use hg::errors::HgError;

use hg::revlog::index::Index as CoreIndex;

use hg::revlog::inner_revlog::RevisionBuffer;

use pyo3::buffer::{Element, PyBuffer};

use pyo3::exceptions::PyValueError;

use pyo3::prelude::*;

use pyo3::types::{PyBytes, PyDict};

use pyo3_sharedref::SharedByPyObject;

use stable_deref_trait::StableDeref;

use crate::revlog::{InnerRevlog, PySharedIndex};

/// Create the module, with `__package__` given from parent

///

/// According to PyO3 documentation, which links to

/// <https://github.com/PyO3/pyo3/issues/1517>, the same convoluted

/// write to sys.modules has to be made as with the `cpython` crate.

pub(crate) fn new_submodule<'py>(

    py: Python<'py>,

    package_name: &str,

    name: &str,

) -> PyResult<Bound<'py, PyModule>> {

    let dotted_name = &format!("{}.{}", package_name, name);

    let m = PyModule::new(py, name)?;

    m.add("__package__", package_name)?;

    let sys = PyModule::import(py, "sys")?;

    // according to the doc, we could make a static PyString out of

    // "modules" with the `intern!` macro, but this is used only at

    // registration so it may not be worth the effort.

    let sys_modules: Bound<'_, PyDict> = sys.getattr("modules")?.extract()?;

    sys_modules.set_item(dotted_name, &m)?;

    // Example C code (see pyexpat.c and import.c) will "give away the

    // reference", but we won't because it will be consumed once the

    // Rust PyObject is dropped.

    Ok(m)

}

/// Retrieve the shared index wrapper (which contains the core index)

/// from the Python index proxy.

pub fn py_rust_index_to_graph(

    index_proxy: &Bound<'_, PyAny>,

) -> PyResult<SharedByPyObject<PySharedIndex>> {

    let py_irl = index_proxy.getattr("inner")?;

    let py_irl_ref = py_irl.downcast::<InnerRevlog>()?.borrow();

    let shareable_irl = &py_irl_ref.irl;

    // Safety: the owner is the actual one and we do not leak any

    // internal reference.

    let index =

        unsafe { shareable_irl.share_map(&py_irl, |irl| (&irl.index).into()) };

    Ok(index)

}

/// Error propagation for an [`SharedByPyObject`] wrapping a [`Result`]

///

/// It would be nice for [`SharedByPyObject`] to provide this directly as

/// a variant of the `map` method with a signature such as:

///

/// ```

///   unsafe fn map_or_err(&self,

///                        py: Python,

///                        f: impl FnOnce(T) -> Result(U, E),

///                        convert_err: impl FnOnce(E) -> PyErr)

/// ```

///

/// This would spare users of the `pyo3` crate the additional `unsafe` deref

/// to inspect the error and return it outside `SharedByPyObject`, and the

/// subsequent unwrapping that this function performs.

pub(crate) fn py_shared_or_map_err<T, E: std::fmt::Debug + Copy>(

    py: Python,

    leaked: SharedByPyObject<Result<T, E>>,

    convert_err: impl FnOnce(E) -> PyErr,

) -> PyResult<SharedByPyObject<T>> {

    // Safety: we don't leak the "faked" reference out of `SharedByPyObject`

    if let Err(e) = *unsafe { leaked.try_borrow(py)? } {

        return Err(convert_err(e));

    }

    // Safety: we don't leak the "faked" reference out of `SharedByPyObject`

    Ok(unsafe {

        leaked.map(py, |res| {

            res.expect("Error case should have already be treated")

        })

    })

}

/// Full extraction of the proxy index object as received in PyO3 to a

/// [`CoreIndex`] reference.

///

/// # Safety

///

/// The invariants to maintain are those of the underlying

/// [`SharedByPyObject::try_borrow`]: the caller must not leak the inner

/// reference.

pub(crate) unsafe fn proxy_index_extract<'py>(

    index_proxy: &Bound<'py, PyAny>,

) -> PyResult<&'py CoreIndex> {

    let py_shared = py_rust_index_to_graph(index_proxy)?;

    let py_shared = &*unsafe { py_shared.try_borrow(index_proxy.py())? };

    Ok(unsafe { py_shared.static_inner() })

}

/// Type shortcut for the kind of bytes slice trait objects that are used in

/// particular for mmap data

type BoxedBytesSlice =

    Box<dyn std::ops::Deref<Target = [u8]> + Send + Sync + 'static>;

/// Take a Python object backed by a Python buffer, and return the underlying

/// [`PyBuffer`] along with the Rust slice into said buffer.

///

/// The caller needs to make sure that the Python buffer is not freed before

/// the slice, otherwise we'd get a dangling pointer once the incoming

/// object is freed from Python side. This can be achieved by storing it a

/// Python object.

///

/// The typical use case is to extract mmap data to make it useable in the

/// constructs from the `hg` crate.

///

/// # Safety

///

/// The caller must make sure that the incoming Python object is kept around

/// for at least as long as the returned [`BoxedBytesSlice`].

// TODO in PyO3, we already get a reference with two lifetimes, and we

// could even take a `Borrowed<'a, 'py, T>`.

// So perhaps we could tie everything together with a lifetime so that is

// is, after all, safe, and this could be called something like `share_buffer`.

