//#![feature(adt_const_params)]
//#![feature(type_alias_impl_trait)]
#![feature(if_let_guard)]
#![feature(impl_trait_in_fn_trait_return)]
#![feature(const_precise_live_drops)]
extern crate const_panic;
use const_panic::PanicFmt;
use std::fmt::Debug;
pub(crate) use ::{
    std::sync::Arc,
    std::error::Error,
    konst::iter::for_each,
    konst::string::{str_from, str_range, char_indices},
    thiserror::Error,
    tengri_core::*
};
pub(crate) use self::DslError::*;
mod dsl_conv; pub use self::dsl_conv::*;
#[cfg(test)] mod dsl_test;
// Trait that designates any string-like as potentially parsable DSL.
flex_trait!(Dsl: Debug + Send + Sync + Sized {
    fn src (&self) -> DslPerhaps<&str> { unreachable!("Dsl::src default impl") }
});
impl<'x> Dsl for &'x str {
    fn src (&self) -> DslPerhaps<&str> { Ok(Some(self)) }
}
impl Dsl for Arc<str> {
    fn src (&self) -> DslPerhaps<&str> { Ok(Some(self.as_ref())) }
}
impl<D: Dsl> Dsl for Option<D> {
    fn src (&self) -> DslPerhaps<&str> {Ok(if let Some(dsl) = self { dsl.src()? } else { None })}
}
impl<D: Dsl> Dsl for Result<D, DslError> {
    fn src (&self) -> DslPerhaps<&str> {match self {Ok(dsl) => Ok(dsl.src()?), Err(e) => Err(*e)}}
}
/// DSL-specific result type.
pub type DslResult<T> = Result<T, DslError>;
/// DSL-specific optional result type.
pub type DslPerhaps<T> = Result<Option<T>, DslError>;
/// DSL-specific error codes.
#[derive(Error, Debug, Copy, Clone, PartialEq, PanicFmt)]
pub enum DslError {
    #[error("parse failed: not implemented")]
    Unimplemented,
    #[error("parse failed: empty")]
    Empty,
    #[error("parse failed: incomplete")]
    Incomplete,
    #[error("parse failed: unexpected character '{0}'")]
    Unexpected(char, Option<usize>, Option<&'static str>),
    #[error("parse failed: error #{0}")]
    Code(u8),
    #[error("end reached")]
    End
}
pub const fn peek (src: &str) -> DslPerhaps<&str> {
    Ok(Some(if let Ok(Some(expr)) = expr_peek(src) { expr } else
            if let Ok(Some(word)) = word_peek(src) { word } else
            //if let Ok(Some(num))  = num_peek(src)  { num  } else
            if let Ok(Some(text)) = text_peek(src) { text } else
            if let Err(e) = no_trailing_non_space(src, 0, Some("peek")) { return Err(e) }
            else { return Ok(None) }))
}
pub const fn seek (src: &str) -> DslPerhaps<(usize, usize)> {
    Ok(Some(if let Ok(Some(expr)) = expr_seek(src) { expr } else
            if let Ok(Some(word)) = word_seek(src) { word } else
            //if let Ok(Some(num))  = num_seek(src)  { num  } else
            if let Ok(Some(text)) = text_seek(src) { text } else
            if let Err(e) = no_trailing_non_space(src, 0, Some("seek")) { return Err(e) }
            else { return Ok(None) }))
}
pub const fn peek_tail (src: &str) -> DslPerhaps<&str> {
    match seek(src) {
        Err(e) => Err(e),
        Ok(None) => Ok(None),
        Ok(Some((start, length))) => {
            let tail = str_range(src, start + length, src.len());
            for_each!((_i, c) in char_indices(tail) => if !is_space(c) { return Ok(Some(tail)) });
            Ok(None)
        },
    }
}
pub const fn expr_peek_inner (src: &str) -> DslPerhaps<&str> {
    match expr_peek(src) {
        Ok(Some(peeked)) => {
            let len = peeked.len();
            let start = if len > 0 { 1 } else { 0 };
            Ok(Some(str_range(src, start, start + len.saturating_sub(2))))
        },
        e => e
    }
}
pub const fn expr_peek_inner_only (src: &str) -> DslPerhaps<&str> {
    match expr_seek(src) {
        Err(e) => Err(e),
        Ok(None) => Ok(None),
        Ok(Some((start, length))) => {
            if let Err(e) = no_trailing_non_space(src, start + length, Some("expr_peek_inner_only")) {
                Err(e)
            } else {
                let peeked = str_range(src, start, start + length);
