Move cart to separate file

src/emulator/cart.rs

@@ -0,0 +1,63 @@
+use anyhow::Result;
+use rand::Rng;
+use std::{
+    fs::{self, File},
+    io::{Read, Seek as _, SeekFrom, Write as _},
+    path::{Path, PathBuf},
+};
+
+use crate::emulator::SimId;
+
+pub struct Cart {
+    pub file_path: PathBuf,
+    pub rom: Vec<u8>,
+    sram_file: File,
+    pub sram: Vec<u8>,
+}
+
+impl Cart {
+    pub fn load(file_path: &Path, sim_id: SimId) -> Result<Self> {
+        let rom = fs::read(file_path)?;
+
+        let mut sram_file = File::options()
+            .read(true)
+            .write(true)
+            .create(true)
+            .truncate(false)
+            .open(sram_path(file_path, sim_id))?;
+
+        let sram = if sram_file.metadata()?.len() == 0 {
+            // new SRAM file, randomize the contents
+            let mut sram = vec![0; 8 * 1024];
+            let mut rng = rand::rng();
+            for dst in sram.iter_mut().step_by(2) {
+                *dst = rng.random();
+            }
+            sram
+        } else {
+            let mut sram = Vec::with_capacity(8 * 1024);
+            sram_file.read_to_end(&mut sram)?;
+            sram
+        };
+
+        Ok(Cart {
+            file_path: file_path.to_path_buf(),
+            rom,
+            sram_file,
+            sram,
+        })
+    }
+
+    pub fn save_sram(&mut self) -> Result<()> {
+        self.sram_file.seek(SeekFrom::Start(0))?;
+        self.sram_file.write_all(&self.sram)?;
+        Ok(())
+    }
+}
+
+fn sram_path(file_path: &Path, sim_id: SimId) -> PathBuf {
+    match sim_id {
+        SimId::Player1 => file_path.with_extension("p1.sram"),
+        SimId::Player2 => file_path.with_extension("p2.sram"),
+    }
+}