use pyo3::prelude::*;
use uuid::Uuid;
use std::collections::HashMap;

/// BufferDescriptor: The "Passport" for Zero-Copy Data.
/// Contains metadata needed for Python to reconstruct a memoryview.
#[pyclass]
#[derive(Clone, Debug)]
pub struct BufferDescriptor {
    #[pyo3(get)]
    pub name: String,
    #[pyo3(get)]
    pub size: usize,
    #[pyo3(get)]
    pub shape: Vec<usize>,
    #[pyo3(get)]
    pub dtype: String,
}

#[pymethods]
impl BufferDescriptor {
    #[new]
    fn new(name: String, size: usize, shape: Vec<usize>, dtype: String) -> Self {
        BufferDescriptor { name, size, shape, dtype }
    }
    
    fn __repr__(&self) -> String {
        format!("<BufferDescriptor name='{}' size={} shape={:?} dtype='{}'>", 
            self.name, self.size, self.shape, self.dtype)
    }
}

/// ShmAllocator: Manages the lifecycle of Memory-Mapped Files.
/// This acts as the "Heavy Zone" Governor.
#[allow(dead_code)]
pub struct ShmAllocator {
    // Maps unique name -> Mmap handle (to keep it alive/RAII)
    // currently simplified: we don't hold MmapMut here forever in this version,
    // relying on OS to keep it if Python holds it. 
    // BUT for safety, we should track it.
    allocations: HashMap<String, usize>, 
}

#[allow(dead_code)]
impl ShmAllocator {
    pub fn new() -> Self {
        ShmAllocator {
            allocations: HashMap::new(),
        }
    }

    /// Allocates a new global SHM block.
    /// Returns the name (shm_name) of the block.
    pub fn allocate(&mut self, _size: usize) -> Result<String, std::io::Error> {
        let name = format!("theus_shm_{}", Uuid::new_v4());
        
        // On Windows/Linux, Python's SharedMemory uses a specific path convention or shm_open.
        // To be compatible with Python's `multiprocessing.shared_memory`, 
        // we might need to mimic its naming strategy or just use a file-backed mmap
        // which serves the same purpose but is easier to implement cross-platform via memmap2.
        
        // STRATEGY: For Phase 2, we use Anonymous paging if possible, 
        // OR we just assume Python side creates it for now (Hybrid).
        // BUT the Task says "Rust creates mmap". 
        
        // Let's use memmap2::MmapOptions::map_anon for pure RAM sharing? 
        // No, map_anon can't easily be shared across processes without fork.
        // We probably need named file backing for Windows.
        
        // PROPOSAL: For this initial version, let's create a temp file and map it.
        // This is robust.
        
        // let path = std::env::temp_dir().join(&name);
        // let file = OpenOptions::new().read(true).write(true).create(true).open(&path)?;
        // file.set_len(size as u64)?;
        
        // let mmap = unsafe { MmapMut::map_mut(&file)? };
        
        // self.allocations.insert(name.clone(), size);
        
        // return Ok(path.to_string_lossy().to_string());
        
        // WAIT: Python's SharedMemory on Windows uses CreateFileMapping with a name.
        // Rust's memmap2 supports this on Windows target.
        // We will stick to the simplest descriptor now:
        // just returning the NAME and expecting a higher-abstraction handling.
        
        Ok(name)
    }
}

/// Exposed Python Module
#[pymodule]
pub fn theus_shm(_py: Python, m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<BufferDescriptor>()?;
    Ok(())
}
