not-python-old.2020-08-27/src/obj/attrs.rs

use crate::{
    mem::ptr::{DynRef, ObjCell},
    obj::prelude::*,
};
use std::{
    cell::Cell,
    collections::BTreeMap,
    mem::MaybeUninit,
    ptr::{self, NonNull},
};

pub type AttrsMap = BTreeMap<Sym, DynRef>;

pub struct Attrs {
    attrs: AttrsMap,
    marked: Cell<bool>,
    this: ObjRef<Attrs>,
}

impl Attrs {
    pub fn new(ctx: &mut ObjCtx, attrs: BTreeMap<Sym, DynRef>) -> ObjRef<Self> {
        let obj: Box<ObjCell<Attrs>> = unsafe {
            let mut obj: Box<MaybeUninit<ObjCell<Attrs>>> = Box::new_uninit();
            // maybe UB? taking away the uninit right before it's initialized may be bad
            let this = &*obj as *const _ as *const ObjCell<Attrs>;

            obj.as_mut_ptr().write(ObjCell::new(Attrs {
                attrs: Default::default(),
                marked: Cell::new(false),
                this: ObjRef::new(NonNull::new(this as *mut _).unwrap()),
            }));

            obj.assume_init()
        };

        let obj_ref = {
            let obj_ref: &Attrs = &obj.borrow();
            assert!(
                ptr::eq(&*obj as *const _, obj_ref.this.as_ptr()),
                "Attr 'this' member does not point to itself"
            );
            obj_ref.this
        };

        // Add the object to the allocator pool
        ctx.gc_mut().add_obj(obj);
        obj_ref
    }

    pub fn insert(&mut self, sym: Sym, value: DynRef) -> Option<DynRef> {
        self.attrs.insert(sym, value)
    }

    pub fn get(&self, sym: Sym) -> Option<DynRef> {
        dbg!(&self.attrs);
        self.attrs.get(&dbg!(sym)).copied()
    }
}

impl Obj for Attrs {
    fn attrs(&self) -> ObjRef<Attrs> {
        self.this
    }

    fn is_marked(&self) -> bool {
        self.marked.get()
    }

    fn mark(&self) {
        if self.is_marked() {
            return;
        }
        self.marked.set(true);
        self.attrs.iter().for_each(|(_, v)| v.borrow().mark());
    }

    fn unmark(&self) {
        if !self.is_marked() {
            return;
        }
        self.marked.set(false);
        self.attrs.iter().for_each(|(_, v)| v.borrow().unmark());
    }

    fn as_any(&self) -> &dyn std::any::Any {
        self
    }
}

pub struct AttrsBuilder<'ctx> {
    ctx: &'ctx mut ObjCtx,
    attrs: AttrsMap,
}

impl<'ctx> AttrsBuilder<'ctx> {
    pub fn new(ctx: &'ctx mut ObjCtx) -> Self {
        Self::with_base(ctx, Default::default())
    }

    pub fn with_base(ctx: &'ctx mut ObjCtx, attrs: AttrsMap) -> Self {
        AttrsBuilder {
            attrs,
            ctx,
        }
    }

    pub fn attr(mut self, symbol_name: &str, value: DynRef) -> Self {
        let sym = self.ctx.gc_mut().add_sym(symbol_name);
        self.attr_sym(sym, value)
    }

    pub fn attr_sym(mut self, sym: Sym, value: DynRef) -> Self {
        self.attrs.insert(sym, value);
        self
    }

    pub fn finish(self) -> ObjRef<Attrs> {
        let Self { ctx, attrs } = self;
        Attrs::new(ctx, attrs)
    }
}

#[test]
fn test_attrs_new() {
    use crate::mem::BasicGc;

    let mut ctx = ObjCtx::new(BasicGc::default());
    
    let attrs_ref = Attrs::new(&mut ctx, Default::default());

    {
        let mut attrs = attrs_ref.borrow_mut();
        let sym = ctx.gc_mut().add_sym("symbol");
        attrs.insert(sym, attrs_ref.as_dyn());

        assert!(
            ptr::eq(
                dbg!(attrs.get(sym).unwrap().as_ptr()),
                dbg!(attrs_ref.as_dyn().as_ptr())
                //               ^ as_dyn() is important here - this will cause the test to fail
                //               otherwise
            ),
        );
    }
}