Stop player save snapshots sharing mutable state with the player

engine/src/main/kotlin/world/gregs/voidps/engine/data/PlayerSave.kt

@@ -389,7 +389,7 @@ data class PlayerSave(
                 colours = colours,
                 variables = variables,
                 inventories = inventories,
-                friends = friends,
+                friends = friends.toMap(),
                 ignores = ignores,
                 offers = offers,
                 history = history,
@@ -410,8 +410,8 @@ internal fun Player.copy() = PlayerSave(
     colours = body.colours.copyOf(),
     variables = variables.data.toMap(),
     inventories = inventories.instances.mapValues { it.value.items.map { itm -> itm.copy() }.toTypedArray() },
-    friends = friends,
+    friends = friends.toMap(),
     ignores = ignores.toList(),
-    offers = offers.copyOf(),
+    offers = Array(offers.size) { offers[it].copy() },
     history = history.toList(),
 )

engine/src/test/kotlin/world/gregs/voidps/engine/data/PlayerSaveTest.kt

@@ -0,0 +1,32 @@
+package world.gregs.voidps.engine.data
+
+import org.junit.jupiter.api.Test
+import world.gregs.voidps.engine.data.exchange.ExchangeOffer
+import world.gregs.voidps.engine.entity.character.player.Player
+import world.gregs.voidps.engine.entity.character.player.chat.clan.ClanRank
+import kotlin.test.assertEquals
+
+internal class PlayerSaveTest {
+
+    @Test
+    fun `Snapshot doesn't share the player's friends`() {
+        val player = Player(accountName = "name")
+        player.friends["first"] = ClanRank.Friend
+
+        val save = player.copy()
+        player.friends["second"] = ClanRank.Friend
+
+        assertEquals(mapOf("first" to ClanRank.Friend), save.friends, "Snapshot changed after the player edited their friends list")
+    }
+
+    @Test
+    fun `Snapshot doesn't share the player's exchange offers`() {
+        val player = Player(accountName = "name")
+        player.offers[0] = ExchangeOffer(id = 1, item = "coins", amount = 10, price = 5)
+
+        val save = player.copy()
+        player.offers[0].completed = 7
+
+        assertEquals(0, save.offers[0].completed, "Snapshot changed after the player's offer progressed")
+    }
+}