// Copyright (C) 2021-2022 Soni L.
// SPDX-License-Identifier: MIT OR Apache-2.0

use regex::Regex;
use serde::Serialize;

use crate::Predicate;
//use crate::errors::MatchError;

pub(crate) const MAX_CALLS: usize = 250;

//type Matches<'a, 'b, T> = BTreeMap<&'a str, KVPair<'b, T>>;

// TODO: use a builder for this?
/// The constant pool for a pattern.
pub(crate) struct PatternConstants<O: Serialize> {
    // last proto is implicitly the whole pattern.
    pub(crate) protos: Vec<Vec<PatternElement>>,
    // Note that we can borrow these when creating the output map.
    // https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=da26f9175e96273fa0b94971a4e6172f
    pub(crate) strings: Vec<String>,
    pub(crate) regices: Vec<Regex>,
    pub(crate) predicates: Vec<Box<Predicate>>,
    // NOTE these are part of the constant pool and so have lifetime analogous
    // to 'a (consistently used to indicate constant pool lifetime) when used
    // elsewhere. In particular, they can't be yielded by the iterator.
    pub(crate) defs: Vec<O>,
}

impl<O: Serialize> Default for PatternConstants<O> {
    fn default() -> Self {
        Self {
            protos: Default::default(),
            strings: Default::default(),
            regices: Default::default(),
            predicates: Default::default(),
            defs: Default::default(),
        }
    }
}

/// A pattern element.
#[derive(Copy, Clone)]
pub(crate) enum PatternElement {
    Arrow,

    Identifier(usize),

    StringKey(usize, bool),
    RegexKey(usize, bool),
    ParameterKey(usize, bool),
    KeySubtree(usize, bool),
    ValueSubtree(usize, bool),
    ApplyPredicate(usize, bool),

