/* 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> {
    if let Ctr::Seg(ref cond_form) = *ast.car {
        if let Ctr::Bool(cond) = *eval(cond_form, syms)? {
            if let Ctr::Seg(ref first_form) = *ast.cdr {
                if cond {
                    match *first_form.car {
                        Ctr::Seg(ref first_arg) => Ok(*eval(first_arg, syms)?),
                        _ => Ok(*eval(&Seg::from_mono(first_form.car.clone()), syms)?),
                    }
                } else {
                    if let Ctr::Seg(ref second_form) = *first_form.cdr {
                        match *second_form.car {
                            Ctr::Seg(ref second_arg) => Ok(*eval(second_arg, syms)?),
                            _ => Ok(*eval(&Seg::from_mono(second_form.car.clone()), syms)?),
                        }
                    } else {
                        Err("impossible condition: args not in standard form".to_string())
                    }
                }
            } else {
                Err("impossible condition: not 3 args to if".to_string())
            }
        } else {
            Err("first argument to if must evaluate to be a boolean".to_string())
        }
    } else {
        Err("impossible condition: not 3 args to if".to_string())
    }
}

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

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

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