use std;
#[cfg(feature = "legacy-runtime")]
use std::any::Any;
use std::boxed::Box;
use std::cell::Cell;
use std::mem::MaybeUninit;
use std::os::raw::c_void;
#[cfg(feature = "legacy-runtime")]
use std::panic::{AssertUnwindSafe, catch_unwind, resume_unwind};
use neon_runtime;
use neon_runtime::raw;
use neon_runtime::scope::Root;
#[cfg(feature = "legacy-runtime")]
use neon_runtime::try_catch::TryCatchControl;
use types::{JsObject, JsValue};
use handle::Handle;
use object::class::ClassMap;
use result::NeonResult;
use super::ModuleContext;

#[cfg(feature = "legacy-runtime")]
#[repr(C)]
#[derive(Clone, Copy)]
pub struct Env(raw::Isolate);

#[cfg(feature = "napi-runtime")]
#[repr(C)]
#[derive(Clone, Copy)]
pub struct Env(raw::Env);

extern "C" fn drop_class_map(map: Box<ClassMap>) {
    std::mem::drop(map);
}

impl Env {
    #[cfg(feature = "legacy-runtime")]
    pub(crate) fn to_raw(self) -> raw::Isolate {
        let Self(ptr) = self;
        ptr
    }

    #[cfg(feature = "napi-runtime")]
    pub(crate) fn to_raw(self) -> raw::Env {
        let Self(ptr) = self;
        ptr
    }

    pub(crate) fn class_map(&mut self) -> &mut ClassMap {
        let mut ptr: *mut c_void = unsafe { neon_runtime::class::get_class_map(self.to_raw()) };
        if ptr.is_null() {
            let b: Box<ClassMap> = Box::new(ClassMap::new());
            let raw = Box::into_raw(b);
            ptr = unsafe { std::mem::transmute(raw) };
            let free_map: *mut c_void = unsafe { std::mem::transmute(drop_class_map as usize) };
            unsafe {
                neon_runtime::class::set_class_map(self.to_raw(), ptr, free_map);
            }
        }
        unsafe { std::mem::transmute(ptr) }
    }

    #[cfg(feature = "napi-runtime")]
    pub(crate) fn current() -> Env {
        panic!("Context::current() will not implemented with n-api")
    }

    #[cfg(feature = "legacy-runtime")]
    pub(crate) fn current() -> Env {
        unsafe {
            std::mem::transmute(neon_runtime::call::current_isolate())
        }
    }
}

pub struct ScopeMetadata {
    env: Env,
    active: Cell<bool>
}

pub struct Scope<'a, R: Root + 'static> {
    pub metadata: ScopeMetadata,
    pub handle_scope: &'a mut R
}

impl<'a, R: Root + 'static> Scope<'a, R> {
    pub fn with<T, F: for<'b> FnOnce(Scope<'b, R>) -> T>(env: Env, f: F) -> T {
        let mut handle_scope: R = unsafe { R::allocate() };
        unsafe {
            handle_scope.enter(env.to_raw());
        }
        let result = {
            let scope = Scope {
                metadata: ScopeMetadata {
                    env,
                    active: Cell::new(true)
                },
                handle_scope: &mut handle_scope
            };
            f(scope)
        };
        unsafe {
            handle_scope.exit(env.to_raw());
        }
        result
    }
}

pub trait ContextInternal<'a>: Sized {
    fn scope_metadata(&self) -> &ScopeMetadata;

    fn env(&self) -> Env {
        self.scope_metadata().env
    }

    fn is_active(&self) -> bool {
        self.scope_metadata().active.get()
    }

    fn check_active(&self) {
        if !self.is_active() {
            panic!("execution context is inactive");
        }
    }

    fn activate(&self) { self.scope_metadata().active.set(true); }
    fn deactivate(&self) { self.scope_metadata().active.set(false); }

