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#[cfg(engine)]
use crate::errors::*;
#[cfg(engine)]
use tokio::{
    fs::{create_dir_all, File},
    io::{AsyncReadExt, AsyncWriteExt},
};

/// An immutable storage system used by Perseus' engine to store build artifacts
/// and the like, which will then be used by the server or the export process.
/// By default, this is set to a path inside the `dist/` folder at the root of
/// your project, which you should only change if you have special requirements,
/// as the CLI expects the default paths to be used, with no option for
/// customization yet.
///
/// Note that this is only used for immutable data, which can be read-only in
/// production, meaning there are no consequences of using this on a read-only
/// production filesystem (e.g. in a serverless function). Data that do need to
/// change use a [`MutableStore`](super::MutableStore) instead.
#[derive(Clone, Debug)]
pub struct ImmutableStore {
    #[cfg(engine)]
    root_path: String,
}
impl ImmutableStore {
    /// Creates a new immutable store. You should provide a path like `dist`
    /// here. Note that any trailing slashes will be automatically stripped.
    #[cfg(engine)]
    pub fn new(root_path: String) -> Self {
        let root_path = root_path
            .strip_prefix('/')
            .unwrap_or(&root_path)
            .to_string();
        Self { root_path }
    }
    /// Gets the filesystem path used for this immutable store.
    ///
    /// This is designed to be used in particular by the engine to work out
    /// where to put static assets and the like when exporting.
    #[cfg(engine)]
    pub fn get_path(&self) -> &str {
        &self.root_path
    }
    /// Reads the given asset from the filesystem asynchronously.
    #[cfg(engine)]
    pub async fn read(&self, name: &str) -> Result<String, StoreError> {
        let asset_path = format!("{}/{}", self.root_path, name);
        let file_res = File::open(&asset_path).await;
        let mut file = match file_res {
            Ok(file) => file,
            Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                return Err(StoreError::NotFound { name: asset_path })
            }
            Err(err) => {
                return Err(StoreError::ReadFailed {
                    name: asset_path,
                    source: err.into(),
                })
            }
        };
        let metadata = file.metadata().await;

        match metadata {
            Ok(_) => {
                let mut contents = String::new();
                file.read_to_string(&mut contents)
                    .await
                    .map_err(|err| StoreError::ReadFailed {
                        name: asset_path,
                        source: err.into(),
                    })?;
                Ok(contents)
            }
            Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                Err(StoreError::NotFound { name: asset_path })
            }
            Err(err) => Err(StoreError::ReadFailed {
                name: asset_path,
                source: err.into(),
            }),
        }
    }
    /// Writes the given asset to the filesystem asynchronously. This must only
    /// be used at build-time, and must not be changed afterward. Note that this
    /// will automatically create any missing parent directories.
    #[cfg(engine)]
    pub async fn write(&self, name: &str, content: &str) -> Result<(), StoreError> {
        let asset_path = format!("{}/{}", self.root_path, name);
        let mut dir_tree: Vec<&str> = asset_path.split('/').collect();
        dir_tree.pop();

        create_dir_all(dir_tree.join("/"))
            .await
            .map_err(|err| StoreError::WriteFailed {
                name: asset_path.clone(),
                source: err.into(),
            })?;

        // This will either create the file or truncate it if it already exists
        let mut file = File::create(&asset_path)
            .await
            .map_err(|err| StoreError::WriteFailed {
                name: asset_path.clone(),
                source: err.into(),
            })?;
        file.write_all(content.as_bytes())
            .await
            .map_err(|err| StoreError::WriteFailed {
                name: asset_path.clone(),
                source: err.into(),
            })?;
        // TODO Can we use `sync_data()` here to reduce I/O?
        file.sync_all()
            .await
            .map_err(|err| StoreError::WriteFailed {
                name: asset_path,
                source: err.into(),
            })?;

        Ok(())
    }
}