use num_bigint::BigInt;
use num_complex::Complex64;
use num_traits::ToPrimitive;
use std::any::Any;
use std::collections::HashMap;
use std::fmt;
use std::marker::PhantomData;
use std::ops::Deref;

use crate::builtins::builtinfunc::PyNativeFuncDef;
use crate::builtins::bytearray;
use crate::builtins::bytes;
use crate::builtins::code;
use crate::builtins::code::PyCodeRef;
use crate::builtins::complex::PyComplex;
use crate::builtins::dict::{PyDict, PyDictRef};
use crate::builtins::float::PyFloat;
use crate::builtins::function::PyBoundMethod;
use crate::builtins::getset::{IntoPyGetterFunc, IntoPySetterFunc, PyGetSet};
use crate::builtins::int::{PyInt, PyIntRef};
use crate::builtins::iter::PySequenceIterator;
use crate::builtins::list::PyList;
use crate::builtins::namespace::PyNamespace;
use crate::builtins::object;
use crate::builtins::pystr;
use crate::builtins::pytype::{self, PyType, PyTypeRef};
use crate::builtins::set;
use crate::builtins::singletons::{PyNone, PyNoneRef, PyNotImplemented, PyNotImplementedRef};
use crate::builtins::slice::PyEllipsis;
use crate::builtins::staticmethod::PyStaticMethod;
use crate::builtins::tuple::{PyTuple, PyTupleRef};
pub use crate::common::borrow::BorrowValue;
use crate::common::lock::{PyRwLock, PyRwLockReadGuard};
use crate::common::rc::PyRc;
use crate::common::static_cell;
use crate::dictdatatype::Dict;
use crate::exceptions::{self, PyBaseExceptionRef};
use crate::function::{IntoFuncArgs, IntoPyNativeFunc};
use crate::iterator;
pub use crate::pyobjectrc::{PyObject, PyObjectRef, PyObjectWeak, PyRef, PyWeakRef};
use crate::slots::{PyTpFlags, PyTypeSlots};
use crate::types::{create_type_with_slots, TypeZoo};
use crate::vm::VirtualMachine;

/* Python objects and references.

Okay, so each python object itself is an class itself (PyObject). Each
python object can have several references to it (PyObjectRef). These
references are Rc (reference counting) rust smart pointers. So when
all references are destroyed, the object itself also can be cleaned up.
Basically reference counting, but then done by rust.

*/

/*
 * Good reference: https://github.com/ProgVal/pythonvm-rust/blob/master/src/objects/mod.rs
 */

/// Use this type for functions which return a python object or an exception.
/// Both the python object and the python exception are `PyObjectRef` types
/// since exceptions are also python objects.
pub type PyResult<T = PyObjectRef> = Result<T, PyBaseExceptionRef>; // A valid value, or an exception

/// For attributes we do not use a dict, but a hashmap. This is probably
/// faster, unordered, and only supports strings as keys.
/// TODO: class attributes should maintain insertion order (use IndexMap here)
pub type PyAttributes = HashMap<String, PyObjectRef, ahash::RandomState>;

// TODO: remove this impl
impl fmt::Display for PyObjectRef {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if let Some(PyType { ref name, .. }) = self.payload::<PyType>() {
            let type_name = self.class().name.clone();
            // We don't have access to a vm, so just assume that if its parent's name
            // is type, it's a type
            if type_name == "type" {
                return write!(f, "type object '{}'", name);
            } else {
                return write!(f, "'{}' object", type_name);
            }
        }

        write!(f, "'{}' object", self.class().name)
    }
}

#[derive(Debug, Clone)]
pub struct PyContext {
    pub true_value: PyIntRef,
    pub false_value: PyIntRef,
    pub none: PyNoneRef,
    pub empty_tuple: PyTupleRef,
    pub ellipsis: PyRef<PyEllipsis>,
    pub not_implemented: PyNotImplementedRef,

    pub types: TypeZoo,
    pub exceptions: exceptions::ExceptionZoo,
    pub int_cache_pool: Vec<PyIntRef>,
    // there should only be exact objects of str in here, no non-strs and no subclasses
    pub(crate) string_cache: Dict<()>,
    tp_new_wrapper: PyObjectRef,
}

// Basic objects:
impl PyContext {
    pub const INT_CACHE_POOL_MIN: i32 = -5;
    pub const INT_CACHE_POOL_MAX: i32 = 256;

    fn init() -> Self {
        flame_guard!("init PyContext");
        let types = TypeZoo::init();
        let exceptions = exceptions::ExceptionZoo::init();

        fn create_object<T: PyObjectPayload + PyValue>(payload: T, cls: &PyTypeRef) -> PyRef<T> {
            PyRef::new_ref(payload, cls.clone(), None)
        }

        let none = create_object(PyNone, PyNone::static_type());
        let ellipsis = create_object(PyEllipsis, PyEllipsis::static_type());
        let not_implemented = create_object(PyNotImplemented, PyNotImplemented::static_type());

        let int_cache_pool = (Self::INT_CACHE_POOL_MIN..=Self::INT_CACHE_POOL_MAX)
            .map(|v| PyRef::new_ref(PyInt::from(BigInt::from(v)), types.int_type.clone(), None))
            .collect();

