entity, pos.clone()));
+                }
+            }
+        }
+    }
+    const DROP_ONE_IN_THIS_MANY_TIMES: i32 = 6;
+    let mut to_return: Vec<Entity> = Vec::new();
+    for drop in to_drop.iter() {
+        if rng.roll_dice(1, DROP_ONE_IN_THIS_MANY_TIMES) == 1 {
+            equipped.remove(drop.0);
+            carried.remove(drop.0);
+            positions.insert(drop.0, drop.1.clone()).expect("Unable to insert Position{}.");
+        } else {
+            to_return.push(drop.0);
+        }
+    }
+    return to_return;
+}