simple-bitset 0.1.4

use core::fmt;
use core::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Index};
#[cfg(feature = "serde")]
use {
    sequential_storage::map::PostcardValue,
    serde::{Deserialize, Serialize},
};

/// A memory-efficient 64-bit set for embedded environments.
// Note that it data is a singlet: this makes comparison with `BitSet128` duplet clearer.
#[derive(Clone, Copy, Debug, Ord, PartialOrd, Eq, PartialEq)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct BitSet64(u64);

impl BitSet64 {
    /// Create a new empty bitset.
    #[must_use]
    pub const fn new() -> Self {
        Self(0)
    }
}

#[cfg(feature = "serde")]
impl PostcardValue<'_> for BitSet64 {}

impl Default for BitSet64 {
    fn default() -> Self {
        Self::new()
    }
}

impl BitSet64 {
    /// Resets all bits to 0.
    #[inline]
    pub fn reset_all(&mut self) {
        self.0 = 0;
    }

    /// Resets the bit at `index` to 0. Does nothing if the index is out of bounds.
    #[inline]
    pub fn reset(&mut self, index: u8) {
        if index < 64 {
            self.0 &= !(1u64 << index);
        }
    }

    /// Sets all bits to 1.
    #[inline]
    pub fn set_all(&mut self) {
        self.0 = u64::MAX;
    }

    /// Sets the bit at `index` to 1. Does nothing if the index is out of bounds.
    #[inline]
    pub fn set(&mut self, index: u8) {
        if index < 64 {
            self.0 |= 1u64 << index;
        }
    }

    /// Flips the bit at `index`. Does nothing if the index is out of bounds.
    #[inline]
    pub fn flip(&mut self, index: u8) {
        if index < 64 {
            self.0 ^= 1u64 << index;
        }
    }

    /// Flips all bits in the bitset (0s become 1s, and 1s become 0s).
    #[inline]
    pub fn flip_all(&mut self) {
        self.0 = !self.0;
    }

    /// In-place Difference / Mask-Clear. Clears any bits that are set in `other`.
    /// This represents the mathematical operation: `self = self AND NOT other`.
    #[inline]
    pub fn and_not(&mut self, other: Self) {
        self.0 &= !other.0;
    }

    /// Tests if the bit at `index` is 1.
    /// Returns false if the bit is 0 or index is out of bounds.
    #[inline]
    #[must_use]
    pub fn test(&self, index: u8) -> bool {
        if index < 64 {
            (self.0 & (1u64 << index)) != 0
        } else {
            false
        }
    }

    /// Returns the number of set bits (population count).
    #[inline]
    #[must_use]
    pub const fn count_ones(&self) -> u32 {
        self.0.count_ones()
    }

    /// Returns the number of leading zeros in the bitset,
    /// counting from the most significant bit (index 63).
    #[inline]
    #[must_use]
    pub const fn leading_zeros(&self) -> u32 {
        self.0.leading_zeros()
    }

    /// Returns true if no bits are set.
    #[inline]
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        self.0 == 0
    }

    /// Returns the highest index set, or None if the bitset is empty.
    /// Useful for finding the "top" of a priority queue or resource map.
    #[inline]
    #[must_use]
    pub const fn last_set(&self) -> Option<u8> {
        if self.is_empty() {
            None
        } else {
            // Cast is safe as (63 - leading) is guaranteed to be between 0 and 63.
            #[allow(clippy::cast_possible_truncation)]
            Some(63 - self.0.leading_zeros() as u8)
        }
    }

    /// Returns true if this bitset contains all the bits set in `other`.
    #[inline]
    #[must_use]
    pub const fn is_superset(&self, other: BitSet64) -> bool {
        // A bitset is a superset if clearing any bits not present in self
        // results in exactly the other bitset configuration for both halves.
        (self.0 & other.0) == other.0
    }

    /// Returns true if this bitset is a subset of `other`.
    #[inline]
    #[must_use]
    pub const fn is_subset(&self, other: BitSet64) -> bool {
        other.is_superset(*self)
    }

    /// Returns true if this bitset shares at least one common set bit with `other`.
    /// Returns false if there is no overlap or if either bitset is empty.
    #[inline]
    #[must_use]
    pub const fn intersects(&self, other: Self) -> bool {
        // Run a bitwise AND between bitsets.
        // If the result is non-zero, an intersection exists.
        self.0 & other.0 != 0
    }

    /// Returns an iterator over the indices of the set bits.
    #[inline]
    #[must_use]
    pub fn iter(&self) -> BitSet64Iter {
        self.into_iter()
    }
}

