llvm-native-core 0.1.16

//! clang_stl4 — Extended C++ Standard Library behavioral models (Part 4).
//!
//! Covers:
//! - <execution>: execution policies (seq, par, par_unseq), parallel algorithms integration
//! - <latch>/<barrier>/<semaphore>: full C++20 concurrency primitives
//! - <syncstream>: synchronized output stream buffer
//! - <spanstream>: span-based string streams (C++23)
//! - <flat_map>/<flat_set>: sorted vector-based associative containers (C++23)
//! - <mdspan>: multi-dimensional span views (C++23)
//! - <generator>: std::generator<T> coroutine-based generator (C++23)
//! - <print>: std::print, std::println for type-safe formatted output (C++23)
//! - <stacktrace>: std::stacktrace, std::stacktrace_entry, basic_stacktrace (C++23)
//! - <debugging>: breakpoint, is_debugger_present utilities (C++26)
//! - <text_encoding>: text encoding identification and conversion (C++26)
//! - <inplace_vector>: fixed-capacity vector with internal storage (C++26)
//! - <hive>: bucket-array associative container (proposed)
//!
//! Clean-room reconstruction from ISO/IEC 14882:2020, 14882:2023, and published proposals.

use std::fmt;

// ============================================================================
// <execution> — Execution Policies
// ============================================================================

/// Execution policy type for parallel algorithms (C++17/20).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ExecutionPolicy {
    /// Sequential execution (no parallelism).
    SequencedPolicy,
    /// Parallel execution (multiple threads, no vectorization requirement).
    ParallelPolicy,
    /// Parallel + unsequenced execution (SIMD vectorization allowed).
    ParallelUnsequencedPolicy,
    /// Unsequenced execution only (vectorization, single thread).
    UnsequencedPolicy,
}

impl ExecutionPolicy {
    pub fn is_parallel(&self) -> bool {
        matches!(self, Self::ParallelPolicy | Self::ParallelUnsequencedPolicy)
    }

    pub fn allows_vectorization(&self) -> bool {
        matches!(self, Self::ParallelUnsequencedPolicy | Self::UnsequencedPolicy)
    }

    pub fn name(&self) -> &str {
        match self {
            Self::SequencedPolicy => "seq",
            Self::ParallelPolicy => "par",
            Self::ParallelUnsequencedPolicy => "par_unseq",
            Self::UnsequencedPolicy => "unseq",
        }
    }
}

impl fmt::Display for ExecutionPolicy {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "std::execution::{}", self.name())
    }
}

/// Parallel algorithm configuration.
#[derive(Debug, Clone)]
pub struct ParallelAlgorithmConfig {
    pub policy: ExecutionPolicy,
    pub chunk_size: usize,
    pub min_elements_for_parallel: usize,
    pub vectorization_width: Option<usize>,
}

impl ParallelAlgorithmConfig {
    pub fn new(policy: ExecutionPolicy) -> Self {
        Self { policy, chunk_size: 2048, min_elements_for_parallel: 10000, vectorization_width: None }
    }

    pub fn should_parallelize(&self, element_count: usize) -> bool {
        self.policy.is_parallel() && element_count >= self.min_elements_for_parallel
    }

    pub fn parallel_for_each<T>(&self, data: &[T], mut f: impl FnMut(&T)) {
        let n = data.len();
        if self.should_parallelize(n) {
            let chunks = (n + self.chunk_size - 1) / self.chunk_size;
            for chunk in 0..chunks {
                let start = chunk * self.chunk_size;
                let end = std::cmp::min(start + self.chunk_size, n);
                for i in start..end { f(&data[i]); }
            }
        } else {
            for item in data { f(item); }
        }
    }
}

// ============================================================================
// <latch> — std::latch (C++20)
// ============================================================================

/// A downward counter of type ptrdiff_t which can be used to synchronize
/// threads. The value of the counter is initialized on construction.
/// Threads may block on the latch until the counter is decremented to zero.
#[derive(Debug, Clone)]
pub struct Latch {
    count: isize,
    initial_count: isize,
}

impl Latch {
    pub fn new(count: isize) -> Self {
        assert!(count >= 0, "Latch count must be non-negative");
        Self { count, initial_count: count }
    }

    pub fn count_down(&mut self, n: isize) {
        self.count = std::cmp::max(0, self.count - n);
    }

    pub fn count_down_one(&mut self) {
        self.count_down(1);
    }

    pub fn try_wait(&self) -> bool {
        self.count == 0
    }

    pub fn wait(&self) {
        while self.count > 0 { std::hint::spin_loop(); }
    }

    pub fn arrive_and_wait(&mut self, n: isize) {
        self.count_down(n);
        self.wait();
    }

    pub fn reset(&mut self) {
        self.count = self.initial_count;
    }

    pub fn current_count(&self) -> isize {
        self.count
    }
}

// ============================================================================
// <barrier> — std::barrier (C++20)
// ============================================================================

/// Completion function type for barriers.
pub type BarrierCompletionFn = Box<dyn Fn() + Send>;

/// A thread coordination mechanism that allows a set of participating threads
/// to block until an operation is completed. Unlike a latch, a barrier is
/// reusable: once the participating threads are released from a barrier's
/// synchronization point, they can re-use the same barrier.
#[derive(Debug)]
pub struct Barrier {
    expected: usize,
    arrived: usize,
    phase: BarrierPhase,
    completion: Option<BarrierCompletionFn>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BarrierPhase { Phase0, Phase1 }

impl Barrier {
    pub fn new(expected: usize) -> Self {
        Self { expected, arrived: 0, phase: BarrierPhase::Phase0, completion: None }
    }

    pub fn with_completion(expected: usize, f: BarrierCompletionFn) -> Self {
        Self { expected, arrived: 0, phase: BarrierPhase::Phase0, completion: Some(f) }
    }

    pub fn arrive(&mut self, n: usize) -> BarrierArrivalToken {
        self.arrived += n;
        BarrierArrivalToken { phase: self.phase }
    }

    pub fn arrive_one(&mut self) -> BarrierArrivalToken {
        self.arrive(1)
    }

    pub fn wait(&self, token: BarrierArrivalToken) {
        if token.phase != self.phase { return; }
        while self.arrived < self.expected { std::hint::spin_loop(); }
    }

    pub fn arrive_and_wait(&mut self) {
        self.arrived += 1;
        while self.arrived < self.expected { std::hint::spin_loop(); }
        if self.arrived >= self.expected {
            self.arrived = 0;
            self.phase = match self.phase {
                BarrierPhase::Phase0 => BarrierPhase::Phase1,
                BarrierPhase::Phase1 => BarrierPhase::Phase0,
            };
            if let Some(ref f) = self.completion { f(); }
        }
    }

    pub fn arrive_and_drop(&mut self) {
        self.expected -= 1;
    }

    pub fn expected_count(&self) -> usize { self.expected }
}

/// Arrival token returned by barrier::arrive.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct BarrierArrivalToken {
    phase: BarrierPhase,
}

// ============================================================================
// <semaphore> — std::counting_semaphore / std::binary_semaphore (C++20)
// ============================================================================

/// A counting semaphore with a maximum value.
/// Models std::counting_semaphore<LeastMaxValue>.
#[derive(Debug, Clone)]
pub struct CountingSemaphore<const LEAST_MAX: isize = { isize::MAX }> {
    count: isize,
    max_count: isize,
}

/// std::binary_semaphore is a counting_semaphore<1>.
pub type BinarySemaphore = CountingSemaphore<1>;

impl<const N: isize> CountingSemaphore<N> {
    pub fn new(desired: isize) -> Self {
        assert!(desired >= 0 && desired <= N, "Semaphore count out of range");
        Self { count: desired, max_count: N }
    }

    pub fn release(&mut self, update: isize) {
        assert!(update > 0, "Release requires positive update");
        let new_count = self.count.saturating_add(update);
        self.count = std::cmp::min(new_count, self.max_count);
    }

    pub fn release_one(&mut self) { self.release(1); }

    pub fn acquire(&mut self) {
        while self.count == 0 { std::hint::spin_loop(); }
        self.count -= 1;
    }

    pub fn try_acquire(&mut self) -> bool {
        if self.count > 0 { self.count -= 1; true } else { false }
    }

    pub fn try_acquire_for(&mut self, timeout_ms: u64) -> bool {
        let start = std::time::Instant::now();
        while self.count == 0 {
            if start.elapsed().as_millis() as u64 >= timeout_ms { return false; }
            std::hint::spin_loop();
        }
        self.count -= 1;
        true
    }

    pub fn max(&self) -> isize { self.max_count }
}

// ============================================================================
// <syncstream> — std::basic_osyncstream (C++20)
// ============================================================================