    End
}

//struct Frame<'a, 'b, T: PatternTypes> {
//    //obj: RefOwn<'b, T::Ref, T::Own>,
//    ops: &'a [PatternElement],
//    iar: Option<usize>,
//    depth: usize,
//    path: Vec<Holder<'a, 'b, T>>,
//    in_key: bool,
//}
//
//impl<'a, 'b, T: PatternTypes> Frame<'a, 'b, T> {
//    /// Advances the instruction address register.
//    ///
//    /// # Returns
//    ///
//    /// `true` if successful, `false` otherwise.
//    fn next(&mut self) -> bool {
//        let new = self.iar.map_or(0, |v| v + 1);
//        new < self.ops.len() && {
//            self.iar = Some(new);
//            true
//        }
//    }
//
//    /// Returns the current instruction.
//    fn op(&self) -> PatternElement {
//        self.ops[self.iar.expect("ops[iar]")]
//    }
//
//    /// Rewinds the instruction address register.
//    ///
//    /// # Returns
//    ///
//    /// `true` if successful, `false` otherwise.
//    fn prev(&mut self) -> bool {
//        let new = self.iar.expect("iar").checked_sub(1);
//        new.is_some() && {
//            self.iar = new;
//            true
//        }
//    }
//}
//
///// Stores a single match.
/////
///// See also Holder.
//enum HolderState<'a, 'b, T: PatternTypes> {
//    /// Empty holder, for a key-value pair.
//    EmptyKey,
//    /// Empty holder, for a Matcher and a key-value pair.
//    EmptyKeySubtree,
//    // /// Empty holder, for a Matcher and a value.
//    // EmptyValueSubtree,
//    /// Occupied holder, for a key-value pair..
//    Key(KVPair<'b, T>),
//    /// Occupied holder, for a Matcher and a key-value pair.
//    KeySubtree(Peekable<Matcher<'a, 'b, T>>, KVPair<'b, T>),
//    /// Occupied holder, for a Matcher and a value. The empty variant is
//    /// omitted as it would never be used otherwise.
//    ValueSubtree(Peekable<Matcher<'a, 'b, T>>, RefOwn<'b, T::Ref, T::Own>),
//    /// Occupied holder, for a value. The empty variant is omitted as it would
//    /// never be used otherwise.
//    Value(RefOwn<'b, T::Ref, T::Own>),
//}
//
///// Helper enum for HolderState.
//#[derive(Copy, Clone, Debug, Eq, PartialEq)]
//enum HolderKind {
//    Key,
//    KeySubtree,
//    ValueSubtree,
//    Value
//}
//
////impl<'a, 'b, T: PatternTypes> Clone for HolderState<'a, 'b, T> {
////    fn clone(&self) -> Self {
////        match self {
////            HolderState::EmptyKey => HolderState::EmptyKey,
////            HolderState::EmptySubtree => HolderState::EmptySubtree,
////            HolderState::Key(v) => HolderState::Key(*v),
////            HolderState::KeySubtree(m, v) => HolderState::KeySubtree(m.clone(), *v),
////            HolderState::ValueSubtree(m, v) => HolderState::ValueSubtree(m.clone(), *v),
////            HolderState::Value(v) => HolderState::Value(*v),
////        }
////    }
////}
//
//impl<'a, 'b, T: PatternTypes> HolderState<'a, 'b, T> {
//    #[rustfmt::skip]
//    fn is_empty(&self) -> bool {
//        match self {
//            | HolderState::EmptyKey
//            | HolderState::EmptyKeySubtree
//            //| HolderState::EmptyValueSubtree
//            => true, _ => false
//        }
//    }
//
//    fn has_value(&self) -> bool {
//        !self.is_empty()
//    }
//
//    fn kind(&self) -> HolderKind {
//        match self {
//            | HolderState::EmptyKey
//            | HolderState::Key(_)
//            => HolderKind::Key,
//            | HolderState::EmptyKeySubtree
//            | HolderState::KeySubtree(_, _)
//            => HolderKind::KeySubtree,
//            //| HolderState::EmptyValueSubtree
//            | HolderState::ValueSubtree(_, _)
//            => HolderKind::ValueSubtree,
//            | HolderState::Value(_)
//            => HolderKind::Value,
//        }
//    }
//
//    fn value(&self) -> Option<RefOwn<'b, T::Ref, T::Own>> {
//        match *self {
//            HolderState::Key((_, value)) => Some(value),
//            HolderState::KeySubtree(_, (_, value)) => Some(value),
//            HolderState::ValueSubtree(_, value) => Some(value),
//            HolderState::Value(value) => Some(value),
//            _ => None
//        }
//    }
//
//    fn key(&self) -> Option<RefOwn<'b, T::Ref, T::Own>> {
//        match *self {
//            HolderState::Key((key, _)) => Some(key),
//            HolderState::KeySubtree(_, (key, _)) => Some(key),
//            _ => None
//        }
//    }
//
//    fn pair(&self) -> Option<KVPair<'b, T>> {
//        match *self {
