/*
 * Datafu - Rust library for extracting data from object graphs.
 * Copyright (C) 2021  Soni L.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

pub mod errors;
mod parser;
mod pattern;
mod vm;

pub use pattern::Pattern;

// TODO replace with GATs
/// A borrowed or owned value of various types.
pub enum RefOwn<'b, T: ?Sized, U> {
    /// Borrowed T.
    Ref(&'b T),
    /// Borrowed string.
    Str(&'b str),
    /// Owned U.
    Own(U),
}

impl<'b, T, U> PartialEq for RefOwn<'b, T, U> 
where
    T: ?Sized + PartialEq<T> + PartialEq<U> + PartialEq<str>,
    U: PartialEq<T> + PartialEq<U> + PartialEq<str>,
    str: PartialEq<T> + PartialEq<U> + PartialEq<str>
{
    fn eq(&self, other: &Self) -> bool {
        match (self, other) {
            (RefOwn::Ref(l), RefOwn::Ref(r)) => l.eq(r),
            (RefOwn::Own(l), RefOwn::Own(r)) => l.eq(r),
            (RefOwn::Str(l), RefOwn::Str(r)) => l.eq(r),
            (RefOwn::Ref(l), RefOwn::Own(r)) => PartialEq::eq(*l, r),
            (RefOwn::Own(l), RefOwn::Str(r)) => PartialEq::eq(l, *r),
            (RefOwn::Str(l), RefOwn::Ref(r)) => l.eq(r),
            (RefOwn::Ref(l), RefOwn::Str(r)) => l.eq(r),
            (RefOwn::Own(l), RefOwn::Ref(r)) => PartialEq::eq(l, *r),
            (RefOwn::Str(l), RefOwn::Own(r)) => PartialEq::eq(*l, r),
        }
    }
}

impl<'b, T: ?Sized, U: Copy> Copy for RefOwn<'b, T, U> {
}

impl<'b, T: ?Sized, U: Clone> Clone for RefOwn<'b, T, U> {
    fn clone(&self) -> Self {
        match self {
            RefOwn::Ref(r) => RefOwn::Ref(r),
            RefOwn::Str(r) => RefOwn::Str(r),
            RefOwn::Own(v) => RefOwn::Own(v.clone()),
        }
    }
}

pub type KVPair<'b, T> = (RefOwn<'b, <T as PatternTypes>::Ref, <T as PatternTypes>::Own>, RefOwn<'b, <T as PatternTypes>::Ref, <T as PatternTypes>::Own>);

impl<'b, T, U> From<&'b T> for RefOwn<'b, T, U> {
    fn from(x: &'b T) -> RefOwn<'b, T, U> {
        RefOwn::Ref(x)
    }
}

// TODO investigate if this should be PatternTypes: Default
/// Defines the types and operations used for matching.
pub trait PatternTypes {
    /// The borrowed type.
    type Ref: ?Sized;

    // TODO replace with GATs.
    // TODO potentially relax with Clone?
    /// The owned type.
    type Own: Copy + 'static;

    /// Returns an iterator over key-value pairs contained within an item, or
    /// None if this operation is unsupported for the given value.
    fn pairs<'b>(
        item: RefOwn<'b, Self::Ref, Self::Own>
    ) -> Option<Box<dyn Iterator<Item=KVPair<'b, Self>> + 'b>> {
        // TODO remove these default impls that only exist for testing purposes
        let x = None;
        Some(Box::new(x.into_iter()))
    }

    /// Returns an optional key-value pair keyed by the given key, or None if
    /// this operation is unsupported for the given value.
    fn get<'a, 'b>(
        item: RefOwn<'b, Self::Ref, Self::Own>,
        key: RefOwn<'a, Self::Ref, Self::Own>
    ) -> Option<Option<KVPair<'b, Self>>> {
        // TODO remove these default impls that only exist for testing purposes
        Some(None)
    }

    // TODO replace with GATs + newtypes
    /// Returns whether two keys/values are the same/equivalent. This must provide
    /// the same guarantees as PartialEq. In fact, this is a replacement for
    /// PartialEq for cases where it's not possible to just use PartialEq.
    fn matches(
        left: RefOwn<'_, Self::Ref, Self::Own>,
        right: RefOwn<'_, Self::Ref, Self::Own>
    ) -> bool;
}

// TODO
type Predicate<T> = dyn (Fn(RefOwn<<T as PatternTypes>::Ref, <T as PatternTypes>::Own>) -> bool) + Send + Sync;