/// Synchronized output stream that buffers operations and emits atomically.
#[derive(Debug, Clone)]
pub struct BasicOsyncstream {
    buffer: Vec<u8>,
    target: Option<String>,
    emit_on_sync: bool,
}

impl BasicOsyncstream {
    pub fn new(target: Option<&str>) -> Self {
        Self { buffer: Vec::new(), target: target.map(|s| s.to_string()), emit_on_sync: true }
    }

    pub fn write(&mut self, data: &str) { self.buffer.extend_from_slice(data.as_bytes()); }
    pub fn write_bytes(&mut self, data: &[u8]) { self.buffer.extend_from_slice(data); }

    pub fn emit(&mut self) -> Vec<u8> {
        let result = self.buffer.clone();
        self.buffer.clear();
        result
    }

    pub fn flush(&mut self) -> Vec<u8> { self.emit() }

    pub fn get_buffer(&self) -> &[u8] { &self.buffer }

    pub fn set_emit_on_sync(&mut self, flag: bool) { self.emit_on_sync = flag; }
}

impl fmt::Write for BasicOsyncstream {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.write(s);
        Ok(())
    }
}

// ============================================================================
// <spanstream> — std::basic_spanbuf / std::basic_ispanstream / std::basic_ospanstream (C++23)
// ============================================================================

/// A stream buffer that uses a fixed span of memory (not dynamically allocated).
#[derive(Debug, Clone)]
pub struct SpanStreamBuffer {
    data: Vec<u8>,
    read_pos: usize,
    write_pos: usize,
}

impl SpanStreamBuffer {
    pub fn new(capacity: usize) -> Self {
        Self { data: vec![0u8; capacity], read_pos: 0, write_pos: 0 }
    }

    pub fn from_slice(slice: &[u8]) -> Self {
        Self { data: slice.to_vec(), read_pos: 0, write_pos: slice.len() }
    }

    pub fn read(&mut self, buf: &mut [u8]) -> usize {
        let available = self.write_pos - self.read_pos;
        let to_read = std::cmp::min(available, buf.len());
        buf[..to_read].copy_from_slice(&self.data[self.read_pos..self.read_pos + to_read]);
        self.read_pos += to_read;
        to_read
    }

    pub fn write(&mut self, buf: &[u8]) -> usize {
        let available = self.data.len() - self.write_pos;
        let to_write = std::cmp::min(available, buf.len());
        self.data[self.write_pos..self.write_pos + to_write].copy_from_slice(&buf[..to_write]);
        self.write_pos += to_write;
        to_write
    }

    pub fn available_for_read(&self) -> usize { self.write_pos - self.read_pos }
    pub fn available_for_write(&self) -> usize { self.data.len() - self.write_pos }
    pub fn span(&self) -> &[u8] { &self.data[..self.write_pos] }
    pub fn reset(&mut self) { self.read_pos = 0; self.write_pos = 0; }
}

/// Input span stream — reads from a fixed memory region.
#[derive(Debug, Clone)]
pub struct BasicIspanstream {
    buffer: SpanStreamBuffer,
}

impl BasicIspanstream {
    pub fn new(data: &[u8]) -> Self { Self { buffer: SpanStreamBuffer::from_slice(data) } }
    pub fn read(&mut self, buf: &mut [u8]) -> usize { self.buffer.read(buf) }
    pub fn available(&self) -> usize { self.buffer.available_for_read() }
}

/// Output span stream — writes to a fixed memory region.
#[derive(Debug, Clone)]
pub struct BasicOspanstream {
    buffer: SpanStreamBuffer,
}

impl BasicOspanstream {
    pub fn new(capacity: usize) -> Self { Self { buffer: SpanStreamBuffer::new(capacity) } }
    pub fn write(&mut self, data: &[u8]) -> usize { self.buffer.write(data) }
    pub fn span(&self) -> &[u8] { self.buffer.span() }
    pub fn available(&self) -> usize { self.buffer.available_for_write() }
}

// ============================================================================
// <flat_map> / <flat_set> — Sorted Vector-Based Containers (C++23)
// ============================================================================

/// A flat map: sorted vector of key-value pairs for cache-friendly access.
#[derive(Debug, Clone)]
pub struct FlatMap<K: Ord, V> {
    entries: Vec<(K, V)>,
}

impl<K: Ord + Clone, V: Clone> FlatMap<K, V> {
    pub fn new() -> Self { Self { entries: Vec::new() } }
    pub fn with_capacity(cap: usize) -> Self { Self { entries: Vec::with_capacity(cap) } }

    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
        match self.entries.binary_search_by(|(k, _)| k.cmp(&key)) {
            Ok(idx) => {
                let old = std::mem::replace(&mut self.entries[idx].1, value);
                Some(old)
            }
            Err(idx) => {
                self.entries.insert(idx, (key, value));
                None
            }
        }
    }

    pub fn get(&self, key: &K) -> Option<&V> {
        self.entries.binary_search_by(|(k, _)| k.cmp(key))
            .ok().map(|idx| &self.entries[idx].1)
    }

    pub fn remove(&mut self, key: &K) -> Option<V> {
        self.entries.binary_search_by(|(k, _)| k.cmp(key))
            .ok().map(|idx| self.entries.remove(idx).1)
    }

    pub fn contains_key(&self, key: &K) -> bool {
        self.entries.binary_search_by(|(k, _)| k.cmp(key)).is_ok()
    }

    pub fn len(&self) -> usize { self.entries.len() }
    pub fn is_empty(&self) -> bool { self.entries.is_empty() }
    pub fn keys(&self) -> impl Iterator<Item = &K> { self.entries.iter().map(|(k, _)| k) }
    pub fn values(&self) -> impl Iterator<Item = &V> { self.entries.iter().map(|(_, v)| v) }
    pub fn iter(&self) -> impl Iterator<Item = (&K, &V)> { self.entries.iter().map(|(k, v)| (k, v)) }
    pub fn clear(&mut self) { self.entries.clear(); }
}

impl<K: Ord + Clone, V: Clone> Default for FlatMap<K, V> {
    fn default() -> Self { Self::new() }
}

/// A flat set: sorted vector of unique keys for cache-friendly access.
#[derive(Debug, Clone)]
pub struct FlatSet<K: Ord> {
    entries: Vec<K>,
}

impl<K: Ord + Clone> FlatSet<K> {
    pub fn new() -> Self { Self { entries: Vec::new() } }
    pub fn with_capacity(cap: usize) -> Self { Self { entries: Vec::with_capacity(cap) } }

    pub fn insert(&mut self, key: K) -> bool {
        match self.entries.binary_search(&key) {
            Ok(_) => false,
            Err(idx) => { self.entries.insert(idx, key); true }
        }
    }

    pub fn contains(&self, key: &K) -> bool {
        self.entries.binary_search(key).is_ok()
    }

    pub fn remove(&mut self, key: &K) -> bool {
        self.entries.binary_search(key).ok().map(|idx| { self.entries.remove(idx); }).is_some()
    }

    pub fn len(&self) -> usize { self.entries.len() }
    pub fn is_empty(&self) -> bool { self.entries.is_empty() }
    pub fn iter(&self) -> impl Iterator<Item = &K> { self.entries.iter() }
    pub fn clear(&mut self) { self.entries.clear(); }
}

impl<K: Ord + Clone> Default for FlatSet<K> {
    fn default() -> Self { Self::new() }
}

// ============================================================================
// <mdspan> — Multi-Dimensional Span View (C++23)
// ============================================================================

/// Layout policy for mdspan.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MdspanLayout {
    RowMajor,
    ColMajor,
    Strided { strides: Vec<usize> },
}

/// A multi-dimensional view over a contiguous array (C++23 std::mdspan).
#[derive(Debug, Clone)]
pub struct Mdspan<T: Clone> {
    data: Vec<T>,
    extents: Vec<usize>,
    layout: MdspanLayout,
}

impl<T: Clone + Default> Mdspan<T> {
    pub fn new(extents: &[usize]) -> Self {
        let total: usize = extents.iter().product();
        Self { data: vec![T::default(); total], extents: extents.to_vec(), layout: MdspanLayout::RowMajor }
    }

    pub fn from_data(data: Vec<T>, extents: &[usize]) -> Self {
        let total: usize = extents.iter().product();
        assert_eq!(data.len(), total, "Data size mismatch");
        Self { data, extents: extents.to_vec(), layout: MdspanLayout::RowMajor }
    }

    pub fn with_layout(mut self, layout: MdspanLayout) -> Self { self.layout = layout; self }

    fn linear_index(&self, indices: &[usize]) -> usize {
        assert_eq!(indices.len(), self.extents.len());
        match &self.layout {
            MdspanLayout::RowMajor => {
                let mut idx = 0;
                let mut stride = 1;
                for i in (0..indices.len()).rev() {
                    idx += indices[i] * stride;
                    stride *= self.extents[i];
                }
                idx
            }
            MdspanLayout::ColMajor => {
                let mut idx = 0;
                let mut stride = 1;
                for i in 0..indices.len() {
                    idx += indices[i] * stride;
                    stride *= self.extents[i];
                }
                idx
            }
            MdspanLayout::Strided { strides } => {
                indices.iter().zip(strides.iter()).map(|(&i, &s)| i * s).sum()
            }
        }
    }

    pub fn get(&self, indices: &[usize]) -> &T {
        let idx = self.linear_index(indices);
        &self.data[idx]
    }

    pub fn get_mut(&mut self, indices: &[usize]) -> &mut T {
        let idx = self.linear_index(indices);
        &mut self.data[idx]
    }

    pub fn rank(&self) -> usize { self.extents.len() }
    pub fn extent(&self, dim: usize) -> usize { self.extents[dim] }
    pub fn extents(&self) -> &[usize] { &self.extents }
    pub fn size(&self) -> usize { self.data.len() }
    pub fn is_empty(&self) -> bool { self.data.is_empty() }

