/*  Mycelium Scheme
 *  Copyright (C) 2025 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 <https://www.gnu.org/licenses/>.
 */

use core::fmt::{self, Formatter};
use core::ops::Index;
use core::cell::RefCell;

use alloc::format;
use alloc::rc::Rc;
use alloc::vec::Vec;
use alloc::string::String;

use organelle::Number;

#[derive(Default, Clone, PartialEq)]
pub enum Datum {
    Number(Number),
    Bool(bool),
    List(Rc<Ast>),
    Symbol(String),
    Char(u8),
    String(Vec<u8>),
    Vector(RefCell<Vec<Rc<Datum>>>),
    ByteVector(RefCell<Vec<u8>>),
    #[default]
    None,
}

fn byte_to_escaped_char(b: u8) -> String {
    // alarm, backspace, delete
    match b {
         _ if b > 31 && b < 127 => String::from(b as char),
         _ => format!("x{:x}", b),
    }
}

fn fmt_vec<T: fmt::Display>(ve: &RefCell<Vec<T>>) -> String {
    let v = ve.borrow();
    if v.len() == 0 {
        return String::new()
    }
    let mut s = format!("{}", v[0]);
    let mut i = v.iter();
    i.next(); // discard
    i.for_each(|e| {
        s = format!("{} {}", s, e);
    });

    s
}

impl fmt::Display for Datum {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match self {
            Datum::Number(n) => write!(f, "{}", Into::<String>::into(*n)),
            Datum::Bool(n) => write!(f, "{}", if *n {"#t"} else {"#f"}),
            Datum::List(n) => write!(f, "{n}"),
            Datum::Symbol(n) => write!(f, "{n}"),
            Datum::Char(n) => write!(f, "#\\{}",
                    byte_to_escaped_char(*n)),
            Datum::String(n) =>
                write!(f, "\"{}\"", String::from_utf8_lossy(&*n)),
            Datum::Vector(n) => write!(f, "#({})", fmt_vec(n)),
            Datum::ByteVector(n) => write!(f, "#u8({})", fmt_vec(n)),
            Datum::None => Ok(())
        }
    }
}

/* WARNING
 * This is in a sense overloaded.
 * Instead of using this to print debugging information for the
 * Rust code, I have instead overloaded it to print the most
 * maximal expanded valid syntax for this Datum
 */
impl fmt::Debug for Datum {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match self {
            Datum::Number(n) => write!(f, "{}", Into::<String>::into(*n)),
            Datum::Bool(n) => write!(f, "{}", if *n {"#t"} else {"#f"}),
            Datum::List(n) => write!(f, "{n}"),
            Datum::Char(n) => write!(f, "{}",
                    byte_to_escaped_char(*n)),
            Datum::Symbol(n) => write!(f, "{n}"),
            Datum::String(n) =>
                write!(f, "\"{}\"", String::from_utf8_lossy(&*n)),
            Datum::Vector(n)  => write!(f, "#({n:?})"),
            Datum::ByteVector(n) => write!(f, "#u8({n:?})"),
            Datum::None => Ok(())
        }
    }
}


#[derive(Default, Clone, PartialEq)]
pub struct Ast(pub Rc<Datum>, pub Rc<Datum>);

impl Ast {
    pub fn subsl(&self, start: isize, end: isize) -> Ast {
        if end - start == 1 {
            return Ast(Rc::from(self[start as usize].clone()), Rc::from(Datum::None))
        }

        if end == 0 {
            return Ast(
                Rc::from((*(self.0)).clone()),
                Rc::from(Datum::None)
            )
        }

        let Datum::List(ref next) = *self.1 else {
            panic!("index into improper list form")
        };

        if start <= 0 {
            Ast(
                Rc::from((*(self.0)).clone()),
                Rc::from(Datum::List(
                    Rc::from(next.subsl(start - 1, end - 1))))
            )

        } else {
            next.subsl(start - 1, end - 1)
        }
    }

    pub fn len(&self) -> usize {
        let Datum::List(ref next) = *self.1 else {
            return 1
        };
        1 + next.len()
    }
}

impl Iterator for Ast {
    type Item = Rc<Datum>;

    fn next(&mut self) -> Option<Self::Item> {
        if let Datum::List(n) = &*self.1 {
            let tmp_pair = n;
            self.0 = tmp_pair.0.clone();
            self.1 = tmp_pair.1.clone();
            return Some(self.0.clone());
        }

        if let Datum::None = *self.1 {
            return None;
        }

        let tmp = self.1.clone();
        self.0 = Rc::from(Datum::None);
        self.1 = Rc::from(Datum::None);
        return Some(tmp);
    }
}

impl Index<usize> for Ast {
    type Output = Datum;
    fn index(&self, index: usize) -> &Self::Output {
        if index == 0 {
            if let Datum::None = *self.0 {
                panic!("out of bounds indexing into AST")
            } else {
                self.0.as_ref()
            }
        } else {
            let Datum::List(ref next) = *self.1 else {
                panic!("out of bounds indexing into AST")
            };

            next.index(index - 1)
        }
    }
}

impl fmt::Display for Ast {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}", self.0)?;
        let mut cur = self;
        while let Datum::List(next) = &*cur.1 {
            cur = &next;
            write!(f, " {}", cur.0)?;
        }

        if let Datum::None = &*cur.1 {
            write!(f, ")")
        } else {
            write!(f, " . {})", cur.1)
        }
    }
}

impl fmt::Debug for Ast {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "({}", self.0)?;
        let mut cur = self;
        let mut end = 1;
        while let Datum::List(next) = &*cur.1 {
            cur = &next;
            end += 1;
            write!(f, "({} . ", cur.0)?
        }
        write!(f, "{}{}", cur.1, ")".repeat(end))
    }
}