        let true_value = create_object(PyInt::from(1), &types.bool_type);
        let false_value = create_object(PyInt::from(0), &types.bool_type);

        let empty_tuple = create_object(
            PyTuple::_new(Vec::new().into_boxed_slice()),
            &types.tuple_type,
        );

        let string_cache = Dict::default();

        let new_str = PyRef::new_ref(pystr::PyStr::from("__new__"), types.str_type.clone(), None);
        let tp_new_wrapper = create_object(
            PyNativeFuncDef::new(pytype::tp_new_wrapper.into_func(), new_str).into_function(),
            &types.builtin_function_or_method_type,
        )
        .into_object();

        let context = PyContext {
            true_value,
            false_value,
            not_implemented,
            none,
            empty_tuple,
            ellipsis,

            types,
            exceptions,
            int_cache_pool,
            string_cache,
            tp_new_wrapper,
        };
        TypeZoo::extend(&context);
        exceptions::ExceptionZoo::extend(&context);
        context
    }
    pub fn new() -> Self {
        rustpython_common::static_cell! {
            static CONTEXT: PyContext;
        }
        CONTEXT.get_or_init(Self::init).clone()
    }

    pub fn none(&self) -> PyObjectRef {
        self.none.clone().into_object()
    }

    pub fn ellipsis(&self) -> PyObjectRef {
        self.ellipsis.clone().into_object()
    }

    pub fn not_implemented(&self) -> PyObjectRef {
        self.not_implemented.clone().into_object()
    }

    #[inline]
    pub fn new_int<T: Into<BigInt> + ToPrimitive>(&self, i: T) -> PyObjectRef {
        if let Some(i) = i.to_i32() {
            if i >= Self::INT_CACHE_POOL_MIN && i <= Self::INT_CACHE_POOL_MAX {
                let inner_idx = (i - Self::INT_CACHE_POOL_MIN) as usize;
                return self.int_cache_pool[inner_idx].as_object().clone();
            }
        }
        PyObject::new(PyInt::from(i), self.types.int_type.clone(), None)
    }

    #[inline]
    pub fn new_bigint(&self, i: &BigInt) -> PyObjectRef {
        if let Some(i) = i.to_i32() {
            if i >= Self::INT_CACHE_POOL_MIN && i <= Self::INT_CACHE_POOL_MAX {
                let inner_idx = (i - Self::INT_CACHE_POOL_MIN) as usize;
                return self.int_cache_pool[inner_idx].as_object().clone();
            }
        }
        PyObject::new(PyInt::from(i.clone()), self.types.int_type.clone(), None)
    }

    pub fn new_float(&self, value: f64) -> PyObjectRef {
        PyObject::new(PyFloat::from(value), self.types.float_type.clone(), None)
    }

    pub fn new_complex(&self, value: Complex64) -> PyObjectRef {
        PyObject::new(
            PyComplex::from(value),
            self.types.complex_type.clone(),
            None,
        )
    }

    pub fn new_str<S>(&self, s: S) -> PyObjectRef
    where
        S: Into<pystr::PyStr>,
    {
        PyObject::new(s.into(), self.types.str_type.clone(), None)
    }

    pub fn new_bytes(&self, data: Vec<u8>) -> PyObjectRef {
        PyObject::new(
            bytes::PyBytes::from(data),
            self.types.bytes_type.clone(),
            None,
        )
    }

    pub fn new_bytearray(&self, data: Vec<u8>) -> PyObjectRef {
        PyObject::new(
            bytearray::PyByteArray::from(data),
            self.types.bytearray_type.clone(),
            None,
        )
    }

    #[inline]
    pub fn new_bool(&self, b: bool) -> PyObjectRef {
        let value = if b {
            &self.true_value
        } else {
            &self.false_value
        };
        value.clone().into_object()
    }

    pub fn new_tuple(&self, elements: Vec<PyObjectRef>) -> PyObjectRef {
        PyTupleRef::with_elements(elements, self).into_object()
    }

    pub fn new_list(&self, elements: Vec<PyObjectRef>) -> PyObjectRef {
        PyObject::new(PyList::from(elements), self.types.list_type.clone(), None)
    }

    pub fn new_set(&self) -> set::PySetRef {
        // Initialized empty, as calling __hash__ is required for adding each object to the set
        // which requires a VM context - this is done in the set code itself.
        PyRef::new_ref(set::PySet::default(), self.types.set_type.clone(), None)
    }

    pub fn new_dict(&self) -> PyDictRef {
        PyRef::new_ref(PyDict::default(), self.types.dict_type.clone(), None)
    }

    pub fn new_class(&self, name: &str, base: &PyTypeRef, slots: PyTypeSlots) -> PyTypeRef {
        create_type_with_slots(name, &self.types.type_type, base, slots)
    }

    pub fn new_namespace(&self) -> PyObjectRef {
        PyObject::new(
            PyNamespace,
            self.types.namespace_type.clone(),
            Some(self.new_dict()),
        )
    }

    pub(crate) fn new_stringref(&self, s: String) -> pystr::PyStrRef {
        PyRef::new_ref(pystr::PyStr::from(s), self.types.str_type.clone(), None)
    }

