tiny-counter 0.1.0

/// Query builders for fluent event querying.
use std::ops::Range;
use std::sync::Arc;

use chrono::Duration;

use crate::{EventStoreInner, TimeUnit};

/// Builder for constructing queries on a single event.
///
/// Created by `EventStore::query()`, this builder provides methods to specify
/// time ranges before executing aggregation operations.
#[must_use = "query builders do nothing unless consumed"]
pub struct Query {
    store: Arc<EventStoreInner>,
    event_id: String,
}

impl Query {
    /// Creates a new Query builder.
    ///
    /// This is typically called by EventStore, not directly by users.
    pub(crate) fn new(store: Arc<EventStoreInner>, event_id: String) -> Self {
        Self { store, event_id }
    }

    pub(crate) fn last(self, n: usize, unit: TimeUnit) -> RangeQuery {
        RangeQuery::new(self.store, self.event_id, unit, 0..n)
    }

    /// Query the last N seconds.
    pub fn last_seconds(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Seconds)
    }

    /// Query the last N minutes.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    ///
    /// let store = EventStore::new();
    /// store.record("event");
    ///
    /// let count = store.query("event").last_minutes(60).sum();
    /// assert_eq!(count, Some(1));
    /// ```
    pub fn last_minutes(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Minutes)
    }

    /// Query the last N hours.
    pub fn last_hours(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Hours)
    }

    /// Query the last N days.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    ///
    /// let store = EventStore::new();
    /// store.record("app_launch");
    ///
    /// let count = store.query("app_launch").last_days(7).sum();
    /// assert_eq!(count, Some(1));
    /// ```
    pub fn last_days(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Days)
    }

    /// Query the last N weeks.
    pub fn last_weeks(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Weeks)
    }

    /// Query the last N months (28-day approximation).
    pub fn last_months(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Months)
    }

    /// Query the last N years (365-day approximation).
    pub fn last_years(self, n: usize) -> RangeQuery {
        self.last(n, TimeUnit::Years)
    }

    /// Query all available data (all buckets).
    ///
    /// Uses the longest time unit configured for this event to capture
    /// the maximum available history.
    pub fn ever(self) -> RangeQuery {
        // Use TimeUnit::Ever to defer resolution until query execution
        // This avoids loading the counter twice
        self.last(usize::MAX, TimeUnit::Ever)
    }

    /// Query a specific range of days.
    pub fn days(self, range: Range<usize>) -> RangeQuery {
        RangeQuery::new(self.store, self.event_id, TimeUnit::Days, range)
    }

    /// Start building a query from an offset of days.
    ///
    /// Use with `.take(n)` to specify the range length.
    pub fn days_from(self, offset: usize) -> RangeQuery {
        RangeQuery::new(
            self.store,
            self.event_id,
            TimeUnit::Days,
            offset..usize::MAX,
        )
    }

    /// Returns the time since the event was last seen.
    ///
    /// Returns None if the event has never been recorded or doesn't exist.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    /// use chrono::Duration;
    ///
    /// let store = EventStore::new();
    /// store.record("settings_visit");
    ///
    /// let time_since = store.query("settings_visit").last_seen();
    /// assert!(time_since.is_some());
    ///
    /// // Check for events never recorded
    /// let never_seen = store.query("never_happened").last_seen();
    /// assert!(never_seen.is_none());
    /// ```
    pub fn last_seen(self) -> Option<Duration> {
        let clock_now = self.store.clock_now();
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let mut counter = counter_arc.lock().unwrap();

        counter.advance_if_needed(clock_now);

        // Get time units from counter and sort from smallest to largest
        let configs = self.store.config.configs();

        // Try to find the event in any time unit, starting with the finest granularity
        for interval_idx in 0..configs.len() {
            let config = &configs[interval_idx];
            let time_unit = config.time_unit();

            if let Some(bucket_idx) = counter.last_seen_in(time_unit) {
                // SAFETY: This cannot panic. We got `config` from the counter's own interval list,
                // so the time_unit MUST exist in the counter. If this panics, it's a bug in
                // tiny-counter's internal logic, not user error.
                let interval_start = counter.interval_start(time_unit).expect(
                    "BUG: Interval must exist - we just retrieved config from counter's intervals",
                );

                // If this is the smallest interval, we have the most precise answer
                if interval_idx == 0 {
                    let estimate = time_unit.bucket_midway(clock_now, interval_start, bucket_idx);
                    return Some(clock_now - estimate);
                }

                // Check for gap: event not in smaller interval but is in this larger one
                // Since we iterate smallest→largest, if we're here, smaller interval returned None
                let prev_config = &configs[interval_idx - 1];

