use crate::ffi_ptr_ext::FfiPtrExt;
use crate::py_result_ext::PyResultExt;
use crate::sync::PyOnceLock;
#[cfg(Py_LIMITED_API)]
use crate::types::PyAnyMethods;
use crate::types::{PyType, PyTypeMethods};
use crate::{ffi, Bound, Py, PyAny, PyErr, PyResult};

/// A Python iterator object.
///
/// Values of this type are accessed via PyO3's smart pointers, e.g. as
/// [`Py<PyIterator>`][crate::Py] or [`Bound<'py, PyIterator>`][Bound].
///
/// # Examples
///
/// ```rust
/// use pyo3::prelude::*;
///
/// # fn main() -> PyResult<()> {
/// Python::attach(|py| -> PyResult<()> {
///     let list = py.eval(c"iter([1, 2, 3, 4])", None, None)?;
///     let numbers: PyResult<Vec<usize>> = list
///         .try_iter()?
///         .map(|i| i.and_then(|i|i.extract::<usize>()))
///         .collect();
///     let sum: usize = numbers?.iter().sum();
///     assert_eq!(sum, 10);
///     Ok(())
/// })
/// # }
/// ```
#[repr(transparent)]
pub struct PyIterator(PyAny);

pyobject_native_type_core!(
    PyIterator,
    |py| {
        static TYPE: PyOnceLock<Py<PyType>> = PyOnceLock::new();
        TYPE.import(py, "collections.abc", "Iterator")
            .unwrap()
            .as_type_ptr()
    },
    "collections.abc",
    "Iterator",
    #module=Some("collections.abc"),
    #checkfunction=ffi::PyIter_Check
);

impl PyIterator {
    /// Builds an iterator for an iterable Python object; the equivalent of calling `iter(obj)` in Python.
    ///
    /// Usually it is more convenient to write [`obj.try_iter()`][crate::types::any::PyAnyMethods::try_iter],
    /// which is a more concise way of calling this function.
    pub fn from_object<'py>(obj: &Bound<'py, PyAny>) -> PyResult<Bound<'py, PyIterator>> {
        unsafe {
            ffi::PyObject_GetIter(obj.as_ptr())
                .assume_owned_or_err(obj.py())
                .cast_into_unchecked()
        }
    }
}

/// Outcomes from sending a value into a python generator
#[derive(Debug)]
#[cfg(all(not(PyPy), Py_3_10))]
pub enum PySendResult<'py> {
    /// The generator yielded a new value
    Next(Bound<'py, PyAny>),
    /// The generator completed, returning a (possibly None) final value
    Return(Bound<'py, PyAny>),
}

#[cfg(all(not(PyPy), Py_3_10))]
impl<'py> Bound<'py, PyIterator> {
    /// Sends a value into a python generator. This is the equivalent of calling
    /// `generator.send(value)` in Python. This resumes the generator and continues its execution
    /// until the next `yield` or `return` statement. When the generator completes, the (optional)
    /// return value will be returned as `PySendResult::Return`. All subsequent calls will return
    /// `PySendResult::Return(None)`. The first call to `send` must be made with `None` as the
    /// argument to start the generator, failing to do so will raise a `TypeError`.
    #[inline]
    pub fn send(&self, value: &Bound<'py, PyAny>) -> PyResult<PySendResult<'py>> {
        let py = self.py();
        let mut result = core::ptr::null_mut();
        match unsafe { ffi::PyIter_Send(self.as_ptr(), value.as_ptr(), &mut result) } {
            ffi::PySendResult::PYGEN_ERROR => Err(PyErr::fetch(py)),
            ffi::PySendResult::PYGEN_RETURN => Ok(PySendResult::Return(unsafe {
                result.assume_owned_unchecked(py)
            })),
            ffi::PySendResult::PYGEN_NEXT => Ok(PySendResult::Next(unsafe {
                result.assume_owned_unchecked(py)
            })),
        }
    }
}

impl<'py> Iterator for Bound<'py, PyIterator> {
    type Item = PyResult<Bound<'py, PyAny>>;

    /// Retrieves the next item from an iterator.
    ///
    /// Returns `None` when the iterator is exhausted.
    /// If an exception occurs, returns `Some(Err(..))`.
    /// Further `next()` calls after an exception occurs are likely
    /// to repeatedly result in the same exception.
    fn next(&mut self) -> Option<Self::Item> {
        let py = self.py();
        let mut item = core::ptr::null_mut();

        // SAFETY: `self` is a valid iterator object, `item` is a valid pointer to receive the next item
        match unsafe { ffi::compat::PyIter_NextItem(self.as_ptr(), &mut item) } {
            core::ffi::c_int::MIN..=-1 => Some(Err(PyErr::fetch(py))),
            0 => None,
            // SAFETY: `item` is guaranteed to be a non-null strong reference
            1..=core::ffi::c_int::MAX => Some(Ok(unsafe { item.assume_owned_unchecked(py) })),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        match length_hint(self) {
            Ok(hint) => (hint, None),
            Err(e) => {
                e.write_unraisable(self.py(), Some(self));
                (0, None)
            }
        }
    }
}

