use std::path::{Path, PathBuf};
use std::time::SystemTime;
use std::pin::Pin;
use std::future::Future;
use std::io::{self, SeekFrom};

use tokio::fs;
use tokio::io::{AsyncReadExt, AsyncWriteExt, AsyncSeekExt};

use super::{VfsError, VfsStat, VfsDirEntry, open_flags::OpenFlags};

/// Async VFS 文件實現（使用 tokio::fs）
pub struct AsyncLocalFile {
    file: fs::File,
    path: PathBuf,
    is_write: bool,
}

impl AsyncLocalFile {
    pub fn new(file: fs::File, path: PathBuf, is_write: bool) -> Self {
        Self { file, path, is_write }
    }
}

impl super::AsyncVfsFile for AsyncLocalFile {
    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Pin<Box<dyn Future<Output = Result<usize, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            self.file.read(buf).await
                .map_err(|e| VfsError::Io(e.to_string()))
        })
    }

    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Pin<Box<dyn Future<Output = Result<usize, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            self.file.write(buf).await
                .map_err(|e| VfsError::Io(e.to_string()))
        })
    }

    fn seek<'a>(&'a mut self, pos: SeekFrom) -> Pin<Box<dyn Future<Output = Result<u64, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            self.file.seek(pos).await
                .map_err(|e| VfsError::Io(e.to_string()))
        })
    }

    fn flush<'a>(&'a mut self) -> Pin<Box<dyn Future<Output = Result<(), VfsError>> + Send + 'a>> {
        Box::pin(async move {
            self.file.flush().await
                .map_err(|e| VfsError::Io(e.to_string()))
        })
    }
}

/// Async VFS 后端實現（使用 tokio::fs）
pub struct AsyncLocalFs {
    root: PathBuf,
}

impl Default for AsyncLocalFs {
    fn default() -> Self {
        Self::new()
    }
}

impl AsyncLocalFs {
    pub fn new() -> Self {
        Self { root: PathBuf::new() }
    }

    pub fn with_root(root: PathBuf) -> Self {
        Self { root }
    }

    fn map_io_error(path: &Path, e: io::Error) -> VfsError {
        match e.kind() {
            io::ErrorKind::NotFound => VfsError::NotFound(path.to_string_lossy().to_string()),
            io::ErrorKind::PermissionDenied => VfsError::PermissionDenied(path.to_string_lossy().to_string()),
            io::ErrorKind::AlreadyExists => VfsError::AlreadyExists(path.to_string_lossy().to_string()),
            _ => VfsError::Io(e.to_string()),
        }
    }

    fn stat_from_metadata(meta: &std::fs::Metadata) -> VfsStat {
        VfsStat {
            size: meta.len(),
            mode: 0o644,
            uid: 0,
            gid: 0,
            atime: meta.accessed().unwrap_or(SystemTime::UNIX_EPOCH),
            mtime: meta.modified().unwrap_or(SystemTime::UNIX_EPOCH),
            is_dir: meta.is_dir(),
            is_symlink: meta.file_type().is_symlink(),
        }
    }
}

impl Clone for AsyncLocalFs {
    fn clone(&self) -> Self {
        Self { root: self.root.clone() }
    }
}

impl super::AsyncVfsBackend for AsyncLocalFs {
    fn clone_boxed(&self) -> Box<dyn super::AsyncVfsBackend> {
        Box::new(self.clone())
    }

    fn read_dir<'a>(&'a self, path: &'a Path) -> Pin<Box<dyn Future<Output = Result<Vec<VfsDirEntry>, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            let mut entries = Vec::new();
            let mut dir = fs::read_dir(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            
            while let Some(entry) = dir.next_entry().await.map_err(|e| Self::map_io_error(path, e))? {
                let name = entry.file_name().to_string_lossy().to_string();
                let long_name = name.clone();
                let meta = entry.metadata().await.map_err(|e| Self::map_io_error(path, e))?;
                let stat = Self::stat_from_metadata(&meta);
                entries.push(VfsDirEntry { name, long_name, stat });
            }
            