    #[cfg(feature = "legacy-runtime")]
    fn try_catch_internal<'b: 'a, T, F>(&mut self, f: F) -> Result<T, Handle<'a, JsValue>>
        where F: FnOnce(&mut Self) -> NeonResult<T>,
    {
        // A closure does not have a guaranteed layout, so we need to box it in order to pass
        // a pointer to it across the boundary into C++.
        let rust_thunk = Box::into_raw(Box::new(f));

        let mut ok: MaybeUninit<T> = MaybeUninit::zeroed();
        let mut err: MaybeUninit<raw::Local> = MaybeUninit::zeroed();
        let mut unwind_value: MaybeUninit<*mut c_void> = MaybeUninit::zeroed();

        let ctrl = unsafe {
            neon_runtime::try_catch::with(try_catch_glue::<Self, T, F>,
                                          rust_thunk as *mut c_void,
                                          (self as *mut Self) as *mut c_void,
                                          ok.as_mut_ptr() as *mut c_void,
                                          err.as_mut_ptr(),
                                          unwind_value.as_mut_ptr())
        };

        match ctrl {
            TryCatchControl::Panicked => {
                let unwind_value: Box<dyn Any + Send> = *unsafe {
                    Box::from_raw(unwind_value.assume_init() as *mut Box<dyn Any + Send>)
                };
                resume_unwind(unwind_value);
            }
            TryCatchControl::Returned => Ok(unsafe { ok.assume_init() }),
            TryCatchControl::Threw => {
                let err = unsafe { err.assume_init() };
                Err(JsValue::new_internal(err))
            }
            TryCatchControl::UnexpectedErr => {
                panic!("try_catch: unexpected Err(Throw) when VM is not in a throwing state");
            }
        }
    }

    #[cfg(feature = "napi-runtime")]
    fn try_catch_internal<'b: 'a, T, F>(&mut self, f: F) -> Result<T, Handle<'a, JsValue>>
        where F: FnOnce(&mut Self) -> NeonResult<T>
    {
        let result = f(self);
        let mut local: MaybeUninit<raw::Local> = MaybeUninit::zeroed();
        unsafe {
            if neon_runtime::error::catch_error(self.env().to_raw(), local.as_mut_ptr()) {
                Err(JsValue::new_internal(local.assume_init()))
            } else if let Ok(result) = result {
                Ok(result)
            } else {
                panic!("try_catch: unexpected Err(Throw) when VM is not in a throwing state");
            }
        }
    }
}

#[cfg(feature = "legacy-runtime")]
extern "C" fn try_catch_glue<'a, 'b: 'a, C, T, F>(rust_thunk: *mut c_void,
                                                  cx: *mut c_void,
                                                  returned: *mut c_void,
                                                  unwind_value: *mut *mut c_void) -> TryCatchControl
    where C: ContextInternal<'a>,
          F: FnOnce(&mut C) -> NeonResult<T>,
{
    let f: F = *unsafe { Box::from_raw(rust_thunk as *mut F) };
    let cx: &mut C = unsafe { std::mem::transmute(cx) };

    // The mutable reference to the context is a fiction of the Neon library,
    // since it doesn't actually contain any data in the Rust memory space,
    // just a link to the JS VM. So we don't need to do any kind of poisoning
    // of the context when a panic occurs. So we suppress the Rust compiler
    // errors from using the mutable reference across an unwind boundary.
    match catch_unwind(AssertUnwindSafe(|| f(cx))) {
        // No Rust panic, no JS exception.
        Ok(Ok(result)) => unsafe {
            (returned as *mut T).write(result);
            TryCatchControl::Returned
        }
        // No Rust panic, caught a JS exception.
        Ok(Err(_)) => {
            TryCatchControl::Threw
        }
        // Rust panicked.
        Err(err) => unsafe {
            // A panic value has an undefined layout, so wrap it in an extra box.
            let boxed = Box::new(err);
            *unwind_value = Box::into_raw(boxed) as *mut c_void;
            TryCatchControl::Panicked
        }
    }
}

#[cfg(feature = "legacy-runtime")]
pub fn initialize_module(exports: Handle<JsObject>, init: fn(ModuleContext) -> NeonResult<()>) {
    let env = Env::current();

    ModuleContext::with(env, exports, |cx| {
        let _ = init(cx);
    });
}

#[cfg(feature = "napi-runtime")]
pub fn initialize_module(env: raw::Env, exports: Handle<JsObject>, init: fn(ModuleContext) -> NeonResult<()>) {
    neon_runtime::setup();
    ModuleContext::with(Env(env), exports, |cx| {
        let _ = init(cx);
    });
}