// **** Bit operations ****

impl BitOr for BitSet64 {
    type Output = Self;
    fn bitor(self, other: Self) -> Self::Output {
        Self(self.0 | other.0)
    }
}

impl BitAnd for BitSet64 {
    type Output = Self;
    fn bitand(self, other: Self) -> Self::Output {
        Self(self.0 & other.0)
    }
}

impl BitXor for BitSet64 {
    type Output = Self;
    fn bitxor(self, other: Self) -> Self::Output {
        Self(self.0 ^ other.0)
    }
}

impl BitOrAssign for BitSet64 {
    fn bitor_assign(&mut self, other: Self) {
        self.0 |= other.0;
    }
}

impl BitAndAssign for BitSet64 {
    fn bitand_assign(&mut self, other: Self) {
        self.0 &= other.0;
    }
}

impl BitXorAssign for BitSet64 {
    fn bitxor_assign(&mut self, other: Self) {
        self.0 ^= other.0;
    }
}

impl Index<u8> for BitSet64 {
    type Output = bool;

    fn index(&self, index: u8) -> &Self::Output {
        // We use static booleans because we must return a reference
        if self.test(index) { &true } else { &false }
    }
}

impl Index<usize> for BitSet64 {
    type Output = bool;

    #[allow(clippy::cast_possible_truncation)]
    fn index(&self, index: usize) -> &Self::Output {
        // We use static booleans because we must return a reference
        if self.test(index as u8) { &true } else { &false }
    }
}

/// `BitSet64` from `u32`.
impl From<u32> for BitSet64 {
    #[inline]
    fn from(a: u32) -> Self {
        Self(u64::from(a))
    }
}

/// `BitSet64` from `(u32,u32)`.
impl From<(u32, u32)> for BitSet64 {
    #[inline]
    fn from((a, b): (u32, u32)) -> Self {
        Self(u64::from(a) << 32 | u64::from(b))
    }
}

// **** Iter ****

/// Iterator for `BitSet64`.
#[derive(Debug, Default, Eq, PartialEq)]
pub struct BitSet64Iter(u64);

/// Consuming iterator.
impl Iterator for BitSet64Iter {
    type Item = u8;

    fn next(&mut self) -> Option<Self::Item> {
        if self.0 == 0 {
            None
        } else {
            // Find the index of the least significant bit set to 1
            #[allow(clippy::cast_possible_truncation)]
            let index = self.0.trailing_zeros() as u8;
            // Clear the least significant bit to prep for next iteration
            self.0 &= self.0 - 1;
            Some(index)
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        // We know exactly how many bits are left to yield at any moment!
        let len = self.0.count_ones() as usize;
        (len, Some(len))
    }
}

// Implementing ExactSizeIterator unlocks additional optimizations automatically
impl ExactSizeIterator for BitSet64Iter {}
impl core::iter::FusedIterator for BitSet64Iter {}

/// Non-consuming iterator for bitset reference.
impl IntoIterator for &BitSet64 {
    type Item = u8;
    type IntoIter = BitSet64Iter;

    fn into_iter(self) -> Self::IntoIter {
        // Since `BitSet64` is `Copy` and just a `(u64)`,
        // we just pass the underlying value to the iterator.
        BitSet64Iter(self.0)
    }
}

/// Non-consuming iterator for bitset.
impl IntoIterator for BitSet64 {
    type Item = u8;
    type IntoIter = BitSet64Iter;

    fn into_iter(self) -> Self::IntoIter {
        // Since `BitSet64` is `Copy` and just a `(u64)`,
        // we just pass the underlying value to the iterator.
        BitSet64Iter(self.0)
    }
}

/// From iterator for bitset.
impl FromIterator<u8> for BitSet64 {
    fn from_iter<I: IntoIterator<Item = u8>>(iter: I) -> Self {
        let mut bitset = Self::new();
        for index in iter {
            bitset.set(index);
        }
        bitset
    }
}

impl Extend<u8> for BitSet64 {
    fn extend<I: IntoIterator<Item = u8>>(&mut self, iter: I) {
        for index in iter {
            self.set(index);
        }
    }
}

// **** fmt ****

impl fmt::Binary for BitSet64 {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Handle the "0b" prefix if requested via {:#b}
        if f.alternate() {
            f.write_str("0b")?;
        }
        // Print from high bits to low bits (left-to-right)
        for i in (0..64).rev() {
            let val = (self.0 >> i) & 1;
            write!(f, "{val}")?;
        }

        Ok(())
    }
}

impl fmt::UpperHex for BitSet64 {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if f.alternate() {
            f.write_str("0x")?;
        }
        write!(f, "{:016X}", self.0)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn is_normal<T: Sized + Send + Sync + Unpin>() {}
    fn is_full<T: Sized + Send + Sync + Unpin + Copy + Clone + Default + PartialEq>() {}
    #[cfg(feature = "serde")]
    fn is_config<T: Serialize + for<'a> Deserialize<'a>>() {}