                let len = peeked.len();
                let start = if len > 0 { 1 } else { 0 };
                Ok(Some(str_range(peeked, start, start + len.saturating_sub(2))))
            }
        },
    }
}
pub const fn is_space (c: char) -> bool {
    matches!(c, ' '|'\n'|'\r'|'\t')
}
pub const fn no_trailing_non_space (
    src: &str, offset: usize, context: Option<&'static str>
) -> DslResult<()> {
    Ok(for_each!((i, c) in char_indices(str_range(src, offset, src.len())) => if !is_space(c) {
        return Err(Unexpected(c, Some(offset + i), if let Some(context) = context {
            Some(context)
        } else {
            Some("trailing non-space")
        }))
    }))
}
pub const fn is_word_char (c: char) -> bool {
    matches!(c, 'a'..='z'|'A'..='Z'|'0'..='9'|'-'|'/'|'@'|':')
}
pub const fn is_word_end (c: char) -> bool { is_space(c) || is_expr_end(c) }
pub const fn is_text_start (c: char) -> bool { matches!(c, '"') }
pub const fn is_text_end (c: char) -> bool { matches!(c, '"') }
pub const fn is_expr_start (c: char) -> bool { c == '(' }
pub const fn is_expr_end (c: char) -> bool { c == ')' }
pub const fn is_digit (c: char) -> bool { matches!(c, '0'..='9') }
pub const fn to_number (digits: &str) -> Result<usize, DslError> {
    let mut iter = char_indices(digits);
    let mut value = 0;
    while let Some(((_, c), next)) = iter.next() {
        match to_digit(c) {
            Ok(digit) => value = 10 * value + digit,
            Err(e) => return Err(e),
        }
        iter = next;
    }
    Ok(value)
}
pub const fn to_digit (c: char) -> Result<usize, DslError> {
    Ok(match c {
        '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
        '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
        _ => return Err(Unexpected(c, None, Some("parse digit")))
    })
}
#[macro_export] macro_rules! dsl_type (($T:ident { $($trait:tt)* } {
    pub const fn $peek:ident      $($_1:tt)?;
    pub const fn $peek_only:ident $($_2:tt)?;
    pub const fn $seek:ident      $($_3:tt)?;
    pub const fn $seek_start:ident  ($source1:ident) $body1:block
    pub const fn $seek_length:ident ($source2:ident) $body2:block
})=>{
    pub trait $T: Dsl { $($trait)* }
    impl<D: Dsl> $T for D {}
    pub const fn $seek_start  ($source1: &str) -> DslPerhaps<usize> $body1
    pub const fn $seek_length ($source2: &str) -> DslPerhaps<usize> $body2
    /// Find a start and length corresponding to a syntax token.
    pub const fn $seek (source: &str) -> DslPerhaps<(usize, usize)> {
        match $seek_start(source) {
            Err(e) => Err(e),
            Ok(None) => Ok(None),
            Ok(Some(start)) => match $seek_length(str_from(source, start)) {
                Ok(Some(length)) => Ok(Some((start, length))),
                Ok(None) => Ok(None),
                Err(e) => Err(e),
            },
        }
    }
    /// Find a slice corrensponding to a syntax token.
    pub const fn $peek (source: &str) -> DslPerhaps<&str> {
        match $seek(source) {
            Err(e) => Err(e),
            Ok(None) => Ok(None),
            Ok(Some((start, length))) => Ok(Some(str_range(source, start, start + length))),
        }
    }
    /// Find a slice corrensponding to a syntax token
    /// but return an error if it isn't the only thing
    /// in the source.
    pub const fn $peek_only (source: &str) -> DslPerhaps<&str> {
        match $seek(source) {
            Err(e) => Err(e),
            Ok(None) => Ok(None),
            Ok(Some((start, length))) => {
                if let Err(e) = no_trailing_non_space(source, start + length, Some("peek_only")) {
                    Err(e)
                } else {
                    Ok(Some(str_range(source, start, start + length)))
                }
            }
        }
    }
});

