use std::collections::{HashMap, VecDeque};

use crsn::asm::data::{Rd, RdObj, Wr};
use crsn::asm::data::literal::Value;
use crsn::asm::instr::Cond;
use crsn::module::{EvalRes, OpTrait};
use crsn::runtime::fault::Fault;
use crsn::runtime::run_thread::{state::RunState, ThreadInfo};
use crsn::sexp;
use crsn::sexp::Sexp;
use crsn::utils::A;

use crate::defs::StackOp;

#[derive(Debug, Default)]
struct Stacks {
    store: HashMap<Value, VecDeque<Value>>,
}

impl OpTrait for StackOp {
    fn execute(&self, info: &ThreadInfo, state: &mut RunState) -> Result<EvalRes, Fault> {
        let eres = EvalRes::default();
        match self {
            StackOp::NewStack { dst } => {
                let id = info.unique_handle();
                let stacks: &mut Stacks = state.ext_mut();
                stacks.store.insert(id, VecDeque::new());

                state.write(*dst, id)?;
            }
            StackOp::Push { obj, src } => {
                prepare_push(state, obj, src,
                             |stack, val| stack.push_back(val))?;
            }
            StackOp::ReversePush { obj, src } => {
                prepare_push(state, obj, src,
                             |stack, val| stack.push_front(val))?;
            }
            StackOp::Pop { dst, obj } => {
                prepare_pop(state, dst, obj,
                            |stack| stack.pop_back())?;
            }
            StackOp::ReversePop { dst, obj } => {
                prepare_pop(state, dst, obj,
                            |stack| stack.pop_front())?;
            }
        }

        Ok(eres)
    }

    fn to_sexp(&self) -> Sexp {
        match self {
            StackOp::NewStack { dst } => sexp::list(&[A("stack"), A(dst)]),
            StackOp::Push { obj, src } => sexp::list(&[A("push"), A(obj), A(src)]),
            StackOp::Pop { dst, obj } => sexp::list(&[A("pop"), A(dst), A(obj)]),
            StackOp::ReversePush { obj, src } => sexp::list(&[A("rpush"), A(obj), A(src)]),
            StackOp::ReversePop { dst, obj } => sexp::list(&[A("rpop"), A(dst), A(obj)]),
        }
    }
}


pub(crate) fn drop_obj(state: &mut RunState, handle: Value) -> Result<Option<()>, Fault> {
    let stacks: &mut Stacks = state.ext_mut();
    Ok(stacks.store.remove(&handle).map(|_| ()))
}

fn prepare_push(state: &mut RunState, obj: &RdObj, src: &Rd, pushfn: impl FnOnce(&mut VecDeque<Value>, Value) -> ()) -> Result<(), Fault> {
    state.clear_status();
    let handle = state.read_obj(*obj)?;
    let val = state.read(*src)?;

    let stacks: &mut Stacks = state.ext_mut();
    let mutable = stacks.store.get_mut(&handle)
        .ok_or_else(|| Fault::ObjectNotExist(handle))?;

    pushfn(mutable, val);
    Ok(())
}

fn prepare_pop(state: &mut RunState, dst: &Wr, obj: &RdObj, popfn: impl FnOnce(&mut VecDeque<Value>) -> Option<Value>) -> Result<(), Fault> {
    state.clear_status();
    let handle = state.read_obj(*obj)?;

    let stacks: &mut Stacks = state.ext_mut();
    let stack = stacks.store.get_mut(&handle)
        .ok_or_else(|| Fault::ObjectNotExist(handle))?;

    let val = popfn(stack);

    if stack.is_empty() {
        state.set_flag(Cond::Zero, true);
    }

    let val = match val {
        None => {
            state.set_flag(Cond::Overflow, true);
            0
        }
        Some(val) => {
            val
        }
    };

    state.write(*dst, val)?;
    Ok(())
}