use std::{ptr::NonNull, marker::PhantomData};

use crate::{world::World, View, Query, Access};

pub mod graph;

/// A system that does not mutate the world
pub trait System {
    fn world_access(&self) -> Access;
    fn execute(&mut self, world: NonNull<World>) -> anyhow::Result<()>;
}

/// A trait for converting something into a system.
pub trait IntoSystem<T> {
    type System: System;

    fn into_system(self) -> Self::System;
}

pub trait FnArgFetcher {
    type Arg<'a>: FnArg<Fetcher = Self>;

    fn new() -> Self;

    /// Return the appropriate world access if this fetcher gets the world directly.
    /// Return [`Access::None`] if you're only fetching components, or resources.
    fn world_access(&self) -> Access {
        Access::None
    }

    /// Get the arg from the world
    unsafe fn get<'a>(&mut self, world: NonNull<World>) -> Self::Arg<'a>;
}

pub trait FnArg {
    type Fetcher: FnArgFetcher;
}

pub struct FnSystem<F, Args> {
    inner: F,
    args: Args,
}

impl<F, A> System for FnSystem<F, A>
where
    A: FnArgFetcher,
    F: for<'a> FnMut(A::Arg<'a>) -> anyhow::Result<()>,
{
    fn world_access(&self) -> Access {
        todo!()
    }

    fn execute(&mut self, world: NonNull<World>) -> anyhow::Result<()> {
        let mut a = A::new();

        let a = unsafe { a.get(world) };

        (self.inner)(a)?;
        
        Ok(())
    }
}

impl<F, A> IntoSystem<A> for F
where
    A: FnArg,
    F: FnMut(A) -> anyhow::Result<()>,
    F: for<'a> FnMut(<A::Fetcher as FnArgFetcher>::Arg<'a>) -> anyhow::Result<()>,
{
    type System = FnSystem<F, A::Fetcher>;

    fn into_system(self) -> Self::System {
        FnSystem {
            args: A::Fetcher::new(),
            inner: self
        }
    }
}

/// An ArgFetcher implementation for query [`View`]s
pub struct ViewArgFetcher<Q> {
    query: Q
}

impl<'a, Q: Query> FnArg for View<'a, Q> {
    type Fetcher = ViewArgFetcher<Q>;
}

impl<Q: Query> FnArgFetcher for ViewArgFetcher<Q> {
    type Arg<'a> = View<'a, Q>;

    fn new() -> Self {
        ViewArgFetcher {
            query: Q::new(),
        }
    }

    unsafe fn get<'a>(&mut self, world: NonNull<World>) -> Self::Arg<'a> {
        let world = &*world.as_ptr();
        let arch = world.archetypes.values().collect();
        let v = View::new(world, self.query, arch);

        v
    }
}

/// An ArgFetcher implementation for borrowing the [`World`].
pub struct WorldArgFetcher;

impl<'a> FnArg for &'a World {
    type Fetcher = WorldArgFetcher;
}

impl FnArgFetcher for WorldArgFetcher {
    type Arg<'a> = &'a World;

    fn new() -> Self {
        WorldArgFetcher
    }

    fn world_access(&self) -> Access {
        Access::Read
    }

    unsafe fn get<'a>(&mut self, world: NonNull<World>) -> Self::Arg<'a> {
        &*world.as_ptr()
    }

}

/// An ArgFetcher implementation for mutably borrowing the [`World`].
pub struct WorldMutArgFetcher;

impl<'a> FnArg for &'a mut World {
    type Fetcher = WorldMutArgFetcher;
}

impl FnArgFetcher for WorldMutArgFetcher {
    type Arg<'a> = &'a mut World;

    fn new() -> Self {
        WorldMutArgFetcher
    }

    fn world_access(&self) -> Access {
        Access::Write
    }

    unsafe fn get<'a>(&mut self, world: NonNull<World>) -> Self::Arg<'a> {
        &mut *world.as_ptr()
    }
}

#[cfg(test)]
mod tests {
    use std::ptr::NonNull;

    use crate::{tests::{Vec2, Vec3}, View, QueryBorrow, world::World};
    use super::{System, IntoSystem};

    struct SomeCounter(u32);

    #[test]
    fn simple_system() {
        let mut world = World::new();
        let vecs = &[Vec2::rand(), Vec2::rand(), Vec2::rand(), Vec2::rand()];
        world.spawn((vecs[0],));
        world.spawn((vecs[1],));
        world.spawn((vecs[2],));
        world.spawn((vecs[3],));

        let mut count = 0;

        let test_system = |view: View<QueryBorrow<Vec2>>| -> anyhow::Result<()> {
            let mut vecs = vecs.to_vec();
            for v in view.into_iter() {
                let pos = vecs.iter().position(|vec| *vec == *v)
                    .expect("Failure to find vec inside list");
                vecs.remove(pos);

                println!("Got v at: {:?}", v);
                count += 1;
            }

            Ok(())
        };

        test_system.into_system().execute(NonNull::from(&world)).unwrap();

        assert_eq!(count, 4);
    }

    #[test]
    fn multi_system() {
        let mut world = World::new();
        world.spawn((Vec2::rand(), Vec3::rand()));
        world.spawn((Vec2::rand(), Vec3::rand()));
        world.spawn((Vec2::rand(),));
        world.spawn((Vec2::rand(),));

        let mut count = 0;

        let test_system = |view: View<(QueryBorrow<Vec2>, QueryBorrow<Vec3>)>| -> anyhow::Result<()> {
            for (v2, v3) in view.into_iter() {
                println!("Got v2 at '{:?}' and v3 at: '{:?}'", v2, v3);
                count += 1;
            }

            Ok(())
        };

        test_system.into_system().execute(NonNull::from(&world)).unwrap();

        assert_eq!(count, 2);
    }

    #[test]
    fn world_system() {
        let mut world = World::new();
        world.spawn((Vec2::rand(), Vec3::rand()));
        world.spawn((Vec2::rand(), Vec3::rand()));
        world.add_resource(SomeCounter(0));

        let test_system = |world: &World| -> anyhow::Result<()> {
            let mut counter = world.get_resource_mut::<SomeCounter>();
            counter.0 += 10;

            Ok(())
        };

        test_system.into_system().execute(NonNull::from(&world)).unwrap();

        let counter = world.get_resource::<SomeCounter>();
        assert_eq!(counter.0, 10);
    }
}