implement optional palette id for room

src/room.rs

@@ -3,7 +3,7 @@ use crate::{Exit, ExitInstance, Instance, Position, from_base36, ToBase36, optio
 #[derive(Debug, Eq, PartialEq)]
 pub struct Room {
     pub id: u64,
-    pub palette_id: u64, // id
+    pub palette_id: Option<u64>, // optional in very early versions
     pub name: Option<String>,
     pub tiles: Vec<String>, // tile ids
     pub items: Vec<Instance>,
@@ -25,6 +25,14 @@ impl Room {
             "".to_string()
         }
     }
+
+    fn palette_line(&self) -> String {
+        if self.palette_id.is_some() {
+            optional_data_line("PAL", Some(self.palette_id.unwrap().to_base36()))
+        } else {
+            "".to_string()
+        }
+    }
 }
 
 impl From<String> for Room {
@@ -34,7 +42,7 @@ impl From<String> for Room {
         let mut lines: Vec<&str> = string.lines().collect();
         let id = from_base36(&lines[0]);
         let mut name = None;
-        let mut palette_id = 0;
+        let mut palette_id = None;
         let mut items: Vec<Instance> = Vec::new();
         let mut exits: Vec<ExitInstance> = Vec::new();
         let mut endings: Vec<Instance> = Vec::new();
@@ -50,7 +58,7 @@ impl From<String> for Room {
             } else if last_line.starts_with("NAME") {
                 name = Some(last_line.replace("NAME ", "").to_string());
             } else if last_line.starts_with("PAL") {
-                palette_id = from_base36(&last_line.replace("PAL ", ""));
+                palette_id = Some(from_base36(&last_line.replace("PAL ", "")));
             } else if last_line.starts_with("ITM") {
                 let last_line = last_line.replace("ITM ", "");
                 let item_position: Vec<&str> = last_line.split(' ').collect();
@@ -152,7 +160,7 @@ impl ToString for Room {
         }
 
         format!(
-            "ROOM {}\n{}{}{}{}{}{}\nPAL {}",
+            "ROOM {}\n{}{}{}{}{}{}{}",
             self.id.to_base36(),
             tiles,
             self.name_line(),
@@ -160,7 +168,7 @@ impl ToString for Room {
             items,
             exits,
             endings,
-            self.palette_id.to_base36()
+            self.palette_line()
         )
     }
 }