                // Calculate where the smaller interval coverage ends
                // SAFETY: This cannot panic. prev_config came from counter's intervals (index interval_idx-1).
                // If this panics, it's a bug in tiny-counter, not user error.
                let prev_interval_start = counter.interval_start(prev_config.time_unit()).expect(
                    "BUG: Smaller interval must exist - we just retrieved prev_config from counter's intervals",
                );
                let prev_coverage_end = prev_config.first_moment_ever(prev_interval_start);

                // Which bucket in THIS interval does that coverage end fall into?
                let coverage_end_bucket = time_unit
                    .bucket_idx(interval_start, prev_coverage_end)
                    .unwrap_or_default();

                // If event is in the same bucket (or earlier) where coverage ends, it's in the gap
                if bucket_idx <= coverage_end_bucket {
                    // GAP DETECTED!
                    // Gap boundaries: between the far end of this bucket and where smaller interval coverage ends

                    // Far end of the bucket (earliest time, furthest from now)
                    // For bucket 0, this is one full bucket duration ago
                    let gap_earliest = time_unit.bucket_start(clock_now, bucket_idx);
                    // End of smaller interval coverage (latest time, closest to now within gap)
                    let gap_latest = prev_coverage_end;

                    // Calculate gap midpoint as a timestamp
                    let gap_midpoint = gap_earliest + ((gap_latest - gap_earliest) / 2);

                    // Return duration from now to gap midpoint
                    return Some(clock_now - gap_midpoint);
                }

                // Event is beyond the gap, use normal estimation
                let estimate = time_unit.bucket_midway(clock_now, interval_start, bucket_idx);
                return Some(clock_now - estimate);
            }
        }
        None
    }

    /// Returns an estimate for the time since the event was first seen.
    ///
    /// Returns None if the event has never been recorded or doesn't exist.
    /// This searches for the oldest non-zero bucket across all tracked time units.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    /// use chrono::Duration;
    ///
    /// let store = EventStore::new();
    /// store.record("user_signup");
    ///
    /// let time_since = store.query("user_signup").first_seen();
    /// assert!(time_since.is_some());
    ///
    /// // Check for events never recorded
    /// let never_seen = store.query("never_happened").first_seen();
    /// assert!(never_seen.is_none());
    /// ```
    pub fn first_seen(self) -> Option<Duration> {
        let clock_now = self.store.clock_now();
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);

        // Get configs in ascending order, iterate in reverse for largest to smallest
        let configs = self.store.config.configs();

        // Iterate from largest to smallest (end to start)
        for interval_idx in (0..configs.len()).rev() {
            let config = &configs[interval_idx];
            let time_unit = config.time_unit();
            if let Some(bucket_idx) = counter.first_seen_in(time_unit) {
                // SAFETY: This cannot panic. We got `config` from the counter's own interval list,
                // so the time_unit MUST exist in the counter. If this panics, it's a bug in
                // tiny-counter's internal logic, not user error.
                let interval_start = counter.interval_start(time_unit).expect(
                    "BUG: Interval must exist - we just retrieved config from counter's intervals",
                );
                // Check if we're on the smallest interval (e.g. minutes)
                if interval_idx == 0 {
                    // Last interval - we have to accept this as our result.
                    let midway = time_unit.bucket_midway(clock_now, interval_start, bucket_idx);
                    return Some(clock_now - midway);
                }

                // Get the next smaller interval
                let next_config = &configs[interval_idx - 1];

                // Starting bucket is the bucket in larger config which an event that would
                // have been recorded in the last bucket of the smaller config.

                // SAFETY: This cannot panic. next_config came from counter's intervals (index interval_idx-1).
                // If this panics, it's a bug in tiny-counter, not user error.
                let next_interval_start = counter.interval_start(next_config.time_unit()).expect(
                    "BUG: Smaller interval must exist - we just retrieved next_config from counter's intervals",
                );

                let starting_moment = next_config.first_moment_ever(next_interval_start);
                let starting_bucket = time_unit
                    .bucket_idx(interval_start, starting_moment)
                    .unwrap_or_default()
                    + 1;

                // If the bucket where we found the earliest event doesn't correspond to
                // a bucket of smaller granularity, then we guess the midpoint of the larger bucket.
                if bucket_idx > starting_bucket {
                    // Beyond starting bucket - this is our answer
                    let midway = time_unit.bucket_midway(clock_now, interval_start, bucket_idx);
                    return Some(clock_now - midway);
                }
                // Next, we check if all the events between the starting point and now
                // are accounted for by the buckets of smaller granularity.
                let this_count = counter
                    .sum_range(time_unit, 0..starting_bucket + 1)
                    .unwrap_or(0);
                let next_count = counter
                    .sum_range(next_config.time_unit(), 0..usize::MAX)
                    .unwrap_or(0);