    #[test]
    fn normal_types() {
        is_full::<BitSet64>();
        #[cfg(feature = "serde")]
        is_config::<BitSet64>();
        is_normal::<BitSet64Iter>();
    }

    #[test]
    fn new() {
        let mut bits = BitSet64::new();
        bits.set(42);
        assert!(bits[42u8]);
        assert!(bits.test(42));
    }

    #[test]
    fn const_new() {
        const FLAGS: BitSet64 = BitSet64::new();
        const EMPTY_CHECK: bool = FLAGS.is_empty(); // Evaluated at compile time
        assert_eq!(0, FLAGS.0);
        #[allow(clippy::assertions_on_constants)]
        {
            assert!(EMPTY_CHECK);
        }
    }

    #[test]
    fn assign() {
        let mut bits = BitSet64::new();
        bits.set(42);
        assert!(bits[42u8]);
        assert!(bits.test(42));
        let mask = bits;
        assert!(mask.test(42));
    }

    #[test]
    fn from() {
        let _bits = BitSet64::from((0xab_u32, 0x12_u32));
    }

    #[test]
    fn flip_all() {
        let mut bitset = BitSet64::new();

        // Alternating pattern test
        bitset.set(0);
        bitset.set(32);

        bitset.flip_all();

        // Bit 0 and 64 should now be 0, others should be 1
        assert!(!bitset.test(0));
        assert!(!bitset.test(32));
        assert!(bitset.test(1));
        assert!(bitset.test(33));

        // Full cycle test (Empty -> Full -> Empty)
        let mut empty_set = BitSet64::new();
        empty_set.flip_all(); // Should become full

        let mut full_set = BitSet64::new();
        full_set.set_all();

        assert_eq!(empty_set, full_set);

        empty_set.flip_all(); // Should return to completely empty
        assert!(empty_set.is_empty());
    }

    #[test]
    fn leading_zeros() {
        let mut bitset = BitSet64::new();

        // Completely empty set should return 64 zeros
        assert_eq!(bitset.leading_zeros(), 64);

        // Setting the absolute most significant bit (index 63) leaves 0 leading zeros
        bitset.set(63);
        assert_eq!(bitset.leading_zeros(), 0);

        // Setting index 62 leaves exactly 1 leading zero
        bitset.reset_all();
        bitset.set(62);
        assert_eq!(bitset.leading_zeros(), 1);
    }

    #[test]
    fn last_set() {
        let mut bitset = BitSet64::new();

        // Empty set should return None
        assert_eq!(bitset.last_set(), None);

        // Single lowest bit set
        bitset.set(0);
        assert_eq!(bitset.last_set(), Some(0));

        // Multiple bits set, should return the highest one
        bitset.set(10);
        bitset.set(45);
        assert_eq!(bitset.last_set(), Some(45));

        // Boundary verification at the top of the lower u64
        bitset.reset_all();
        bitset.set(63);
        assert_eq!(bitset.last_set(), Some(63));
    }

    #[test]
    fn is_superset() {
        let mut set_a = BitSet64::new();
        let mut set_b = BitSet64::new();

        // An empty set is always a superset of another empty set
        assert!(set_a.is_superset(set_b));

        // Setup indices spanning across the 64-bit boundary
        set_a.set(10);
        set_a.set(60);

        set_b.set(10);

        // set_a has [10, 60], set_b has [10] -> Should be true
        assert!(set_a.is_superset(set_b));
        // set_b is missing 80 -> Should be false
        assert!(!set_b.is_superset(set_a));

        // Test exact match
        set_b.set(60);
        assert!(set_a.is_superset(set_b));

        // Test failure where lower matches but higher fails (Catches the original bug)
        let mut set_c = BitSet64::new();
        let mut set_d = BitSet64::new();
        set_c.set(15); // Higher element (.1) is 0

        set_d.set(15);
        set_d.set(55); // Higher element (.1) is non-zero

        // Lower halves match, but set_c is missing bit 95.
        // Your old function would mistakenly return true here.
        assert!(!set_c.is_superset(set_d));
    }

    #[test]
    fn intersects() {
        let mut set_a = BitSet64::new();
        let mut set_b = BitSet64::new();

        // Empty sets should never intersect
        assert!(!set_a.intersects(set_b));

        // Add an item to set_a only
        set_a.set(15);
        assert!(!set_a.intersects(set_b));

        // Match the item in set_b (Intersection in the lower u64 block)
        set_b.set(15);
        assert!(set_a.intersects(set_b));
        assert!(set_b.intersects(set_a));

        // Test disjoint sets across the 64-bit split boundary
        set_a.reset_all();
        set_b.reset_all();
        set_a.set(10);
        set_b.set(60);
        assert!(!set_a.intersects(set_b));

        // Test intersection purely inside the higher u64 block (index >= 64)
        set_a.set(60);
        assert!(set_a.intersects(set_b));
    }