    /// Create a subspan view into this mdspan.
    pub fn subspan(&self, offset: &[usize], count: &[usize]) -> Self {
        // Simplified: returns a flat subspan copy
        let total: usize = count.iter().product();
        let mut result = Self::new(count);
        // Copy the relevant data
        for idx in 0..total {
            let mut src = vec![0usize; offset.len()];
            let mut remaining = idx;
            for i in (0..count.len()).rev() {
                src[i] = offset[i] + remaining % count[i];
                remaining /= count[i];
            }
            result.data[idx] = self.get(&src).clone();
        }
        result
    }
}

// ============================================================================
// <generator> — std::generator<T> (C++23)
// ============================================================================

/// A coroutine-based generator that yields values of type T.
/// Models std::generator<T> from C++23.
#[derive(Debug, Clone)]
pub struct StdGenerator<T> {
    items: Vec<T>,
    position: usize,
}

impl<T: Clone> StdGenerator<T> {
    pub fn new() -> Self { Self { items: Vec::new(), position: 0 } }

    pub fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        Self { items: iter.into_iter().collect(), position: 0 }
    }

    pub fn from_fn<F: FnMut() -> Option<T>>(mut f: F, count: usize) -> Self {
        let mut items = Vec::with_capacity(count);
        for _ in 0..count {
            if let Some(item) = f() { items.push(item); } else { break; }
        }
        Self { items, position: 0 }
    }

    pub fn next(&mut self) -> Option<T> {
        if self.position < self.items.len() {
            let item = self.items[self.position].clone();
            self.position += 1;
            Some(item)
        } else {
            None
        }
    }

    pub fn peek(&self) -> Option<&T> {
        self.items.get(self.position)
    }

    pub fn reset(&mut self) { self.position = 0; }
    pub fn remaining(&self) -> usize { self.items.len() - self.position }
    pub fn is_done(&self) -> bool { self.position >= self.items.len() }

    /// Map each element.
    pub fn map<U: Clone, F: Fn(&T) -> U>(self, f: F) -> StdGenerator<U> {
        StdGenerator { items: self.items.iter().map(|x| f(x)).collect(), position: 0 }
    }

    /// Filter elements.
    pub fn filter<F: Fn(&T) -> bool>(self, predicate: F) -> StdGenerator<T> {
        StdGenerator { items: self.items.into_iter().filter(|x| predicate(x)).collect(), position: 0 }
    }

    /// Collect all remaining items.
    pub fn collect_all(&mut self) -> Vec<T> {
        let result: Vec<T> = self.items[self.position..].to_vec();
        self.position = self.items.len();
        result
    }
}

impl<T: Clone> Default for StdGenerator<T> {
    fn default() -> Self { Self::new() }
}

impl<T: Clone> Iterator for StdGenerator<T> {
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> { self.next() }
    fn size_hint(&self) -> (usize, Option<usize>) {
        let rem = self.remaining();
        (rem, Some(rem))
    }
}

// ============================================================================
// <print> — std::print / std::println (C++23)
// ============================================================================

/// Type-safe formatted print (C++23 std::print).
#[derive(Debug, Clone)]
pub struct PrintFormatter {
    buffer: String,
    locale_sensitive: bool,
}

impl PrintFormatter {
    pub fn new() -> Self { Self { buffer: String::new(), locale_sensitive: false } }

    pub fn print(&mut self, msg: &str) -> String {
        self.buffer.push_str(msg);
        self.buffer.clone()
    }

    pub fn println(&mut self, msg: &str) -> String {
        let mut result = String::new();
        result.push_str(msg);
        result.push('\n');
        self.buffer.push_str(&result);
        result
    }

    pub fn flush(&self) -> String { self.buffer.clone() }
}

/// Global print functions modeled after std::print / std::println.
pub fn std_print(msg: &str) { println!("{}", msg); }

pub fn std_println(msg: &str) { println!("{}", msg); }

/// Format args for print (simplified model of std::print with format args).
#[derive(Debug, Clone)]
pub struct PrintArgs {
    pub format_string: String,
    pub args: Vec<String>,
}

impl PrintArgs {
    pub fn new(fmt: &str, args: Vec<String>) -> Self { Self { format_string: fmt.to_string(), args } }

    pub fn to_string(&self) -> String {
        let mut result = self.format_string.clone();
        for (i, arg) in self.args.iter().enumerate() {
            let placeholder = format!("{{{}}}", i);
            result = result.replace(&placeholder, arg);
        }
        result
    }
}

// ============================================================================
// <stacktrace> — std::stacktrace (C++23)
// ============================================================================

/// A single entry in a stack trace.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct StacktraceEntry {
    pub description: String,
    pub source_file: Option<String>,
    pub source_line: Option<u32>,
    pub function_name: Option<String>,
    pub address: Option<u64>,
}

impl StacktraceEntry {
    pub fn new(desc: &str) -> Self {
        Self { description: desc.to_string(), source_file: None,
            source_line: None, function_name: None, address: None }
    }

    pub fn with_source(mut self, file: &str, line: u32) -> Self {
        self.source_file = Some(file.to_string());
        self.source_line = Some(line);
        self
    }

    pub fn with_function(mut self, func: &str) -> Self {
        self.function_name = Some(func.to_string());
        self
    }

    pub fn with_address(mut self, addr: u64) -> Self {
        self.address = Some(addr);
        self
    }
}

impl fmt::Display for StacktraceEntry {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if let Some(ref func) = self.function_name {
            write!(f, "{} at ", func)?;
        }
        write!(f, "{}", self.description)?;
        if let Some(ref file) = self.source_file {
            write!(f, " [{}", file)?;
            if let Some(line) = self.source_line {
                write!(f, ":{}", line)?;
            }
            write!(f, "]")?;
        }
        Ok(())
    }
}

/// A basic stack trace (C++23 std::stacktrace).
#[derive(Debug, Clone)]
pub struct BasicStacktrace {
    entries: Vec<StacktraceEntry>,
    max_depth: usize,
}

impl BasicStacktrace {
    pub fn new(max_depth: usize) -> Self {
        Self { entries: Vec::with_capacity(max_depth), max_depth }
    }

    /// Capture current stack trace. In our model, callers push frames explicitly.
    pub fn current() -> Self {
        Self { entries: Vec::new(), max_depth: 128 }
    }

    pub fn with_depth(max_depth: usize) -> Self {
        Self { entries: Vec::with_capacity(max_depth), max_depth }
    }

    pub fn push(&mut self, entry: StacktraceEntry) {
        if self.entries.len() < self.max_depth {
            self.entries.push(entry);
        }
    }

    pub fn size(&self) -> usize { self.entries.len() }
    pub fn is_empty(&self) -> bool { self.entries.is_empty() }
    pub fn entries(&self) -> &[StacktraceEntry] { &self.entries }
    pub fn get(&self, index: usize) -> Option<&StacktraceEntry> { self.entries.get(index) }
}

impl fmt::Display for BasicStacktrace {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "Stack trace ({} frames):", self.entries.len())?;
        for (i, entry) in self.entries.iter().enumerate() {
            writeln!(f, "  #{} {}", i, entry)?;
        }
        Ok(())
    }
}

// ============================================================================
// <debugging> — std::debugging utilities (C++26)
// ============================================================================

/// Debugging utilities (C++26 <debugging> header).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct DebuggerState {
    pub is_present: bool,
    pub is_attached: bool,
}

impl DebuggerState {
    pub fn new() -> Self { Self { is_present: false, is_attached: false } }

    /// Check if a debugger is currently attached to this process.
    pub fn is_debugger_present(&self) -> bool { self.is_present }

    /// Break into the debugger if one is attached.
    pub fn breakpoint(&self) {
        if self.is_present {
            // In native code: __builtin_debugtrap() or __debugbreak()
            eprintln!("BREAKPOINT: Debugger is present.");
        }
    }

    /// Break if condition is true and debugger is attached.
    pub fn break_if_debugging(&self, condition: bool) {
        if condition && self.is_present { self.breakpoint(); }
    }

    /// Set debugger present state (simulated).
    pub fn set_present(mut self, present: bool) -> Self {
        self.is_present = present;
        self
    }
}

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

// ============================================================================
// <text_encoding> — Text Encoding (C++26)
// ============================================================================

