/* 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>>> {
        match self.0.get(&id) {
            Some(s) => Some(s.clone()),
            None => None,
        }
    }

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

    pub fn new() -> VTable<'a> {
        VTable{0: HashMap::<String, Box<Ctr>>::new()}
    }
}

// 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(
            move |ast: &Seg, vars: &mut VTable, funcs: &mut FTable| -> Ctr {
                _export_callback(ast, vars, funcs, env_cfg)
            },
        )),
    };
}


fn _export_callback<'a> (ast: &'a Seg, vars: &'a mut VTable, funcs: &'a mut FTable, env_cfg: bool) -> Ctr<'a> {
    if let Ctr::Symbol(ref identifier) = *ast.car {
        match *ast.cdr {
            Ctr::Seg(data_tree) => match eval(&Box::new(data_tree), vars, funcs, false) {
                Ok(seg) => match *seg {
                    Ctr::Seg(val) => {
                        vars.insert(identifier.clone(), val.car);
                        if env_cfg {
                            env::set_var(identifier.clone(), val.car.to_string())
                        }
                    },
                    _ =>  eprintln!("impossible args to export"),
                },
                Err(e) =>  eprintln!("couldnt eval symbol: {}", e),
            },
            Ctr::None => {
                vars.remove(identifier.to_string());
                if env_cfg {
                    env::remove_var(identifier.to_string());
                }
            },
            _ =>  eprintln!("args not in standard form"),
        }
    } else {
        eprintln!("first argument to export must be a symbol");
    }
    return Ctr::None;
}