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// Copyright (c) 2017-present PyO3 Project and Contributors
//! Python Iterator Interface.
//! Trait and support implementation for implementing iterators

use crate::callback::{CallbackConverter, PyObjectCallbackConverter};
use crate::conversion::IntoPyObject;
use crate::err::PyResult;
use crate::ffi;
use crate::instance::PyRefMut;
use crate::python::{IntoPyPointer, Python};
use crate::typeob::PyTypeInfo;
use std::ptr;

/// Python Iterator Interface.
///
/// more information
/// `https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_iter`
#[allow(unused_variables)]
pub trait PyIterProtocol<'p>: PyTypeInfo + Sized {
    fn __iter__(slf: PyRefMut<'p, Self>) -> Self::Result
    where
        Self: PyIterIterProtocol<'p>,
    {
        unimplemented!()
    }

    fn __next__(slf: PyRefMut<'p, Self>) -> Self::Result
    where
        Self: PyIterNextProtocol<'p>,
    {
        unimplemented!()
    }
}

pub trait PyIterIterProtocol<'p>: PyIterProtocol<'p> {
    type Success: crate::IntoPyObject;
    type Result: Into<PyResult<Self::Success>>;
}

pub trait PyIterNextProtocol<'p>: PyIterProtocol<'p> {
    type Success: crate::IntoPyObject;
    type Result: Into<PyResult<Option<Self::Success>>>;
}

#[doc(hidden)]
pub trait PyIterProtocolImpl {
    fn tp_as_iter(_typeob: &mut ffi::PyTypeObject) {}
}

impl<T> PyIterProtocolImpl for T {}

impl<'p, T> PyIterProtocolImpl for T
where
    T: PyIterProtocol<'p>,
{
    #[inline]
    fn tp_as_iter(typeob: &mut ffi::PyTypeObject) {
        typeob.tp_iter = Self::tp_iter();
        typeob.tp_iternext = Self::tp_iternext();
    }
}

trait PyIterIterProtocolImpl {
    fn tp_iter() -> Option<ffi::getiterfunc> {
        None
    }
}

impl<'p, T> PyIterIterProtocolImpl for T where T: PyIterProtocol<'p> {}

impl<T> PyIterIterProtocolImpl for T
where
    T: for<'p> PyIterIterProtocol<'p>,
{
    #[inline]
    fn tp_iter() -> Option<ffi::getiterfunc> {
        py_unary_pyref_func!(
            PyIterIterProtocol,
            T::__iter__,
            T::Success,
            PyObjectCallbackConverter
        )
    }
}

trait PyIterNextProtocolImpl {
    fn tp_iternext() -> Option<ffi::iternextfunc> {
        None
    }
}

impl<'p, T> PyIterNextProtocolImpl for T where T: PyIterProtocol<'p> {}

impl<T> PyIterNextProtocolImpl for T
where
    T: for<'p> PyIterNextProtocol<'p>,
{
    #[inline]
    fn tp_iternext() -> Option<ffi::iternextfunc> {
        py_unary_pyref_func!(
            PyIterNextProtocol,
            T::__next__,
            Option<T::Success>,
            IterNextConverter
        )
    }
}

struct IterNextConverter;

impl<T> CallbackConverter<Option<T>> for IterNextConverter
where
    T: IntoPyObject,
{
    type R = *mut ffi::PyObject;

    fn convert(val: Option<T>, py: Python) -> *mut ffi::PyObject {
        match val {
            Some(val) => val.into_object(py).into_ptr(),
            None => unsafe {
                ffi::PyErr_SetNone(ffi::PyExc_StopIteration);
                ptr::null_mut()
            },
        }
    }

    #[inline]
    fn error_value() -> *mut ffi::PyObject {
        ptr::null_mut()
    }
}