                // If there was an over count, then we know the first event happened somewhere
                // after the larger bucket started, but before all of the smaller buckets started.
                if this_count > next_count {
                    // So we guess at the midpoint between those two.
                    let earliest = clock_now - time_unit.bucket_end(interval_start, bucket_idx);
                    let latest = clock_now - next_config.first_moment_ever(next_interval_start);
                    return Some((earliest + latest) / 2);
                }
                // If not, then: we know that there is a more granular count available,
                // and we just go to the next time unit.
            }
        }

        None
    }

    /// Returns the time since the event was first seen in a specific time unit.
    ///
    /// Returns None if the event has never been recorded, doesn't exist,
    /// or the time unit is not tracked.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::{EventStore, TimeUnit};
    /// use chrono::Duration;
    ///
    /// let store = EventStore::new();
    /// store.record("page_view");
    ///
    /// let time_since = store.query("page_view").first_seen_in(TimeUnit::Days);
    /// assert!(time_since.is_some());
    /// ```
    pub fn first_seen_in(self, time_unit: TimeUnit) -> Option<Duration> {
        let clock_now = self.store.clock_now();
        let time_unit = self.store.config.specified_time_unit(time_unit);
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);

        if let Some(bucket_idx) = counter.first_seen_in(time_unit) {
            // Convert bucket index to duration
            let duration = time_unit.duration() * bucket_idx as i32;
            Some(duration)
        } else {
            None
        }
    }
}

/// Builder for querying a specific time range.
///
/// Provides aggregation methods like sum(), average(), and iteration over buckets.
#[must_use = "query builders do nothing unless consumed"]
pub struct RangeQuery {
    store: Arc<EventStoreInner>,
    event_id: String,
    time_unit: TimeUnit,
    range: Range<usize>,
}

impl RangeQuery {
    /// Creates a new RangeQuery.
    fn new(
        store: Arc<EventStoreInner>,
        event_id: String,
        time_unit: TimeUnit,
        range: Range<usize>,
    ) -> Self {
        Self {
            store,
            event_id,
            time_unit,
            range,
        }
    }

    /// Limit the range to at most N buckets.
    pub fn take(mut self, n: usize) -> Self {
        self.range.end = self.range.start + n;
        self
    }

    /// Sum all events in the range.
    ///
    /// Returns None if the event doesn't exist or the time unit isn't tracked.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    ///
    /// let store = EventStore::new();
    /// store.record_count("clicks", 10);
    ///
    /// let total = store.query("clicks").last_days(7).sum();
    /// assert_eq!(total, Some(10));
    /// ```
    pub fn sum(self) -> Option<u32> {
        let clock_now = self.store.clock_now();
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let time_unit = self.store.config.specified_time_unit(self.time_unit);
        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);
        counter.sum_range(time_unit, self.range)
    }

    /// Calculate the average count per bucket.
    ///
    /// Returns None if the event doesn't exist, the time unit isn't tracked,
    /// or there's no data in the range.
    ///
    /// # Examples
    ///
    /// ```
    /// use tiny_counter::EventStore;
    ///
    /// let store = EventStore::new();
    /// store.record_count("api_calls", 100);
    ///
    /// let avg = store.query("api_calls").last_days(7).average();
    /// assert!(avg.is_some());
    /// ```
    pub fn average(self) -> Option<f64> {
        let count = (self.range.end - self.range.start) as f64;
        let sum = self.sum()?;
        match sum {
            0 => Some(0.0),
            s => {
                if count > 0.0 {
                    Some(s as f64 / count)
                } else {
                    None
                }
            }
        }
    }

    /// Calculate the average excluding zero buckets.
    ///
    /// Returns None if the event doesn't exist, the time unit isn't tracked,
    /// or there are no non-zero buckets.
    pub fn average_nonzero(self) -> Option<f64> {
        let buckets = self.into_buckets();
        if buckets.is_empty() {
            return None;
        }

        let non_zero: Vec<u32> = buckets.iter().copied().filter(|&x| x > 0).collect();
        if non_zero.is_empty() {
            return None;
        }

        let sum: u64 = non_zero
            .iter()
            .fold(0u64, |acc, &val| acc.saturating_add(val as u64));
        let avg = sum as f64 / non_zero.len() as f64;
        Some(avg)
    }