/// Text encoding identification (C++26 <text_encoding>).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum TextEncoding {
    // Unicode encodings
    Utf8,
    Utf16LE,
    Utf16BE,
    Utf32LE,
    Utf32BE,
    // Legacy encodings
    Ascii,
    Latin1,
    Windows1252,
    ShiftJIS,
    EucJp,
    Iso2022Jp,
    Gb2312,
    Gbk,
    Gb18030,
    Big5,
    EucKr,
    Koi8R,
    Koi8U,
    // Generic
    Other { name: String },
    Unknown,
}

impl TextEncoding {
    pub fn name(&self) -> &str {
        match self {
            Self::Utf8 => "UTF-8",
            Self::Utf16LE => "UTF-16LE",
            Self::Utf16BE => "UTF-16BE",
            Self::Utf32LE => "UTF-32LE",
            Self::Utf32BE => "UTF-32BE",
            Self::Ascii => "ASCII",
            Self::Latin1 => "ISO-8859-1",
            Self::Windows1252 => "Windows-1252",
            Self::ShiftJIS => "Shift_JIS",
            Self::EucJp => "EUC-JP",
            Self::Iso2022Jp => "ISO-2022-JP",
            Self::Gb2312 => "GB2312",
            Self::Gbk => "GBK",
            Self::Gb18030 => "GB18030",
            Self::Big5 => "Big5",
            Self::EucKr => "EUC-KR",
            Self::Koi8R => "KOI8-R",
            Self::Koi8U => "KOI8-U",
            Self::Other { ref name } => name,
            Self::Unknown => "unknown",
        }
    }

    pub fn is_unicode(&self) -> bool {
        matches!(self, Self::Utf8 | Self::Utf16LE | Self::Utf16BE | Self::Utf32LE | Self::Utf32BE)
    }

    pub fn is_multi_byte(&self) -> bool {
        matches!(self, Self::Utf8 | Self::ShiftJIS | Self::EucJp | Self::Iso2022Jp |
            Self::Gbk | Self::Gb18030 | Self::Big5 | Self::EucKr)
    }

    pub fn min_bytes_per_char(&self) -> usize {
        match self {
            Self::Utf8 | Self::Ascii | Self::Latin1 | Self::Windows1252 | Self::Koi8R | Self::Koi8U => 1,
            Self::Utf16LE | Self::Utf16BE => 2,
            Self::Utf32LE | Self::Utf32BE => 4,
            _ => 1,
        }
    }

    pub fn max_bytes_per_char(&self) -> usize {
        match self {
            Self::Utf8 => 4,
            Self::Utf16LE | Self::Utf16BE => 4,
            Self::Utf32LE | Self::Utf32BE => 4,
            Self::Gb18030 => 4,
            _ => self.min_bytes_per_char(),
        }
    }

    /// Detect encoding from BOM (byte order mark) if present.
    pub fn detect_from_bom(bytes: &[u8]) -> Option<Self> {
        if bytes.len() >= 3 && bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF {
            Some(Self::Utf8)
        } else if bytes.len() >= 2 && bytes[0] == 0xFE && bytes[1] == 0xFF {
            Some(Self::Utf16BE)
        } else if bytes.len() >= 2 && bytes[0] == 0xFF && bytes[1] == 0xFE {
            Some(Self::Utf16LE)
        } else if bytes.len() >= 4 && bytes[0] == 0x00 && bytes[1] == 0x00 && bytes[2] == 0xFE && bytes[3] == 0xFF {
            Some(Self::Utf32BE)
        } else if bytes.len() >= 4 && bytes[0] == 0xFF && bytes[1] == 0xFE && bytes[2] == 0x00 && bytes[3] == 0x00 {
            Some(Self::Utf32LE)
        } else {
            None
        }
    }

    /// Guess encoding from heuristics.
    pub fn guess_from_content(bytes: &[u8]) -> Self {
        if bytes.is_empty() { return Self::Unknown; }
        // Try UTF-8 validation
        if std::str::from_utf8(bytes).is_ok() { return Self::Utf8; }
        // Check for ASCII
        if bytes.iter().all(|&b| b < 0x80) { return Self::Ascii; }
        Self::Unknown
    }
}

impl fmt::Display for TextEncoding {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.name())
    }
}

// ============================================================================
// <inplace_vector> — Fixed-Capacity Vector (C++26)
// ============================================================================

/// A vector with fixed capacity whose storage is within the object itself.
/// Models std::inplace_vector<T, N> from C++26.
#[derive(Debug)]
pub struct InplaceVector<T: Copy, const N: usize> {
    data: [Option<T>; N],
    len: usize,
}

impl<T: Copy + Default, const N: usize> InplaceVector<T, N> {
    pub fn new() -> Self {
        Self { data: [None; N], len: 0 }
    }

    pub fn push_back(&mut self, value: T) -> Result<(), &'static str> {
        if self.len >= N { return Err("inplace_vector capacity exceeded"); }
        self.data[self.len] = Some(value);
        self.len += 1;
        Ok(())
    }

    pub fn pop_back(&mut self) -> Option<T> {
        if self.len == 0 { return None; }
        self.len -= 1;
        self.data[self.len].take()
    }

    pub fn get(&self, index: usize) -> Option<&T> {
        self.data.get(index).and_then(|o| o.as_ref())
    }

    pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
        self.data.get_mut(index).and_then(|o| o.as_mut())
    }

    pub fn len(&self) -> usize { self.len }
    pub fn is_empty(&self) -> bool { self.len == 0 }
    pub fn is_full(&self) -> bool { self.len >= N }
    pub fn capacity(&self) -> usize { N }
    pub fn clear(&mut self) {
        for i in 0..self.len { self.data[i] = None; }
        self.len = 0;
    }

    pub fn as_slice(&self) -> &[Option<T>] { &self.data[..self.len] }
}

impl<T: Copy + Default, const N: usize> Default for InplaceVector<T, N> {
    fn default() -> Self { Self::new() }
}

impl<T: Copy + Default + fmt::Debug, const N: usize> fmt::Display for InplaceVector<T, N> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "[")?;
        for i in 0..self.len {
            if i > 0 { write!(f, ", ")?; }
            write!(f, "{:?}", self.data[i])?;
        }
        write!(f, "]")
    }
}

// ============================================================================
// <hive> — Bucket-Array Associative Container (Proposed)
// ============================================================================

/// A bucket-array container with stable references.
/// Proposed as std::hive — provides O(1) insertion, O(n) iteration,
/// and stable element addresses.
#[derive(Debug, Clone)]
pub struct Hive<T: Clone> {
    buckets: Vec<Vec<T>>,
    bucket_capacity: usize,
    size: usize,
}

impl<T: Clone> Hive<T> {
    pub fn new() -> Self {
        Self { buckets: vec![Vec::new()], bucket_capacity: 64, size: 0 }
    }

    pub fn with_bucket_capacity(cap: usize) -> Self {
        Self { buckets: vec![Vec::with_capacity(cap)], bucket_capacity: cap, size: 0 }
    }

    pub fn insert(&mut self, value: T) -> HiveIndex {
        if self.buckets.last().map_or(true, |b| b.len() >= self.bucket_capacity) {
            self.buckets.push(Vec::with_capacity(self.bucket_capacity));
        }
        let bucket_idx = self.buckets.len() - 1;
        let elem_idx = self.buckets[bucket_idx].len();
        self.buckets[bucket_idx].push(value);
        self.size += 1;
        HiveIndex { bucket: bucket_idx, element: elem_idx }
    }

    pub fn get(&self, index: &HiveIndex) -> Option<&T> {
        self.buckets.get(index.bucket).and_then(|b| b.get(index.element))
    }

    pub fn remove(&mut self, index: &HiveIndex) -> Option<T> {
        if let Some(bucket) = self.buckets.get_mut(index.bucket) {
            if index.element < bucket.len() {
                let last = bucket.pop().unwrap();
                if index.element < bucket.len() {
                    let removed = std::mem::replace(&mut bucket[index.element], last);
                    self.size -= 1;
                    return Some(removed);
                } else {
                    self.size -= 1;
                    return Some(last);
                }
            }
        }
        None
    }

    pub fn iter(&self) -> impl Iterator<Item = &T> {
        self.buckets.iter().flat_map(|b| b.iter())
    }

    pub fn len(&self) -> usize { self.size }
    pub fn is_empty(&self) -> bool { self.size == 0 }
    pub fn bucket_count(&self) -> usize { self.buckets.len() }
}

impl<T: Clone + Default> Default for Hive<T> {
    fn default() -> Self { Self::new() }
}

/// Index into a hive.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct HiveIndex {
    bucket: usize,
    element: usize,
}

// ============================================================================
// STL4 Feature Registry
// ============================================================================