//            HolderState::Key(pair) => Some(pair),
//            HolderState::KeySubtree(_, pair) => Some(pair),
//            _ => None
//        }
//    }
//
//    fn subtree(&mut self) -> Option<&mut Peekable<Matcher<'a, 'b, T>>> {
//        match *self {
//            HolderState::KeySubtree(ref mut subtree, _) => Some(subtree),
//            HolderState::ValueSubtree(ref mut subtree, _) => Some(subtree),
//            _ => None
//        }
//    }
//
//    fn clear(&mut self) {
//        *self = match self.kind() {
//            HolderKind::Key => HolderState::EmptyKey,
//            HolderKind::KeySubtree => HolderState::EmptyKeySubtree,
//            HolderKind::ValueSubtree => unreachable!(), //HolderState::EmptyValueSubtree,
//            HolderKind::Value => unreachable!(),
//        };
//        assert!(self.is_empty());
//    }
//}
//
///// Stores a single match and associated metadata.
/////
///// A single match is generally a key-value pair, but may be a collection of
///// named pairs in the case of subtree matches, or just a value for the initial
///// holder.
//struct Holder<'a, 'b, T: PatternTypes> {
//     name: Option<&'a str>,
//     value: HolderState<'a, 'b, T>,
//     parent: Option<RefOwn<'b, T::Ref, T::Own>>,
//     iterator: Option<Box<dyn Iterator<Item=KVPair<'b, T>> + 'b>>,
//     filters: Vec<Box<dyn (for<'c> Fn(&'c mut HolderState<'a, 'b, T>) -> Result<(), MatchError>) + 'a>>,
//}
//
//impl<'a, 'b, T: PatternTypes> Holder<'a, 'b, T> {
//    fn next(&mut self) -> Result<bool, MatchError> {
//        self.ensure_iterator()?;
//        if let Self {
//            value: ref mut v,
//            iterator: Some(ref mut it),
//            ref filters,
//            ..
//        } = self {
//            // check if we're in a subtree and (not) done.
//            if let Some(matcher) = v.subtree() {
//                if let Some(res) = matcher.peek() {
//                    // report any errors
//                    return res.as_ref().map(|_| true).map_err(|e| e.clone());
//                }
//            }
//            let kind = v.kind();
//            let mut next_v;
//            loop {
//                next_v = match it.next() {
//                    Some(pair) => HolderState::Key(pair),
//                    None => return Ok(false)
//                };
//                for filter in filters {
//                    filter(&mut next_v)?;
//                    if next_v.is_empty() {
//                        break;
//                    }
//                }
//                if next_v.has_value() {
//                    break;
//                }
//            }
//            assert!(next_v.has_value());
//            assert_eq!(next_v.kind(), kind);
//            *v = next_v;
//            Ok(true)
//        } else {
//            unreachable!()
//        }
//    }
//
//    /// Ensure `self.iterator.is_some()`, creating an iterator if necessary.
//    fn ensure_iterator(&mut self) -> Result<(), MatchError> {
//        if self.iterator.is_none() {
//            let iter = T::pairs(self.parent.unwrap());
//            if iter.is_none() {
//                return Err(MatchError::UnsupportedOperation);
//            }
//            self.iterator = iter;
//        }
//        assert!(self.iterator.is_some());
//        Ok(())
//    }
//}
//
//impl<'a, 'b, T: PatternTypes> Default for Holder<'a, 'b, T> {
//    fn default() -> Self {
//        Self {
//            name: Default::default(),
//            value: HolderState::EmptyKey,
//            parent: Default::default(),
//            iterator: Default::default(),
//            filters: Default::default(),
//        }
//    }
//}
//
//pub struct Matcher<'a, 'b, T: PatternTypes> {
//    defs: &'a PatternConstants<T>,
//    frame: Frame<'a, 'b, T>,
//}
//
//// TODO:
////
//// [x] Arrow
//// [x] StringKey
//// [x] RegexKey
//// [x] KeySubtree
//// [x] ValueSubtree
//// [x] Ident
//// [x] Param (untested)
//// [x] ApplyPredicate
//// [x] End
//
///// Helper for `PatternElement::StringKey`.
//fn on_string_key<'a, 'b, T: PatternTypes>(
//    matcher: &mut Matcher<'a, 'b, T>,
//    id: usize,
//    skippable: bool,
//) -> Result<bool, MatchError> {
//    let path = matcher.frame.path.last_mut().unwrap();
//    assert!(path.iterator.is_none());
//    let key = &matcher.defs.strings[id];
//    let iter = T::get(path.parent.unwrap(), RefOwn::Str(key));
//    match iter {
//        Some(None) if !skippable => Err(MatchError::ValidationError),