#[cfg(not(Py_LIMITED_API))]
fn length_hint(iter: &Bound<'_, PyIterator>) -> PyResult<usize> {
    // SAFETY: `iter` is a valid iterator object
    let hint = unsafe { ffi::PyObject_LengthHint(iter.as_ptr(), 0) };
    if hint < 0 {
        Err(PyErr::fetch(iter.py()))
    } else {
        Ok(hint as usize)
    }
}

/// On the limited API, we cannot use `PyObject_LengthHint`, so we fall back to calling
/// `operator.length_hint()`, which is documented equivalent to calling `PyObject_LengthHint`.
#[cfg(Py_LIMITED_API)]
fn length_hint(iter: &Bound<'_, PyIterator>) -> PyResult<usize> {
    static LENGTH_HINT: PyOnceLock<Py<PyAny>> = PyOnceLock::new();
    let length_hint = LENGTH_HINT.import(iter.py(), "operator", "length_hint")?;
    length_hint.call1((iter, 0))?.extract()
}

impl<'py> IntoIterator for &Bound<'py, PyIterator> {
    type Item = PyResult<Bound<'py, PyAny>>;
    type IntoIter = Bound<'py, PyIterator>;

    fn into_iter(self) -> Self::IntoIter {
        self.clone()
    }
}

#[cfg(test)]
mod tests {
    use super::PyIterator;
    #[cfg(all(not(PyPy), Py_3_10))]
    use super::PySendResult;
    use crate::exceptions::PyTypeError;
    #[allow(unused_imports, reason = "conditionally used")]
    use crate::platform::prelude::*;
    #[cfg(all(not(PyPy), Py_3_10))]
    use crate::types::PyNone;
    use crate::types::{PyAnyMethods, PyDict, PyList, PyListMethods};
    #[cfg(feature = "macros")]
    use crate::PyErr;
    use crate::{IntoPyObject, PyTypeInfo, Python};

    #[test]
    fn vec_iter() {
        Python::attach(|py| {
            let inst = vec![10, 20].into_pyobject(py).unwrap();
            let mut it = inst.try_iter().unwrap();
            assert_eq!(
                10_i32,
                it.next().unwrap().unwrap().extract::<'_, i32>().unwrap()
            );
            assert_eq!(
                20_i32,
                it.next().unwrap().unwrap().extract::<'_, i32>().unwrap()
            );
            assert!(it.next().is_none());
        });
    }

    #[test]
    fn iter_refcnt() {
        let (obj, count) = Python::attach(|py| {
            let obj = vec![10, 20].into_pyobject(py).unwrap();
            let count = obj._get_refcnt();
            (obj.unbind(), count)
        });

        Python::attach(|py| {
            let inst = obj.bind(py);
            let mut it = inst.try_iter().unwrap();

            assert_eq!(
                10_i32,
                it.next().unwrap().unwrap().extract::<'_, i32>().unwrap()
            );
        });

        Python::attach(move |py| {
            assert_eq!(count, obj._get_refcnt(py));
        });
    }

    #[test]
    fn iter_item_refcnt() {
        Python::attach(|py| {
            let count;
            let obj = py.eval(c"object()", None, None).unwrap();
            let list = {
                let list = PyList::empty(py);
                list.append(10).unwrap();
                list.append(&obj).unwrap();
                count = obj._get_refcnt();
                list
            };

            {
                let mut it = list.iter();

                assert_eq!(10_i32, it.next().unwrap().extract::<'_, i32>().unwrap());
                assert!(it.next().unwrap().is(&obj));
                assert!(it.next().is_none());
            }
            assert_eq!(count, obj._get_refcnt());
        });
    }

    #[test]
    fn fibonacci_generator() {
        let fibonacci_generator = cr#"
def fibonacci(target):
    a = 1
    b = 1
    for _ in range(target):
        yield a
        a, b = b, a + b
"#;

        Python::attach(|py| {
            let context = PyDict::new(py);
            py.run(fibonacci_generator, None, Some(&context)).unwrap();

            let generator = py.eval(c"fibonacci(5)", None, Some(&context)).unwrap();
            for (actual, expected) in generator.try_iter().unwrap().zip(&[1, 1, 2, 3, 5]) {
                let actual = actual.unwrap().extract::<usize>().unwrap();
                assert_eq!(actual, *expected)
            }
        });
    }

    #[test]
    #[cfg(all(not(PyPy), Py_3_10))]
    fn send_generator() {
        let generator = cr#"
def gen():
    value = None
    while(True):
        value = yield value
        if value is None:
            return
"#;

        Python::attach(|py| {
            let context = PyDict::new(py);
            py.run(generator, None, Some(&context)).unwrap();

            let generator = py.eval(c"gen()", None, Some(&context)).unwrap();

            let one = 1i32.into_pyobject(py).unwrap();
            assert!(matches!(
                generator.try_iter().unwrap().send(&PyNone::get(py)).unwrap(),
                PySendResult::Next(value) if value.is_none()
            ));
            assert!(matches!(
                generator.try_iter().unwrap().send(&one).unwrap(),
                PySendResult::Next(value) if value.is(&one)
            ));
            assert!(matches!(
                generator.try_iter().unwrap().send(&PyNone::get(py)).unwrap(),
                PySendResult::Return(value) if value.is_none()
            ));
        });
    }

