4 files changed, 749 insertions, 0 deletions
diff --git a/systems/asset/src/asset.rs b/systems/asset/src/asset.rs
new file mode 100644
index 0000000..247a654
--- /dev/null
+++ b/systems/asset/src/asset.rs
@@ -0,0 +1,552 @@
+use std::{
+    borrow::Cow,
+    collections::HashSet,
+    ffi::OsStr,
+    marker::PhantomData,
+    path::{Path, PathBuf},
+};
+
+use constants::{LOCK_FILE_PREFIX, TEMP_FILE_PREFIX};
+use string_proc::format_path::format_path;
+
+use crate::{
+    error::{DataApplyError, DataReadError, DataWriteError, HandleLockError, PrecheckFailed},
+    rw::RWData,
+};
+
+pub struct ReadOnlyAsset<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    _data_type: PhantomData<RWDataType>,
+    path: PathBuf,
+}
+
+/// Nothing special, I'm just too lazy
+macro_rules! asset_from {
+    (|$v:ident| $src:ty => $expr:expr) => {
+        impl<RWDataType> From<$src> for ReadOnlyAsset<RWDataType>
+        where
+            RWDataType: RWData<RWDataType>,
+        {
+            fn from($v: $src) -> Self {
+                ReadOnlyAsset {
+                    _data_type: PhantomData,
+                    path: $expr,
+                }
+            }
+        }
+    };
+}
+
+asset_from!(|v| PathBuf => v);
+asset_from!(|v| &Path => v.to_path_buf());
+asset_from!(|v| String => PathBuf::from(v));
+asset_from!(|v| &str => PathBuf::from(v));
+
+impl<RWDataType> AsRef<Path> for ReadOnlyAsset<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    fn as_ref(&self) -> &Path {
+        self.path.as_ref()
+    }
+}
+
+impl<RWDataType> From<ReadOnlyAsset<RWDataType>> for PathBuf
+where
+    RWDataType: RWData<RWDataType>,
+{
+    fn from(value: ReadOnlyAsset<RWDataType>) -> Self {
+        value.path
+    }
+}
+
+impl<RWDataType> ReadOnlyAsset<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    /// Read asset content from `ReadOnlyAsset`
+    /// ```ignore
+    /// let sheet_asset: ReadOnlyAsset<Sheet> = "my_sheet.sheet".into();
+    /// let sheet = sheet_asset.read().await.unwrap();
+    /// ```
+    pub async fn read(&self) -> Result<RWDataType, DataReadError> {
+        RWDataType::read(&self.path).await
+    }
+
+    /// Create a `Handle` from `ReadOnlyAsset` to exclusively edit this `ReadOnlyAsset`
+    /// ```ignore
+    /// let sheet_asset: ReadOnlyAsset<Sheet> = "my_sheet.sheet".into();
+    /// let mut sheet_handle = sheet_asset.get_handle().await.unwrap();
+    /// ```
+    pub async fn get_handle(&self) -> Result<Handle<RWDataType>, HandleLockError> {
+        let asset_path = &self.path;
+
+        // If the asset file does not exist, cannot create an editable handle
+        if !asset_path.exists() {
+            return Err(HandleLockError::AssetFileNotFound(asset_path.clone()));
+        }
+
+        // Get the lock path and temp path
+        let lock_path = self.get_lock_path()?;
+        let temp_path = self.get_temp_path()?;
+
+        // Attempt to create the lock file; success means the lock does not exist and editing is allowed
+        match tokio::fs::OpenOptions::new()
+            .write(true)
+            .create_new(true)
+            .open(&lock_path)
+            .await
+        {
+            Ok(_) => {
+                return Ok(Handle {
+                    _data_type: PhantomData,
+                    writed: false,
+                    asset_path: self.path.clone(),
+                    lock_path,
+                    temp_path,
+                });
+            }
+            Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => {
+                return Err(HandleLockError::AssetLocked);
+            }
+            Err(e) => {
+                return Err(HandleLockError::IoError(e));
+            }
+        }
+    }
+
+    /// Get the lock file name for the current `ReadOnlyAsset`
+    /// ```
+    /// # use asset::rw::FooData;
+    /// # use asset::asset::ReadOnlyAsset;
+    /// let foo_asset = ReadOnlyAsset::<FooData>::from("my/foo.txt");
+    /// let lock_path = foo_asset
+    ///     .get_lock_path()
+    ///     .unwrap();
+    /// assert_eq!(lock_path.to_string_lossy(), "my/~foo.txt");
+    /// ```
+    pub fn get_lock_path(&self) -> Result<PathBuf, HandleLockError> {