    /// Sum the number of non-zero buckets.
    ///
    /// Returns None if the event doesn't exist or the time unit isn't tracked.
    pub fn count_nonzero(self) -> Option<usize> {
        let buckets = self.into_buckets();
        if buckets.is_empty() {
            return None;
        }

        let count = buckets.iter().filter(|&&x| x > 0).count();
        Some(count)
    }

    /// Returns the bucket index of the last seen event.
    ///
    /// Returns None if the event doesn't exist, the time unit isn't tracked,
    /// or the event has never been recorded.
    pub fn last_seen(self) -> Option<usize> {
        let clock_now = self.store.clock_now();
        let time_unit = self.store.config.specified_time_unit(self.time_unit);
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);
        counter.last_seen_in(time_unit)
    }

    /// Returns the bucket index of the first seen event.
    ///
    /// Returns None if the event doesn't exist, the time unit isn't tracked,
    /// or the event has never been recorded.
    pub fn first_seen(self) -> Option<usize> {
        let clock_now = self.store.clock_now();
        let time_unit = self.store.config.specified_time_unit(self.time_unit);
        let counter_arc = self.store.get_counter_for_query(&self.event_id)?;
        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);
        counter.first_seen_in(time_unit)
    }

    /// Returns a vector of bucket counts for the range.
    pub fn into_buckets(self) -> Vec<u32> {
        let clock_now = self.store.clock_now();
        let time_unit = self.store.config.specified_time_unit(self.time_unit);

        let counter_arc = match self.store.get_counter_for_query(&self.event_id) {
            Some(arc) => arc,
            None => return Vec::new(),
        };

        let mut counter = counter_arc.lock().unwrap();
        counter.advance_if_needed(clock_now);

        let interval = match counter.interval(time_unit) {
            Some(interval) => interval,
            None => return Vec::new(),
        };

        let end = self.range.end.min(interval.bucket_count());

        (self.range.start..end)
            .filter_map(|i| interval.bucket_value(i))
            .collect()
    }
}

/// Builder for querying multiple events.
#[must_use = "query builders do nothing unless consumed"]
pub struct MultiQuery {
    store: Arc<EventStoreInner>,
    event_ids: Vec<String>,
}

impl MultiQuery {
    /// Creates a new MultiQuery builder.
    pub(crate) fn new(store: Arc<EventStoreInner>, event_ids: Vec<String>) -> Self {
        Self { store, event_ids }
    }

    pub(crate) fn last(self, n: usize, unit: TimeUnit) -> MultiRangeQuery {
        MultiRangeQuery::new(self.store, self.event_ids, unit, 0..n)
    }

    /// Query the last N seconds.
    pub fn last_seconds(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Seconds)
    }

    /// Query the last N minutes across all events.
    pub fn last_minutes(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Minutes)
    }

    /// Query the last N hours across all events.
    pub fn last_hours(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Hours)
    }

    /// Query the last N days across all events.
    pub fn last_days(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Days)
    }

    /// Query the last N weeks across all events.
    pub fn last_weeks(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Weeks)
    }

    /// Query the last N months across all events.
    pub fn last_months(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Months)
    }

    /// Query the last N years across all events.
    pub fn last_years(self, n: usize) -> MultiRangeQuery {
        self.last(n, TimeUnit::Years)
    }

    /// Query all available data across all events.
    pub fn ever(self) -> MultiRangeQuery {
        // Use TimeUnit::Ever which will be resolved per-event during query execution
        // For multi-event queries, we take the minimum across events
        self.last(usize::MAX, TimeUnit::Ever)
    }
}

/// Range query over multiple events.
#[must_use = "query builders do nothing unless consumed"]
pub struct MultiRangeQuery {
    store: Arc<EventStoreInner>,
    event_ids: Vec<String>,
    time_unit: TimeUnit,
    range: Range<usize>,
}

impl MultiRangeQuery {
    fn new(
        store: Arc<EventStoreInner>,
        event_ids: Vec<String>,
        time_unit: TimeUnit,
        range: Range<usize>,
    ) -> Self {
        Self {
            store,
            event_ids,
            time_unit,
            range,
        }
    }

    /// Sum all events across all tracked counters.
    ///
    /// Uses saturating addition - if the sum exceeds u32::MAX, it saturates.
    pub fn sum(self) -> Option<u32> {
        let clock_now = self.store.clock_now();

        let mut total = 0u32;
        let mut found_any = false;
        let time_unit = self.store.config.specified_time_unit(self.time_unit);
        for event_id in &self.event_ids {
            if let Some(counter_arc) = self.store.get_counter_for_query(event_id) {
                let mut counter = counter_arc.lock().unwrap();
                counter.advance_if_needed(clock_now);
                if let Some(sum) = counter.sum_range(time_unit, self.range.clone()) {
                    total = total.saturating_add(sum);
                    found_any = true;
                }
            }
        }

        if found_any {
            Some(total)
        } else {
            None
        }
    }

