feat: add error handling and thread-local last error tracking for wfassoc-dylib

Implement error handling with custom Error enum and thread-local storage
for tracking last error message to improve FFI interoperability.

wfassoc_dylib/src/lib.rs

@@ -1,3 +1,79 @@
+use std::cell::RefCell;
+use std::ffi::{CString, c_char};
+use thiserror::Error as TeError;
+
+// region: Error
+
+/// Error occurs in this crate.
+#[derive(Debug, TeError)]
+enum Error {
+    /// Error occurs in wfassoc core.
+    #[error("{0}")]
+    Core(#[from] wfassoc::Error),
+
+    #[error("error occurs when parsing into C/C++ string")]
+    CastIntoCStr(#[from] std::ffi::NulError),
+    #[error("error occurs when parsing from C/C++ string")]
+    CastFromCStr(#[from] std::ffi::IntoStringError),
+}
+
+/// Result type used in this crate.
+type Result<T> = std::result::Result<T, Error>;
+
+// endregion
+
+// region: Last Error
+
+struct LastError {
+    msg: CString,
+}
+
+impl LastError {
+    fn new() -> Self {
+        Self {
+            msg: CString::new("").expect("empty string must be valid for CString"),
+        }
+    }
+
+    pub fn set_msg(&mut self, msg: &str) {
+        self.msg = CString::new(msg).expect("unexpected blank in error message output");
+    }
+
+    pub fn get_msg(&self) -> *const c_char {
+        self.msg.as_ptr()
+    }
+
+    pub fn clear_msg(&mut self) {
+        self.msg = CString::new("").expect("empty string must be valid for CString");
+    }
+}
+
+thread_local! {
+    static LAST_ERROR: RefCell<LastError> = RefCell::new(LastError::new());
+}
+
+fn set_last_error(msg: &str) {
+    LAST_ERROR.with(|e| {
+        e.borrow_mut().set_msg(msg);
+    });
+}
+
+fn get_last_error() -> *const c_char {
+    LAST_ERROR.with(|e| e.borrow().get_msg())
+}
+
+fn clear_last_error() {
+    LAST_ERROR.with(|e| {
+        e.borrow_mut().clear_msg();
+    });
+}
+
+// endregion
+
+// region: Macros
+
+
+// endregion
 
 #[unsafe(no_mangle)]
 pub extern "C" fn WFAdd(left: u32, right: u32) -> u32 {