//! optional syntax tree nodes ([`Option`], [`Exists`])
use std::borrow::Cow;
use std::marker::PhantomData;

use crate::syntax::{Epsilon, Metadata, MetadataBuilder, Result as SynResult};
use crate::{Lexicon, Parser, Produce, Production, ToSpan};

use super::Node;

// Option<T> => T | epsilon
#[doc(hidden)]
pub struct OptionProd<T: Production>(PhantomData<T>);

impl<T: Production> Production for OptionProd<T> {
    type L = T::L;
    #[inline]
    fn debug() -> Cow<'static, str> {
        let inner = T::debug();
        if let Some(rest) = inner.strip_prefix('(') {
            if let Some(inner) = rest.strip_suffix(")+") {
                return Cow::Owned(format!("({})*", inner));
            }
            if let Some(inner) = rest.strip_suffix("]+") {
                return Cow::Owned(format!("({}]*", inner));
            }
        }
        Cow::Owned(format!("({})?", T::debug()))
    }

    fn register(meta: &mut MetadataBuilder<Self::L>) {
        crate::register_union!(meta, T, Epsilon<T::L>)
    }
}

/// Node that stores an optional subtree
#[derive(Node, ToSpan, Clone, PartialEq)]
#[doc(alias = "Option")]
pub struct Optional<T: Produce>(pub Node<Option<T>>);

impl<T: std::fmt::Debug + Produce> std::fmt::Debug for Optional<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.0.value {
            Some(node) => f.debug_tuple("Some").field(&node).finish(),
            None => f.debug_tuple("None").field(&self.0.span).finish(),
        }
    }
}

impl<T: Produce> Produce for Optional<T> {
    type Prod = OptionProd<T::Prod>;
    fn produce(
        parser: &mut Parser<'_, <Self::Prod as Production>::L>,
        meta: &Metadata<<Self::Prod as Production>::L>,
    ) -> SynResult<Self, <Self::Prod as Production>::L> {
        produce_option(parser, meta, |x| x).map(Self::from)
    }
}

/// Node that stores if an optional subtree is produced
#[derive(Node, ToSpan, Clone, PartialEq)]
pub struct Exists<T: Produce>(Node<bool>, PhantomData<T>);

impl<T: Produce> std::fmt::Debug for Exists<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}

impl<T: Produce> Produce for Exists<T> {
    type Prod = OptionProd<T::Prod>;
    fn produce(
        parser: &mut Parser<'_, <Self::Prod as Production>::L>,
        meta: &Metadata<<Self::Prod as Production>::L>,
    ) -> SynResult<Self, <Self::Prod as Production>::L> {
        produce_option(parser, meta, |x: Option<T>| x.is_some()).map(Self::from)
    }
}
fn produce_option<T, O, F: FnOnce(Option<T>) -> O, L: Lexicon>(
    parser: &mut Parser<'_, L>,
    meta: &Metadata<L>,
    f: F,
) -> SynResult<Node<O>, L>
where
    T: Produce + ToSpan,
    T::Prod: Production<L = L>,
{
    let token = parser.peek_token_src();
    if token.is_none() {
        // produces epsilon
        return SynResult::Success(Node::new(parser.current_span_empty(), f(None)));
    }
    let first = meta.first.get(&T::prod_id());
    if !first.contains(token) {
        // produces epsilon
        return SynResult::Success(Node::new(parser.current_span_empty(), f(None)));
    }
    // if parse fails, delay to parent to panic
    match T::produce(parser, meta) {
        SynResult::Success(t) => SynResult::Success(Node::new(t.span(), f(Some(t)))),
        SynResult::Recovered(t, error) => {
            SynResult::Recovered(Node::new(t.span(), f(Some(t))), error)
        }
        SynResult::Panic(error) => {
            SynResult::Recovered(Node::new(parser.current_span_empty(), f(None)), error)
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::prelude::*;
    use crate::GrammarError;

    use crate::lex::Token;
    use crate::test::prelude::*;
    use crate::test::MathTokenType as T;
    use crate::test::{Ident, OpAdd};

    #[derive_syntax]
    #[teleparse(root)]
    #[derive(Debug, PartialEq, Clone)]
    struct OptIdent(tp::Option<Ident>);

    #[test]
    fn test_none() -> Result<(), GrammarError> {
        let t = OptIdent::parse("+")?.unwrap();
        let t_str = format!("{:?}", t.0);
        assert_eq!(t_str, "None(0)");
        assert_eq!(t, OptIdent(Node::new(0..0, None).into()));

        Ok(())
    }

    #[test]
    fn test_some() {
        let t = OptIdent::parse("a").unwrap().unwrap();
        let t_str = format!("{:?}", t.0);
        assert_eq!(t_str, "Some(token Ident(0..1))");
        assert_eq!(
            t,
            OptIdent(Node::new(0..1, Some(Ident(Token::new(0..1, T::Ident)))).into())
        );
    }

    #[test]
    fn test_use_as_option() -> Result<(), GrammarError> {
        let t = OptIdent::parse("a")?.unwrap();
        assert!(t.0.is_some());

        Ok(())
    }

    #[derive_syntax]
    #[teleparse(root, no_test)]
    struct Seq(tp::Option<OpAdd>, OpAdd);

    #[test]
    fn test_seq_not_ll1() {
        assert_not_ll1!(
            Seq,
            GrammarError::FirstFollowSeqConflict(
                "Seq".to_string(),
                "(+)?".to_string(),
                "+".to_string(),
                "\"+\"".to_string()
            )
        );
    }

    #[derive_syntax]
    #[teleparse(root, no_test)]
    struct Nested(super::Optional<super::Optional<Ident>>);

    #[test]
    fn test_nested_not_ll1() {
        assert_not_ll1!(
            Nested,
            GrammarError::FirstFirstConflict(
                "((Ident)?)?".to_string(),
                "(Ident)?".to_string(),
                "()".to_string(),
                "<empty>".to_string(),
            )
        );
    }

    #[derive_syntax]
    #[teleparse(root)]
    #[derive(Debug, PartialEq, Clone)]
    struct ExistIdent(tp::Exists<Ident>);

    #[test]
    #[allow(clippy::bool_assert_comparison)]
    fn parse_exist() {
        let t = ExistIdent::parse("a").unwrap().unwrap();
        let t_str = format!("{:?}", t.0);
        assert_eq!(t_str, "0..1 => true");
        assert_eq!(t, ExistIdent(Node::new(0..1, true).into()));
        assert_eq!(*t.0, true);

        let t = ExistIdent::parse("+").unwrap().unwrap();
        let t_str = format!("{:?}", t.0);
        assert_eq!(t_str, "0 => false");
        assert_eq!(t, ExistIdent(Node::new(0..0, false).into()));
        assert_eq!(*t.0, false);
    }
}