// Copyright (c) 2015 Daniel Grunwald
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

use libc::c_int;
use std::ffi::CString;
use std::marker::PhantomData;

use crate::err::{self, PyErr, PyResult};
use crate::ffi;
use crate::objects::{PyBool, PyDict, PyModule, PyObject, PyType};
use crate::pythonrun::GILGuard;

/// Marker type that indicates that the GIL is currently held.
///
/// The 'Python' struct is a zero-size marker struct that is required for most Python operations.
/// This is used to indicate that the operation accesses/modifies the Python interpreter state,
/// and thus can only be called if the Python interpreter is initialized and the
/// Python global interpreter lock (GIL) is acquired.
/// The lifetime `'p` represents the lifetime of the Python interpreter.
///
/// You can imagine the GIL to be a giant `Mutex<PythonInterpreterState>`.
/// The type `Python<'p>` then acts like a reference `&'p PythonInterpreterState`.
#[derive(Copy, Clone)]
pub struct Python<'p>(PhantomData<&'p GILGuard>);

/// Trait implemented by all Python object types.
pub trait PythonObject: crate::conversion::ToPyObject + Send + Sized + 'static {
    /// Casts the Python object to PyObject.
    fn as_object(&self) -> &PyObject;

    /// Casts the Python object to PyObject.
    fn into_object(self) -> PyObject;

    /// Unchecked downcast from PyObject to Self.
    /// Undefined behavior if the input object does not have the expected type.
    unsafe fn unchecked_downcast_from(obj: PyObject) -> Self;

    /// Unchecked downcast from PyObject to Self.
    /// Undefined behavior if the input object does not have the expected type.
    unsafe fn unchecked_downcast_borrow_from(obj: &PyObject) -> &Self;
}

// Marker type that indicates an error while downcasting
pub struct PythonObjectDowncastError<'p> {
    pub(crate) py: Python<'p>,
    pub(crate) expected_type_name: String,
    pub(crate) received_type: PyType,
}

impl<'p> PythonObjectDowncastError<'p> {
    pub fn new(
        py: Python<'p>,
        expected_type_name: impl Into<String>,
        received_type: PyType,
    ) -> Self {
        let expected_type_name = expected_type_name.into();
        PythonObjectDowncastError {
            py,
            expected_type_name,
            received_type,
        }
    }
}

/// Trait implemented by Python object types that allow a checked downcast.
pub trait PythonObjectWithCheckedDowncast: PythonObject {
    /// Cast from PyObject to a concrete Python object type.
    fn downcast_from(py: Python<'_>, obj: PyObject) -> Result<Self, PythonObjectDowncastError<'_>>;

    /// Cast from PyObject to a concrete Python object type.
    fn downcast_borrow_from<'a, 'p>(
        py: Python<'p>,
        obj: &'a PyObject,
    ) -> Result<&'a Self, PythonObjectDowncastError<'p>>;
}

/// Trait implemented by Python object types that have a corresponding type object.
pub trait PythonObjectWithTypeObject: PythonObjectWithCheckedDowncast {
    /// Retrieves the type object for this Python object type.
    fn type_object(py: Python) -> PyType;
}

pub trait PyClone: Sized {
    fn clone_ref(&self, py: Python) -> Self;
}

impl<T> PyClone for T
where
    T: PythonObject,
{
    #[inline]
    fn clone_ref(&self, py: Python) -> T {
        let ptr = self.as_object().as_ptr();
        unsafe { T::unchecked_downcast_from(PyObject::from_borrowed_ptr(py, ptr)) }
    }
}

impl<T> PyClone for Option<T>
where
    T: PyClone,
{
    #[inline]
    fn clone_ref(&self, py: Python) -> Option<T> {
        self.as_ref().map(|v| v.clone_ref(py))
    }
}

pub trait PyDrop: Sized {
    fn release_ref(self, py: Python);
}

impl<T> PyDrop for T
where
    T: PythonObject,
{
    #[inline]
    fn release_ref(self, _py: Python) {
        let ptr = self.into_object().steal_ptr();
        unsafe {
            ffi::Py_DECREF(ptr);
        }
    }
}

impl<T> PyDrop for Option<T>
where
    T: PyDrop,
{
    #[inline]
    fn release_ref(self, py: Python) {
        if let Some(v) = self {
            v.release_ref(py)
        }
    }
}