+        // Get the file name
+        let Some(file_name) = self.path.file_name() else {
+            return Err(HandleLockError::ReadFileNameFailed);
+        };
+
+        let file_name_str = check_path(file_name)?;
+
+        let mut edit_path = self.path.clone();
+        edit_path.set_file_name(format!("{}{}", LOCK_FILE_PREFIX, file_name_str));
+
+        let Ok(edit_path) = format_path(edit_path) else {
+            return Err(HandleLockError::ParsePathFailed);
+        };
+
+        Ok(edit_path)
+    }
+
+    /// Get the name of the temporary editing file for the current `ReadOnlyAsset`
+    /// ```
+    /// # use asset::rw::FooData;
+    /// # use asset::asset::ReadOnlyAsset;
+    /// let foo_asset = ReadOnlyAsset::<FooData>::from("my/foo.txt");
+    /// let temp_path = foo_asset
+    ///     .get_temp_path()
+    ///     .unwrap();
+    /// assert_eq!(temp_path.to_string_lossy(), "my/.tmp_foo.txt");
+    /// ```
+    pub fn get_temp_path(&self) -> Result<PathBuf, HandleLockError> {
+        // Get the file name
+        let Some(file_name) = self.path.file_name() else {
+            return Err(HandleLockError::ReadFileNameFailed);
+        };
+
+        let file_name_str = check_path(file_name)?;
+
+        let mut temp_path = self.path.clone();
+        temp_path.set_file_name(format!("{}{}", TEMP_FILE_PREFIX, file_name_str));
+
+        let Ok(edit_path) = format_path(temp_path) else {
+            return Err(HandleLockError::ParsePathFailed);
+        };
+
+        Ok(edit_path)
+    }
+}
+
+pub struct Handle<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    _data_type: PhantomData<RWDataType>,
+    writed: bool,
+    asset_path: PathBuf,
+    lock_path: PathBuf,
+    temp_path: PathBuf,
+}
+
+impl<RWDataType> Drop for Handle<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    fn drop(&mut self) {
+        if self.lock_path.exists() {
+            let _ = std::fs::remove_file(&self.lock_path);
+        }
+    }
+}
+
+impl<RWDataType> Handle<RWDataType>
+where
+    RWDataType: RWData<RWDataType>,
+{
+    /// Write content into the `Handle`, this will not affect the associated `ReadOnlyAsset`
+    pub async fn write(&mut self, data: RWDataType) -> Result<(), DataWriteError> {
+        self.writed = true;
+        RWDataType::write(data, &self.temp_path).await
+    }
+
+    /// Read the content of this `Handle`;
+    /// if the `Handle` has never been written to, read the content of the original `ReadOnlyAsset`
+    pub async fn read(&self) -> Result<RWDataType, DataReadError> {
+        let path = if self.writed {
+            &self.temp_path
+        } else {
+            &self.asset_path
+        };
+        RWDataType::read(path).await
+    }
+
+    /// Atomically write the content of the `Handle` to the `ReadOnlyAsset`
+    pub async fn apply(self) -> Result<(), DataApplyError> {
+        let from = &self.temp_path;
+        let to = &self.asset_path;
+
+        // Cannot perform Apply operation when the target file does not exist
+        // Reason: Cannot apply modifications to a non-existent file, even if editing was declared
+        if !to.exists() {
+            return Err(DataApplyError::AssetFileNotFound(to.clone()));
+        }
+
+        if self.writed {
+            tokio::fs::rename(&from, &to)
+                .await
+                .map_err(|e| DataApplyError::IoError(e))?;
+        }
+        Ok(())
+    }
+
+    pub fn get_rename_operation(&self) -> (PathBuf, PathBuf) {
+        (self.temp_path.clone(), self.asset_path.clone())
+    }
+}
+
+/// Strict Apply precheck
+///
+/// It checks:
+/// 1. Whether related files exist
+/// 2. If the Handle has been written to, whether the written content can be found
+/// 3. Whether the Handle and its ReadOnlyAsset are in the same directory
+/// 4. Whether the ReadOnlyAsset is locked (preventing writes/renames)
+/// 5. Whether the Handle is locked (preventing writes/renames)
+///
+/// > This is only necessary when you need to ensure `multiple Handles must either all succeed or all fail together`
+///
+/// If you only need to ensure a single Handle can Apply correctly,
+/// use:
+/// ```ignore
+/// // ...
