android.rs

use crate::io::{get_meta_path, AssetReader, AssetReaderError, PathStream, Reader, VecReader};
use alloc::{borrow::ToOwned, boxed::Box, ffi::CString, vec::Vec};
use futures_lite::stream;
use std::path::Path;

/// [`AssetReader`] implementation for Android devices, built on top of Android's [`AssetManager`].
///
/// Implementation details:
///
/// - All functions use the [`AssetManager`] to load files.
/// - [`is_directory`](AssetReader::is_directory) tries to open the path
/// as a normal file and treats an error as if the path is a directory.
/// - Watching for changes is not supported. The watcher method will do nothing.
///
/// [AssetManager]: https://developer.android.com/reference/android/content/res/AssetManager
pub struct AndroidAssetReader;

impl AssetReader for AndroidAssetReader {
    async fn read<'a>(&'a self, path: &'a Path) -> Result<impl Reader + 'a, AssetReaderError> {
        let asset_manager = bevy_android::ANDROID_APP
            .get()
            .expect("Bevy must be setup with the #[bevy_main] macro on Android")
            .asset_manager();
        let mut opened_asset = asset_manager
            .open(&CString::new(path.to_str().unwrap()).unwrap())
            .ok_or(AssetReaderError::NotFound(path.to_path_buf()))?;
        let bytes = opened_asset.buffer()?;
        let reader = VecReader::new(bytes.to_vec());
        Ok(reader)
    }

    async fn read_meta<'a>(&'a self, path: &'a Path) -> Result<impl Reader + 'a, AssetReaderError> {
        let meta_path = get_meta_path(path);
        let asset_manager = bevy_android::ANDROID_APP
            .get()
            .expect("Bevy must be setup with the #[bevy_main] macro on Android")
            .asset_manager();
        let mut opened_asset = asset_manager
            .open(&CString::new(meta_path.to_str().unwrap()).unwrap())
            .ok_or(AssetReaderError::NotFound(meta_path))?;
        let bytes = opened_asset.buffer()?;
        let reader = VecReader::new(bytes.to_vec());
        Ok(reader)
    }

    async fn read_directory<'a>(
        &'a self,
        path: &'a Path,
    ) -> Result<Box<PathStream>, AssetReaderError> {
        let asset_manager = bevy_android::ANDROID_APP
            .get()
            .expect("Bevy must be setup with the #[bevy_main] macro on Android")
            .asset_manager();
        let opened_assets_dir = asset_manager
            .open_dir(&CString::new(path.to_str().unwrap()).unwrap())
            .ok_or(AssetReaderError::NotFound(path.to_path_buf()))?;

        let mapped_stream = opened_assets_dir
            .filter_map(move |f| {
                let file_path = path.join(Path::new(f.to_str().unwrap()));
                // filter out meta files as they are not considered assets
                if let Some(ext) = file_path.extension().and_then(|e| e.to_str()) {
                    if ext.eq_ignore_ascii_case("meta") {
                        return None;
                    }
                }
                Some(file_path.to_owned())
            })
            .collect::<Vec<_>>();

        let read_dir: Box<PathStream> = Box::new(stream::iter(mapped_stream));
        Ok(read_dir)
    }

    async fn is_directory<'a>(&'a self, path: &'a Path) -> Result<bool, AssetReaderError> {
        let asset_manager = bevy_android::ANDROID_APP
            .get()
            .expect("Bevy must be setup with the #[bevy_main] macro on Android")
            .asset_manager();
        // HACK: `AssetManager` does not provide a way to check if path
        // points to a directory or a file
        // `open_dir` succeeds for both files and directories and will only
        // fail if the path does not exist at all
        // `open` will fail for directories, but it will work for files
        // The solution here was to first use `open_dir` to eliminate the case
        // when the path does not exist at all, and then to use `open` to
        // see if that path is a file or a directory
        let cpath = CString::new(path.to_str().unwrap()).unwrap();
        let _ = asset_manager
            .open_dir(&cpath)
            .ok_or(AssetReaderError::NotFound(path.to_path_buf()))?;
        Ok(asset_manager.open(&cpath).is_none())
    }
}