qubit-progress 0.8.3

// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Metric configuration and immutable metric snapshots.
// qubit-style: allow multiple-public-types

use std::hint::spin_loop;
use std::sync::Arc;
use std::sync::atomic::AtomicU64;
use std::sync::atomic::Ordering;
use std::thread;

use qubit_fast_cas::CasCell;
#[cfg(feature = "serde")]
use serde::Deserialize;
#[cfg(feature = "serde")]
use serde::Deserializer;
#[cfg(feature = "serde")]
use serde::Serialize;
#[cfg(feature = "serde")]
use serde::de::Error;

use crate::MetricError;
use crate::internal::OperationState;
#[cfg(feature = "serde")]
use crate::validation::validate_metrics;
#[cfg(feature = "serde")]
use crate::validation::validate_snapshot_counts;

/// Stable metadata for one metric in a progress operation.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Metric {
    /// Machine-readable identifier.
    pub(crate) id: Arc<str>,
    /// Human-readable name.
    pub(crate) name: Arc<str>,
    /// Optional configured total.
    pub(crate) total: Option<u64>,
}

impl Metric {
    /// Creates metric metadata without a known total.
    ///
    /// The ID and name are validated when the enclosing progress operation is
    /// started, so this constructor never panics.
    #[must_use]
    pub fn new(id: &str, name: &str) -> Self {
        Self {
            id: Arc::from(id),
            name: Arc::from(name),
            total: None,
        }
    }

    /// Records the total work for this metric.
    ///
    /// The value is carried automatically by all future events from the
    /// operation that owns this metric.
    #[must_use]
    pub const fn total(mut self, total: u64) -> Self {
        self.total = Some(total);
        self
    }

    /// Returns the metric's stable ID.
    #[must_use]
    pub fn id(&self) -> &str {
        &self.id
    }

    /// Returns the metric's display name.
    #[must_use]
    pub fn name(&self) -> &str {
        &self.name
    }

    /// Returns the configured total, if it is known.
    #[must_use]
    pub const fn configured_total(&self) -> Option<u64> {
        self.total
    }
}

/// One atomic batch of additive metric lifecycle changes.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct MetricDelta {
    /// Work moving from not-started to active.
    started: u64,
    /// Active work becoming completed without an outcome classification.
    unclassified: u64,
    /// Active work becoming successful.
    succeeded: u64,
    /// Active work becoming failed.
    failed: u64,
    /// Active work becoming cancelled.
    cancelled: u64,
}

impl MetricDelta {
    /// Creates a zero delta.
    #[must_use]
    pub const fn new() -> Self {
        Self {
            started: 0,
            unclassified: 0,
            succeeded: 0,
            failed: 0,
            cancelled: 0,
        }
    }

    /// Sets the number of work items entering the active state.
    #[must_use]
    pub const fn started(mut self, count: u64) -> Self {
        self.started = count;
        self
    }

    /// Sets the number of work items completing without classification.
    #[must_use]
    pub const fn unclassified(mut self, count: u64) -> Self {
        self.unclassified = count;
        self
    }

    /// Sets the number of work items completing successfully.
    #[must_use]
    pub const fn succeeded(mut self, count: u64) -> Self {
        self.succeeded = count;
        self
    }

    /// Sets the number of work items completing with failure.
    #[must_use]
    pub const fn failed(mut self, count: u64) -> Self {
        self.failed = count;
        self
    }

    /// Sets the number of work items completing by cancellation.
    #[must_use]
    pub const fn cancelled(mut self, count: u64) -> Self {
        self.cancelled = count;
        self
    }
}

/// Cloneable capability for one live metric owned by a progress operation.
///
/// All mutation methods are serialized by one CAS gate critical section.
/// A handle remains readable after its progress operation closes, but rejects
/// all later mutations.
#[derive(Clone)]
pub struct MetricHandle {
    /// Shared metadata and mutable count state.
    inner: Arc<MetricInner>,
    /// Shared lifecycle gate owned by the enclosing progress operation.
    operation_state: Arc<OperationState>,
}

impl MetricHandle {
    /// Creates one live handle from validated metric metadata.
    pub(crate) fn new(
        metric: Metric,
        operation_state: Arc<OperationState>,
    ) -> Self {
        Self {
            inner: Arc::new(MetricInner::new(metric)),
            operation_state,
        }
    }

    /// Returns the stable metric ID.
    #[must_use]
    pub fn id(&self) -> &str {
        self.inner.metric.id()
    }

    /// Returns the stable metric display name.
    #[must_use]
    pub fn name(&self) -> &str {
        self.inner.metric.name()
    }