    #[inline]
    pub fn make_funcdef<F, FKind>(&self, name: impl Into<String>, f: F) -> PyNativeFuncDef
    where
        F: IntoPyNativeFunc<FKind>,
    {
        PyNativeFuncDef::new(f.into_func(), self.new_stringref(name.into()))
    }

    pub fn new_function<F, FKind>(&self, name: impl Into<String>, f: F) -> PyObjectRef
    where
        F: IntoPyNativeFunc<FKind>,
    {
        self.make_funcdef(name, f).build_function(self)
    }

    pub fn new_method<F, FKind>(&self, name: impl Into<String>, f: F) -> PyObjectRef
    where
        F: IntoPyNativeFunc<FKind>,
    {
        self.make_funcdef(name, f).build_method(self)
    }

    pub fn new_classmethod<F, FKind>(&self, name: impl Into<String>, f: F) -> PyObjectRef
    where
        F: IntoPyNativeFunc<FKind>,
    {
        self.make_funcdef(name, f).build_classmethod(self)
    }
    pub fn new_staticmethod<F, FKind>(&self, name: impl Into<String>, f: F) -> PyObjectRef
    where
        F: IntoPyNativeFunc<FKind>,
    {
        PyObject::new(
            PyStaticMethod::from(self.new_method(name, f)),
            self.types.staticmethod_type.clone(),
            None,
        )
    }

    pub fn new_readonly_getset<F, T>(&self, name: impl Into<String>, f: F) -> PyObjectRef
    where
        F: IntoPyGetterFunc<T>,
    {
        PyObject::new(
            PyGetSet::new(name.into()).with_get(f),
            self.types.getset_type.clone(),
            None,
        )
    }

    pub fn new_getset<G, S, T, U>(&self, name: impl Into<String>, g: G, s: S) -> PyObjectRef
    where
        G: IntoPyGetterFunc<T>,
        S: IntoPySetterFunc<U>,
    {
        PyObject::new(
            PyGetSet::new(name.into()).with_get(g).with_set(s),
            self.types.getset_type.clone(),
            None,
        )
    }

    /// Create a new `PyCodeRef` from a `code::CodeObject`. If you have a non-mapped codeobject or
    /// this is giving you a type error even though you've passed a `CodeObject`, try
    /// [`vm.new_code_object()`](VirtualMachine::new_code_object) instead.
    pub fn new_code_object(&self, code: code::CodeObject) -> PyCodeRef {
        PyRef::new_ref(code::PyCode::new(code), self.types.code_type.clone(), None)
    }

    pub fn new_bound_method(&self, function: PyObjectRef, object: PyObjectRef) -> PyObjectRef {
        PyObject::new(
            PyBoundMethod::new(object, function),
            self.types.bound_method_type.clone(),
            None,
        )
    }

    pub fn new_base_object(&self, class: PyTypeRef, dict: Option<PyDictRef>) -> PyObjectRef {
        PyObject::new(object::PyBaseObject, class, dict)
    }

    pub fn add_tp_new_wrapper(&self, ty: &PyTypeRef) {
        if !ty.attributes.read().contains_key("__new__") {
            let new_wrapper =
                self.new_bound_method(self.tp_new_wrapper.clone(), ty.clone().into_object());
            ty.set_str_attr("__new__", new_wrapper);
        }
    }

    pub fn is_tp_new_wrapper(&self, obj: &PyObjectRef) -> bool {
        obj.payload::<PyBoundMethod>()
            .map_or(false, |bound| bound.function.is(&self.tp_new_wrapper))
    }
}

impl Default for PyContext {
    fn default() -> Self {
        PyContext::new()
    }
}

impl<T> TryFromObject for PyRef<T>
where
    T: PyValue,
{
    #[inline]
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        let class = T::class(vm);
        if obj.isinstance(class) {
            obj.downcast()
                .map_err(|obj| pyref_payload_error(vm, class, obj))
        } else {
            Err(pyref_type_error(vm, class, obj))
        }
    }
}
// the impl Borrow allows to pass PyObjectRef or &PyObjectRef
fn pyref_payload_error(
    vm: &VirtualMachine,
    class: &PyTypeRef,
    obj: impl std::borrow::Borrow<PyObjectRef>,
) -> PyBaseExceptionRef {
    vm.new_runtime_error(format!(
        "Unexpected payload '{}' for type '{}'",
        &*class.name,
        &*obj.borrow().class().name,
    ))
}
fn pyref_type_error(
    vm: &VirtualMachine,
    class: &PyTypeRef,
    obj: impl std::borrow::Borrow<PyObjectRef>,
) -> PyBaseExceptionRef {
    let expected_type = &*class.name;
    let actual_type = &*obj.borrow().class().name;
    vm.new_type_error(format!(
        "Expected type '{}', not '{}'",
        expected_type, actual_type,
    ))
}

impl<'a, T: PyValue> From<&'a PyRef<T>> for &'a PyObjectRef {
    fn from(obj: &'a PyRef<T>) -> Self {
        obj.as_object()
    }
}

