/* 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::eval::eval;
use crate::func::{Args, FTable, Function, Operation};
use crate::segment::{Seg, Ctr};
use std::collections::HashMap;
use std::env;
/* Mapping between a string token and a tree of Segments
 * The string token can be found in any Ctr::Symbol value
 * it is expected that the trees stored are already evaluated
 */
pub struct VTable<'a>(HashMap<String, Box<Ctr<'a>>>);

impl<'a> VTable<'a> {
    // WARNING: make sure var_tree is properly evaluated before storing
    pub fn insert(&'a mut self, identifier: String, data: Box<Ctr<'a>>) {
        if let Some(datum) = self.0.insert(identifier, data) {
            drop(datum);
        }
    }

    pub fn get(&'a self, id: String) -> Option<Box<Ctr<'a>>> {
        return self.0.get(&id);
    }

    pub fn remove(&self, id: String) {
        self.0.remove(&id);
    }
}

// returns a callback for the stdlib var export function with env_sync on or off
pub fn get_export<'a> (env_cfg: bool) -> Function<'a> {
    return Function {
        name: String::from("export"),
        loose_syms: true,
        eval_lazy: true,
        args: Args::Lazy(2),
        function: Operation::Internal(Box::new(
            |ast: &Seg, vars: &mut VTable, funcs: &mut FTable| -> Ctr {
                if let Ctr::Symbol(identifier) = *ast.car {
                    match *ast.cdr {
                        Ctr::Seg(ref data_tree) => match eval(&Box::new(data_tree), vars, funcs, false) {
                            Ok(seg) => match *seg {
                                Ctr::Seg(val) => {
                                    vars.insert(identifier, val.car);
                                    if env_cfg {
                                        env::set_var(identifier, val.car.to_string())
                                    }
                                },
                                _ =>  eprintln!("impossible args to export"),
                            },
                            Err(e) =>  eprintln!("couldnt eval symbol: {}", e),
                        },
                        Ctr::None => {
                            vars.remove(identifier);
                            if env_cfg {
                                env::remove_var(identifier);
                            }
                        },
                        _ =>  eprintln!("args not in standard form"),
                    }
                } else {
                    eprintln!("first argument to export must be a symbol");
                }
                return Ctr::None;
            },
        )),
    };
}