/* 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::{Ctr, Seg};
use crate::eval::eval;
use crate::sym::SymTable;

pub fn if_callback (ast: &Seg, syms: &mut SymTable) -> Result<Ctr, String> {
    let cond: bool;
    match *ast.car {
        Ctr::Seg(ref cond_form) => {
            if let Ctr::Bool(cond_from_eval) = *eval(cond_form, syms)? {
                cond = cond_from_eval;
            } else {
                return Err("first argument to if must evaluate to be a boolean".to_string())
            }
        }

        Ctr::Bool(cond_from_car) => cond = cond_from_car,
        _ => {
            return Err("first argument to if must evaluate to be a boolean".to_string())
        }
    }

    let then_form: &Seg;
    if let Ctr::Seg(ref s) = *ast.cdr {
        then_form = s;
    } else {
        return Err("impossible condition: not enough args to if".to_string())
    }

    if cond {
        // then
        match *then_form.car {
            Ctr::Seg(ref first_arg) => Ok(*eval(first_arg, syms)?),
            _ => {
                //Ok(*eval(&Seg::from_mono(then_form.car.clone()), syms)?)},
                let eval_tree = &Seg::from_mono(then_form.car.clone());
                let eval_res = *eval(eval_tree, syms)?;
                if let Ctr::Seg(ref s) = eval_res {
                    Ok(*s.car.clone())
                } else {
                    Err("impossible condition: list evals to non list".to_string())
                }
            },
        }

    } else {
        // else
        if let Ctr::Seg(ref else_form) = *then_form.cdr {
            match *else_form.car {
                Ctr::Seg(ref second_arg) => Ok(*eval(second_arg, syms)?),
                _ => {
                    //Ok(*eval(&Seg::from_mono(then_form.car.clone()), syms)?)},
                    let eval_tree = &Seg::from_mono(else_form.car.clone());
                    let eval_res = *eval(eval_tree, syms)?;
                    if let Ctr::Seg(ref s) = eval_res {
                        Ok(*s.car.clone())
                    } else {
                        Err("impossible condition: list evals to non list".to_string())
                    }
                },
            }
        } else {
            Err("impossible condition: args not in standard form".to_string())
        }
    }
}

pub fn let_callback (_ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    todo!()
}

pub fn while_callback (_ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    todo!()
}

pub fn map_callback (_ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    todo!()
}

pub fn circuit_callback (_ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    todo!()
}