use std::any::{type_name, Any, TypeId};
use std::cell::{RefCell, RefMut};
use std::collections::HashMap;

use seq_macro::seq;

use crate::component::Component;
use crate::system::util::check_params_are_compatible;
use crate::system::{ComponentRefMut, Into as IntoSystem, Param, System, TypeErased};
use crate::tuple::{
    Filter as TupleFilter,
    FilterExclude as TupleFilterExclude,
    IntoInOptions as TupleIntoInOptions,
    TakeOptionElementResult as TupleTakeOptionElementResult,
    WithOptionElements as TupleWithOptionElements,
};
use crate::WorldData;

/// A stateful system.
pub struct Stateful<Func>
{
    func: Func,
    local_components: HashMap<TypeId, RefCell<Box<dyn Component>>>,
}

macro_rules! impl_system {
    ($c: tt) => {
        seq!(I in 0..$c {
            impl<'world, Func, #(TParam~I,)*> System<'world, fn(&'world (), #(TParam~I,)*)>
                for Stateful<Func>
            where
                Func: Fn(#(TParam~I,)*) + Copy + 'static,
                #(TParam~I: Param<'world>,)*
                #(TParam~I::Input: 'static,)*
                (#(TParam~I::Input,)*): TupleFilter,
                <(#(TParam~I::Input,)*) as TupleFilter>::Out: TupleIntoInOptions
            {
                type Input = <(#(TParam~I::Input,)*) as TupleFilter>::Out;

                fn initialize(mut self, input: Self::Input) -> Self
                {
                    let mut option_input = input.into_in_options();

                    #(
                        if TypeId::of::<TParam~I::Input>() !=
                            TypeId::of::<TupleFilterExclude>()
                        {
                            let input = match option_input.take::<TParam~I::Input>() {
                                TupleTakeOptionElementResult::Found(input) => input,
                                TupleTakeOptionElementResult::NotFound => {
                                    panic!(
                                        "Parameter input {} not found",
                                        type_name::<TParam~I::Input>()
                                    );
                                }
                                TupleTakeOptionElementResult::AlreadyTaken => {
                                    panic!(
                                        concat!(
                                            "Parameter {} is already initialized. ",
                                            "System cannot contain multiple inputs with ",
                                            "the same type",
                                        ),
                                        type_name::<TParam~I>()
                                    );

                                }
                            };

                            TParam~I::initialize(
                                &mut self,
                                input
                            );
                        }
                    )*

                    self
                }

                fn run<'this>(&'this self, world_data: &'world WorldData)
                where
                    'this: 'world
                {
                    #(
                        check_params_are_compatible!(I, TParam~I, $c);
                    )*

                    let func = self.func;

                    func(#({
                        TParam~I::new(self, world_data)
                    },)*);
                }

                fn into_type_erased(self) -> TypeErased
                {
                    TypeErased {
                        data: Box::new(self),
                        func: Box::new(|data, world_data| {
                            // SAFETY: The caller of TypeErased::run ensures the lifetime
                            // is correct
                            let data = unsafe { &*(data as *const dyn Any) };

                            let me = data.downcast_ref::<Self>().unwrap();

                            // SAFETY: The caller of TypeErased::run ensures the lifetime
                            // is correct
                            let world_data = unsafe {
                                &*(world_data as *const WorldData)
                            };

                            me.run(world_data);
                        }),
                    }
                }

                fn get_local_component_mut<LocalComponent: Component>(
                    &self,
                ) -> Option<ComponentRefMut<LocalComponent>>
                {
                    let local_component = self.local_components
                        .get(&TypeId::of::<LocalComponent>())?
                        .borrow_mut();

                    Some(ComponentRefMut::new(RefMut::filter_map(
                        local_component,
                        |local_component| local_component.downcast_mut()
                    ).ok()?))
                }

                fn set_local_component<LocalComponent: Component>(
                    &mut self,
                    local_component: LocalComponent,
                )
                {
                    self.local_components
                        .insert(
                            TypeId::of::<LocalComponent>(),
                            RefCell::new(Box::new(local_component))
                        );
                }
            }

            impl<Func, #(TParam~I,)*> IntoSystem<fn(#(TParam~I,)*)>
                for Func
            where
                Func: Fn(#(TParam~I,)*) + Copy + 'static,
            {
                type System = Stateful<Func>;

                fn into_system(self) -> Self::System
                {
                    Self::System {
                        func: self,
                        local_components: HashMap::new(),
                    }
                }
            }
        });
    };
}

seq!(C in 1..16 {
    impl_system!(C);
});