impl<T: PyValue> From<PyRef<T>> for PyObjectRef {
    fn from(obj: PyRef<T>) -> Self {
        obj.into_object()
    }
}

impl<T: fmt::Display> fmt::Display for PyRef<T>
where
    T: PyObjectPayload + fmt::Display,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&**self, f)
    }
}

pub struct PyRefExact<T: PyObjectPayload> {
    obj: PyRef<T>,
}
impl<T: PyValue> TryFromObject for PyRefExact<T> {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        let target_cls = T::class(vm);
        let cls = obj.class();
        if cls.is(target_cls) {
            drop(cls);
            let obj = obj.downcast().map_err(|obj| {
                vm.new_runtime_error(format!(
                    "Unexpected payload '{}' for type '{}'",
                    target_cls.name,
                    obj.class().name,
                ))
            })?;
            Ok(Self { obj })
        } else if cls.issubclass(target_cls) {
            Err(vm.new_type_error(format!(
                "Expected an exact instance of '{}', not a subclass '{}'",
                target_cls.name, cls.name,
            )))
        } else {
            Err(vm.new_type_error(format!(
                "Expected type '{}', not '{}'",
                target_cls.name, cls.name,
            )))
        }
    }
}
impl<T: PyValue> Deref for PyRefExact<T> {
    type Target = PyRef<T>;
    fn deref(&self) -> &PyRef<T> {
        &self.obj
    }
}
impl<T: PyValue> IntoPyObject for PyRefExact<T> {
    #[inline]
    fn into_pyobject(self, _vm: &VirtualMachine) -> PyObjectRef {
        self.obj.into_object()
    }
}
impl<T: PyValue> TryIntoRef<T> for PyRefExact<T> {
    fn try_into_ref(self, _vm: &VirtualMachine) -> PyResult<PyRef<T>> {
        Ok(self.obj)
    }
}

#[derive(Clone, Debug)]
pub struct PyCallable {
    obj: PyObjectRef,
}

impl PyCallable {
    #[inline]
    pub fn invoke(&self, args: impl IntoFuncArgs, vm: &VirtualMachine) -> PyResult {
        vm.invoke(&self.obj, args)
    }

    #[inline]
    pub fn into_object(self) -> PyObjectRef {
        self.obj
    }
}

impl TryFromObject for PyCallable {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        if vm.is_callable(&obj) {
            Ok(PyCallable { obj })
        } else {
            Err(vm.new_type_error(format!("'{}' object is not callable", obj.class().name)))
        }
    }
}

pub type Never = std::convert::Infallible;

impl PyValue for Never {
    fn class(_vm: &VirtualMachine) -> &PyTypeRef {
        unreachable!()
    }
}

pub trait IdProtocol {
    fn get_id(&self) -> usize;
    fn is<T>(&self, other: &T) -> bool
    where
        T: IdProtocol,
    {
        self.get_id() == other.get_id()
    }
}

impl<T: ?Sized> IdProtocol for PyRc<T> {
    fn get_id(&self) -> usize {
        &**self as *const T as *const Never as usize
    }
}

impl<T: PyObjectPayload> IdProtocol for PyRef<T> {
    fn get_id(&self) -> usize {
        self.as_object().get_id()
    }
}

impl<'a, T: PyObjectPayload> IdProtocol for PyLease<'a, T> {
    fn get_id(&self) -> usize {
        self.inner.get_id()
    }
}

impl<T: IdProtocol> IdProtocol for &'_ T {
    fn get_id(&self) -> usize {
        (&**self).get_id()
    }
}

/// A borrow of a reference to a Python object. This avoids having clone the `PyRef<T>`/
/// `PyObjectRef`, which isn't that cheap as that increments the atomic reference counter.
pub struct PyLease<'a, T: PyObjectPayload> {
    inner: PyRwLockReadGuard<'a, PyRef<T>>,
}

impl<'a, T: PyObjectPayload + PyValue> PyLease<'a, T> {
    // Associated function on purpose, because of deref
    #[allow(clippy::wrong_self_convention)]
    pub fn into_pyref(zelf: Self) -> PyRef<T> {
        zelf.inner.clone()
    }
}

impl<'a, T: PyObjectPayload + PyValue> Deref for PyLease<'a, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}

impl<'a, T> fmt::Display for PyLease<'a, T>
where
    T: PyValue + fmt::Display,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&**self, f)
    }
}

pub trait TypeProtocol {
    fn class(&self) -> PyLease<'_, PyType>;

    fn clone_class(&self) -> PyTypeRef {
        PyLease::into_pyref(self.class())
    }

    fn get_class_attr(&self, attr_name: &str) -> Option<PyObjectRef> {
        self.class().get_attr(attr_name)
    }

    fn has_class_attr(&self, attr_name: &str) -> bool {
        self.class().has_attr(attr_name)
    }