//        Some(opt) => {
//            path.iterator = Some(Box::new(opt.into_iter()));
//            Ok(true)
//        }
//        None => Err(MatchError::UnsupportedOperation),
//    }
//}
//
///// Helper for `PatternElement::ParameterKey`.
//fn on_parameter_key<'a, 'b, T: PatternTypes>(
//    matcher: &mut Matcher<'a, 'b, T>,
//    id: usize,
//    skippable: bool,
//) -> Result<bool, MatchError> {
//    let path = matcher.frame.path.last_mut().unwrap();
//    assert!(path.iterator.is_none());
//    let key = matcher.defs.defs[id];
//    let iter = T::get(path.parent.unwrap(), RefOwn::Own(key));
//    match iter {
//        Some(None) if !skippable => Err(MatchError::ValidationError),
//        Some(opt) => {
//            path.iterator = Some(Box::new(opt.into_iter()));
//            Ok(true)
//        }
//        None => Err(MatchError::UnsupportedOperation),
//    }
//}
//
///// Helper for `PatternElement::RegexKey`.
//fn on_regex_key<'a, 'b, T: PatternTypes>(
//    matcher: &mut Matcher<'a, 'b, T>,
//    id: usize,
//    skippable: bool,
//) -> Result<bool, MatchError> {
//    matcher.frame.path.last_mut().unwrap().ensure_iterator()?;
//    let re = &matcher.defs.regices[id];
//    let path = matcher.frame.path.last_mut().unwrap();
//    path.filters.push(Box::new(move |value| {
//        let s = T::as_str(value.key().unwrap());
//        match (s.map_or(false, |s| re.is_match(s)), skippable) {
//            (true, _) => Ok(()),
//            (false, true) => {
//                value.clear();
//                Ok(())
//            },
//            (false, false) => Err(MatchError::ValidationError),
//        }
//    }));
//    Ok(true)
//}
//
///// Helper for `PatternElement::KeySubtree`.
//fn on_key_subtree<'a, 'b, T: PatternTypes>(
//    matcher: &mut Matcher<'a, 'b, T>,
//    id: usize,
//    skippable: bool,
//) -> Result<bool, MatchError> {
//    let _ = skippable; // FIXME what should a skippable KeySubtree even do?!
//    matcher.frame.path.last_mut().unwrap().ensure_iterator()?;
//    let defs = matcher.defs;
//    let rlimit: usize = matcher.frame.depth;
//    let path = matcher.frame.path.last_mut().unwrap();
//    assert!(path.value.is_empty());
//    assert_eq!(path.value.kind(), HolderKind::Key);
//    path.value = HolderState::EmptyKeySubtree;
//    path.filters.push(Box::new(move |value| {
//        let key = value.key().unwrap();
//        let mut subtree = Matcher::new(key, defs, id, rlimit)?.peekable();
//        match subtree.peek() {
//            Some(&Ok(_)) => {
//                *value = HolderState::KeySubtree(subtree, value.pair().unwrap());
//                Ok(())
//            },
//            Some(&Err(ref e)) => {
//                Err(e.clone())
//            },
//            None => {
//                value.clear();
//                Ok(())
//            }
//        }
//    }));
//    Ok(true)
//}
//
//const DUMMY_OPS: &'static [PatternElement] = &[];
//
//impl<'a, 'b, T: PatternTypes> Matcher<'a, 'b, T> {
//    pub(crate) fn new(obj: RefOwn<'b, T::Ref, T::Own>, defs: &'a PatternConstants<T>, proto: usize, rlimit: usize) -> Result<Self, MatchError> {
//        let ops: &[_] = &defs.protos[proto];
//        Self::with_ops(obj, defs, ops, rlimit)
//    }
//
//    /// Constructs a Matcher that yields a single dummy result.
//    fn with_ops(obj: RefOwn<'b, T::Ref, T::Own>, defs: &'a PatternConstants<T>, ops: &'a [PatternElement], rlimit: usize) -> Result<Self, MatchError> {
//        let depth = rlimit.checked_sub(1).ok_or(MatchError::StackOverflow)?;
//        Ok(Self {
//            defs: defs,
//            frame: Frame {
//                //obj: obj,
//                ops: ops,
//                iar: None,
//                depth: depth,
//                path: {
//                    let mut holder = Holder::default();
//                    holder.value = HolderState::Value(obj);
//                    holder.iterator = Some(Box::new(std::iter::empty()));
//                    vec![holder]
//                },
//                in_key: false,
//            },
//        })
//    }
//
//    fn on_in_key(&mut self) -> Result<bool, MatchError> {
//        match self.frame.op() {
//            PatternElement::End => {
//                let path = self.frame.path.last_mut().unwrap();
//                if path.next()? {
//                    Ok(false)
//                } else {
//                    drop(path);
