int_interval/

u8.rs

use crate::res::{OneTwo, ZeroOneTwo};

#[cfg(test)]
mod between_tests;
#[cfg(test)]
mod convex_hull_tests;
#[cfg(test)]
mod difference_tests;
#[cfg(test)]
mod intersection_tests;
#[cfg(test)]
mod symmetric_difference_tests;
#[cfg(test)]
mod transform_tests;
#[cfg(test)]
mod union_tests;

#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
pub struct U8CO {
    start: u8,
    end_excl: u8,
}

// ------------------------------------------------------------
// low-level api: construction / accessors / predicates
// ------------------------------------------------------------

mod construction_accessors_predicates {

    use super::*;

    impl U8CO {
        #[inline]
        pub const fn try_new(start: u8, end_excl: u8) -> Option<Self> {
            if start < end_excl {
                Some(Self { start, end_excl })
            } else {
                None
            }
        }

        #[inline]
        pub(super) const fn new_unchecked(start: u8, end_excl: u8) -> Self {
            debug_assert!(start < end_excl);
            Self { start, end_excl }
        }

        #[inline]
        pub const fn start(self) -> u8 {
            self.start
        }

        #[inline]
        pub const fn end_excl(self) -> u8 {
            self.end_excl
        }

        #[inline]
        pub const fn end_incl(self) -> u8 {
            // u8_low_bound =< start < end_excl
            self.end_excl - 1
        }

        #[inline]
        pub const fn len(self) -> u8 {
            self.end_excl - self.start
        }

        #[inline]
        pub const fn contains(self, x: u8) -> bool {
            self.start <= x && x < self.end_excl
        }

        #[inline]
        pub const fn iter(self) -> core::ops::Range<u8> {
            self.start..self.end_excl
        }

        #[inline]
        pub const fn intersects(self, other: Self) -> bool {
            !(self.end_excl <= other.start || other.end_excl <= self.start)
        }

        #[inline]
        pub const fn is_adjacent(self, other: Self) -> bool {
            self.end_excl == other.start || other.end_excl == self.start
        }

        #[inline]
        pub const fn is_contiguous_with(self, other: Self) -> bool {
            self.intersects(other) || self.is_adjacent(other)
        }
    }
}

// ------------------------------------------------------------
// interval algebra api: intersection / convex_hull / between / union / difference / symmetric_difference
// ------------------------------------------------------------

mod interval_algebra {

    use super::*;

    impl U8CO {
        /// Returns the intersection of two intervals.
        ///
        /// If the intervals do not overlap, returns `None`.
        #[inline]
        pub const fn intersection(self, other: Self) -> Option<Self> {
            let start = if self.start >= other.start {
                self.start
            } else {
                other.start
            };

            let end_excl = if self.end_excl <= other.end_excl {
                self.end_excl
            } else {
                other.end_excl
            };

            Self::try_new(start, end_excl)
        }

        /// Returns the convex hull (smallest interval containing both) of two intervals.
        ///
        /// Always returns a valid `U8CO`.
        #[inline]
        pub const fn convex_hull(self, other: Self) -> Self {
            let start = if self.start <= other.start {
                self.start
            } else {
                other.start
            };

            let end_excl = if self.end_excl >= other.end_excl {
                self.end_excl
            } else {
                other.end_excl
            };

            Self { start, end_excl }
        }

        /// Returns the interval strictly between two intervals.
        ///
        /// If the intervals are contiguous or overlap, returns `None`.
        #[inline]
        pub const fn between(self, other: Self) -> Option<Self> {
            let (left, right) = if self.start <= other.start {
                (self, other)
            } else {
                (other, self)
            };

            Self::try_new(left.end_excl, right.start)
        }

        /// Returns the union of two intervals.
        ///
        /// - If intervals are contiguous or overlapping, returns `One` containing the merged interval.
        /// - Otherwise, returns `Two` containing both intervals in ascending order.
        #[inline]
        pub const fn union(self, other: Self) -> OneTwo<Self> {
            if self.is_contiguous_with(other) {
                OneTwo::One(self.convex_hull(other))
            } else if self.start <= other.start {
                OneTwo::Two(self, other)
            } else {
                OneTwo::Two(other, self)
            }
        }

        /// Returns the difference of two intervals (self - other).
        ///
        /// - If no overlap, returns `One(self)`.
        /// - If partial overlap, returns `One` or `Two` depending on remaining segments.
        /// - If fully contained, returns `Zero`.
        #[inline]
        pub const fn difference(self, other: Self) -> ZeroOneTwo<Self> {
            match self.intersection(other) {
                None => ZeroOneTwo::One(self),
                Some(inter) => {
                    let left = Self::try_new(self.start, inter.start);
                    let right = Self::try_new(inter.end_excl, self.end_excl);

                    match (left, right) {
                        (None, None) => ZeroOneTwo::Zero,
                        (Some(x), None) | (None, Some(x)) => ZeroOneTwo::One(x),
                        (Some(x), Some(y)) => ZeroOneTwo::Two(x, y),
                    }
                }
            }
        }

        /// Returns the symmetric difference of two intervals.
        ///
        /// Equivalent to `(self - other) ∪ (other - self)`.
        /// - If intervals do not overlap, returns `Two(self, other)` in order.
        /// - If intervals partially overlap, returns remaining non-overlapping segments as `One` or `Two`.
        #[inline]
        pub const fn symmetric_difference(self, other: Self) -> ZeroOneTwo<Self> {
            match self.intersection(other) {
                None => {
                    if self.start <= other.start {
                        ZeroOneTwo::Two(self, other)
                    } else {
                        ZeroOneTwo::Two(other, self)
                    }
                }
                Some(inter) => {
                    let hull = self.convex_hull(other);
                    let left = Self::try_new(hull.start, inter.start);
                    let right = Self::try_new(inter.end_excl, hull.end_excl);

                    match (left, right) {
                        (None, None) => ZeroOneTwo::Zero,
                        (Some(x), None) | (None, Some(x)) => ZeroOneTwo::One(x),
                        (Some(x), Some(y)) => ZeroOneTwo::Two(x, y),
                    }
                }
            }
        }
    }
}

// ------------------------------------------------------------
// interval arithmetic / transform api: scale / shift / scale_then_shift / shift_then_scale
// ------------------------------------------------------------

mod interval_arithmetic {

    use super::*;

    impl U8CO {
        #[inline]
        pub const fn scale(self, factor: u8) -> Option<Self> {
            if factor == 0 || self.end_excl > u8::MAX / factor {
                return None;
            }
            Some(U8CO::new_unchecked(
                self.start * factor,
                self.end_excl * factor,
            ))
        }

        #[inline]
        pub const fn shift(self, offset: u8) -> Option<Self> {
            if self.end_excl > u8::MAX - offset {
                return None;
            }
            Some(U8CO::new_unchecked(
                self.start + offset,
                self.end_excl + offset,
            ))
        }
    }
}