/// Registry tracking which C++23/26 library features are enabled.
#[derive(Debug, Clone)]
pub struct Stl4Registry {
    pub execution_policies: bool,
    pub latch_enabled: bool,
    pub barrier_enabled: bool,
    pub counting_semaphore_enabled: bool,
    pub syncstream_enabled: bool,
    pub spanstream_enabled: bool,
    pub flat_map_enabled: bool,
    pub flat_set_enabled: bool,
    pub mdspan_enabled: bool,
    pub generator_enabled: bool,
    pub print_enabled: bool,
    pub stacktrace_enabled: bool,
    pub debugging_enabled: bool,
    pub text_encoding_enabled: bool,
    pub inplace_vector_enabled: bool,
    pub hive_enabled: bool,
    pub standard_year: u32,
}

impl Stl4Registry {
    pub fn new() -> Self {
        Self {
            execution_policies: false, latch_enabled: false, barrier_enabled: false,
            counting_semaphore_enabled: false, syncstream_enabled: false, spanstream_enabled: false,
            flat_map_enabled: false, flat_set_enabled: false, mdspan_enabled: false,
            generator_enabled: false, print_enabled: false, stacktrace_enabled: false,
            debugging_enabled: false, text_encoding_enabled: false, inplace_vector_enabled: false,
            hive_enabled: false, standard_year: 0,
        }
    }

    pub fn with_standard(mut self, year: u32) -> Self {
        self.standard_year = year;
        match year {
            202002 => {
                self.execution_policies = true;
                self.latch_enabled = true;
                self.barrier_enabled = true;
                self.counting_semaphore_enabled = true;
                self.syncstream_enabled = true;
            }
            202302 => {
                self.execution_policies = true;
                self.latch_enabled = true;
                self.barrier_enabled = true;
                self.counting_semaphore_enabled = true;
                self.syncstream_enabled = true;
                self.spanstream_enabled = true;
                self.flat_map_enabled = true;
                self.flat_set_enabled = true;
                self.mdspan_enabled = true;
                self.generator_enabled = true;
                self.print_enabled = true;
                self.stacktrace_enabled = true;
            }
            202602 | _ if year >= 202602 => {
                self.execution_policies = true;
                self.latch_enabled = true;
                self.barrier_enabled = true;
                self.counting_semaphore_enabled = true;
                self.syncstream_enabled = true;
                self.spanstream_enabled = true;
                self.flat_map_enabled = true;
                self.flat_set_enabled = true;
                self.mdspan_enabled = true;
                self.generator_enabled = true;
                self.print_enabled = true;
                self.stacktrace_enabled = true;
                self.debugging_enabled = true;
                self.text_encoding_enabled = true;
                self.inplace_vector_enabled = true;
            }
            _ => {}
        }
        self.hive_enabled = true; // Always available as proposed
        self
    }

    pub fn feature_count(&self) -> usize {
        let mut count = 0;
        if self.execution_policies { count += 1; }
        if self.latch_enabled { count += 1; }
        if self.barrier_enabled { count += 1; }
        if self.counting_semaphore_enabled { count += 1; }
        if self.syncstream_enabled { count += 1; }
        if self.spanstream_enabled { count += 1; }
        if self.flat_map_enabled { count += 1; }
        if self.flat_set_enabled { count += 1; }
        if self.mdspan_enabled { count += 1; }
        if self.generator_enabled { count += 1; }
        if self.print_enabled { count += 1; }
        if self.stacktrace_enabled { count += 1; }
        if self.debugging_enabled { count += 1; }
        if self.text_encoding_enabled { count += 1; }
        if self.inplace_vector_enabled { count += 1; }
        if self.hive_enabled { count += 1; }
        count
    }

    pub fn headers_for_standard(&self) -> Vec<String> {
        let mut h = Vec::new();
        if self.execution_policies { h.push("<execution>".to_string()); }
        if self.latch_enabled { h.push("<latch>".to_string()); }
        if self.barrier_enabled { h.push("<barrier>".to_string()); }
        if self.counting_semaphore_enabled { h.push("<semaphore>".to_string()); }
        if self.syncstream_enabled { h.push("<syncstream>".to_string()); }
        if self.spanstream_enabled { h.push("<spanstream>".to_string()); }
        if self.flat_map_enabled { h.push("<flat_map>".to_string()); }
        if self.flat_set_enabled { h.push("<flat_set>".to_string()); }
        if self.mdspan_enabled { h.push("<mdspan>".to_string()); }
        if self.generator_enabled { h.push("<generator>".to_string()); }
        if self.print_enabled { h.push("<print>".to_string()); }
        if self.stacktrace_enabled { h.push("<stacktrace>".to_string()); }
        if self.debugging_enabled { h.push("<debugging>".to_string()); }
        if self.text_encoding_enabled { h.push("<text_encoding>".to_string()); }
        if self.inplace_vector_enabled { h.push("<inplace_vector>".to_string()); }
        if self.hive_enabled { h.push("<hive>".to_string()); }
        h
    }
}

// ============================================================================
// Tests
// ============================================================================

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

    // ── <execution> tests ──────────────────────────────────────────────
    #[test]
    fn test_execution_policy_is_parallel() {
        assert!(!ExecutionPolicy::SequencedPolicy.is_parallel());
        assert!(ExecutionPolicy::ParallelPolicy.is_parallel());
        assert!(ExecutionPolicy::ParallelUnsequencedPolicy.is_parallel());
    }

    #[test]
    fn test_parallel_algorithm_should_parallelize() {
        let config = ParallelAlgorithmConfig::new(ExecutionPolicy::ParallelPolicy);
        assert!(!config.should_parallelize(100));
        assert!(config.should_parallelize(50000));
    }

    // ── <latch> tests ──────────────────────────────────────────────────
    #[test]
    fn test_latch_new() { let l = Latch::new(5); assert_eq!(l.current_count(), 5); }
    #[test]
    fn test_latch_count_down() { let mut l = Latch::new(3); l.count_down_one(); l.count_down_one(); assert_eq!(l.current_count(), 1); }
    #[test]
    fn test_latch_try_wait() { let l = Latch::new(0); assert!(l.try_wait()); }
    #[test]
    fn test_latch_reset() { let mut l = Latch::new(3); l.count_down_one(); l.reset(); assert_eq!(l.current_count(), 3); }

    // ── <barrier> tests ────────────────────────────────────────────────
    #[test]
    fn test_barrier_new() { let b = Barrier::new(4); assert_eq!(b.expected_count(), 4); }
    #[test]
    fn test_barrier_arrive_and_wait() { let mut b = Barrier::new(1); b.arrive_and_wait(); }
    #[test]
    fn test_barrier_arrive_and_drop() { let mut b = Barrier::new(3); b.arrive_and_drop(); assert_eq!(b.expected_count(), 2); }

    // ── <semaphore> tests ──────────────────────────────────────────────
    #[test]
    fn test_counting_semaphore_acquire_release() {
        let mut sem: CountingSemaphore<5> = CountingSemaphore::new(2);
        assert!(sem.try_acquire());
        sem.release_one();
        assert_eq!(sem.try_acquire_for(100), true);
    }

    #[test]
    fn test_binary_semaphore() {
        let mut sem: BinarySemaphore = BinarySemaphore::new(1);
        assert!(sem.try_acquire());
        assert!(!sem.try_acquire());
        sem.release_one();
        assert!(sem.try_acquire());
    }

    // ── <syncstream> tests ─────────────────────────────────────────────
    #[test]
    fn test_osyncstream_write_emit() {
        let mut stream = BasicOsyncstream::new(None);
        stream.write("hello");
        stream.write(" world");
        let result = stream.emit();
        assert_eq!(String::from_utf8_lossy(&result), "hello world");
    }

    // ── <spanstream> tests ─────────────────────────────────────────────
    #[test]
    fn test_ospanstream_write() {
        let mut stream = BasicOspanstream::new(256);
        assert_eq!(stream.write(b"test"), 4);
        assert_eq!(stream.span(), b"test");
    }

    #[test]
    fn test_ispanstream_read() {
        let data = b"hello world";
        let mut stream = BasicIspanstream::new(data);
        let mut buf = [0u8; 5];
        assert_eq!(stream.read(&mut buf), 5);
        assert_eq!(&buf, b"hello");
    }

    // ── <flat_map> / <flat_set> tests ──────────────────────────────────
    #[test]
    fn test_flat_map_insert_get() {
        let mut m: FlatMap<i32, String> = FlatMap::new();
        assert!(m.insert(1, "one".into()).is_none());
        assert_eq!(m.get(&1), Some(&"one".to_string()));
        assert!(m.insert(1, "ONE".into()).is_some());
        assert_eq!(m.get(&1), Some(&"ONE".to_string()));
    }

    #[test]
    fn test_flat_map_remove() {
        let mut m: FlatMap<i32, i32> = FlatMap::new();
        m.insert(1, 100); m.insert(2, 200);
        assert_eq!(m.remove(&1), Some(100));
        assert_eq!(m.len(), 1);
    }

    #[test]
    fn test_flat_set_insert_contains() {
        let mut s: FlatSet<i32> = FlatSet::new();
        assert!(s.insert(42));
        assert!(s.contains(&42));
        assert!(!s.insert(42));
        assert!(s.remove(&42));
        assert!(!s.contains(&42));
    }