+/// let mut handle = my_asset.get_handle().await?;
+/// handle.write(/* Your Data */).await?;
+/// handle.apply().await?;
+/// ```
+pub async fn apply_precheck<D>(handle: &Handle<D>) -> Result<(), PrecheckFailed>
+where
+    D: RWData<D>,
+{
+    let Ok(from) = format_path(&handle.temp_path) else {
+        return Err(PrecheckFailed::FormatPathFailed);
+    };
+    let Ok(to) = format_path(&handle.asset_path) else {
+        return Err(PrecheckFailed::FormatPathFailed);
+    };
+
+    tokio::try_join!(
+        check_lock_file_exist(handle),
+        check_asset_file_exist(handle),
+        check_temp_file_exist_when_writed(handle),
+        check_asset_path(handle),
+        check_handle_is_cross_directory(&from, &to),
+    )?;
+    Ok(())
+}
+
+/// Check if all rename operations to be performed are valid
+pub async fn apply_precheck_rename_operations(
+    rename_operations: &[(PathBuf, PathBuf)],
+) -> Result<(), PrecheckFailed> {
+    let mut seen = HashSet::new();
+
+    for (from, to) in rename_operations {
+        if !seen.insert(from) {
+            return Err(PrecheckFailed::HasSamePath);
+        }
+        if !seen.insert(to) {
+            return Err(PrecheckFailed::HasSamePath);
+        }
+    }
+
+    // This validation must be executed sequentially
+    // Because on Unix, we need to attempt writing files to directories
+    // If executed in parallel, conflicts may arise
+
+    for (from, to) in rename_operations {
+        #[cfg(windows)]
+        check_temp_file_moveable_windows(from, to).await?;
+
+        #[cfg(windows)]
+        check_asset_file_writeable_windows(to).await?;
+
+        #[cfg(unix)]
+        check_temp_file_moveable_unix(from, to).await?;
+
+        #[cfg(unix)]
+        check_asset_file_writeable_unix(to).await?;
+    }
+    Ok(())
+}
+
+async fn check_lock_file_exist<D>(handle: &Handle<D>) -> Result<(), PrecheckFailed>
+where
+    D: RWData<D>,
+{
+    if !handle.lock_path.exists() {
+        return Err(PrecheckFailed::LockNotFound);
+    }
+    Ok(())
+}
+
+async fn check_asset_file_exist<D>(handle: &Handle<D>) -> Result<(), PrecheckFailed>
+where
+    D: RWData<D>,
+{
+    if !handle.asset_path.exists() {
+        return Err(PrecheckFailed::AssetNotFound);
+    }
+    Ok(())
+}
+
+async fn check_temp_file_exist_when_writed<D>(handle: &Handle<D>) -> Result<(), PrecheckFailed>
+where
+    D: RWData<D>,
+{
+    if handle.writed && !handle.temp_path.exists() {
+        return Err(PrecheckFailed::WritedButTempNotFound);
+    }
+    Ok(())
+}
+
+async fn check_asset_path<D>(handle: &Handle<D>) -> Result<(), PrecheckFailed>
+where
+    D: RWData<D>,
+{
+    if let Some(file_name) = handle.asset_path.file_name() {
+        if check_path(file_name).is_ok() {
+            return Ok(());
+        }
+    }
+    Err(PrecheckFailed::AssetPathInvalid)
+}
+
+async fn check_handle_is_cross_directory(
+    from: &PathBuf,
+    to: &PathBuf,
+) -> Result<(), PrecheckFailed> {
+    let from_parent = from.parent();
+    let to_parent = to.parent();
+
+    // "Huh? You ask why we report an error when the parent directory doesn't exist?"
+    //
+    // Operations are not allowed in the root directory or when there is no parent directory.