    /// Determines if `obj` actually an instance of `cls`, this doesn't call __instancecheck__, so only
    /// use this if `cls` is known to have not overridden the base __instancecheck__ magic method.
    #[inline]
    fn isinstance(&self, cls: &PyTypeRef) -> bool {
        self.class().issubclass(cls)
    }
}

impl TypeProtocol for PyObjectRef {
    fn class(&self) -> PyLease<'_, PyType> {
        PyLease {
            inner: self.class_lock().read(),
        }
    }
}

impl<T: PyObjectPayload> TypeProtocol for PyRef<T> {
    fn class(&self) -> PyLease<'_, PyType> {
        self.as_object().class()
    }
}

impl<T: TypeProtocol> TypeProtocol for &'_ T {
    fn class(&self) -> PyLease<'_, PyType> {
        (&**self).class()
    }
}

/// The python item protocol. Mostly applies to dictionaries.
/// Allows getting, setting and deletion of keys-value pairs.
pub trait ItemProtocol<T>
where
    T: IntoPyObject + ?Sized,
{
    fn get_item(&self, key: T, vm: &VirtualMachine) -> PyResult;
    fn set_item(&self, key: T, value: PyObjectRef, vm: &VirtualMachine) -> PyResult<()>;
    fn del_item(&self, key: T, vm: &VirtualMachine) -> PyResult<()>;
}

impl<T> ItemProtocol<T> for PyObjectRef
where
    T: IntoPyObject,
{
    fn get_item(&self, key: T, vm: &VirtualMachine) -> PyResult {
        vm.call_method(self, "__getitem__", (key,))
    }

    fn set_item(&self, key: T, value: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
        vm.call_method(self, "__setitem__", (key, value)).map(drop)
    }

    fn del_item(&self, key: T, vm: &VirtualMachine) -> PyResult<()> {
        vm.call_method(self, "__delitem__", (key,)).map(drop)
    }
}

/// An iterable Python object.
///
/// `PyIterable` implements `FromArgs` so that a built-in function can accept
/// an object that is required to conform to the Python iterator protocol.
///
/// PyIterable can optionally perform type checking and conversions on iterated
/// objects using a generic type parameter that implements `TryFromObject`.
pub struct PyIterable<T = PyObjectRef> {
    iterable: PyObjectRef,
    iterfn: Option<crate::slots::IterFunc>,
    _item: PhantomData<T>,
}

impl<T> PyIterable<T> {
    /// Returns an iterator over this sequence of objects.
    ///
    /// This operation may fail if an exception is raised while invoking the
    /// `__iter__` method of the iterable object.
    pub fn iter<'a>(&self, vm: &'a VirtualMachine) -> PyResult<PyIterator<'a, T>> {
        let iter_obj = match self.iterfn {
            Some(f) => f(self.iterable.clone(), vm)?,
            None => PySequenceIterator::new_forward(self.iterable.clone()).into_object(vm),
        };

        let length_hint = iterator::length_hint(vm, iter_obj.clone())?;

        Ok(PyIterator {
            vm,
            obj: iter_obj,
            length_hint,
            _item: PhantomData,
        })
    }
}

impl<T> TryFromObject for PyIterable<T>
where
    T: TryFromObject,
{
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        let iterfn;
        {
            let cls = obj.class();
            iterfn = cls.mro_find_map(|x| x.slots.iter.load());
            if iterfn.is_none() && !cls.has_attr("__getitem__") {
                return Err(vm.new_type_error(format!("'{}' object is not iterable", cls.name)));
            }
        }
        Ok(PyIterable {
            iterable: obj,
            iterfn,
            _item: PhantomData,
        })
    }
}

pub struct PyIterator<'a, T> {
    vm: &'a VirtualMachine,
    obj: PyObjectRef,
    length_hint: Option<usize>,
    _item: PhantomData<T>,
}

impl<'a, T> Iterator for PyIterator<'a, T>
where
    T: TryFromObject,
{
    type Item = PyResult<T>;

    fn next(&mut self) -> Option<Self::Item> {
        iterator::get_next_object(self.vm, &self.obj)
            .transpose()
            .map(|x| x.and_then(|obj| T::try_from_object(self.vm, obj)))
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.length_hint.unwrap_or(0), self.length_hint)
    }
}

impl TryFromObject for PyObjectRef {
    #[inline]
    fn try_from_object(_vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        Ok(obj)
    }
}

impl<T: TryFromObject> TryFromObject for Option<T> {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        if vm.is_none(&obj) {
            Ok(None)
        } else {
            T::try_from_object(vm, obj).map(Some)
        }
    }
}

/// Allows coercion of a types into PyRefs, so that we can write functions that can take
/// refs, pyobject refs or basic types.
pub trait TryIntoRef<T: PyObjectPayload> {
    fn try_into_ref(self, vm: &VirtualMachine) -> PyResult<PyRef<T>>;
}

impl<T: PyObjectPayload> TryIntoRef<T> for PyRef<T> {
    #[inline]
    fn try_into_ref(self, _vm: &VirtualMachine) -> PyResult<PyRef<T>> {
        Ok(self)
    }
}

impl<T> TryIntoRef<T> for PyObjectRef
where
    T: PyValue,
{
    fn try_into_ref(self, vm: &VirtualMachine) -> PyResult<PyRef<T>> {
        TryFromObject::try_from_object(vm, self)
    }
}