    // ── <mdspan> tests ─────────────────────────────────────────────────
    #[test]
    fn test_mdspan_create_get() {
        let data = vec![1, 2, 3, 4, 5, 6];
        let span = Mdspan::from_data(data, &[2, 3]);
        assert_eq!(span.rank(), 2);
        assert_eq!(*span.get(&[0, 0]), 1);
        assert_eq!(*span.get(&[1, 2]), 6);
    }

    #[test]
    fn test_mdspan_row_major() {
        let data: Vec<i32> = (0..24).collect();
        let span = Mdspan::from_data(data, &[2, 3, 4]);
        assert_eq!(*span.get(&[1, 2, 3]), 23);
    }

    // ── <generator> tests ──────────────────────────────────────────────
    #[test]
    fn test_generator_from_iter() {
        let mut gen = StdGenerator::from_iter(vec![1, 2, 3, 4, 5]);
        assert_eq!(gen.next(), Some(1));
        assert_eq!(gen.next(), Some(2));
        assert_eq!(gen.collect_all(), vec![3, 4, 5]);
        assert!(gen.is_done());
    }

    #[test]
    fn test_generator_map() {
        let gen = StdGenerator::from_iter(vec![1, 2, 3]);
        let mapped = gen.map(|x| *x * 2);
        assert_eq!(mapped.items, vec![2, 4, 6]);
    }

    #[test]
    fn test_generator_filter() {
        let gen = StdGenerator::from_iter(vec![1, 2, 3, 4, 5, 6]);
        let filtered = gen.filter(|x| *x % 2 == 0);
        assert_eq!(filtered.items, vec![2, 4, 6]);
    }

    // ── <print> tests ─────────────────────────────────────────────────
    #[test]
    fn test_print_args_to_string() {
        let args = PrintArgs::new("Hello {} from {}", vec!["world".into(), "Rust".into()]);
        assert_eq!(args.to_string(), "Hello world from Rust");
    }

    // ── <stacktrace> tests ─────────────────────────────────────────────
    #[test]
    fn test_stacktrace_entry_display() {
        let entry = StacktraceEntry::new("main.cpp:42")
            .with_function("main")
            .with_source("main.cpp", 42);
        let s = entry.to_string();
        assert!(s.contains("main"));
        assert!(s.contains("main.cpp"));
    }

    #[test]
    fn test_basic_stacktrace_push() {
        let mut st = BasicStacktrace::with_depth(10);
        st.push(StacktraceEntry::new("frame0").with_function("f0"));
        st.push(StacktraceEntry::new("frame1").with_function("f1"));
        assert_eq!(st.size(), 2);
    }

    // ── <debugging> tests ──────────────────────────────────────────────
    #[test]
    fn test_debugger_state_default() {
        let ds = DebuggerState::new();
        assert!(!ds.is_debugger_present());
    }

    #[test]
    fn test_debugger_state_set_present() {
        let ds = DebuggerState::new().set_present(true);
        assert!(ds.is_debugger_present());
        ds.break_if_debugging(true);
    }

    // ── <text_encoding> tests ───────────────────────────────────────────
    #[test]
    fn test_text_encoding_name() {
        assert_eq!(TextEncoding::Utf8.name(), "UTF-8");
        assert_eq!(TextEncoding::ShiftJIS.name(), "Shift_JIS");
    }

    #[test]
    fn test_text_encoding_is_unicode() {
        assert!(TextEncoding::Utf8.is_unicode());
        assert!(!TextEncoding::Ascii.is_unicode());
    }

    #[test]
    fn test_text_encoding_detect_from_bom_utf8() {
        let bom = [0xEF, 0xBB, 0xBF, 0x48, 0x65];
        assert_eq!(TextEncoding::detect_from_bom(&bom), Some(TextEncoding::Utf8));
    }

    #[test]
    fn test_text_encoding_guess_utf8() {
        assert_eq!(TextEncoding::guess_from_content(b"Hello World"), TextEncoding::Utf8);
    }

    #[test]
    fn test_text_encoding_guess_ascii() {
        assert_eq!(TextEncoding::guess_from_content(b"ASCII"), TextEncoding::Ascii);
    }

    // ── <inplace_vector> tests ──────────────────────────────────────────
    #[test]
    fn test_inplace_vector_push_pop() {
        let mut v: InplaceVector<i32, 5> = InplaceVector::new();
        assert!(v.push_back(10).is_ok());
        assert!(v.push_back(20).is_ok());
        assert_eq!(v.len(), 2);
        assert_eq!(v.pop_back(), Some(20));
        assert_eq!(v.pop_back(), Some(10));
    }

    #[test]
    fn test_inplace_vector_capacity() {
        let mut v: InplaceVector<i32, 3> = InplaceVector::new();
        assert!(v.push_back(1).is_ok());
        assert!(v.push_back(2).is_ok());
        assert!(v.push_back(3).is_ok());
        assert!(v.push_back(4).is_err());
        assert!(v.is_full());
    }

    // ── <hive> tests ────────────────────────────────────────────────────
    #[test]
    fn test_hive_insert_get() {
        let mut hive: Hive<i32> = Hive::new();
        let idx = hive.insert(42);
        assert_eq!(hive.get(&idx), Some(&42));
    }

    #[test]
    fn test_hive_iter() {
        let mut hive: Hive<i32> = Hive::new();
        hive.insert(1); hive.insert(2); hive.insert(3);
        let sum: i32 = hive.iter().sum();
        assert_eq!(sum, 6);
    }

    #[test]
    fn test_hive_remove() {
        let mut hive: Hive<i32> = Hive::new();
        let idx = hive.insert(99);
        assert_eq!(hive.remove(&idx), Some(99));
        assert_eq!(hive.len(), 0);
    }

    // ── Stl4Registry tests ──────────────────────────────────────────────
    #[test]
    fn test_stl4_registry_default() {
        let reg = Stl4Registry::new();
        assert_eq!(reg.feature_count(), 0);
    }

    #[test]
    fn test_stl4_registry_cpp20() {
        let reg = Stl4Registry::new().with_standard(202002);
        assert!(reg.execution_policies);
        assert!(reg.latch_enabled);
        assert!(!reg.generator_enabled);
        assert!(reg.feature_count() >= 6);
    }

    #[test]
    fn test_stl4_registry_cpp23() {
        let reg = Stl4Registry::new().with_standard(202302);
        assert!(reg.flat_map_enabled);
        assert!(reg.mdspan_enabled);
        assert!(reg.generator_enabled);
        assert!(reg.print_enabled);
        assert!(reg.feature_count() >= 13);
    }

    #[test]
    fn test_stl4_registry_cpp26() {
        let reg = Stl4Registry::new().with_standard(202602);
        assert!(reg.debugging_enabled);
        assert!(reg.text_encoding_enabled);
        assert!(reg.inplace_vector_enabled);
        assert!(reg.feature_count() == 16);
    }

    #[test]
    fn test_stl4_registry_headers_cpp23() {
        let reg = Stl4Registry::new().with_standard(202302);
        let headers = reg.headers_for_standard();
        assert!(headers.contains(&"<flat_map>".to_string()));
        assert!(headers.contains(&"<generator>".to_string()));
        assert!(!headers.contains(&"<debugging>".to_string()));
    }

    #[test]
    fn test_stl4_registry_headers_cpp26() {
        let reg = Stl4Registry::new().with_standard(202602);
        let headers = reg.headers_for_standard();
        assert!(headers.contains(&"<debugging>".to_string()));
        assert!(headers.contains(&"<text_encoding>".to_string()));
    }
}

// ============================================================================
// Extended MDSPAN: Subspans, Slices, and Layouts
// ============================================================================

/// Slice specifier for mdspan subspan operations.
#[derive(Debug, Clone)]
pub enum MdspanSlice {
    Single(usize),
    Range { start: usize, end: usize },
    All,
    StridedRange { start: usize, end: usize, stride: usize },
}

impl MdspanSlice {
    pub fn count(&self, full_extent: usize) -> usize {
        match self {
            Self::Single(_) => 1,
            Self::Range { start, end } => end - start,
            Self::All => full_extent,
            Self::StridedRange { start, end, stride } => (end - start + stride - 1) / stride,
        }
    }
}

/// Extended mdspan with subspan slicing support.
#[derive(Debug, Clone)]
pub struct MdspanExt<T: Clone> {
    inner: Mdspan<T>,
}

impl<T: Clone + Default> MdspanExt<T> {
    pub fn new(extents: &[usize]) -> Self {
        Self { inner: Mdspan::new(extents) }
    }

    pub fn from_data(data: Vec<T>, extents: &[usize]) -> Self {
        Self { inner: Mdspan::from_data(data, extents) }
    }

    pub fn get(&self, indices: &[usize]) -> &T { self.inner.get(indices) }
    pub fn get_mut(&mut self, indices: &[usize]) -> &mut T { self.inner.get_mut(indices) }
    pub fn rank(&self) -> usize { self.inner.rank() }
    pub fn extents(&self) -> &[usize] { self.inner.extents() }
    pub fn size(&self) -> usize { self.inner.size() }

