pub mod op;
pub mod frame;

use crate::{
    obj::prelude::*,
    mem::gc::Gc,
    vm::{
        op::Op,
        frame::Frame,
    }
};
use std::rc::Rc;

fn root_ns<I: Intern, G: Gc>(intern: &mut I, gc: &mut G) -> Ns {
    let mut ns: Ns = Default::default();
    ns.insert(intern.intern_sym("Unit"), Attrs::new(gc, Default::default()));
    ns
}

pub struct State<I: Intern, G: Gc> {
    intern: I,
    gc: G,
    root_ns: Ns,
    frames: Vec<Frame>,
}

impl<I: Intern, G: Gc> State<I, G> {
    pub fn new(mut intern: I, mut gc: G) -> Self {
        let root_ns = root_ns(&mut intern, &mut gc);
        State { intern, gc, root_ns, frames: Default::default(), }
    }

    pub fn frames(&self) -> &Vec<Frame> {
        &self.frames
    }

    pub fn frames_mut(&mut self) -> &mut Vec<Frame> {
        &mut self.frames
    }

    pub fn frame(&self) -> &Frame {
        self.frames
            .last()
            .unwrap()
    }

    pub fn frame_mut(&mut self) -> &mut Frame {
        self.frames
            .last_mut()
            .unwrap()
    }

    pub fn push_stack(&mut self, value: DynRef) {
        self.frame_mut()
            .push(value);
    }

    pub fn pop_stack(&mut self) -> Option<DynRef> {
        self.frame_mut()
            .pop()
    }

    pub fn ip(&self) -> usize {
        self.frame().ip()
    }

    pub fn set_ip(&mut self, ip: usize) {
        self.frame_mut().set_ip(ip);
    }

    pub fn get_local(&self, sym: Sym) -> Option<DynRef> {
        self.frame().get_local(sym)
    }

    pub fn set_local(&mut self, sym: Sym, obj_ref: DynRef) -> Option<DynRef> {
        self.frame_mut().set_local(sym, obj_ref)
    }

    pub fn ops(&self) -> &Rc<Vec<Op>> {
        self.frame().ops()
    }

    pub fn resume(&mut self) {
        while !self.frames().is_empty() {
            self.resume_fun();
            let _frame = self.frames_mut().pop().unwrap();
            // Push return value?
        }
    }

    pub fn resume_fun(&mut self) {
        while self.ip() < self.ops().len() {
            self.step();
        }
    }

    pub fn step(&mut self) {
        let mut next_ip = self.ip() + 1;
        match self.ops()[self.ip()] {
            Op::Push(sym) => {
                // TODO - local not found
                let obj_ref = self.get_local(sym)
                    .expect("TODO - local not found");
                self.push_stack(obj_ref);
            }
            Op::Pop(sym) => {
                // stack should not underflow
                let obj_ref = self.pop_stack()
                    .expect("misaligned stack for pop");
                if let Some(sym) = sym {
                    self.set_local(sym, obj_ref);
                }
            }
            Op::GetAttr(sym) => {
                let top = self.pop_stack()
                    .expect("misaligned stack for getattrs");
                let obj_ref = {
                    let top_ref = top.borrow();
                    let attrs = top_ref.attrs();
                    let attrs_ref = attrs.borrow();
                    // TODO - local not found
                    attrs_ref.get(sym)
                        .expect("TODO - local not found")
                };
                self.push_stack(obj_ref);
            }
            Op::Call(argc) => {
                let fun = self.pop_stack()
                    .expect("misaligned stack for function call");
                let mut argv = Vec::with_capacity(argc);
                for _ in 0 .. argc {
                    let arg = self.pop_stack()
                        .expect("misaligned stack for argv");
                    argv.push(arg);
                }
                // reverse since arguments are pushed in order of being passed
                argv.reverse();

                // TODO
                // move ops pointer to the stack frame
                if let Some(_fun) = fun.borrow().as_any().downcast_ref::<Fun>() {
                    self.set_ip(next_ip);
                    next_ip = 0;
                    todo!("New stack frame");
                } else if let Some(_fun) = fun.borrow().as_any().downcast_ref::<NativeFun>() {
                    todo!();
                } else {
                    todo!("TODO - not a function");
                }

            }
        }
        self.set_ip(next_ip);
    }
}