/// Implemented by any type that can be created from a Python object.
///
/// Any type that implements `TryFromObject` is automatically `FromArgs`, and
/// so can be accepted as a argument to a built-in function.
pub trait TryFromObject: Sized {
    /// Attempt to convert a Python object to a value of this type.
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self>;
}

/// Marks a type that has the exact same layout as PyObjectRef, e.g. a type that is
/// `repr(transparent)` over PyObjectRef.
///
/// # Safety
/// Can only be implemented for types that are `repr(transparent)` over a PyObjectRef `obj`,
/// and logically valid so long as `check(vm, obj)` returns `Ok(())`
pub unsafe trait TransmuteFromObject: Sized {
    fn check(vm: &VirtualMachine, obj: &PyObjectRef) -> PyResult<()>;
}

unsafe impl<T: PyValue> TransmuteFromObject for PyRef<T> {
    fn check(vm: &VirtualMachine, obj: &PyObjectRef) -> PyResult<()> {
        let class = T::class(vm);
        if obj.isinstance(class) {
            if obj.payload_is::<T>() {
                Ok(())
            } else {
                Err(pyref_payload_error(vm, class, obj))
            }
        } else {
            Err(pyref_type_error(vm, class, obj))
        }
    }
}

pub trait IntoPyRef<T: PyObjectPayload> {
    fn into_pyref(self, vm: &VirtualMachine) -> PyRef<T>;
}

impl<T, P> IntoPyRef<P> for T
where
    P: PyValue + IntoPyObject + From<T>,
{
    fn into_pyref(self, vm: &VirtualMachine) -> PyRef<P> {
        P::from(self).into_ref(vm)
    }
}

/// Implemented by any type that can be returned from a built-in Python function.
///
/// `IntoPyObject` has a blanket implementation for any built-in object payload,
/// and should be implemented by many primitive Rust types, allowing a built-in
/// function to simply return a `bool` or a `usize` for example.
pub trait IntoPyObject {
    fn into_pyobject(self, vm: &VirtualMachine) -> PyObjectRef;
}

impl<T: PyObjectPayload> IntoPyObject for PyRef<T> {
    #[inline]
    fn into_pyobject(self, _vm: &VirtualMachine) -> PyObjectRef {
        self.into_object()
    }
}

impl IntoPyObject for PyCallable {
    #[inline]
    fn into_pyobject(self, _vm: &VirtualMachine) -> PyObjectRef {
        self.into_object()
    }
}

impl IntoPyObject for PyObjectRef {
    #[inline]
    fn into_pyobject(self, _vm: &VirtualMachine) -> PyObjectRef {
        self
    }
}

// Allows a built-in function to return any built-in object payload without
// explicitly implementing `IntoPyObject`.
impl<T> IntoPyObject for T
where
    T: PyValue + Sized,
{
    #[inline]
    fn into_pyobject(self, vm: &VirtualMachine) -> PyObjectRef {
        PyValue::into_object(self, vm)
    }
}

pub trait IntoPyResult {
    fn into_pyresult(self, vm: &VirtualMachine) -> PyResult;
}

impl<T> IntoPyResult for T
where
    T: IntoPyObject,
{
    fn into_pyresult(self, vm: &VirtualMachine) -> PyResult {
        Ok(self.into_pyobject(vm))
    }
}

impl<T> IntoPyResult for PyResult<T>
where
    T: IntoPyObject,
{
    fn into_pyresult(self, vm: &VirtualMachine) -> PyResult {
        self.map(|res| T::into_pyobject(res, vm))
    }
}

cfg_if::cfg_if! {
    if #[cfg(feature = "threading")] {
        pub trait PyThreadingConstraint: Send + Sync {}
        impl<T: Send + Sync> PyThreadingConstraint for T {}
    } else {
        pub trait PyThreadingConstraint {}
        impl<T> PyThreadingConstraint for T {}
    }
}

pub trait PyValue: fmt::Debug + PyThreadingConstraint + Sized + 'static {
    fn class(vm: &VirtualMachine) -> &PyTypeRef;

    #[inline]
    fn into_object(self, vm: &VirtualMachine) -> PyObjectRef {
        self.into_ref(vm).into_object()
    }

    fn into_ref(self, vm: &VirtualMachine) -> PyRef<Self> {
        let cls = Self::class(vm).clone();
        let dict = if cls.slots.flags.has_feature(PyTpFlags::HAS_DICT) {
            Some(vm.ctx.new_dict())
        } else {
            None
        };
        PyRef::new_ref(self, cls, dict)
    }

    fn into_ref_with_type(self, vm: &VirtualMachine, cls: PyTypeRef) -> PyResult<PyRef<Self>> {
        let exact_class = Self::class(vm);
        if cls.issubclass(exact_class) {
            let dict = if cls.slots.flags.has_feature(PyTpFlags::HAS_DICT) {
                Some(vm.ctx.new_dict())
            } else {
                None
            };
            Ok(PyRef::new_ref(self, cls, dict))
        } else {
            let subtype = vm.to_str(cls.as_object())?;
            let basetype = vm.to_str(exact_class.as_object())?;
            Err(vm.new_type_error(format!("{} is not a subtype of {}", subtype, basetype)))
        }
    }
}