    /// Slice along multiple dimensions.
    pub fn slice(&self, slices: &[MdspanSlice]) -> Self {
        assert_eq!(slices.len(), self.rank());
        let new_extents: Vec<usize> = slices.iter()
            .zip(self.extents().iter())
            .map(|(s, &e)| s.count(e))
            .collect();
        // Simplified slicing: create new storage
        let total: usize = new_extents.iter().product();
        let mut new_data = vec![T::default(); total];
        // Copy relevant elements (simplified to linear scan)
        for new_idx in 0..total {
            let mut remaining = new_idx;
            let mut src_indices = vec![0usize; self.rank()];
            for dim in (0..self.rank()).rev() {
                let base = match &slices[dim] {
                    MdspanSlice::Single(i) => *i,
                    MdspanSlice::Range { start, .. } | MdspanSlice::StridedRange { start, .. } => *start,
                    MdspanSlice::All => 0,
                };
                src_indices[dim] = base + remaining % new_extents[dim];
                remaining /= new_extents[dim];
            }
            new_data[new_idx] = self.get(&src_indices).clone();
        }
        MdspanExt { inner: Mdspan::from_data(new_data, &new_extents) }
    }
}

// ============================================================================
// Parallel Reduce and Transform-Reduce (Execution Policies)
// ============================================================================

/// Parallel reduction with execution policy.
#[derive(Debug, Clone)]
pub struct ParallelReducer {
    pub policy: ExecutionPolicy,
    pub chunk_size: usize,
}

impl ParallelReducer {
    pub fn new(policy: ExecutionPolicy) -> Self { Self { policy, chunk_size: 1024 } }

    pub fn reduce<T: Clone + std::ops::Add<Output = T> + Default>(
        &self, data: &[T]
    ) -> T {
        let n = data.len();
        if !self.policy.is_parallel() || n < 10000 {
            return data.iter().fold(T::default(), |a, b| a + b.clone());
        }
        let chunks = (n + self.chunk_size - 1) / self.chunk_size;
        let mut partials: Vec<T> = vec![T::default(); chunks];
        for (chunk_idx, chunk) in data.chunks(self.chunk_size).enumerate() {
            partials[chunk_idx] = chunk.iter().fold(T::default(), |a, b| a + b.clone());
        }
        partials.into_iter().fold(T::default(), |a, b| a + b)
    }

    pub fn reduce_by_key<K: Eq + Clone, V: Clone + std::ops::Add<Output = V> + Default>(
        &self, keys: &[K], values: &[V]
    ) -> Vec<(K, V)> {
        use std::collections::HashMap;
        let mut map: HashMap<K, V> = HashMap::new();
        for (k, v) in keys.iter().zip(values.iter()) {
            map.entry(k.clone()).or_insert_with(V::default);
            if let Some(entry) = map.get_mut(k) {
                *entry = entry.clone() + v.clone();
            }
        }
        map.into_iter().collect()
    }

    pub fn inclusive_scan<T: Clone + std::ops::Add<Output = T> + Default>(
        &self, data: &[T]
    ) -> Vec<T> {
        let mut result = Vec::with_capacity(data.len());
        let mut acc = T::default();
        for item in data {
            acc = acc + item.clone();
            result.push(acc.clone());
        }
        result
    }
}

// ============================================================================
// Coroutine Generator Extensions
// ============================================================================

/// Generator with async transformation support.
#[derive(Debug, Clone)]
pub struct AsyncGenerator<T: Clone> {
    items: Vec<T>,
    position: usize,
    batch_size: usize,
}

impl<T: Clone> AsyncGenerator<T> {
    pub fn new(items: Vec<T>) -> Self { Self { items, position: 0, batch_size: 1 } }

    pub fn with_batch_size(mut self, size: usize) -> Self { self.batch_size = size; self }

    pub fn next_batch(&mut self) -> Vec<T> {
        let start = self.position;
        let end = std::cmp::min(start + self.batch_size, self.items.len());
        let batch: Vec<T> = self.items[start..end].to_vec();
        self.position = end;
        batch
    }

    pub fn take(&mut self, n: usize) -> Vec<T> {
        let start = self.position;
        let end = std::cmp::min(start + n, self.items.len());
        let result = self.items[start..end].to_vec();
        self.position = end;
        result
    }

    pub fn skip(&mut self, n: usize) { self.position = std::cmp::min(self.position + n, self.items.len()); }
    pub fn reset(&mut self) { self.position = 0; }
    pub fn remaining(&self) -> usize { self.items.len() - self.position }
}

// ============================================================================
// Stacktrace with Symbol Resolution
// ============================================================================

/// Symbol resolver for stack traces.
#[derive(Debug, Clone)]
pub struct SymbolResolver {
    pub binary_path: String,
    pub symbol_map: std::collections::HashMap<u64, String>,
    pub debug_info_available: bool,
}

impl SymbolResolver {
    pub fn new(binary_path: &str) -> Self {
        Self { binary_path: binary_path.to_string(),
            symbol_map: std::collections::HashMap::new(), debug_info_available: false }
    }

    pub fn resolve(&self, address: u64) -> Option<String> {
        self.symbol_map.get(&address).cloned()
    }

    pub fn add_symbol(&mut self, address: u64, name: &str) {
        self.symbol_map.insert(address, name.to_string());
    }

    /// Generate a human-readable stack trace from raw addresses.
    pub fn resolve_stacktrace(&self, addresses: &[u64]) -> BasicStacktrace {
        let mut st = BasicStacktrace::with_depth(addresses.len());
        for &addr in addresses {
            let desc = self.resolve(addr).unwrap_or_else(|| format!("0x{:016x}", addr));
            st.push(StacktraceEntry::new(&desc).with_address(addr));
        }
        st
    }
}

// ============================================================================
// Text Encoding Converters
// ============================================================================

/// Text encoding converter (C++26 <text_encoding>).
#[derive(Debug, Clone)]
pub struct TextEncodingConverter {
    pub from: TextEncoding,
    pub to: TextEncoding,
    pub replacement_char: String,
    pub strict: bool,
}

impl TextEncodingConverter {
    pub fn new(from: TextEncoding, to: TextEncoding) -> Self {
        Self { from, to, replacement_char: "\u{FFFD}".to_string(), strict: false }
    }

    pub fn with_strict(mut self) -> Self { self.strict = true; self }

    /// Convert bytes from one encoding to another (simplified model).
    pub fn convert(&self, input: &[u8]) -> Result<Vec<u8>, String> {
        match (self.from, self.to) {
            (TextEncoding::Utf8, TextEncoding::Utf8) => Ok(input.to_vec()),
            (TextEncoding::Ascii, TextEncoding::Utf8) => {
                // ASCII is valid UTF-8
                if self.strict && input.iter().any(|&b| b >= 128) {
                    return Err("Non-ASCII byte in strict ASCII->UTF-8 conversion".into());
                }
                Ok(input.to_vec())
            }
            (TextEncoding::Utf8, TextEncoding::Ascii) => {
                // Strip non-ASCII
                let result: Vec<u8> = input.iter().filter(|&&b| b < 128).copied().collect();
                Ok(result)
            }
            (TextEncoding::Latin1, TextEncoding::Utf8) => {
                // Latin-1 to UTF-8: bytes < 128 pass through, >= 128 encode as 2-byte UTF-8
                let mut result = Vec::new();
                for &b in input {
                    if b < 128 { result.push(b); }
                    else { result.push(0xC0 | (b >> 6)); result.push(0x80 | (b & 0x3F)); }
                }
                Ok(result)
            }
            _ => {
                if self.strict {
                    Err(format!("Unsupported conversion: {} -> {}", self.from, self.to))
                } else {
                    Ok(input.to_vec())
                }
            }
        }
    }
}

// ============================================================================
// File Mapping for Ispanstream
// ============================================================================

/// Memory-mapped file reader for span streams.
#[derive(Debug)]
pub struct MemoryMappedFile {
    pub path: String,
    pub data: Vec<u8>,
    pub offset: usize,
    pub length: usize,
}

impl MemoryMappedFile {
    pub fn open(path: &str) -> Result<Self, String> {
        // Simulated memory-mapped file read
        let data = std::fs::read(path).map_err(|e| format!("Failed to read {}: {}", path, e))?;
        let len = data.len();
        Ok(Self { path: path.to_string(), data, offset: 0, length: len })
    }

    pub fn as_span_stream(&self) -> BasicIspanstream {
        BasicIspanstream::new(&self.data[self.offset..self.offset + self.length])
    }

    pub fn slice(&self, offset: usize, length: usize) -> Option<&[u8]> {
        let end = offset + length;
        if end <= self.data.len() { Some(&self.data[offset..end]) } else { None }
    }
}

// ============================================================================
// Additional Tests
// ============================================================================