dsl_type!(DslWord {
    fn word (&self) -> DslPerhaps<&str> {ok_flat(self.src()?.map(word_peek_only))}
} {
    pub const fn word_peek      [generated];
    pub const fn word_peek_only [generated];
    pub const fn word_seek      [generated];
    pub const fn word_seek_start (src) {
        for_each!((i, c) in char_indices(src) => if
            is_word_char(c)  { return Ok(Some(i)) } else
            if !is_space(c) { return Err(Unexpected(c, Some(i), Some("word_seek_start"))) });
        Ok(None)
    }
    pub const fn word_seek_length (src) {
        for_each!((i, c) in char_indices(src) => if !is_word_char(c) { return Ok(Some(i)) });
        Ok(Some(src.len()))
    }
});

dsl_type!(DslText {
    fn text (&self) -> DslPerhaps<&str> { ok_flat(self.src()?.map(text_peek_only)) }
} {
    pub const fn text_peek      [generated];
    pub const fn text_peek_only [generated];
    pub const fn text_seek      [generated];
    pub const fn text_seek_start (src) {
        for_each!((i, c) in char_indices(src) =>
            if is_text_start(c) { return Ok(Some(i)) } else
            if !is_space(c)     { return Err(Unexpected(c, Some(i), None)) });
        Ok(None)
    }
    pub const fn text_seek_length (src) {
        for_each!((i, c) in char_indices(src) =>
            if is_text_end(c) { return Ok(Some(i)) });
        Ok(None)
    }
});

dsl_type!(DslExpr {
    fn expr  (&self) -> DslPerhaps<&str> {ok_flat(self.src()?.map(expr_peek_inner_only))}
    fn head (&self) -> DslPerhaps<&str> {ok_flat(self.src()?.map(peek))}
    fn tail (&self) -> DslPerhaps<&str> {ok_flat(self.src()?.map(peek_tail))}
    /// my other car is a cdr :<
    fn each (&self, mut cb: impl FnMut(&str)->Usually<()>) -> Usually<()> {
        Ok(if let Some(head) = self.head()? {
            cb(head)?;
            if let Some(tail) = self.tail()? {
                tail.each(cb)?;
            }
        })
    }
} {
    pub const fn expr_peek      [generated];
    pub const fn expr_peek_only [generated];
    pub const fn expr_seek      [generated];
    pub const fn expr_seek_start (src) {
        for_each!((i, c) in char_indices(src) =>
            if is_expr_start(c) { return Ok(Some(i)) } else
            if !is_space(c) { return Err(Unexpected(c, Some(i), Some("expected expression start"))) });
        Ok(None)
    }
    pub const fn expr_seek_length (src) {
        let mut depth = 0;
        for_each!((i, c) in char_indices(src) =>
            if is_expr_start(c) { depth += 1; } else
            if is_expr_end(c) {
                if depth == 0 {
                    return Err(Unexpected(c, Some(i), Some("expected expression end")))
                } else if depth == 1 {
                    return Ok(Some(i + 1))
                } else {
                    depth -= 1;
                }
            });
        Err(Incomplete)
    }
});

fn ok_flat <T> (x: Option<DslPerhaps<T>>) -> DslPerhaps<T> {
    Ok(x.transpose()?.flatten())
}

