use std::sync::{Arc, RwLock};
use std::collections::BTreeMap;
pub use clojure_reader::edn::Edn;


//#[derive(Debug, Copy, Clone, Default, PartialEq)]
//pub struct Items<'a>(&'a [Item<'a>]);
//impl<'a> Items<'a> {
    //fn iter (&'a self) -> ItemsIterator<'a> {
        //ItemsIterator(0, self.0)
    //}
//}

//pub struct ItemsIterator<'a>(usize, &'a [Item<'a>]);
//impl<'a> Iterator for ItemsIterator<'a> {
    //type Item = &'a Item<'a>;
    //fn next (&mut self) -> Option<Self::Item> {
        //let item = self.1.get(self.0);
        //self.0 += 1;
        //item
    //}
//}

/*

nice but doesn't work without compile time slice concat
(which i guess could be implemeted using an unsafe linked list?)
never done that one before im ny life, might try

use konst::slice_concat;

const fn read <'a> (
    chars: impl Iterator<Item = char>
) -> Result<Range<'a>, ParseError> {
    use Range::*;
    let mut state = Range::Nil;
    let mut tokens: &[Range<'a>] = &[];
    while let Some(c) = chars.next() {
        state = match state {
            // must begin expression
            Nil => match c {
                ' ' => Nil,
                '(' => Exp(&[]),
                ':' => Sym(&[]),
                '1'..'9' => Num(digit(c)),
                'a'..'z' => Key(&[&[c]]),
                _ => return Err(ParseError::Unexpected(c))
            },
            Num(b) => match c {
                ' ' => return Ok(Num(digit(c))),
                '1'..'9' => Num(b*10+digit(c)),
                _ => return Err(ParseError::Unexpected(c))
            }
            Sym([]) => match c {
                'a'..'z' => Sym(&[c]),
                _ => return Err(ParseError::Unexpected(c))
            },
            Sym([b @ ..]) => match c {
                ' ' => return Ok(Sym(&b)),
                'a'..'z' | '0'..'9' | '-' => Sym(&[..b, c]),
                _ => return Err(ParseError::Unexpected(c))
            }
            Key([[b @ ..]]) => match c {
                ' ' => return Ok(Key(&[&b])),
                '/' => Key(&[&b, &[]]),
                'a'..'z' | '0'..'9' | '-' => Key(&[&[..b, c], &[]]),
                _ => return Err(ParseError::Unexpected(c))
            }
            Key([s @ .., []]) => match c {
                'a'..'z' => Key(&[..s, &[c]]),
                _ => return Err(ParseError::Unexpected(c))
            }
            Key([s @ .., [b @ ..]]) => match c {
                '/' => Key([..s, &b, &[]]),
                'a'..'z' | '0'..'9' | '-' => Key(&[..s, &[..b, c]]),
                _ => return Err(ParseError::Unexpected(c))
            }
            // expression must begin with key or symbol
            Exp([]) => match c {
                ' ' => Exp(&[]),
                ')' => return Err(ParseError::Empty),
                ':' => Exp(&[Sym(&[':'])]),
                 c  => Exp(&[Key(&[&[c]])]),
            },

            // expression can't begin with number
            Exp([Num(num)]) => return Err(ParseError::Unexpected(c)),

            // symbol begins with : and lowercase a-z
            Exp([Sym([':'])]) => match c {
                'a'..'z' => Exp(&[Sym(&[':', c])]),
                       _ => return Err(ParseError::Unexpected(c)),
            },

            // any other char is part of symbol until space or )
            Exp([Sym([':', b @ ..])]) => match c {
                ')' => { tokens = &[..tokens, Exp(&[Sym(&[":", ..b])])]; Nil },
                ' ' => Exp(&[Sym(&[':', ..b]), Nil]),
                 c  => Exp(&[Sym(&[':', ..b, c])]),
            },

            // key begins with lowercase a-z
            Exp([Key([])]) => match c {
                'a'..'z' => Exp([Key([[c]])]),
                       _ => return Err(ParseError::Unexpected(c)),
            },

            // any other char is part of key until slash space or )
            Exp([Key([[b @ ..]])]) => match c {
                '/' => Exp(&[Key(&[[..b], []])]),
                ' ' => Exp(&[Key(&[[..b]]), Nil]),
                ')' => { tokens = &[..tokens, Exp(&[Sym(&[":", ..b])])]; Nil },
                 c  => Exp(&[Key(&[[..b, c]])])
            }

            // slash adds new section to key
            Exp([Key([b @ .., []])]) => match c {
                '/' => Exp(&[Key(&[[..b], []])]),
                ' ' => Exp(&[Key(&[[..b]]), Nil]),
                ')' => { tokens = &[..tokens, Exp(&[Sym(&[":", ..b])])]; Nil },
                 c  => Exp(&[Key(&[[..b, c]])])
            }

        }
    }
    Ok(state)
}
*/


/// EDN parsing helper.
#[macro_export] macro_rules! edn {
    ($edn:ident { $($pat:pat => $expr:expr),* $(,)? }) => {
        match $edn { $($pat => $expr),* }
    };
    ($edn:ident in $args:ident { $($pat:pat => $expr:expr),* $(,)? }) => {
        for $edn in $args {
            edn!($edn { $($pat => $expr),* })
        }
    };
}

pub trait FromEdn<C>: Sized {
    const ID: &'static str;
    fn from_edn (context: C, expr: &[Edn<'_>]) ->
        std::result::Result<Self, Box<dyn std::error::Error>>;
}

/// Implements the [FromEdn] trait.
#[macro_export] macro_rules! from_edn {
    ($id:expr => |$context:tt:$Context:ty, $args:ident| -> $T:ty $body:block) => {
        impl FromEdn<$Context> for $T {
            const ID: &'static str = $id;
            fn from_edn <'e> ($context: $Context, $args: &[Edn<'e>]) -> Usually<Self> {
                $body
            }
        }
    }
}