    #[test]
    fn inplace_logical_ops() {
        let mut set_a = BitSet64::new();
        let mut set_b = BitSet64::new();

        // Setup overlapping patterns crossing 64-bit boundaries
        set_a.set(10);
        set_a.set(50);

        set_b.set(10);
        set_b.set(60);

        // Test BitAndAssign (&=)
        let mut result = set_a;
        result &= set_b;
        assert!(result.test(10));
        assert!(!result.test(50));
        assert!(!result.test(60));

        // Test BitOrAssign (|=)
        let mut result = set_a;
        result |= set_b;
        assert!(result.test(10));
        assert!(result.test(50));
        assert!(result.test(60));

        // Test BitXorAssign (^=)
        let mut result = set_a;
        result ^= set_b;
        assert!(!result.test(10)); // Both were 1, turns to 0
        assert!(result.test(50));
        assert!(result.test(60));

        // Test and_not
        let mut result = set_a;
        result.and_not(set_b);
        assert!(!result.test(10)); // Cleared by mask
        assert!(result.test(50)); // Preserved
        assert!(!result.test(60)); // Never present in set_a
    }

    #[test]
    fn exercise() {
        let mut system_flags = BitSet64::new();
        let error_mask = BitSet64::new(); // imagine this has error bits set

        // Combine with OR-assign
        system_flags |= error_mask;

        // Toggle bits with XOR-assign
        system_flags ^= error_mask;

        // Mask out bits with AND-assign
        system_flags &= BitSet64(0x0000_FFFF_FFFF_FFFF);

        let mut set_a = BitSet64::new();
        set_a.set(10);
        set_a.set(20);

        let mut set_b = BitSet64::new();
        set_b.set(20);
        set_b.set(30);

        // Intersection (AND): only bit 20 remains
        let common = set_a & set_b;
        assert!(!common.test(10));
        assert!(common.test(20));
        assert!(!common.test(30));

        // Union (OR): bits 10, 20, and 30 are set
        let all = set_a | set_b;
        assert!(all.test(10));
        assert!(all.test(20));
        assert!(all.test(30));

        // Difference (XOR): bits 10 and 30 are set (20 is cancelled out)
        let diff = set_a ^ set_b;
        assert!(diff.test(10));
        assert!(!diff.test(20));
        assert!(diff.test(30));
    }

    #[test]
    fn iterator_consuming() {
        let mut bits = BitSet64::new();
        bits.set(2);
        bits.set(10);

        let mut sum = 0;
        let mut count = 0;
        for bit in &bits {
            sum += bit;
            count += 1;
        }
        assert_eq!(2, count);
        assert_eq!(12, sum);
    }

    #[test]
    fn into_iter_consuming() {
        let mut bits = BitSet64::new();
        bits.set(0);
        bits.set(10);
        bits.set(63);

        // Consuming iterator
        let mut iter = bits.into_iter();

        assert_eq!(iter.next(), Some(0));
        assert_eq!(iter.next(), Some(10));
        assert_eq!(iter.next(), Some(63));
        assert_eq!(iter.next(), None);

        // bits is moved here and can no longer be used
    }

    #[test]
    fn non_consuming_iterator() {
        let bits = BitSet64(0b1101); // Bits 0, 2, and 3 are set

        let mut sum = 0;
        let mut count = 0;

        // Use reference to bits rather than bits.iter()
        for bit in &bits {
            sum += bit;
            count += 1;
        }
        assert_eq!(3, count);
        assert_eq!(5, sum);

        let mut sum = 0;
        let mut count = 0;
        // Using a reference in a loop
        for bit in &bits {
            sum += bit;
            count += 1;
        }
        assert_eq!(3, count);
        assert_eq!(5, sum);
    }

    #[test]
    fn non_consuming_iterator2() {
        let mut bits = BitSet64::new();
        bits.set(5);
        bits.set(12);

        // Test using the .iter() method
        let count = bits.iter().count();
        assert_eq!(count, 2);

        // Test using & reference in a for-loop
        let mut last_val = 0;
        for bit in &bits {
            last_val = bit;
        }
        assert_eq!(last_val, 12);

        // test original bits is still valid
        assert!(bits.test(5));
    }

    #[test]
    fn from_iterator() {
        let indices = [1, 3, 5];
        // collect() uses FromIterator
        let bits: BitSet64 = indices.iter().copied().collect();

        assert!(bits.test(1));
        assert!(bits.test(3));
        assert!(bits.test(5));
        assert!(!bits.test(2));
    }

    #[test]
    fn empty_and_full() {
        let empty = BitSet64::new();
        assert_eq!(empty.iter().count(), 0);

        let mut full = BitSet64::new();
        full.set_all();
        assert_eq!(full.iter().count(), 64);
    }
}