/* 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, Type};
use crate::eval::eval;
use crate::sym::{SymTable, Symbol, ValueType, Args, UserFn};
use std::env;
use std::rc::Rc;

pub mod control;
pub mod append;
//pub mod str;

/// static_stdlib
/// inserts all stdlib functions that can be inserted without
/// any kind of further configuration data into a symtable
pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
    syms.insert("append".to_string(), Symbol {
        name: String::from("append"),
        args: Args::Infinite,
        conditional_branches: false,
        value: ValueType::Internal(Rc::new(append::append_callback)),
    });

    syms.insert("expand".to_string(), Symbol {
        name: String::from("expand"),
        args: Args::Strict(vec![Type::Seg]),
        conditional_branches: false,
        value: ValueType::Internal(Rc::new(append::expand_callback)),
    });

    syms.insert("if".to_string(), Symbol {
        name: String::from("if"),
        args: Args::Lazy(3),
        conditional_branches: true,
        value: ValueType::Internal(Rc::new(control::if_callback)),
    });

    Ok(())
}

/// dynamic_stdlib
/// takes configuration data and uses it to insert dynamic
/// callbacks with configuration into a symtable
pub fn dynamic_stdlib(env: bool, syms: &mut SymTable) -> Result<(), String> {
    syms.insert("def".to_string(), Symbol {
        name: String::from("define"),
        args: Args::Lazy(2),
        conditional_branches: true,
        value: ValueType::Internal(Rc::new( move |ast: &Seg, syms: &mut SymTable| -> Result<Ctr, String> {
            _store_callback(ast, syms, env)
        },
        )),
    });

    Ok(())
}

fn _store_callback (ast: &Seg, syms: &mut SymTable, env_cfg: bool) -> Result<Ctr, String> {
    let is_var = ast.len() == 2;
    if let Ctr::Symbol(ref identifier) = *ast.car {
        match &*ast.cdr {
            Ctr::Seg(data_tree) if is_var => match eval(&Box::new(data_tree), syms) {
                Ok(seg) => if let Ctr::Seg(ref val) = *seg {
                    syms.insert(identifier.clone(), Symbol{
                        value: ValueType::VarForm(val.car.clone()),
                        name: identifier.clone(),
                        args: Args::None,
                        conditional_branches: false,
                    });
                    if env_cfg {
                        env::set_var(identifier.clone(), val.car.to_string());
                    }
                } else {
                    return Err("impossible args to export".to_string());
                },
                Err(e) => return Err(format!("couldnt eval symbol: {}", e)),
            },
            Ctr::Seg(data_tree) if !is_var => {
                if let Ctr::Seg(ref args) = *data_tree.car {
                    let mut arg_list = vec![];
                    if !args.circuit(&mut |c: &Ctr| -> bool {
                        if let Ctr::Symbol(ref arg) = c {
                            arg_list.push(arg.clone());
                            true
                        } else {
                            false
                        }
                    }) {
                        return Err("all arguments defined for function must be of type symbol".to_string());
                    };

                    if let Ctr::Seg(ref bodies) = *data_tree.cdr {
                        syms.insert(identifier.clone(), Symbol{
                            value: ValueType::FuncForm(UserFn{
                                ast: Box::new(bodies.clone()),
                                arg_syms: arg_list.clone(),
                            }),
                            name: identifier.clone(),
                            args: Args::Strict(arg_list
                                               .into_iter()
                                               .map(Type::from)
                                               .collect()),
                            conditional_branches: false,
                        });
                    } else {
                        return Err("expected one or more function bodies in function definition".to_string());
                    }
                } else {
                    return Err("expected list of arguments in function definition".to_string());
                }
            }
            Ctr::None => {
                syms.remove(&identifier.to_string());
                if env_cfg {
                    env::remove_var(identifier);
                }
            },
            _ =>  return Err("args not in standard form".to_string()),
        }
    } else {
       return Err("first argument to export must be a symbol".to_string());
    }
    Ok(Ctr::None)
}