Add localStorage accessor for storing/retrieving volume between sessions, script execution

src/store.rs

@@ -0,0 +1,54 @@
+pub struct Store;
+
+#[cfg(not(target_os = "emscripten"))]
+impl Store {
+    pub fn volume(&self) -> Option<u32> {
+        None
+    }
+
+    pub fn set_volume(&self, volume: u32) {
+        // Do nothing
+    }
+}
+
+#[cfg(target_os = "emscripten")]
+extern "C" {
+    pub fn emscripten_run_script(script: *const libc::c_char);
+    pub fn emscripten_run_script_string(script: *const libc::c_char) -> *mut libc::c_char;
+}
+
+#[cfg(target_os = "emscripten")]
+impl Store {
+    fn run_script(script: &str) {
+        use std::ffi::CString;
+
+        let script = CString::new(script).unwrap();
+        unsafe {
+            emscripten_run_script(script.as_ptr());
+        }
+    }
+
+    fn run_script_string(script: &str) -> String {
+        use std::ffi::{CStr, CString};
+
+        let script = CString::new(script).unwrap();
+        unsafe {
+            let ptr = emscripten_run_script_string(script.as_ptr());
+            let c_str = CStr::from_ptr(ptr);
+            String::from(c_str.to_str().unwrap())
+        }
+    }
+
+    pub fn volume(&self) -> Option<u32> {
+        // Use local storage to try and read volume
+        let script = "localStorage.getItem('volume')";
+        let response = Store::run_script_string(&script);
+        response.parse::<u32>().ok()
+    }
+
+    pub fn set_volume(&self, volume: u32) {
+        // Use local storage to set volume
+        let script = format!("localStorage.setItem('volume', '{}')", volume);
+        Store::run_script_string(&script);
+    }
+}