    /// Moves work from the not-started state to the active state.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the transition violates aggregate state
    /// invariants or when the owning operation is closed.
    pub fn start(&self, count: u64) -> Result<(), MetricError> {
        self.apply_delta(MetricDelta::new().started(count))
    }

    /// Moves work from the active state to unclassified completion.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the transition violates aggregate state
    /// invariants or when the owning operation is closed.
    pub fn complete(&self, count: u64) -> Result<(), MetricError> {
        self.apply_delta(MetricDelta::new().unclassified(count))
    }

    /// Moves work from the active state to the succeeded state.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the transition violates aggregate state
    /// invariants or when the owning operation is closed.
    pub fn succeed(&self, count: u64) -> Result<(), MetricError> {
        self.apply_delta(MetricDelta::new().succeeded(count))
    }

    /// Moves work from the active state to the failed state.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the transition violates aggregate state
    /// invariants or when the owning operation is closed.
    pub fn fail(&self, count: u64) -> Result<(), MetricError> {
        self.apply_delta(MetricDelta::new().failed(count))
    }

    /// Moves work from the active state to the cancelled state.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the transition violates aggregate state
    /// invariants or when the owning operation is closed.
    pub fn cancel(&self, count: u64) -> Result<(), MetricError> {
        self.apply_delta(MetricDelta::new().cancelled(count))
    }

    /// Applies one atomic additive batch of lifecycle changes.
    ///
    /// # Errors
    ///
    /// Returns a metric error when the delta exceeds active work, violates a
    /// configured total, overflows, or the owning operation is closed. The
    /// metric is unchanged whenever an error is returned.
    pub fn apply_delta(&self, delta: MetricDelta) -> Result<(), MetricError> {
        let metric_id = self.id();
        let total = self.inner.metric.configured_total();
        let _update_guard = self.operation_state.enter_update(metric_id)?;

        self.inner.with_update(|counts| {
            let mut next = *counts;
            apply_delta_to_counts(&mut next, delta, metric_id)?;
            next.validate(metric_id, total)?;
            *counts = next;
            Ok(())
        })
    }

    /// Returns one internally consistent immutable metric snapshot.
    ///
    /// This read remains available after the owning operation closes.
    #[must_use]
    pub fn snapshot(&self) -> MetricSnapshot {
        let counts = self.inner.snapshot_counts();
        MetricSnapshot::from_counts(&self.inner.metric, counts)
    }
}

/// Immutable metadata and atomic dynamic state for one handle.
struct MetricInner {
    /// Fixed metric definition supplied to the progress builder.
    metric: Metric,
    /// Dynamic updates are serialized by this gate.
    gate: CasCell,
    /// Work that has started but is not terminal.
    active: AtomicU64,
    /// Terminal work without explicit success, failure, or cancellation.
    completed_unclassified: AtomicU64,
    /// Terminal work classified as successful.
    succeeded: AtomicU64,
    /// Terminal work classified as failed.
    failed: AtomicU64,
    /// Terminal work classified as cancelled.
    cancelled: AtomicU64,
}

impl MetricInner {
    /// Builds one live metric inner state with zeroed counters.
    fn new(metric: Metric) -> Self {
        Self {
            metric,
            gate: CasCell::new(0),
            active: AtomicU64::new(0),
            completed_unclassified: AtomicU64::new(0),
            succeeded: AtomicU64::new(0),
            failed: AtomicU64::new(0),
            cancelled: AtomicU64::new(0),
        }
    }

    /// Runs one validated update while exclusively holding the gate.
    fn with_update<R, F>(&self, mut update: F) -> Result<R, MetricError>
    where
        F: FnMut(&mut MetricCounts) -> Result<R, MetricError>,
    {
        let mut attempts = 0;
        loop {
            let version = self.gate.load();
            if version & 1 != 0 {
                wait_for_contention(attempts);
                attempts += 1;
                continue;
            }

            match self.gate.compare_set(version, version.wrapping_add(1)) {
                Ok(()) => {
                    let _guard = MetricGateGuard::new(
                        &self.gate,
                        version.wrapping_add(2),
                    );
                    let mut counts = self.read_counts();
                    let result = update(&mut counts);
                    if result.is_ok() {
                        self.write_counts(&counts);
                    }
                    return result;
                }
                Err(_) => {
                    wait_for_contention(attempts);
                    attempts += 1;
                }
            }
        }
    }

    /// Reads all counter fields with acquire order and copies them by value.
    fn read_counts(&self) -> MetricCounts {
        MetricCounts {
            active: self.active.load(Ordering::Acquire),
            completed_unclassified: self
                .completed_unclassified
                .load(Ordering::Acquire),
            succeeded: self.succeeded.load(Ordering::Acquire),
            failed: self.failed.load(Ordering::Acquire),
            cancelled: self.cancelled.load(Ordering::Acquire),
        }
    }