+    // 1. This indicates they are not in the correct location
+    //    (ideally there should be at least one parent directory).
+    // 2. This makes it impossible to compare the two directories.
+    if from_parent.is_none() || to_parent.is_none() {
+        return Err(PrecheckFailed::HandleFileIsNoParent);
+    }
+
+    if from_parent.unwrap() != to_parent.unwrap() {
+        return Err(PrecheckFailed::HandleIsCrossDirectory);
+    }
+
+    Ok(())
+}
+
+fn check_path(file_name: &OsStr) -> Result<Cow<'_, str>, PrecheckFailed> {
+    // When operating on a TEMP_FILE or LOCK_FILE,
+    // names like `~~foo.txt` or `.tmp_.tmp_foo.txt` would be generated
+    // This is not expected and should result in an error
+
+    // Check if the file name starts with ~
+    let file_name_str = file_name.to_string_lossy();
+    if file_name_str.starts_with(LOCK_FILE_PREFIX) {
+        return Err(PrecheckFailed::LockOnLockFile);
+    }
+
+    // Check if the file name starts with .tmp_
+    let file_name_str = file_name.to_string_lossy();
+    if file_name_str.starts_with(TEMP_FILE_PREFIX) {
+        return Err(PrecheckFailed::TempForTempFile);
+    }
+
+    Ok(file_name_str)
+}
+
+#[cfg(windows)]
+async fn check_asset_file_writeable_windows(path: &Path) -> Result<(), PrecheckFailed> {
+    use std::os::windows::fs::MetadataExt;
+
+    let metadata = tokio::fs::metadata(path)
+        .await
+        .map_err(|_| PrecheckFailed::AssetNotWritable)?;
+
+    if metadata.file_attributes() & 0x1 != 0 {
+        return Err(PrecheckFailed::AssetNotWritable);
+    }
+
+    if !check_file_can_be_deleted_windows(path) {
+        return Err(PrecheckFailed::AssetNotWritable);
+    }
+
+    Ok(())
+}
+
+#[cfg(windows)]
+async fn check_temp_file_moveable_windows(temp: &Path, asset: &Path) -> Result<(), PrecheckFailed> {
+    if !check_file_can_be_deleted_windows(temp) {
+        return Err(PrecheckFailed::TempNotMoveable);
+    }
+    if asset.exists() && !check_file_can_be_deleted_windows(asset) {
+        return Err(PrecheckFailed::TempNotMoveable);
+    }
+
+    Ok(())
+}
+
+#[cfg(windows)]
+fn check_file_can_be_deleted_windows(path: &Path) -> bool {
+    use std::os::windows::fs::OpenOptionsExt;
+
+    use winapi::um::winnt::{DELETE, FILE_SHARE_DELETE, FILE_SHARE_READ, FILE_SHARE_WRITE};
+    std::fs::OpenOptions::new()
+        .access_mode(DELETE)
+        .share_mode(FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE)
+        .open(path)
+        .is_ok()
+}
+
+#[cfg(unix)]
+async fn check_asset_file_writeable_unix(path: &Path) -> Result<(), PrecheckFailed> {
+    let parent = path.parent().ok_or(PrecheckFailed::AssetPathInvalid)?;
+
+    if !check_dir_writable_unix(parent) {
+        return Err(PrecheckFailed::AssetNotWritable);
+    }
+
+    Ok(())
+}
+
+#[cfg(unix)]
+async fn check_temp_file_moveable_unix(temp: &Path, asset: &Path) -> Result<(), PrecheckFailed> {
+    if !temp.exists() {
+        return Err(PrecheckFailed::TempNotMoveable);
+    }
+
+    let temp_parent = temp.parent().ok_or(PrecheckFailed::TempNotMoveable)?;
+    if !check_dir_writable_unix(temp_parent) {
+        return Err(PrecheckFailed::TempNotMoveable);
+    }
+
+    let asset_parent = asset.parent().ok_or(PrecheckFailed::TempNotMoveable)?;
+    if !check_dir_writable_unix(asset_parent) {
+        return Err(PrecheckFailed::TempNotMoveable);
+    }
+
+    Ok(())
+}
+
+#[cfg(unix)]
+fn check_dir_writable_unix(dir: &Path) -> bool {
+    use std::fs::OpenOptions;
+
+    let test_path = dir.join(".write_test");
+
+    let result = OpenOptions::new()
+        .create_new(true)
+        .write(true)
+        .open(&test_path);
+
+    match result {
+        Ok(_) => {
+            let _ = std::fs::remove_file(test_path);
+            true
+        }
+        Err(_) => false,
+    }
+}
+
