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

pub use pattern::Pattern;

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

    /// The owned key type. May be uninhabited.
    // TODO replace with GATs.
    type Key;

    /// 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: &'b Self::Value
    ) -> Option<Box<dyn Iterator<Item=(&'b Self::Value, &'b Self::Value)> + '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: &'b Self::Value,
        key: &'a str
    ) -> Option<Option<(&'b Self::Value, &'b Self::Value)>> {
        // TODO remove these default impls that only exist for testing purposes
        Some(None)
    }

    /// Returns whether two 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: &Self::Value, right: &Self::Value) -> bool;
}

// TODO
type Predicate<T> = dyn (Fn(&<T as PatternTypes>::Value) -> bool) + Send + Sync;