    /// Writes all counter fields after successful validation.
    fn write_counts(&self, counts: &MetricCounts) {
        self.active.store(counts.active, Ordering::Release);
        self.completed_unclassified
            .store(counts.completed_unclassified, Ordering::Release);
        self.succeeded.store(counts.succeeded, Ordering::Release);
        self.failed.store(counts.failed, Ordering::Release);
        self.cancelled.store(counts.cancelled, Ordering::Release);
    }

    /// Repeatedly reads counts and validates version stability.
    fn snapshot_counts(&self) -> MetricCounts {
        let mut attempts = 0;
        loop {
            let start = self.gate.load();
            if start & 1 != 0 {
                wait_for_contention(attempts);
                attempts += 1;
                continue;
            }

            let counts = self.read_counts();
            if start == self.gate.load() {
                return counts;
            }

            wait_for_contention(attempts);
            attempts += 1;
        }
    }
}

/// Dynamic metric counts for a CAS transaction.
#[derive(Clone, Copy)]
struct MetricCounts {
    /// Work that has started but is not terminal.
    active: u64,
    /// Terminal work without explicit success, failure, or cancellation.
    completed_unclassified: u64,
    /// Terminal work classified as successful.
    succeeded: u64,
    /// Terminal work classified as failed.
    failed: u64,
    /// Terminal work classified as cancelled.
    cancelled: u64,
}

impl MetricCounts {
    /// Returns the derived public completed count.
    ///
    /// Every transition conserves the total count, which cannot exceed `u64`.
    fn completed(self) -> Option<u64> {
        self.completed_unclassified
            .checked_add(self.succeeded)?
            .checked_add(self.failed)?
            .checked_add(self.cancelled)
    }

    /// Returns active plus completed work.
    fn occupied(self) -> Option<u64> {
        self.completed()?.checked_add(self.active)
    }

    /// Validates the aggregate conservation invariants for one pending state.
    fn validate(
        self,
        metric_id: &str,
        total: Option<u64>,
    ) -> Result<(), MetricError> {
        let occupied =
            self.occupied().ok_or_else(|| MetricError::CountOverflow {
                metric_id: metric_id.into(),
            })?;
        if let Some(total) = total
            && occupied > total
        {
            return Err(MetricError::TotalExceeded {
                metric_id: metric_id.into(),
                total,
                attempted: occupied,
            });
        }
        Ok(())
    }
}

/// Applies one validated additive delta to dynamic metric counts.
fn apply_delta_to_counts(
    counts: &mut MetricCounts,
    delta: MetricDelta,
    metric_id: &str,
) -> Result<(), MetricError> {
    let terminal_delta = delta
        .unclassified
        .checked_add(delta.succeeded)
        .and_then(|value| value.checked_add(delta.failed))
        .and_then(|value| value.checked_add(delta.cancelled))
        .ok_or_else(|| MetricError::CountOverflow {
            metric_id: metric_id.into(),
        })?;
    let available_active = counts
        .active
        .checked_add(delta.started)
        .ok_or_else(|| MetricError::CountOverflow {
            metric_id: metric_id.into(),
        })?;
    if terminal_delta > available_active {
        return Err(MetricError::InsufficientActive {
            metric_id: metric_id.into(),
            requested: terminal_delta,
            available: available_active,
        });
    }

    counts.active = available_active - terminal_delta;
    counts.completed_unclassified = counts
        .completed_unclassified
        .checked_add(delta.unclassified)
        .ok_or_else(|| MetricError::CountOverflow {
            metric_id: metric_id.into(),
        })?;
    counts.succeeded = counts
        .succeeded
        .checked_add(delta.succeeded)
        .ok_or_else(|| MetricError::CountOverflow {
            metric_id: metric_id.into(),
        })?;
    counts.failed =
        counts.failed.checked_add(delta.failed).ok_or_else(|| {
            MetricError::CountOverflow {
                metric_id: metric_id.into(),
            }
        })?;
    counts.cancelled = counts
        .cancelled
        .checked_add(delta.cancelled)
        .ok_or_else(|| MetricError::CountOverflow {
            metric_id: metric_id.into(),
        })?;
    Ok(())
}

/// RAII wrapper that always releases a locked gate.
struct MetricGateGuard<'gate> {
    gate: &'gate CasCell,
    next_version: u64,
}

impl<'gate> MetricGateGuard<'gate> {
    fn new(gate: &'gate CasCell, next_version: u64) -> Self {
        Self { gate, next_version }
    }
}

impl Drop for MetricGateGuard<'_> {
    fn drop(&mut self) {
        self.gate.store(self.next_version);
    }
}