//                    self.frame.path.pop().unwrap();
//                    // stop at previous End, or start of frame
//                    while self.frame.prev() {
//                        if matches!(self.frame.op(), PatternElement::End) {
//                            break;
//                        }
//                    }
//                    // is start of frame?
//                    if !self.frame.prev() {
//                        self.frame.path.clear();
//                    }
//                    Ok(true)
//                }
//            },
//            PatternElement::ApplyPredicate(id, skippable) => {
//                // failing on T::get() is already handled, but we may need a
//                // T::pairs(). construct it here.
//                self.frame.path.last_mut().unwrap().ensure_iterator()?;
//                let pred = &self.defs.predicates[id];
//                let path = self.frame.path.last_mut().unwrap();
//                path.filters.push(Box::new(move |value| {
//                    match (pred(value.value().unwrap()), skippable) {
//                        (true, _) => Ok(()),
//                        (false, true) => {
//                            value.clear();
//                            Ok(())
//                        },
//                        (false, false) => Err(MatchError::ValidationError),
//                    }
//                }));
//                Ok(true)
//            },
//            PatternElement::StringKey(id, skippable) => {
//                on_string_key(self, id, skippable)
//            },
//            PatternElement::ParameterKey(id, skippable) => {
//                on_parameter_key(self, id, skippable)
//            },
//            PatternElement::RegexKey(id, skippable) => {
//                on_regex_key(self, id, skippable)
//            },
//            PatternElement::KeySubtree(id, skippable) => {
//                on_key_subtree(self, id, skippable)
//            },
//            _ => unreachable!("on_in_key")
//        }
//    }
//
//    fn on_not_in_key(&mut self) -> Result<bool, MatchError> {
//        match self.frame.op() {
//            PatternElement::Arrow => {
//                // this *should* always pass.
//                assert!(self.frame.path.last().unwrap().iterator.is_some());
//                let mut holder = Holder::default();
//                holder.parent = self.frame.path.last().unwrap().value.value();
//                assert!(holder.parent.is_some());
//                self.frame.path.push(holder);
//                Ok(false)
//            },
//            PatternElement::Identifier(id) => {
//                let name = self.defs.strings.get(id).map(|s| &**s);
//                let path = self.frame.path.last_mut().unwrap();
//                path.name = name;
//                assert!(path.iterator.is_none());
//                // we don't actually create the iterator here,
//                // as we may still wanna use T::get() instead.
//                Ok(true)
//            },
//            PatternElement::ApplyPredicate(id, skippable) => {
//                assert!(self.frame.path.len() == 1);
//                let pred = &self.defs.predicates[id];
//                let value = self.frame.path.last().unwrap().value.value();
//                match (pred(value.unwrap()), skippable) {
//                    (true, _) => Ok(false),
//                    (false, true) => {
//                        self.frame.path.clear();
//                        // any Ok(_) will do
//                        Ok(false)
//                    },
//                    (false, false) => Err(MatchError::ValidationError),
//                }
//            },
//            PatternElement::StringKey(id, skippable) => {
//                on_string_key(self, id, skippable)
//            },
//            PatternElement::ParameterKey(id, skippable) => {
//                on_parameter_key(self, id, skippable)
//            },
//            PatternElement::RegexKey(id, skippable) => {
//                on_regex_key(self, id, skippable)
//            },
//            PatternElement::KeySubtree(id, skippable) => {
//                on_key_subtree(self, id, skippable)
//            },
//            PatternElement::ValueSubtree(id, skippable) => {
//                let value = self.frame.path.last().unwrap().value.value().unwrap();
//                let mut subtree = Matcher::new(