pub trait PyObjectPayload: Any + fmt::Debug + PyThreadingConstraint + 'static {}

impl<T: PyValue + 'static> PyObjectPayload for T {}

pub enum Either<A, B> {
    A(A),
    B(B),
}

impl<A: PyValue, B: PyValue> Either<PyRef<A>, PyRef<B>> {
    pub fn as_object(&self) -> &PyObjectRef {
        match self {
            Either::A(a) => a.as_object(),
            Either::B(b) => b.as_object(),
        }
    }

    pub fn into_object(self) -> PyObjectRef {
        match self {
            Either::A(a) => a.into_object(),
            Either::B(b) => b.into_object(),
        }
    }
}

impl<A: IntoPyObject, B: IntoPyObject> IntoPyObject for Either<A, B> {
    fn into_pyobject(self, vm: &VirtualMachine) -> PyObjectRef {
        match self {
            Self::A(a) => a.into_pyobject(vm),
            Self::B(b) => b.into_pyobject(vm),
        }
    }
}

/// This allows a builtin method to accept arguments that may be one of two
/// types, raising a `TypeError` if it is neither.
///
/// # Example
///
/// ```
/// use rustpython_vm::VirtualMachine;
/// use rustpython_vm::builtins::{PyStrRef, PyIntRef};
/// use rustpython_vm::pyobject::Either;
///
/// fn do_something(arg: Either<PyIntRef, PyStrRef>, vm: &VirtualMachine) {
///     match arg {
///         Either::A(int)=> {
///             // do something with int
///         }
///         Either::B(string) => {
///             // do something with string
///         }
///     }
/// }
/// ```
impl<A, B> TryFromObject for Either<A, B>
where
    A: TryFromObject,
    B: TryFromObject,
{
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        A::try_from_object(vm, obj.clone())
            .map(Either::A)
            .or_else(|_| B::try_from_object(vm, obj.clone()).map(Either::B))
            .map_err(|_| vm.new_type_error(format!("unexpected type {}", obj.class())))
    }
}

pub trait PyClassDef {
    const NAME: &'static str;
    const MODULE_NAME: Option<&'static str>;
    const TP_NAME: &'static str;
    const DOC: Option<&'static str> = None;
}

pub trait StaticType {
    // Ideally, saving PyType is better than PyTypeRef
    fn static_cell() -> &'static static_cell::StaticCell<PyTypeRef>;
    fn static_metaclass() -> &'static PyTypeRef {
        crate::builtins::pytype::PyType::static_type()
    }
    fn static_baseclass() -> &'static PyTypeRef {
        crate::builtins::object::PyBaseObject::static_type()
    }
    fn static_type() -> &'static PyTypeRef {
        Self::static_cell()
            .get()
            .expect("static type has not been initialized")
    }
    fn init_manually(typ: PyTypeRef) -> &'static PyTypeRef {
        let cell = Self::static_cell();
        cell.set(typ)
            .unwrap_or_else(|_| panic!("double initialization from init_manually"));
        cell.get().unwrap()
    }
    fn init_bare_type() -> &'static PyTypeRef
    where
        Self: PyClassImpl,
    {
        let typ = Self::create_bare_type();
        let cell = Self::static_cell();
        cell.set(typ)
            .unwrap_or_else(|_| panic!("double initialization of {}", Self::NAME));
        cell.get().unwrap()
    }
    fn create_bare_type() -> PyTypeRef
    where
        Self: PyClassImpl,
    {
        create_type_with_slots(
            Self::NAME,
            Self::static_metaclass(),
            Self::static_baseclass(),
            Self::make_slots(),
        )
    }
}

impl<T> PyClassDef for PyRef<T>
where
    T: PyObjectPayload + PyClassDef,
{
    const NAME: &'static str = T::NAME;
    const MODULE_NAME: Option<&'static str> = T::MODULE_NAME;
    const TP_NAME: &'static str = T::TP_NAME;
    const DOC: Option<&'static str> = T::DOC;
}

pub trait PyClassImpl: PyClassDef {
    const TP_FLAGS: PyTpFlags = PyTpFlags::DEFAULT;

    fn impl_extend_class(ctx: &PyContext, class: &PyTypeRef);

    fn extend_class(ctx: &PyContext, class: &PyTypeRef) {
        #[cfg(debug_assertions)]
        {
            assert!(class.slots.flags.is_created_with_flags());
        }
        if Self::TP_FLAGS.has_feature(PyTpFlags::HAS_DICT) {
            class.set_str_attr(
                "__dict__",
                ctx.new_getset("__dict__", object::object_get_dict, object::object_set_dict),
            );
        }
        Self::impl_extend_class(ctx, class);
        ctx.add_tp_new_wrapper(&class);
        if let Some(doc) = Self::DOC {
            class.set_str_attr("__doc__", ctx.new_str(doc));
        }
        if let Some(module_name) = Self::MODULE_NAME {
            class.set_str_attr("__module__", ctx.new_str(module_name));
        }
    }

    fn make_class(ctx: &PyContext) -> PyTypeRef
    where
        Self: StaticType,
    {
        Self::static_cell()
            .get_or_init(|| {
                let typ = Self::create_bare_type();
                Self::extend_class(ctx, &typ);
                typ
            })
            .clone()
    }

    fn extend_slots(slots: &mut PyTypeSlots);

    fn make_slots() -> PyTypeSlots {
        let mut slots = PyTypeSlots {
            flags: Self::TP_FLAGS,
            name: PyRwLock::new(Some(Self::TP_NAME.to_owned())),
            ..Default::default()
        };
        Self::extend_slots(&mut slots);
        slots
    }
}

