/* relish: versatile lisp shell
 * Copyright (C) 2021 Aidan Hahn
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */


use crate::segment::{Seg, Ctr};
use crate::sym::SYM_TABLE;

/* iterates over a syntax tree
 * returns a NEW LIST of values
 * representing the simplest possible form of the input
 */

pub fn eval(
    ast: &Seg,
    sym_loose: bool,
    call_lazy: bool,
) -> Result<Box<Ctr>, String> {
    // data to return
    let mut ret = Box::from(Ctr::None);

    // to be assigned from cloned/evaled data
    let mut car;
    let mut cdr = Box::from(Ctr::None);

    // lets me redirect the input
    let mut arg_car = &ast.car;
    let mut arg_cdr = &ast.cdr;

    // theres probably a better way to do this
    let mut binding_for_vtable_get;

    // doing an initial variable check here allows us
    // to find functions passed in as variables
    if let Ctr::Symbol(tok) = &**arg_car {
        binding_for_vtable_get = vars.get(tok.clone());
        if let Some(ref val) = binding_for_vtable_get {
            arg_car = &val;
        }
    }

    // Is ast a function call?
    if !call_lazy {
        if let Ctr::Symbol(ref tok) = &**arg_car {
            match *ast.cdr {
                Ctr::Seg(ref ast) => {
                    if let Some(ref func) = funcs.get(tok.clone()) {
                        return func.func_call(ast, vars, funcs);
                    } else if !sym_loose {
                        return Err(format!("Couldnt find definition of {}.", tok));
                    }
                }
                Ctr::None => {
                    if let Some(ref func) = funcs.get(tok.clone()) {
                        return (*func).func_call(&Seg::new(), vars, funcs);
                    } else if !sym_loose {
                        return Err(format!("Couldnt find definition of {}.", tok.clone()));
                    }
                }
                _ => return Err(format!("Arguments to function not a list!")),
            }
        }
    }

    // iterate over ast and build out ret
    let mut none = false;
    while !none {
        match &**arg_car {
            Ctr::Seg(ref inner) => {
                match eval(inner, vars, funcs, sym_loose, call_lazy) {
                    Ok(res) => car = res,
                    Err(e) => return Err(format!("Evaluation error: {}", e)),
                }
            }

            Ctr::Symbol(ref tok) => {
                binding_for_vtable_get = vars.get(tok.clone());
                if let Some(ref val) = binding_for_vtable_get {
                    car = val.clone();
                } else if sym_loose {
                    car = arg_car.clone()
                } else {
                    return Err(format!("Undefined variable: {}", tok.clone()));
                }
            }

            _ => {
                car = arg_car.clone();
            }
        }

        match &**arg_cdr {
            Ctr::Symbol(ref tok) => {
                if let Some(val) = vars.get(tok.clone()) {
                    cdr = val.clone();
                } else if sym_loose {
                    cdr = ast.cdr.clone()
                } else {
                    return Err(format!("Undefined variable: {}", tok.clone()));
                }

                none = true;
            }

            Ctr::Seg(ref next) => {
                if let Ctr::None = *ret {
                    *ret = Ctr::Seg(Seg::from(car, cdr.clone()))
                } else if let Ctr::Seg(ref mut s) = *ret {
                    s.append(Box::from(Ctr::Seg(Seg::from(car, cdr.clone()))))
                }
                arg_car = &next.car;
                arg_cdr = &next.cdr
            }

            // if OTHER: clone and set, and then end
            _ => {
                cdr = ast.cdr.clone();
                none = true;
            }
        }

        if let Ctr::None = **arg_car {
            if let Ctr::None = **arg_cdr {
                none = true;
            }
        }
    }

    return Ok(ret);
}