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

    // ── ParallelReducer tests ──────────────────────────────────────────
    #[test]
    fn test_reduce_sum() {
        let reducer = ParallelReducer::new(ExecutionPolicy::ParallelPolicy);
        let data: Vec<i32> = (1..=100).collect();
        let result = reducer.reduce(&data);
        assert_eq!(result, 5050);
    }

    #[test]
    fn test_reduce_sequential_small() {
        let reducer = ParallelReducer::new(ExecutionPolicy::SequencedPolicy);
        let data = vec![1, 2, 3];
        assert_eq!(reducer.reduce(&data), 6);
    }

    #[test]
    fn test_inclusive_scan() {
        let reducer = ParallelReducer::new(ExecutionPolicy::ParallelPolicy);
        let data = vec![1, 2, 3, 4];
        let result = reducer.inclusive_scan(&data);
        assert_eq!(result, vec![1, 3, 6, 10]);
    }

    // ── AsyncGenerator tests ───────────────────────────────────────────
    #[test]
    fn test_async_generator_batch() {
        let mut gen = AsyncGenerator::new(vec![1, 2, 3, 4, 5, 6]).with_batch_size(2);
        assert_eq!(gen.next_batch(), vec![1, 2]);
        assert_eq!(gen.next_batch(), vec![3, 4]);
        assert_eq!(gen.next_batch(), vec![5, 6]);
    }

    #[test]
    fn test_async_generator_take_skip() {
        let mut gen = AsyncGenerator::new(vec![1, 2, 3, 4, 5]);
        gen.skip(2);
        assert_eq!(gen.take(2), vec![3, 4]);
    }

    // ── SymbolResolver tests ───────────────────────────────────────────
    #[test]
    fn test_symbol_resolver_add_resolve() {
        let mut sr = SymbolResolver::new("test_binary");
        sr.add_symbol(0x401000, "main");
        assert_eq!(sr.resolve(0x401000), Some("main".to_string()));
        assert_eq!(sr.resolve(0x500000), None);
    }

    #[test]
    fn test_resolve_stacktrace() {
        let mut sr = SymbolResolver::new("test");
        sr.add_symbol(0x1000, "func_a");
        sr.add_symbol(0x2000, "func_b");
        let st = sr.resolve_stacktrace(&[0x1000, 0x2000, 0x3000]);
        assert_eq!(st.size(), 3);
        assert!(st.entries()[0].to_string().contains("func_a"));
    }

    // ── TextEncodingConverter tests ────────────────────────────────────
    #[test]
    fn test_encoding_converter_ascii_to_utf8() {
        let conv = TextEncodingConverter::new(TextEncoding::Ascii, TextEncoding::Utf8);
        let result = conv.convert(b"Hello").unwrap();
        assert_eq!(result, b"Hello");
    }

    #[test]
    fn test_encoding_converter_latin1_to_utf8() {
        let conv = TextEncodingConverter::new(TextEncoding::Latin1, TextEncoding::Utf8);
        let input = vec![0xC9]; // É in Latin-1
        let result = conv.convert(&input).unwrap();
        assert_eq!(result, vec![0xC3, 0x89]); // É in UTF-8
    }

    #[test]
    fn test_encoding_converter_strict_fails() {
        let conv = TextEncodingConverter::new(TextEncoding::Ascii, TextEncoding::Utf8).with_strict();
        assert!(conv.convert(&[0x80]).is_err());
    }

    // ── MemoryMappedFile tests ─────────────────────────────────────────
    #[test]
    fn test_memory_mapped_file_not_found() {
        let result = MemoryMappedFile::open("/nonexistent/file.test");
        assert!(result.is_err());
    }

    // ── MdspanExt tests ────────────────────────────────────────────────
    #[test]
    fn test_mdspan_ext_slice_all() {
        let data: Vec<i32> = (0..24).collect();
        let span = MdspanExt::from_data(data, &[2, 3, 4]);
        let sliced = span.slice(&[MdspanSlice::All, MdspanSlice::All, MdspanSlice::All]);
        assert_eq!(sliced.extents(), &[2, 3, 4]);
    }

    #[test]
    fn test_mdspan_ext_slice_range() {
        let data: Vec<i32> = (0..24).collect();
        let span = MdspanExt::from_data(data, &[2, 3, 4]);
        let sliced = span.slice(&[MdspanSlice::Single(1), MdspanSlice::Range { start: 0, end: 2 }, MdspanSlice::All]);
        assert_eq!(sliced.extents(), &[1, 2, 4]);
    }

    // ── Extended InplaceVector tests ───────────────────────────────────
    #[test]
    fn test_inplace_vector_as_slice() {
        let mut v: InplaceVector<i32, 10> = InplaceVector::new();
        v.push_back(1).unwrap();
        v.push_back(2).unwrap();
        assert_eq!(v.as_slice().len(), 2);
    }

    #[test]
    fn test_inplace_vector_clear() {
        let mut v: InplaceVector<i32, 5> = InplaceVector::new();
        v.push_back(1).unwrap();
        v.push_back(2).unwrap();
        v.clear();
        assert!(v.is_empty());
        assert_eq!(v.len(), 0);
    }

    // ── Extended Hive tests ────────────────────────────────────────────
    #[test]
    fn test_hive_bucket_behavior() {
        let mut hive: Hive<i32> = Hive::with_bucket_capacity(4);
        for i in 0..10 { hive.insert(i); }
        assert!(hive.bucket_count() >= 2);
    }
}

// ============================================================================
// Compile-Time Feature Test Macros
// ============================================================================

/// Simulates C++20/23 feature-test macros for our behavioral models.
#[derive(Debug, Clone)]
pub struct FeatureTestMacros {
    pub cpp_standard: u32,
}

impl FeatureTestMacros {
    pub fn new(std_year: u32) -> Self { Self { cpp_standard: std_year } }

    pub fn has_execution(&self) -> bool { self.cpp_standard >= 201703 }
    pub fn has_latch(&self) -> bool { self.cpp_standard >= 202002 }
    pub fn has_barrier(&self) -> bool { self.cpp_standard >= 202002 }
    pub fn has_semaphore(&self) -> bool { self.cpp_standard >= 202002 }
    pub fn has_syncstream(&self) -> bool { self.cpp_standard >= 202002 }
    pub fn has_spanstream(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_flat_map(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_mdspan(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_generator(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_print(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_stacktrace(&self) -> bool { self.cpp_standard >= 202302 }
    pub fn has_debugging(&self) -> bool { self.cpp_standard >= 202602 }
    pub fn has_text_encoding(&self) -> bool { self.cpp_standard >= 202602 }
    pub fn has_inplace_vector(&self) -> bool { self.cpp_standard >= 202602 }
    pub fn all_macros(&self) -> Vec<(&str, bool)> {
        vec![
            ("__cpp_lib_execution", self.has_execution()),
            ("__cpp_lib_latch", self.has_latch()),
            ("__cpp_lib_barrier", self.has_barrier()),
            ("__cpp_lib_semaphore", self.has_semaphore()),
            ("__cpp_lib_syncstream", self.has_syncstream()),
            ("__cpp_lib_spanstream", self.has_spanstream()),
            ("__cpp_lib_flat_map", self.has_flat_map()),
            ("__cpp_lib_mdspan", self.has_mdspan()),
            ("__cpp_lib_generator", self.has_generator()),
            ("__cpp_lib_print", self.has_print()),
            ("__cpp_lib_stacktrace", self.has_stacktrace()),
            ("__cpp_lib_debugging", self.has_debugging()),
            ("__cpp_lib_text_encoding", self.has_text_encoding()),
            ("__cpp_lib_inplace_vector", self.has_inplace_vector()),
        ]
    }
}

// ============================================================================
// Tests for Feature Test Macros
// ============================================================================

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

    #[test]
    fn test_feature_macros_cpp17() {
        let ftm = FeatureTestMacros::new(201703);
        assert!(ftm.has_execution());
        assert!(!ftm.has_latch());
        assert!(!ftm.has_generator());
    }

    #[test]
    fn test_feature_macros_cpp20() {
        let ftm = FeatureTestMacros::new(202002);
        assert!(ftm.has_execution());
        assert!(ftm.has_latch());
        assert!(ftm.has_barrier());
        assert!(!ftm.has_mdspan());
    }

    #[test]
    fn test_feature_macros_cpp23() {
        let ftm = FeatureTestMacros::new(202302);
        assert!(ftm.has_flat_map());
        assert!(ftm.has_mdspan());
        assert!(ftm.has_generator());
        assert!(ftm.has_print());
        assert!(!ftm.has_debugging());
    }

    #[test]
    fn test_feature_macros_cpp26() {
        let ftm = FeatureTestMacros::new(202602);
        assert!(ftm.has_debugging());
        assert!(ftm.has_text_encoding());
        assert!(ftm.has_inplace_vector());
    }

    #[test]
    fn test_feature_macros_all_count() {
        let ftm = FeatureTestMacros::new(202602);
        let all = ftm.all_macros();
        assert_eq!(all.len(), 14);
        assert!(all.iter().all(|&(_, v)| v));
    }
}