#[pyimpl]
pub trait PyStructSequence: StaticType + PyClassImpl + Sized + 'static {
    const FIELD_NAMES: &'static [&'static str];

    fn into_tuple(self, vm: &VirtualMachine) -> PyTuple;

    fn into_struct_sequence(self, vm: &VirtualMachine) -> PyResult<PyTupleRef> {
        self.into_tuple(vm)
            .into_ref_with_type(vm, Self::static_type().clone())
    }

    #[pymethod(magic)]
    fn repr(zelf: PyRef<PyTuple>, vm: &VirtualMachine) -> PyResult<String> {
        let format_field = |(value, name)| {
            let s = vm.to_repr(value)?;
            Ok(format!("{}: {}", name, s))
        };
        let (body, suffix) =
            if let Some(_guard) = rustpython_vm::vm::ReprGuard::enter(vm, zelf.as_object()) {
                if Self::FIELD_NAMES.len() == 1 {
                    let value = zelf.borrow_value().first().unwrap();
                    let formatted = format_field((value, Self::FIELD_NAMES[0]))?;
                    (formatted, ",")
                } else {
                    let fields: PyResult<Vec<_>> = zelf
                        .borrow_value()
                        .iter()
                        .zip(Self::FIELD_NAMES.iter().copied())
                        .map(format_field)
                        .collect();
                    (fields?.join(", "), "")
                }
            } else {
                (String::new(), "...")
            };
        Ok(format!("{}({}{})", Self::TP_NAME, body, suffix))
    }

    #[extend_class]
    fn extend_pyclass(ctx: &PyContext, class: &PyTypeRef) {
        for (i, &name) in Self::FIELD_NAMES.iter().enumerate() {
            // cast i to a u8 so there's less to store in the getter closure.
            // Hopefully there's not struct sequences with >=256 elements :P
            let i = i as u8;
            class.set_str_attr(
                name,
                ctx.new_readonly_getset(name, move |zelf: &PyTuple| zelf.fast_getitem(i.into())),
            );
        }
    }
}

// TODO: find a better place to put this impl
impl TryFromObject for std::time::Duration {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        use std::time::Duration;
        u64::try_from_object(vm, obj.clone())
            .map(Duration::from_secs)
            .or_else(|_| f64::try_from_object(vm, obj.clone()).map(Duration::from_secs_f64))
            .map_err(|_| {
                vm.new_type_error(format!(
                    "expected an int or float for duration, got {}",
                    obj.class()
                ))
            })
    }
}

result_like::option_like!(pub PyArithmaticValue, Implemented, NotImplemented);

impl PyArithmaticValue<PyObjectRef> {
    pub fn from_object(vm: &VirtualMachine, obj: PyObjectRef) -> Self {
        if obj.is(&vm.ctx.not_implemented) {
            Self::NotImplemented
        } else {
            Self::Implemented(obj)
        }
    }
}

impl<T: TryFromObject> TryFromObject for PyArithmaticValue<T> {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        PyArithmaticValue::from_object(vm, obj)
            .map(|x| T::try_from_object(vm, x))
            .transpose()
    }
}

impl<T> IntoPyObject for PyArithmaticValue<T>
where
    T: IntoPyObject,
{
    fn into_pyobject(self, vm: &VirtualMachine) -> PyObjectRef {
        match self {
            PyArithmaticValue::Implemented(v) => v.into_pyobject(vm),
            PyArithmaticValue::NotImplemented => vm.ctx.not_implemented(),
        }
    }
}

pub type PyComparisonValue = PyArithmaticValue<bool>;

#[derive(Clone)]
pub struct PySequence<T = PyObjectRef>(Vec<T>);

impl<T> PySequence<T> {
    pub fn into_vec(self) -> Vec<T> {
        self.0
    }
    pub fn as_slice(&self) -> &[T] {
        &self.0
    }
}
impl<T: TryFromObject> TryFromObject for PySequence<T> {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        vm.extract_elements(&obj).map(Self)
    }
}

pub fn hash_iter<'a, I: IntoIterator<Item = &'a PyObjectRef>>(
    iter: I,
    vm: &VirtualMachine,
) -> PyResult<rustpython_common::hash::PyHash> {
    vm.state.hash_secret.hash_iter(iter, |obj| vm._hash(obj))
}

pub fn hash_iter_unordered<'a, I: IntoIterator<Item = &'a PyObjectRef>>(
    iter: I,
    vm: &VirtualMachine,
) -> PyResult<rustpython_common::hash::PyHash> {
    rustpython_common::hash::hash_iter_unordered(iter, |obj| vm._hash(obj))
}