/* relish: versatile lisp shell
 * Copyright (C) 2021 Ava Affine
 *
 * 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 std::fmt;


// Container
#[derive(Debug, Clone, Default)]
pub enum Ctr <'a> {
    Symbol(String),
    String(String),
    Integer(i128),
    Float(f64),
    Bool(bool),
    Seg(Seg<'a>),
    #[default]
    None,
}

// Type of Container
#[derive(PartialEq, Clone)]
pub enum Type {
    Symbol,
    String,
    Integer,
    Float,
    Bool,
    Seg,
    None,
}

/* Segment
 * Holds two Containers.
 * Basic building block for more complex data structures.
 */
#[derive(Clone, Debug, Default)]
pub struct Seg <'a> {
    /* "Contents of Address Register"
     *  Historical way of referring to the first value in a cell.
     */
    pub car: &mut Ctr<'a>,

    /* "Contents of Decrement Register"
     *  Historical way of referring to the second value in a cell.
     */
    pub cdr: &mut Ctr<'a>,
}

impl Ctr<'_> {
    pub fn to_type(&self) -> Type {
        match self {
            Ctr::Symbol(_s) => Type::Symbol,
            Ctr::String(_s) => Type::String,
            Ctr::Integer(_s) => Type::Integer,
            Ctr::Float(_s) => Type::Float,
            Ctr::Bool(_s) => Type::Bool,
            Ctr::Seg(_s) => Type::Seg,
            Ctr::None => Type::None,
        }
    }

}

fn seg_to_string(s: &Seg, parens: bool) -> String {
    let mut string = String::new();
    match s.car {
        Ctr::None => string.push_str("<nil>"),
        _ => string.push_str(s.car),
    }
    string.push(' ');
    match s.cdr {
        Ctr::Seg(inner) => string.push_str(seg_to_string(inner, false)),
        Ctr::None => {},
        _ => string.push_str(s.cdr),
    }

    if parens {
        String::from("(" + string + ")")
    }
}

impl fmt::Display for Ctr <'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Ctr::Symbol(s) => write!(f, "{}", s),
            Ctr::String(s) => write!(f, "\'{}\'", s),
            Ctr::Integer(s) => write!(f, "{}", s),
            Ctr::Float(s) => write!(f, "{}", s),
            Ctr::Bool(s) => {
                if s {
                    write!(f, "T")
                } else {
                    write!(f, "F")
                }
            },
            Ctr::Seg(s) => write!(f, "{}", s),
            Ctr::None => Ok(),
        }
    }
}

impl fmt::Display for Seg<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", seg_to_string(self, true))
    }
}

impl Iterator for Seg<'_> {
    fn next(&self) -> Option<&Seg> {
        if let Ctr::Seg(s) = self.cdr {
            Ok(s)
        } else {
            None()
        }
    }
}

impl Type {
    pub fn to_string(&self) -> String {
        let ret: &str;
        match self {
            Type::Symbol => ret = "symbol",
            Type::String => ret = "string",
            Type::Integer => ret = "integer",
            Type::Float => ret = "float",
            Type::Bool => ret = "bool",
            Type::Seg => ret = "segment",
            Type::None => ret = "none",
        }

        ret.to_owned()
    }
}

/* applies a function across a list in standard form
 * function must take a Ctr and return a bool
 * short circuits on the first false returned.
 * also returns false on a non standard form list
 */
pub fn circuit<F: Fn(&Ctr)>(list: &Seg, func: &mut F) -> bool {
    if func(&list.car) {
        match list.cdr {
            Ctr::None => true,
            Ctr::Seg(l) => circuit(l, func),
            _ => false,
        }
    } else {
        false
    }
}

/* recurs over ast assumed to be list in standard form
 * returns length
 */
pub fn list_len(list: &Seg) -> u128 {
    let mut len = 0;
    circuit(list, &circuit(&mut |c: &Ctr| -> bool { len += 1; true }))
}

/* recurs over tree assumed to be list in standard form
 * returns clone of ctr at index provided
 *
 * TODO: return result (or option?)
 */
pub fn list_idx<'a>(list: &Seg, idx: u128) -> Ctr<'a> {
    if idx > 0 {
        if let Ctr::Seg(s) = list.car {
            list_idx(s, idx - 1)
        } else if idx == 1 {
            list.cdr
        } else {
            Ctr::None
        }
    } else {
        list.car
    }
}

/* recurs over tree assumed to be list in standard form
 * appends object to end of list
 *
 * TODO: return result
 */
pub fn list_append<'a>(list: &Seg, obj: Ctr) {
    if let Ctr::None = list.car {
        list.car = obj;
        return
    }

    if let Ctr::Seg(s) = list.cdr {
        list_append(s, obj)
    }

    if let Ctr::None = list.cdr {
        list.cdr = Ctr::Seg(&Seg{car:obj, cdr:Ctr::None})
    }
}