/// Immutable complete state for one metric in an emitted event.
#[cfg_attr(feature = "serde", derive(Serialize))]
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MetricSnapshot {
    /// Machine-readable metric ID.
    id: Arc<str>,
    /// Human-readable metric name.
    name: Arc<str>,
    /// Configured total, if known.
    total: Option<u64>,
    /// Completed count.
    completed: u64,
    /// Active count.
    active: u64,
    /// Succeeded count.
    succeeded: u64,
    /// Failed count.
    failed: u64,
    /// Cancelled count.
    cancelled: u64,
}

impl MetricSnapshot {
    /// Builds an immutable snapshot from one internally validated metric state.
    fn from_counts(metric: &Metric, counts: MetricCounts) -> Self {
        Self {
            id: Arc::clone(&metric.id),
            name: Arc::clone(&metric.name),
            total: metric.total,
            completed: counts
                .completed()
                .expect("validated metric counts must fit in u64"),
            active: counts.active,
            succeeded: counts.succeeded,
            failed: counts.failed,
            cancelled: counts.cancelled,
        }
    }
    /// Returns the metric's stable ID.
    #[must_use]
    pub fn id(&self) -> &str {
        &self.id
    }
    /// Returns the metric's display name.
    #[must_use]
    pub fn name(&self) -> &str {
        &self.name
    }
    /// Returns the total configured for this event's metric.
    #[must_use]
    pub const fn total(&self) -> Option<u64> {
        self.total
    }
    /// Returns the number of completed work items.
    #[must_use]
    pub const fn completed(&self) -> u64 {
        self.completed
    }
    /// Returns completed work without an explicit outcome classification.
    #[must_use]
    pub const fn unclassified(&self) -> u64 {
        let classified = self
            .succeeded
            .saturating_add(self.failed)
            .saturating_add(self.cancelled);
        self.completed.saturating_sub(classified)
    }
    /// Returns the number of active work items.
    #[must_use]
    pub const fn active(&self) -> u64 {
        self.active
    }
    /// Returns the number of explicitly successful work items.
    #[must_use]
    pub const fn succeeded(&self) -> u64 {
        self.succeeded
    }
    /// Returns the number of explicitly failed work items.
    #[must_use]
    pub const fn failed(&self) -> u64 {
        self.failed
    }
    /// Returns the number of explicitly cancelled work items.
    #[must_use]
    pub const fn cancelled(&self) -> u64 {
        self.cancelled
    }
    /// Returns the completed fraction when the total is positive and known.
    #[must_use]
    pub fn completion_fraction(&self) -> Option<f64> {
        self.total
            .filter(|total| *total > 0)
            .map(|total| self.completed as f64 / total as f64)
    }
}

/// Serializable wire representation used to validate standalone snapshots.
#[cfg(feature = "serde")]
#[derive(Deserialize)]
struct MetricSnapshotWire {
    /// Machine-readable metric ID.
    id: Arc<str>,
    /// Human-readable metric name.
    name: Arc<str>,
    /// Configured total, if known.
    total: Option<u64>,
    /// Completed count.
    completed: u64,
    /// Active count.
    active: u64,
    /// Succeeded count.
    succeeded: u64,
    /// Failed count.
    failed: u64,
    /// Cancelled count.
    cancelled: u64,
}

#[cfg(feature = "serde")]
impl<'de> Deserialize<'de> for MetricSnapshot {
    /// Deserializes and validates one standalone metric snapshot.
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let wire = MetricSnapshotWire::deserialize(deserializer)?;
        let snapshot = Self {
            id: wire.id,
            name: wire.name,
            total: wire.total,
            completed: wire.completed,
            active: wire.active,
            succeeded: wire.succeeded,
            failed: wire.failed,
            cancelled: wire.cancelled,
        };
        let metric = Metric {
            id: Arc::clone(&snapshot.id),
            name: Arc::clone(&snapshot.name),
            total: snapshot.total,
        };
        validate_metrics(std::slice::from_ref(&metric))
            .map_err(Error::custom)?;
        validate_snapshot_counts(&snapshot).map_err(Error::custom)?;
        Ok(snapshot)
    }
}

/// Busy-wait helper for writer contention and snapshot retries.
#[inline]
fn wait_for_contention(attempts: usize) {
    if attempts > 0 && attempts.is_multiple_of(16) {
        thread::yield_now();
    } else {
        spin_loop();
    }
}