/* 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::sym::SymTable;

pub const APPEND_DOCSTRING: &str = "traverses any number of arguments collecting them into a list.
If the first argument is a list, all other arguments are added sequentially to the end of the list contained in the first argument.";

pub fn append_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    if let Ctr::Seg(ref s) = *ast.car {
        let mut temp = s.clone();
        if let Ctr::Seg(ref list) = *ast.cdr {
            list.circuit(&mut |c: &Ctr| -> bool {
                temp.append(Box::new(c.clone()));
                true
            });
        } else {
            temp.append(Box::new(*ast.cdr.clone()));
        }
        Ok(Ctr::Seg(temp))
    } else {
        let mut temp = Seg::new();
        let mut car_iter = &ast.car;
        let mut cdr_iter = &ast.cdr;
        loop {
            temp.append(car_iter.clone());
            if let Ctr::Seg(ref s) = **cdr_iter {
                car_iter = &s.car;
                cdr_iter = &s.cdr;
            } else {
                break;
            }
        }

        Ok(Ctr::Seg(temp))
    }
}

pub const LEN_DOCSTRING: &str = "Takes a single argument, expected to be a list.
Returns the length of said list.
Interpreter will panic if the length of the list is greater than the max value of a signed 128 bit integer";

pub fn len_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    if let Ctr::Seg(ref s) = *ast.car {
        if let Ctr::None = *s.car {
            Ok(Ctr::Integer(0))
        } else {
            Ok(Ctr::Integer(s.len() as i128))
        }
    } else {
        Err("impossible condition: argument to len not a list".to_string())
    }
}

pub const CAR_DOCSTRING: &str = "Takes a single argument, expected to be a list.
Returns a copy of the first value in that list.
If the list is empty, returns an err to avoid passing back a null value.";

pub fn car_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    if let Ctr::Seg(ref s) = *ast.car {
        if let Ctr::None = *s.car {
            Err("argument is empty".to_string())
        } else {
            Ok(*s.car.clone())
        }
    } else {
        Err("impossible condition: argument to car not a list".to_string())
    }
}

pub const CDR_DOCSTRING: &str = "Takes a single argument, expected to be a list.
Returns a copy of the last value in that list.
If the list is empty, returns an err to avoid passing back a null value.";

pub fn cdr_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
    if let Ctr::Seg(ref s) = *ast.car {
        let mut ret = &s.car;
        let mut iter = &s.cdr;
        while let Ctr::Seg(ref next) = **iter {
            ret = &next.car;
            iter = &next.cdr;
        }
        if let Ctr::None = **ret {
            Err("argument is empty".to_string())
        } else {
            Ok(*ret.clone())
        }
    } else {
        Err("impossible condition: argument to cdr not a list".to_string())
    }
}