# `superset_map`

`superset_map` is a library for `Set`s that have an order defined on them. Its main data structure is
`SupersetMap` which is a specialized version of `BTreeMap` where only supersets are stored. This can be
useful when the keys don't fit well or at all with the concept of `RangeBounds`.

Nightly Rust is required. Once
[`BTreeMap` cursors are stabilized](https://github.com/rust-lang/rust/issues/107540), stable Rust will work.

## Example

```rust
use core::{borrow::Borrow, cmp::Ordering};
use superset_map::{zfc::{num_bigint::BigUint, BoundedCardinality, Cardinality, Set}, SetOrd, SupersetSet};
#[derive(Clone, Copy, Eq, PartialEq)]
struct ShortAscii<'a> {
    val: &'a [u8],
}
impl<'a> ShortAscii<'a> {
    fn new(val: &'a [u8]) -> Option<ShortAscii<'a>> {
        (val.len() <= 255 && val.is_ascii()).then_some(Self { val })
    }
    fn len(self) -> u8 {
        self.val.len().try_into().expect("The ShortAscii instance was not constructed properly and contains more than 255 bytes.")
    }
}
#[derive(Clone, Copy, Eq, PartialEq)]
enum WildcardAscii<'a> {
    Plain(ShortAscii<'a>),
    // Represents a ShortAscii<'a> with an implicit wildcard at the end
    // meaning it's all ShortAscii<'a>s that begin with the contained ShortAscii<'a>.val.
    Wildcard(ShortAscii<'a>),
}
impl<'a> WildcardAscii<'a> {
    const fn val(self) -> ShortAscii<'a> {
        match self {
            WildcardAscii::Plain(s) | WildcardAscii::Wildcard(s) => s,
        }
    }
    const fn is_plain(self) -> bool {
        match self {
            WildcardAscii::Plain(_) => true,
            WildcardAscii::Wildcard(_) => false,
        }
    }
    const fn is_wildcard(self) -> bool {
        !self.is_plain()
    }
}
impl<'a> PartialOrd<Self> for WildcardAscii<'a> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}
impl<'a> Ord for WildcardAscii<'a> {
    fn cmp(&self, other: &Self) -> Ordering {
        let len = u8::min(self.val().len(), other.val().len()) as usize;
        match self.val().val[..len].cmp(&other.val().val[..len]) {
            Ordering::Less => Ordering::Less,
            Ordering::Equal => {
                if self.is_wildcard() {
                    if other.is_wildcard() {
                        self.val().len().cmp(&other.val().len()).reverse()
                    } else {
                        Ordering::Greater
                    }
                } else if other.is_wildcard() {
                    Ordering::Less
                } else {
                    self.val().len().cmp(&other.val().len())
                }
            }
            Ordering::Greater => Ordering::Greater,
        }
    }
}
impl<'a> Set for WildcardAscii<'a> {
    type Elem = ShortAscii<'a>;
    fn bounded_cardinality(&self) -> BoundedCardinality {
        BoundedCardinality::new_exact(self.cardinality().unwrap())
    }
    fn cardinality(&self) -> Option<Cardinality> {
        Some(Cardinality::Finite(match *self {
            WildcardAscii::Plain(_) => BigUint::new(vec![1]),
            // Geometric series.
            WildcardAscii::Wildcard(v) => {
                (BigUint::new(vec![128]).pow((u8::MAX - v.len()) as u32 + 1)
                    - BigUint::new(vec![1]))
                    / BigUint::new(vec![127])
            }
        }))
    }
    fn contains<Q>(&self, elem: &Q) -> bool
    where
        Q: Borrow<Self::Elem> + Eq + ?Sized,
    {
        match *self {
            WildcardAscii::Plain(v) => v == *elem.borrow(),
            WildcardAscii::Wildcard(v) => {
                v.len() <= elem.borrow().len() && *v.val == elem.borrow().val[..v.len() as usize]
            }
        }
    }
    fn is_proper_subset(&self, val: &Self) -> bool {
        val.is_wildcard()
            && match val.val().len().cmp(&self.val().len()) {
                Ordering::Less => val.val().val == &self.val().val[..val.val().len() as usize],
                Ordering::Equal => self.is_plain() && self.val() == val.val(),
                Ordering::Greater => false,
            }
    }
    fn is_subset(&self, val: &Self) -> bool {
        self == val || self.is_proper_subset(val)
    }
}
impl<'a> SetOrd for WildcardAscii<'a> {}
fn main() {
    let mut set = SupersetSet::new();
    set.insert(WildcardAscii::Plain(ShortAscii::new(b"foo").unwrap()));
    set.insert(WildcardAscii::Plain(ShortAscii::new(b"bar").unwrap()));
    set.insert(WildcardAscii::Wildcard(ShortAscii::new(b"b").unwrap()));
    set.insert(WildcardAscii::Wildcard(ShortAscii::new(b"bar").unwrap()));
    let mut iter = set.into_iter();
    assert!(iter.next().map_or(false, |s| s
        == WildcardAscii::Wildcard(ShortAscii::new(b"b").unwrap())));
    assert!(iter.next().map_or(false, |s| s
        == WildcardAscii::Plain(ShortAscii::new(b"foo").unwrap())));
    assert!(iter.next().is_none());
}
```

## License

Licensed under either of

* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0).
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT).

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you,
as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

### Status

The crate is only tested on `x86_64-unknown-linux-gnu` and `x86_64-unknown-openbsd` targets, but it should work
on most platforms.