+#[macro_export]
+macro_rules! apply {
+    // Single handle
+    ($handle:expr $(,)?) => {{
+        async {
+            // Single-handle precheck
+            if let Err(e) = asset::asset::apply_precheck(&$handle).await {
+                return Err(asset::error::DataApplyError::PrecheckFailed(e));
+            }
+
+            // Direct apply
+            $handle.apply().await
+        }
+    }};
+
+    // Multiple handles
+    ($first:expr, $($rest:expr),+ $(,)?) => {{
+        async {
+            // Collect rename ops
+            let rename_ops: Vec<(std::path::PathBuf, std::path::PathBuf)> = vec![
+                $first.get_rename_operation(),
+                $(
+                    $rest.get_rename_operation(),
+                )+
+            ];
+
+            // Batch precheck
+            if let Err(e) = asset::asset::apply_precheck_rename_operations(&rename_ops).await {
+                return Err(asset::error::DataApplyError::PrecheckFailed(e));
+            }
+
+            // Per-handle precheck
+            if let Err(e) = asset::asset::apply_precheck(&$first).await {
+                return Err(asset::error::DataApplyError::PrecheckFailed(e));
+            }
+            $(
+                if let Err(e) = asset::asset::apply_precheck(&$rest).await {
+                    return Err(asset::error::DataApplyError::PrecheckFailed(e));
+                }
+            )+
+
+            // Apply
+            if let Err(e) = $first.apply().await {
+                return Err(e);
+            }
+            $(
+                if let Err(e) = $rest.apply().await {
+                    return Err(e);
+                }
+            )+
+
+            Ok(())
+        }
+    }};
+}
diff --git a/systems/asset/src/error.rs b/systems/asset/src/error.rs
new file mode 100644
index 0000000..5dc529f
--- /dev/null
+++ b/systems/asset/src/error.rs
@@ -0,0 +1,106 @@
+use std::path::PathBuf;
+
+#[derive(Debug, thiserror::Error)]
+pub enum DataReadError {
+    #[error("IO error: {0}")]
+    IoError(#[from] std::io::Error),
+
+    #[error("Parse error: {0}")]
+    ParseError(String),
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum DataWriteError {
+    #[error("IO error: {0}")]
+    IoError(#[from] std::io::Error),
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum DataApplyError {
+    #[error("IO error: {0}")]
+    IoError(#[from] std::io::Error),
+
+    #[error("Asset file not found: {0}")]
+    AssetFileNotFound(PathBuf),
+
+    #[error("Pre-check failed: {0}")]
+    PrecheckFailed(#[from] PrecheckFailed),
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum PrecheckFailed {
+    /// Lock file does not exist
+    /// Means trying to apply a modification that cannot be applied
+    #[error("Lock not found")]
+    LockNotFound,
+
+    /// Asset file does not exist
+    /// Apply phase will fail due to this condition
+    #[error("Asset not found")]
+    AssetNotFound,
+
+    // Note: !writed is allowed,
+    // but writed without a TEMP_FILE is not allowed
+    /// Handle produced a write
+    /// but the temporary file does not exist, indicating an abnormal write operation
+    #[error("Temp not found")]
+    WritedButTempNotFound,
+
+    /// Asset path is invalid
+    /// This is not an issue that should arise from normal Handle creation flow
+    #[error("Asset path invalid")]
+    AssetPathInvalid,
+
+    /// Temporary file cannot be moved
+    #[error("Temp file not moveable")]
+    TempNotMoveable,
+
+    /// Asset file cannot be moved
+    #[error("Asset file not writable")]
+    AssetNotWritable,
+
+    /// Handle is processing a cross-directory operation
+    /// This is not atomic
+    #[error("Handle is cross-directory")]
+    HandleIsCrossDirectory,
+
+    /// Asset file has no parent directory
+    /// This is not a valid path for file operations