/// This trait allows retrieving the underlying FFI pointer from Python objects.
pub trait ToPythonPointer {
    /// Retrieves the underlying FFI pointer (as a borrowed pointer).
    fn as_ptr(&self) -> *mut ffi::PyObject;

    /// Retrieves the underlying FFI pointer as a "stolen pointer".
    fn steal_ptr(self, py: Python) -> *mut ffi::PyObject;
}

/// ToPythonPointer for borrowed Python pointers.
impl ToPythonPointer for PyObject {
    #[inline]
    fn as_ptr(&self) -> *mut ffi::PyObject {
        self.as_ptr()
    }

    #[inline]
    fn steal_ptr(self, _py: Python) -> *mut ffi::PyObject {
        self.steal_ptr()
    }
}

/// ToPythonPointer for borrowed Python pointers.
impl<'a, T> ToPythonPointer for &'a T
where
    T: PythonObject,
{
    #[inline]
    fn as_ptr(&self) -> *mut ffi::PyObject {
        self.as_object().as_ptr()
    }

    #[inline]
    fn steal_ptr(self, py: Python) -> *mut ffi::PyObject {
        self.as_object().clone_ref(py).steal_ptr()
    }
}

/// Convert None into a null pointer.
impl<T> ToPythonPointer for Option<T>
where
    T: ToPythonPointer,
{
    #[inline]
    fn as_ptr(&self) -> *mut ffi::PyObject {
        match *self {
            Some(ref t) => t.as_ptr(),
            None => std::ptr::null_mut(),
        }
    }

    #[inline]
    fn steal_ptr(self, py: Python) -> *mut ffi::PyObject {
        match self {
            Some(t) => t.steal_ptr(py),
            None => std::ptr::null_mut(),
        }
    }
}

impl<'p> Python<'p> {
    /// Retrieve Python instance under the assumption that the GIL is already acquired at this point,
    /// and stays acquired for the lifetime `'p`.
    ///
    /// Because the output lifetime `'p` is not connected to any input parameter,
    /// care must be taken that the compiler infers an appropriate lifetime for `'p`
    /// when calling this function.
    #[inline]
    pub unsafe fn assume_gil_acquired() -> Python<'p> {
        Python(PhantomData)
    }

    /// Acquires the global interpreter lock, which allows access to the Python runtime.
    ///
    /// If the Python runtime is not already initialized, this function will initialize it.
    /// See [prepare_freethreaded_python()](fn.prepare_freethreaded_python.html) for details.
    #[inline]
    pub fn acquire_gil() -> GILGuard {
        GILGuard::acquire()
    }

    /// Temporarily releases the GIL, thus allowing other Python threads to run.
    pub fn allow_threads<T, F>(self, f: F) -> T
    where
        F: Send + FnOnce() -> T,
    {
        // The `Send` bound on the closure prevents the user from
        // transferring the `Python` token into the closure.
        unsafe {
            let save = ffi::PyEval_SaveThread();
            let result = f();
            ffi::PyEval_RestoreThread(save);
            result
        }
    }

    /// Evaluates a Python expression in the given context and returns the result.
    ///
    /// If `globals` is `None`, it defaults to Python module `__main__`.
    /// If `locals` is `None`, it defaults to the value of `globals`.
    pub fn eval(
        self,
        code: &str,
        globals: Option<&PyDict>,
        locals: Option<&PyDict>,
    ) -> PyResult<PyObject> {
        self.run_code(code, ffi::Py_eval_input, globals, locals)
    }

    /// Executes one or more Python statements in the given context.
    ///
    /// If `globals` is `None`, it defaults to Python module `__main__`.
    /// If `locals` is `None`, it defaults to the value of `globals`.
    pub fn run(
        self,
        code: &str,
        globals: Option<&PyDict>,
        locals: Option<&PyDict>,
    ) -> PyResult<()> {
        self.run_code(code, ffi::Py_file_input, globals, locals)?;
        Ok(())
    }