/// Define a DSL namespace that provides values to words and expressions.
#[macro_export] macro_rules! dsl_ns (
    // Special form for numeric types
    (num |$state:ident : $State: ty| $($($num:lifetime)? $Type:ty $(=> { $(
        $pat:tt => $body:expr
    ),* $(,)? })?;)+) => {
        $(dsl_ns!(num |$state: $State| -> $($num)? $Type { $( $($pat => $body),* )? });)+
    };
    // Special form for numeric types
    (num |$state:ident : $State: ty| -> $Type:ty { $( $pat:tt => $body:expr ),* $(,)? }) => {
        impl<'t> DslNs<'t, $Type> for $State {
            const WORDS: DslNsMap<'t, fn (&'t $State)->Perhaps<$Type>> =
                DslNsMap::new(&[$(dsl_ns!{@word ($state: $State) -> $Type { $pat => $body }}),*]);
            const EXPRS: DslNsMap<'t, fn (&'t $State, &str)->Perhaps<$Type>> =
                DslNsMap::new(&[$(dsl_ns!{@exp ($state: $State) -> $Type { $pat => $body }}),*]);
            fn from <D: Dsl> (&'t self, dsl: D) -> Perhaps<$Type> {
                if let Ok(Some(src)) = dsl.src() {
                    if let Ok(num) = to_number(src) {
                        Ok(Some(num as $Type))
                    } else if let Ok(Some(src)) = src.word() {
                        self.from_word(src)
                    } else {
                        self.from_expr(src)
                    }
                } else {
                    Ok(None)
                }
            }
        }
    };
    // A namespace may resolve one or more types.
    (|$state:ident : $State: ty| $($Type:ty $(=> { $( $pat:tt => $body:expr ),* $(,)? })? ;)+) => {
        $(dsl_ns!(|$state: $State| -> $Type { $( $($pat => $body),* )? });)+
    };
    // Regular form for single type
    (|$state:ident : $State: ty| -> $Type:ty { $( $pat:tt => $body:expr ),* $(,)? }) => {
        impl<'t> DslNs<'t, $Type> for $State {
            const WORDS: DslNsMap<'t, fn (&'t $State)->Perhaps<$Type>> =
                DslNsMap::new(&[$(dsl_ns!{@word ($state: $State) -> $Type { $pat => $body }}),*]);
            const EXPRS: DslNsMap<'t, fn (&'t $State, &str)->Perhaps<$Type>> =
                DslNsMap::new(&[$(dsl_ns!{@exp ($state: $State) -> $Type { $pat => $body }}),*]);
        }
    };
    // Symbols only.
    (@word ($state:ident: $State:ty) -> $Type:ty {
        $word:literal => $body:expr
    }) => {
        ($word, |$state|Ok(Some($body)))
    };
    // Expression handlers only.
    (@exp ($state:ident: $State:ty) -> $Type:ty {
        ($head:literal $(,$arg:ident:$ty:ty)* $(,)*) => $body:expr
    }) => { ($head, |$state, tail: &str|{
        $(
            let head = tail.head()?.unwrap_or_default();
            let tail = tail.tail()?.unwrap_or_default();
            let $arg: $ty = if let Some(arg) = $state.from(&head)? {
                arg
            } else {
                return Err(format!("{}: missing argument: {} ({}); got: {tail}",
                    $head,
                    stringify!($arg),
                    stringify!($Type),
                ).into())
            };
        )*
        Ok(Some($body))
    }) };
    // Nothing else in symbols.
    (@word ($state:ident: $State:ty) -> $Type:ty { $pat:tt => $body:expr }) => {
        ("", |_|Ok(None)) // FIXME don't emit at all
    };
    // Nothing else in expression handlers.
    (@exp ($state:ident: $State:ty) -> $Type:ty { $pat:tt => $body:expr }) => {
        ("", |_, _|Ok(None)) // FIXME don't emit at all
    };
);

pub trait DslNs<'t, T: 't>: 't {
    /// Known symbols.
    const WORDS: DslNsMap<'t, fn (&'t Self)->Perhaps<T>> = DslNsMap::new(&[]);
    /// Known expressions.
    const EXPRS: DslNsMap<'t, fn (&'t Self, &str)->Perhaps<T>> = DslNsMap::new(&[]);
    /// Resolve an expression or symbol.
    fn from <D: Dsl> (&'t self, dsl: D) -> Perhaps<T> {
        if let Ok(Some(src)) = dsl.src() {
            if let Ok(Some(src)) = src.word() {
                self.from_word(src)
            } else {
                self.from_expr(src)
            }
        } else {
            Ok(None)
        }
    }
    /// Resolve a symbol if known.
    fn from_word <D: Dsl> (&'t self, dsl: D) -> Perhaps<T> {
        if let Some(dsl) = dsl.word()? {
            for (word, get) in Self::WORDS.0 { if dsl == *word { return get(self) } }
        }
        return Ok(None)
    }
    /// Resolve an expression if known.
    fn from_expr <D: Dsl> (&'t self, dsl: D) -> Perhaps<T> {
        if let Some(head) = dsl.expr().head()? {
            for (key, value) in Self::EXPRS.0.iter() {
                if head == *key {
                    return value(self, dsl.expr().tail()?.unwrap_or(""))
                }
            }
        }
        return Ok(None)
    }
}

/// Namespace mapping.
#[derive(Debug)]
pub struct DslNsMap<'t, T: Debug + 't>(pub &'t [(&'t str, T)]);
impl<'t, T: Debug + 't> DslNsMap<'t, T> {
    /// Populate a namespace with pre-existing values.
    pub const fn new (data: &'t [(&'t str, T)]) -> Self { Self(data) /* TODO a search trie */ }
}