Salvage dungeons (#14520)

Content.Shared/Storage/EntitySpawnEntry.cs

@@ -131,6 +131,71 @@ public static class EntitySpawnCollection
         return spawned;
     }
 
+    public static List<string?> GetSpawns(IEnumerable<EntitySpawnEntry> entries,
+        System.Random random)
+    {
+        var spawned = new List<string?>();
+        var ungrouped = CollectOrGroups(entries, out var orGroupedSpawns);
+
+        foreach (var entry in ungrouped)
+        {
+            // Check random spawn
+            // ReSharper disable once CompareOfFloatsByEqualityOperator
+            if (entry.SpawnProbability != 1f && !random.Prob(entry.SpawnProbability))
+                continue;
+
+            var amount = (int) entry.GetAmount(random);
+
+            for (var i = 0; i < amount; i++)
+            {
+                spawned.Add(entry.PrototypeId);
+            }
+        }
+
+        // Handle OrGroup spawns
+        foreach (var spawnValue in orGroupedSpawns)
+        {
+            // For each group use the added cumulative probability to roll a double in that range
+            var diceRoll = random.NextDouble() * spawnValue.CumulativeProbability;
+
+            // Add the entry's spawn probability to this value, if equals or lower, spawn item, otherwise continue to next item.
+            var cumulative = 0.0;
+
+            foreach (var entry in spawnValue.Entries)
+            {
+                cumulative += entry.SpawnProbability;
+                if (diceRoll > cumulative)
+                    continue;
+
+                // Dice roll succeeded, add item and break loop
+                var amount = (int) entry.GetAmount(random);
+
+                for (var i = 0; i < amount; i++)
+                {
+                    spawned.Add(entry.PrototypeId);
+                }
+
+                break;
+            }
+        }
+
+        return spawned;
+    }
+
+    public static double GetAmount(this EntitySpawnEntry entry, System.Random random, bool getAverage = false)
+    {
+        // Max amount is less or equal than amount, so just return the amount
+        if (entry.MaxAmount <= entry.Amount)
+            return entry.Amount;
+
+        // If we want the average, just calculate the expected amount
+        if (getAverage)
+            return (entry.Amount + entry.MaxAmount) / 2.0;
+
+        // Otherwise get a random value in between
+        return random.Next(entry.Amount, entry.MaxAmount);
+    }
+
     /// <summary>
     /// Collects all entries that belong together in an OrGroup, and then returns the leftover ungrouped entries.
     /// </summary>