use crate::fs::{FsBackend, FsEntry, FsError};

/// Virtual Filesystem (VFS) interface for Prometeu.
/// 
/// The VFS provides a sandboxed, unified path interface for user applications.
/// Instead of interacting directly with the host's disk, the VM uses 
/// normalized paths (e.g., `/user/save.dat`). 
/// 
/// The actual storage is provided by an `FsBackend`, which can be a real 
/// directory on disk, an in-memory map, or even a network resource.
pub struct VirtualFS {
    /// The active storage implementation.
    backend: Option<Box<dyn FsBackend>>,
}

impl VirtualFS {
    pub fn new() -> Self {
        Self { backend: None }
    }

    pub fn mount(&mut self, mut backend: Box<dyn FsBackend>) -> Result<(), FsError> {
        backend.mount()?;
        self.backend = Some(backend);
        Ok(())
    }

    pub fn unmount(&mut self) {
        if let Some(mut backend) = self.backend.take() {
            backend.unmount();
        }
    }

    pub fn is_mounted(&self) -> bool {
        self.backend.is_some()
    }

    fn normalize_path(&self, path: &str) -> String {
        let mut normalized = path.replace('\\', "/");
        if !normalized.starts_with('/') {
            normalized = format!("/{}", normalized);
        }
        normalized
    }

    pub fn list_dir(&self, path: &str) -> Result<Vec<FsEntry>, FsError> {
        let normalized = self.normalize_path(path);
        let backend = self.backend.as_ref().ok_or(FsError::NotMounted)?;
        backend.list_dir(&normalized)
    }

    pub fn read_file(&self, path: &str) -> Result<Vec<u8>, FsError> {
        let normalized = self.normalize_path(path);
        let backend = self.backend.as_ref().ok_or(FsError::NotMounted)?;
        backend.read_file(&normalized)
    }

    pub fn write_file(&mut self, path: &str, data: &[u8]) -> Result<(), FsError> {
        let normalized = self.normalize_path(path);
        let backend = self.backend.as_mut().ok_or(FsError::NotMounted)?;
        backend.write_file(&normalized, data)
    }

    pub fn delete(&mut self, path: &str) -> Result<(), FsError> {
        let normalized = self.normalize_path(path);
        let backend = self.backend.as_mut().ok_or(FsError::NotMounted)?;
        backend.delete(&normalized)
    }

    pub fn exists(&self, path: &str) -> bool {
        let normalized = self.normalize_path(path);
        self.backend.as_ref().map(|b| b.exists(&normalized)).unwrap_or(false)
    }

    pub fn is_healthy(&self) -> bool {
        self.backend.as_ref().map(|b| b.is_healthy()).unwrap_or(false)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::HashMap;

    struct MockBackend {
        files: HashMap<String, Vec<u8>>,
        healthy: bool,
    }

    impl MockBackend {
        fn new() -> Self {
            Self {
                files: HashMap::new(),
                healthy: true,
            }
        }
    }

    impl FsBackend for MockBackend {
        fn mount(&mut self) -> Result<(), FsError> { Ok(()) }
        fn unmount(&mut self) {}
        fn list_dir(&self, _path: &str) -> Result<Vec<FsEntry>, FsError> {
            Ok(self.files.keys().map(|name| FsEntry {
                name: name.clone(),
                is_dir: false,
                size: 0,
            }).collect())
        }
        fn read_file(&self, path: &str) -> Result<Vec<u8>, FsError> {
            self.files.get(path).cloned().ok_or(FsError::NotFound)
        }
        fn write_file(&mut self, path: &str, data: &[u8]) -> Result<(), FsError> {
            self.files.insert(path.to_string(), data.to_vec());
            Ok(())
        }
        fn delete(&mut self, path: &str) -> Result<(), FsError> {
            self.files.remove(path);
            Ok(())
        }
        fn exists(&self, path: &str) -> bool {
            self.files.contains_key(path)
        }
        fn is_healthy(&self) -> bool {
            self.healthy
        }
    }

    #[test]
    fn test_virtual_fs_operations() {
        let mut vfs = VirtualFS::new();
        let backend = MockBackend::new();
        
        vfs.mount(Box::new(backend)).unwrap();
        
        let test_file = "/user/test.txt";
        let content = b"hello world";
        
        vfs.write_file(test_file, content).unwrap();
        assert!(vfs.exists(test_file));
        
        let read_content = vfs.read_file(test_file).unwrap();
        assert_eq!(read_content, content);
        
        vfs.delete(test_file).unwrap();
        assert!(!vfs.exists(test_file));
    }

    #[test]
    fn test_virtual_fs_health() {
        let mut vfs = VirtualFS::new();
        let mut backend = MockBackend::new();
        backend.healthy = false;
        
        vfs.mount(Box::new(backend)).unwrap();
        assert!(!vfs.is_healthy());
    }
}