//                    value,
//                    self.defs,
//                    id,
//                    self.frame.depth
//                )?.peekable();
//                let mut dummy = Matcher::with_ops(
//                    value,
//                    self.defs,
//                    DUMMY_OPS,
//                    self.frame.depth
//                )?.peekable();
//                // may panic.
//                let peeked = subtree.peek();
//                // shouldn't panic.
//                let _ = dummy.peek();
//                // push Holder after peek.
//                self.frame.path.push(Holder::default());
//                let mut holder = self.frame.path.last_mut().unwrap();
//                holder.parent = Some(value);
//                holder.iterator = Some(Box::new(std::iter::empty()));
//                match peeked {
//                    None if skippable => {
//                        holder.value = HolderState::ValueSubtree(dummy, value);
//                        Ok(true)
//                    },
//                    Some(&Ok(_)) | None => {
//                        drop(peeked);
//                        holder.value = HolderState::ValueSubtree(subtree, value);
//                        Ok(true)
//                    },
//                    Some(&Err(ref e)) => {
//                        Err(e.clone())
//                    },
//                }
//            },
//            _ => unreachable!("on_not_in_key")
//        }
//    }
//
//    fn collect_results(&mut self) -> Matches<'a, 'b, T> {
//        let mut res: Matches<'a, 'b, T> = Default::default();
//        for holder in &mut self.frame.path {
//            // make sure it's not empty.
//            assert!(holder.value.has_value());
//            // handle subtrees.
//            if let Some(matcher) = holder.value.subtree() {
//                if let Some(matches) = matcher.next() {
//                    // NOTE: we have checked these already.
//                    // (and if we haven't, that's a bug.)
//                    res.extend(matches.unwrap());
//                }
//            }
//            // handle pairs.
//            if let Some(pair) = holder.value.pair() {
//                if let Some(name) = holder.name {
//                    res.insert(name, pair);
//                }
//            }
//        }
//        res
//    }
//
//    fn on_end(&mut self) -> (bool, Matches<'a, 'b, T>) {
//        match self.frame.op() {
//            PatternElement::End => {
//                assert!(!self.frame.path.last().expect("path").value.is_empty());
//                let res = self.collect_results();
//                if !self.frame.prev() {
//                    // NOTE: frame.prev() must always be called, even if this
//                    // gets replaced with debug_assert!() in the future.
//                    assert!(false, "frame.prev()");
//                }
//                (true, res)
//            }
//            PatternElement::ApplyPredicate {..} => {
//                assert!(!self.frame.in_key);
//                let res = self.collect_results();
//                self.frame.path.clear();
//                (false, res)
//            }
//            _ => unreachable!("on_end")
//        }
//    }
//}
//
//impl<'a, 'b, T: PatternTypes> Iterator for Matcher<'a, 'b, T> {
//    type Item = Result<BTreeMap<&'a str, KVPair<'b, T>>, MatchError>;
//
//    fn next(&mut self) -> Option<Self::Item> {
//        if self.frame.ops.is_empty() {
//            if !self.frame.path.is_empty() {
//                self.frame.path.clear();
//                return Some(Ok(Default::default()));
//            }
//        }
//        while !self.frame.path.is_empty() {
//            if !self.frame.next() {
//                let (in_key, res) = self.on_end();
//                self.frame.in_key = in_key;
//                return Some(Ok(res));
//            } else {
//                let in_key = if self.frame.in_key {
//                    self.on_in_key()
//                } else {
//                    self.on_not_in_key()
//                };
//                match in_key {
//                    Ok(in_key) => self.frame.in_key = in_key,
//                    Err(e) => {
//                        self.frame.path.clear();
//                        return Some(Err(e))
//                    },
//                }
//            }
//        }
//        None
//    }
//}