    #[test]
    fn fibonacci_generator_bound() {
        use crate::types::any::PyAnyMethods;
        use crate::Bound;

        let fibonacci_generator = cr#"
def fibonacci(target):
    a = 1
    b = 1
    for _ in range(target):
        yield a
        a, b = b, a + b
"#;

        Python::attach(|py| {
            let context = PyDict::new(py);
            py.run(fibonacci_generator, None, Some(&context)).unwrap();

            let generator: Bound<'_, PyIterator> = py
                .eval(c"fibonacci(5)", None, Some(&context))
                .unwrap()
                .cast_into()
                .unwrap();
            let mut items = vec![];
            for actual in &generator {
                let actual = actual.unwrap().extract::<usize>().unwrap();
                items.push(actual);
            }
            assert_eq!(items, [1, 1, 2, 3, 5]);
        });
    }

    #[test]
    fn int_not_iterable() {
        Python::attach(|py| {
            let x = 5i32.into_pyobject(py).unwrap();
            let err = PyIterator::from_object(&x).unwrap_err();

            assert!(err.is_instance_of::<PyTypeError>(py));
        });
    }

    #[test]
    #[cfg(feature = "macros")]
    fn python_class_not_iterator() {
        use crate::PyErr;

        #[crate::pyclass(crate = "crate")]
        struct Downcaster {
            failed: Option<PyErr>,
        }

        #[crate::pymethods(crate = "crate")]
        impl Downcaster {
            fn downcast_iterator(&mut self, obj: &crate::Bound<'_, crate::PyAny>) {
                self.failed = Some(obj.cast::<PyIterator>().unwrap_err().into());
            }
        }

        // Regression test for 2913
        Python::attach(|py| {
            let downcaster = crate::Py::new(py, Downcaster { failed: None }).unwrap();
            crate::py_run!(
                py,
                downcaster,
                r#"
                    from collections.abc import Sequence

                    class MySequence(Sequence):
                        def __init__(self):
                            self._data = [1, 2, 3]

                        def __getitem__(self, index):
                            return self._data[index]

                        def __len__(self):
                            return len(self._data)

                    downcaster.downcast_iterator(MySequence())
                "#
            );

            assert_eq!(
                downcaster.borrow_mut(py).failed.take().unwrap().to_string(),
                "TypeError: 'MySequence' object is not an instance of 'Iterator'"
            );
        });
    }

    #[test]
    #[cfg(feature = "macros")]
    fn python_class_iterator() {
        #[crate::pyfunction(crate = "crate")]
        fn assert_iterator(obj: &crate::Bound<'_, crate::PyAny>) {
            assert!(obj.cast::<PyIterator>().is_ok())
        }

        // Regression test for 2913
        Python::attach(|py| {
            let assert_iterator = crate::wrap_pyfunction!(assert_iterator, py).unwrap();
            crate::py_run!(
                py,
                assert_iterator,
                r#"
                    class MyIter:
                        def __next__(self):
                            raise StopIteration

                    assert_iterator(MyIter())
                "#
            );
        });
    }

    #[test]
    fn length_hint_becomes_size_hint_lower_bound() {
        Python::attach(|py| {
            let list = py.eval(c"[1, 2, 3]", None, None).unwrap();
            let iter = list.try_iter().unwrap();
            let hint = iter.size_hint();
            assert_eq!(hint, (3, None));
        });
    }

    #[test]
    #[cfg(feature = "macros")]
    fn length_hint_error() {
        #[crate::pyfunction(crate = "crate")]
        fn test_size_hint(obj: &crate::Bound<'_, crate::PyAny>, should_error: bool) {
            let iter = obj.cast::<PyIterator>().unwrap();
            crate::test_utils::UnraisableCapture::enter(obj.py(), |capture| {
                assert_eq!((0, None), iter.size_hint());
                assert_eq!(should_error, capture.take_capture().is_some());
            });
            assert!(PyErr::take(obj.py()).is_none());
        }

        Python::attach(|py| {
            let test_size_hint = crate::wrap_pyfunction!(test_size_hint, py).unwrap();
            crate::py_run!(
                py,
                test_size_hint,
                r#"
                    class NoHintIter:
                        def __next__(self):
                            raise StopIteration

                        def __length_hint__(self):
                            return NotImplemented

                    class ErrorHintIter:
                        def __next__(self):
                            raise StopIteration

                        def __length_hint__(self):
                            raise ValueError("bad hint impl")

                    test_size_hint(NoHintIter(), False)
                    test_size_hint(ErrorHintIter(), True)
                "#
            );
        });
    }

    #[test]
    fn test_type_object() {
        Python::attach(|py| {
            let abc = PyIterator::type_object(py);
            let iter = py.eval(c"iter(())", None, None).unwrap();
            assert!(iter.is_instance(&abc).unwrap());
        })
    }
}