            Ok(entries)
        })
    }

    fn open_file<'a>(&'a self, path: &'a Path, flags: &'a OpenFlags) -> Pin<Box<dyn Future<Output = Result<Box<dyn super::AsyncVfsFile>, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            let mut options = fs::OpenOptions::new();
            
            if flags.read {
                options.read(true);
            }
            if flags.write {
                options.write(true);
            }
            if flags.create {
                options.create(true);
            }
            if flags.truncate {
                options.truncate(true);
            }
            if flags.append {
                options.append(true);
            }
            
            let file = options.open(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            
            Ok(Box::new(AsyncLocalFile::new(file, path.to_path_buf(), flags.write)) as Box<dyn super::AsyncVfsFile>)
        })
    }

    fn stat<'a>(&'a self, path: &'a Path) -> Pin<Box<dyn Future<Output = Result<VfsStat, VfsError>> + Send + 'a>> {
        Box::pin(async move {
            let meta = fs::metadata(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            Ok(Self::stat_from_metadata(&meta))
        })
    }

    fn create_dir<'a>(&'a self, path: &'a Path, _mode: u32) -> Pin<Box<dyn Future<Output = Result<(), VfsError>> + Send + 'a>> {
        Box::pin(async move {
            fs::create_dir(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            Ok(())
        })
    }

    fn remove_dir<'a>(&'a self, path: &'a Path) -> Pin<Box<dyn Future<Output = Result<(), VfsError>> + Send + 'a>> {
        Box::pin(async move {
            fs::remove_dir(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            Ok(())
        })
    }

    fn remove_file<'a>(&'a self, path: &'a Path) -> Pin<Box<dyn Future<Output = Result<(), VfsError>> + Send + 'a>> {
        Box::pin(async move {
            fs::remove_file(path).await
                .map_err(|e| Self::map_io_error(path, e))?;
            Ok(())
        })
    }

    fn rename<'a>(&'a self, from: &'a Path, to: &'a Path) -> Pin<Box<dyn Future<Output = Result<(), VfsError>> + Send + 'a>> {
        Box::pin(async move {
            fs::rename(from, to).await
                .map_err(|e| Self::map_io_error(from, e))?;
            Ok(())
        })
    }

    fn exists<'a>(&'a self, path: &'a Path) -> Pin<Box<dyn Future<Output = bool> + Send + 'a>> {
        Box::pin(async move {
            fs::metadata(path).await.is_ok()
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use tempfile::TempDir;
    use crate::vfs::AsyncVfsBackend;
    use crate::vfs::AsyncVfsFile;

    #[tokio::test]
    async fn test_async_read_dir() {
        let tmp = TempDir::new().unwrap();
        fs::create_dir(tmp.path().join("subdir")).await.unwrap();
        fs::write(tmp.path().join("test.txt"), "content").await.unwrap();

        let vfs = AsyncLocalFs::with_root(tmp.path().to_path_buf());
        let entries = AsyncVfsBackend::read_dir(&vfs, tmp.path()).await.unwrap();
        
        assert_eq!(entries.len(), 2);
        assert!(entries.iter().any(|e| e.name == "subdir" && e.stat.is_dir));
        assert!(entries.iter().any(|e| e.name == "test.txt" && !e.stat.is_dir));
    }

    #[tokio::test]
    async fn test_async_open_read() {
        let tmp = TempDir::new().unwrap();
        fs::write(tmp.path().join("test.txt"), "hello world").await.unwrap();

        let vfs = AsyncLocalFs::with_root(tmp.path().to_path_buf());
        let flags = OpenFlags::new().read();
        let mut file = AsyncVfsBackend::open_file(&vfs, &tmp.path().join("test.txt"), &flags).await.unwrap();
        
        let mut buf = [0u8; 11];
        let n = AsyncVfsFile::read(&mut *file, &mut buf).await.unwrap();
        assert_eq!(n, 11);
        assert_eq!(&buf, b"hello world");
    }

    #[tokio::test]
    async fn test_async_create_dir() {
        let tmp = TempDir::new().unwrap();
        let vfs = AsyncLocalFs::with_root(tmp.path().to_path_buf());
        
        AsyncVfsBackend::create_dir(&vfs, &tmp.path().join("newdir"), 0o755).await.unwrap();
        assert!(AsyncVfsBackend::exists(&vfs, &tmp.path().join("newdir")).await);
    }

    #[tokio::test]
    async fn test_async_remove_file() {
        let tmp = TempDir::new().unwrap();
        fs::write(tmp.path().join("test.txt"), "content").await.unwrap();

        let vfs = AsyncLocalFs::with_root(tmp.path().to_path_buf());
        AsyncVfsBackend::remove_file(&vfs, &tmp.path().join("test.txt")).await.unwrap();
        assert!(!AsyncVfsBackend::exists(&vfs, &tmp.path().join("test.txt")).await);
    }
}