#[deny(unsafe_op_in_unsafe_fn)]

pub unsafe fn take_buffer_with_slice(

    data: &Bound<'_, PyAny>,

) -> PyResult<(PyBuffer<u8>, BoxedBytesSlice)> {

    let buf = PyBuffer::<u8>::get(data)?;

    let len = buf.item_count();

    // Build a slice from the buffer data

    let cbuf = buf.buf_ptr();

    let bytes = if std::mem::size_of::<u8>() == buf.item_size()

        && buf.is_c_contiguous()

        && u8::is_compatible_format(buf.format())

        && buf.dimensions() == 1

        && buf.readonly()

    {

        unsafe { std::slice::from_raw_parts(cbuf as *const u8, len) }

    } else {

        return Err(PyValueError::new_err(

            "buffer has an invalid memory representation",

        ));

    };

    Ok((buf, Box::new(bytes)))

}

/// Takes an initialization function `init` which writes bytes to a

/// Python-backed buffer, to save on a (potentially large) memory allocation

/// and copy. If `init` fails to write the full expected length `len`, an error

/// is raised.

pub fn with_pybytes_buffer<F>(

    py: Python,

    len: usize,

    init: F,

) -> Result<Py<PyBytes>, hg::revlog::RevlogError>

where

    F: FnOnce(

        &mut dyn RevisionBuffer<Target = Py<PyBytes>>,

    ) -> Result<(), hg::revlog::RevlogError>,

{

    // Largely inspired by code in PyO3

    // https://pyo3.rs/main/doc/pyo3/types/struct.pybytes#method.new_bound_with

    unsafe {

        let pyptr = pyo3::ffi::PyBytes_FromStringAndSize(

            std::ptr::null(),

            len as pyo3::ffi::Py_ssize_t,

        );

        let pybytes = Bound::from_owned_ptr_or_err(py, pyptr)

            .map_err(|e| HgError::abort_simple(e.to_string()))?

            .downcast_into_unchecked();

        let buffer: *mut u8 = pyo3::ffi::PyBytes_AsString(pyptr).cast();

        debug_assert!(!buffer.is_null());

        let mut rev_buf = PyRevisionBuffer::new(pybytes.unbind(), buffer, len);

        // Initialise the bytestring in init

        // If init returns an Err, the buffer is deallocated by `pybytes`

        init(&mut rev_buf).map(|_| rev_buf.finish())

    }

}

/// Safe abstraction over a `PyBytes` together with the `&[u8]` slice

/// that borrows it. Implements `Deref<Target = [u8]>`.

///

/// Calling `PyBytes::data` requires a GIL marker but we want to access the

/// data in a thread that (ideally) does not need to acquire the GIL.

/// This type allows separating the call an the use.

///

/// It also enables using a (wrapped) `PyBytes` in GIL-unaware generic code.

pub struct PyBytesDeref {

    #[allow(unused)]

    keep_alive: Py<PyBytes>,

    /// Borrows the buffer inside `self.keep_alive`,

    /// but the borrow-checker cannot express self-referential structs.

    data: &'static [u8],

}

impl PyBytesDeref {

    pub fn new(py: Python, bytes: Py<PyBytes>) -> Self {

        let as_raw: *const [u8] = bytes.as_bytes(py);

        Self {

            // Safety: the raw pointer is valid as long as the PyBytes is still

            // alive, and the objecs owns it.

            data: unsafe { &*as_raw },

            keep_alive: bytes,

        }

    }

    #[allow(unused)]

    pub fn unwrap(self) -> Py<PyBytes> {

        self.keep_alive

    }

}

impl std::ops::Deref for PyBytesDeref {

    type Target = [u8];

    fn deref(&self) -> &[u8] {

        self.data

    }

}

unsafe impl StableDeref for PyBytesDeref {}

fn require_send<T: Send>() {}

#[allow(unused)]

fn static_assert_pybytes_is_send() {

    #[allow(clippy::no_effect)]

    require_send::<Py<PyBytes>>;

}

// Safety: `[Py<PyBytes>]` is Send. Raw pointers are not by default,

// but here sending one to another thread is fine since we ensure it stays

// valid.

unsafe impl Send for PyBytesDeref {}

/// Wrapper around a Python-provided buffer into which the revision contents

/// will be written. Done for speed in order to save a large allocation + copy.

struct PyRevisionBuffer {

    py_bytes: Py<PyBytes>,

    _buf: *mut u8,

    len: usize,

    current_buf: *mut u8,

    current_len: usize,

}

impl PyRevisionBuffer {

    /// # Safety

    ///

    /// `buf` should be the start of the allocated bytes of `bytes`, and `len`

    /// exactly the length of said allocated bytes.

    #[inline]

    unsafe fn new(bytes: Py<PyBytes>, buf: *mut u8, len: usize) -> Self {

        Self {

            py_bytes: bytes,

            _buf: buf,

            len,

            current_len: 0,

            current_buf: buf,

        }

    }

    /// Number of bytes that have been copied to. Will be different to the

    /// total allocated length of the buffer unless the revision is done being

    /// written.

    #[inline]

    fn current_len(&self) -> usize {

        self.current_len

    }

}

impl RevisionBuffer for PyRevisionBuffer {

    type Target = Py<PyBytes>;

    #[inline]

    fn extend_from_slice(&mut self, slice: &[u8]) {

        assert!(self.current_len + slice.len() <= self.len);

        unsafe {

            // We cannot use `copy_from_nonoverlapping` since it's *possible*

            // to create a slice from the same Python memory region using

            // [`PyBytesDeref`]. Probable that LLVM has an optimization anyway?

            self.current_buf.copy_from(slice.as_ptr(), slice.len());

            self.current_buf = self.current_buf.add(slice.len());

        }

        self.current_len += slice.len()

    }

    #[inline]

    fn finish(self) -> Self::Target {

        // catch unzeroed bytes before it becomes undefined behavior

        assert_eq!(

            self.current_len(),

            self.len,

            "not enough bytes read for revision"

        );

        self.py_bytes

    }

}