+    #[error("Asset file has no parent directory")]
+    HandleFileIsNoParent,
+
+    /// A handle with the same path already exists
+    /// This operation will cause a conflict
+    #[error("Handle with same path exists")]
+    HasSamePath,
+
+    #[error("Lock on lock file")]
+    LockOnLockFile,
+
+    #[error("Temp file for temp file")]
+    TempForTempFile,
+
+    #[error("Asset path cannot be formatted")]
+    FormatPathFailed,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum HandleLockError {
+    #[error("Parse path failed")]
+    ParsePathFailed,
+
+    #[error("Asset file not found")]
+    AssetFileNotFound(PathBuf),
+
+    #[error("Read file name failed")]
+    ReadFileNameFailed,
+
+    #[error("Asset locked")]
+    AssetLocked,
+
+    #[error("IO error: {0}")]
+    IoError(#[from] std::io::Error),
+
+    #[error("Pre-check failed: {0}")]
+    PrecheckFailed(#[from] PrecheckFailed),
+}
diff --git a/systems/asset/src/lib.rs b/systems/asset/src/lib.rs
new file mode 100644
index 0000000..ac4317f
--- /dev/null
+++ b/systems/asset/src/lib.rs
@@ -0,0 +1,6 @@
+pub mod asset;
+pub mod error;
+pub mod rw;
+
+#[allow(unused)]
+pub use asset_macros::*;
diff --git a/systems/asset/src/rw.rs b/systems/asset/src/rw.rs
new file mode 100644
index 0000000..784d44d
--- /dev/null
+++ b/systems/asset/src/rw.rs
@@ -0,0 +1,85 @@
+use std::path::PathBuf;
+
+use crate::error::{DataReadError, DataWriteError};
+
+pub trait RWData<DataType> {
+    type DataType;
+
+    /// Implement read logic
+    /// Given a path, return the specific data
+    fn read(path: &PathBuf) -> impl Future<Output = Result<DataType, DataReadError>> + Send + Sync;
+
+    /// Implement write logic
+    /// Given data and a path, write to the filesystem
+    fn write(
+        data: DataType,
+        path: &PathBuf,
+    ) -> impl Future<Output = Result<(), DataWriteError>> + Send + Sync;
+
+    /// Provide test data
+    fn test_data() -> DataType;
+
+    /// Given two sets of data, determine if they are equal
+    ///
+    /// Add RWDataTest derive to your struct to automatically generate tests
+    /// ```ignore
+    /// #[derive(RWDataTest)]
+    /// struct FooData;
+    /// ```
+    fn verify_data(data_a: DataType, data_b: DataType) -> bool;
+}
+
+#[macro_export]
+macro_rules! ensure_eq {
+    ($a:expr, $b:expr) => {
+        if $a != $b {
+            return false;
+        }
+    };
+}
+
+// Test Data
+pub struct FooData {
+    pub age: i32,
+    pub name: String,
+}
+
+impl RWData<FooData> for FooData {
+    type DataType = FooData;
+
+    async fn read(path: &PathBuf) -> Result<FooData, DataReadError> {
+        let content = tokio::fs::read_to_string(path)
+            .await
+            .map_err(|e| DataReadError::IoError(e))?;
+        let parts: Vec<&str> = content.split('=').collect();
+        if parts.len() != 2 {
+            return Err(DataReadError::ParseError("Invalid format".to_string()));
+        }
+        let name = parts[0].to_string();
+        let age: i32 = parts[1]
+            .parse()
+            .map_err(|_| DataReadError::ParseError("Invalid age".to_string()))?;
+        Ok(FooData { age, name })
+    }
+
+    async fn write(data: FooData, path: &PathBuf) -> Result<(), DataWriteError> {
+        let content = format!("{}={}", data.name, data.age);
+        tokio::fs::write(path, content)
+            .await
+            .map_err(|e| DataWriteError::IoError(e))?;
+        Ok(())
+    }
+
+    fn test_data() -> FooData {
+        FooData {
+            age: 24,
+            name: "OneOneFourFiveOneFour".to_string(),
+        }
+    }
+
+    fn verify_data(data_a: FooData, data_b: FooData) -> bool {
+        crate::ensure_eq!(data_a.age, data_b.age);
+        crate::ensure_eq!(data_a.name, data_b.name);
+        return true;
+    }
+}