use std::any::{type_name, TypeId};
use std::collections::HashMap;
use std::ptr::addr_of_mut;

use seq_macro::seq;

use crate::component::Component;
use crate::system::util::check_params_are_compatible;
use crate::system::{
    FilteredInputs,
    InputFilter,
    Into as IntoSystem,
    OptionInputs,
    Param,
    System,
    TakeOptionInputResult,
    TypeErased,
};
use crate::ComponentStorage;

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

macro_rules! impl_system {
    ($c: tt) => {
        seq!(I in 0..=$c {
            impl<'world, Func, #(TParam~I,)*> System<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,)*): InputFilter
            {
                type Input = <(#(TParam~I::Input,)*) as InputFilter>::Filtered;

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

                    #(
                        if TypeId::of::<TParam~I::Input>() != TypeId::of::<()>() {
                            let input = match option_input.take::<TParam~I::Input>() {
                                TakeOptionInputResult::Found(input) => input,
                                TakeOptionInputResult::NotFound => {
                                    panic!(
                                        "Parameter input {} not found",
                                        type_name::<TParam~I::Input>()
                                    );
                                }
                                TakeOptionInputResult::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(&mut self, component_storage: &mut ComponentStorage)
                {
                    #(
                        check_params_are_compatible!(I, TParam~I, $c);
                    )*

                    let func = self.func;

                    func(#({
                        // SAFETY: All parameters are compatible so this is fine
                        let this = unsafe {
                            &mut *addr_of_mut!(*self)
                        };

                        // SAFETY: All parameters are compatible so this is fine
                        let component_storage = unsafe {
                            &mut *addr_of_mut!(*component_storage)
                        };

                        TParam~I::new(this, component_storage)
                    },)*);
                }

                fn into_type_erased(self) -> TypeErased
                {
                    TypeErased {
                        data: Box::new(self),
                        func: Box::new(|data, component_storage| {
                            let me = data.downcast_mut::<Self>().unwrap();

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

                fn get_local_component_mut<LocalComponent: Component>(
                    &mut self,
                ) -> Option<&mut LocalComponent>
                {
                    self.local_components
                        .get_mut(&TypeId::of::<LocalComponent>())?
                        .downcast_mut()
                }

                fn set_local_component<LocalComponent: Component>(
                    &mut self,
                    local_component: LocalComponent,
                )
                {
                    self.local_components
                        .insert(TypeId::of::<LocalComponent>(),
                        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 0..4 {
    impl_system!(C);
});