    /// Runs code in the given context.
    /// `start` indicates the type of input expected:
    /// one of `Py_single_input`, `Py_file_input`, or `Py_eval_input`.
    ///
    /// If `globals` is `None`, it defaults to Python module `__main__`.
    /// If `locals` is `None`, it defaults to the value of `globals`.
    fn run_code(
        self,
        code: &str,
        start: c_int,
        globals: Option<&PyDict>,
        locals: Option<&PyDict>,
    ) -> PyResult<PyObject> {
        let code = CString::new(code).unwrap();

        unsafe {
            let mptr = ffi::PyImport_AddModule("__main__\0".as_ptr() as *const _);

            if mptr.is_null() {
                return Err(PyErr::fetch(self));
            }

            let mdict = ffi::PyModule_GetDict(mptr);

            let globals = match globals {
                Some(g) => g.as_ptr(),
                None => mdict,
            };

            let locals = match locals {
                Some(l) => l.as_ptr(),
                None => globals,
            };

            let res_ptr =
                ffi::PyRun_StringFlags(code.as_ptr(), start, globals, locals, std::ptr::null_mut());

            err::result_from_owned_ptr(self, res_ptr)
        }
    }

    /// Gets the Python builtin value `None`.
    #[allow(non_snake_case)] // the Python keyword starts with uppercase
    #[inline]
    pub fn None(self) -> PyObject {
        unsafe { PyObject::from_borrowed_ptr(self, ffi::Py_None()) }
    }

    /// Gets the Python builtin value `True`.
    #[allow(non_snake_case)] // the Python keyword starts with uppercase
    #[inline]
    pub fn True(self) -> PyBool {
        unsafe { PyObject::from_borrowed_ptr(self, ffi::Py_True()).unchecked_cast_into::<PyBool>() }
    }

    /// Gets the Python builtin value `False`.
    #[allow(non_snake_case)] // the Python keyword starts with uppercase
    #[inline]
    pub fn False(self) -> PyBool {
        unsafe {
            PyObject::from_borrowed_ptr(self, ffi::Py_False()).unchecked_cast_into::<PyBool>()
        }
    }

    /// Gets the Python builtin value `NotImplemented`.
    #[allow(non_snake_case)] // the Python keyword starts with uppercase
    #[inline]
    pub fn NotImplemented(self) -> PyObject {
        unsafe { PyObject::from_borrowed_ptr(self, ffi::Py_NotImplemented()) }
    }

    /// Gets the Python type object for type T.
    pub fn get_type<T>(self) -> PyType
    where
        T: PythonObjectWithTypeObject,
    {
        T::type_object(self)
    }

    /// Import the Python module with the specified name.
    pub fn import(self, name: &str) -> PyResult<PyModule> {
        PyModule::import(self, name)
    }
}

impl<'p> std::fmt::Debug for PythonObjectDowncastError<'p> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        f.write_str("PythonObjectDowncastError")
    }
}

#[cfg(test)]
mod test {
    use crate::{PyDict, Python};

    #[test]
    fn test_eval() {
        let gil = Python::acquire_gil();
        let py = gil.python();

        // Make sure builtin names are accessible
        let v: i32 = py
            .eval("min(1, 2)", None, None)
            .unwrap()
            .extract(py)
            .unwrap();
        assert_eq!(v, 1);

        let d = PyDict::new(py);
        d.set_item(py, "foo", 13).unwrap();

        // Inject our own local namespace
        let v: i32 = py
            .eval("foo + 29", None, Some(&d))
            .unwrap()
            .extract(py)
            .unwrap();
        assert_eq!(v, 42);

        // Make sure builtin names are still accessible when using a local namespace
        let v: i32 = py
            .eval("min(foo, 2)", None, Some(&d))
            .unwrap()
            .extract(py)
            .unwrap();
        assert_eq!(v, 2);
    }
}