    /// Calculate average across all events.
    pub fn average(self) -> Option<f64> {
        let count = (self.range.end - self.range.start) as f64;
        let sum = self.sum();
        match sum {
            None => None,
            Some(0) => Some(0.0),
            Some(s) => {
                if count > 0.0 {
                    Some(s as f64 / count)
                } else {
                    None
                }
            }
        }
    }
}

/// Builder for calculating ratios between two events.
#[must_use = "query builders do nothing unless consumed"]
pub struct RatioQuery {
    store: Arc<EventStoreInner>,
    numerator_id: String,
    denominator_id: String,
}

impl RatioQuery {
    /// Creates a new RatioQuery builder.
    pub(crate) fn new(
        store: Arc<EventStoreInner>,
        numerator_id: String,
        denominator_id: String,
    ) -> Self {
        Self {
            store,
            numerator_id,
            denominator_id,
        }
    }

    pub(crate) fn last(self, n: usize, unit: TimeUnit) -> Option<f64> {
        self.calculate_ratio(unit, 0..n)
    }

    /// Calculate ratio over the last N seconds.
    pub fn last_seconds(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Seconds)
    }

    /// Calculate ratio over the last N minutes.
    pub fn last_minutes(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Minutes)
    }

    /// Calculate ratio over the last N hours.
    pub fn last_hours(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Hours)
    }

    /// Calculate ratio over the last N days.
    pub fn last_days(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Days)
    }

    /// Calculate ratio over the last N weeks.
    pub fn last_weeks(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Weeks)
    }

    /// Calculate ratio over the last N months.
    pub fn last_months(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Months)
    }

    /// Calculate ratio over the last N years.
    pub fn last_years(self, n: usize) -> Option<f64> {
        self.last(n, TimeUnit::Years)
    }

    /// Calculate ratio over all available data.
    pub fn ever(self) -> Option<f64> {
        // Use TimeUnit::Ever which will be resolved during query execution
        self.last(usize::MAX, TimeUnit::Ever)
    }

    fn calculate_ratio(self, time_unit: TimeUnit, range: Range<usize>) -> Option<f64> {
        let clock_now = self.store.clock_now();

        // Resolve TimeUnit::Ever from the configuration
        let time_unit = self.store.config.specified_time_unit(time_unit);

        // Get counters first
        let numerator = self.store.get_counter_for_query(&self.numerator_id)?;
        let mut numerator_counter = numerator.lock().unwrap();
        numerator_counter.advance_if_needed(clock_now);

        let denominator = self.store.get_counter_for_query(&self.denominator_id)?;
        let mut denominator_counter = denominator.lock().unwrap();
        denominator_counter.advance_if_needed(clock_now);

        let numerator_sum = numerator_counter
            .sum_range(time_unit, range.clone())
            .unwrap_or(0);
        let denominator_sum = denominator_counter
            .sum_range(time_unit, range.clone())
            .unwrap_or(0);

        if denominator_sum == 0 {
            None // Avoid division by zero
        } else {
            Some(numerator_sum as f64 / denominator_sum as f64)
        }
    }
}

/// Builder for calculating deltas (net changes) between two events.
#[must_use = "query builders do nothing unless consumed"]
pub struct DeltaQuery {
    store: Arc<EventStoreInner>,
    positive_id: String,
    negative_id: String,
}

impl DeltaQuery {
    /// Creates a new DeltaQuery builder.
    pub(crate) fn new(
        store: Arc<EventStoreInner>,
        positive_id: String,
        negative_id: String,
    ) -> Self {
        Self {
            store,
            positive_id,
            negative_id,
        }
    }

    pub(crate) fn last(self, n: usize, unit: TimeUnit) -> DeltaRangeQuery {
        DeltaRangeQuery::new(self.store, self.positive_id, self.negative_id, unit, 0..n)
    }

    /// Calculate delta over the last N seconds.
    pub fn last_seconds(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Seconds)
    }

    /// Calculate delta over the last N minutes.
    pub fn last_minutes(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Minutes)
    }

    /// Calculate delta over the last N hours.
    pub fn last_hours(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Hours)
    }

    /// Calculate delta over the last N days.
    pub fn last_days(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Days)
    }

    /// Calculate delta over the last N weeks.
    pub fn last_weeks(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Weeks)
    }

    /// Calculate delta over the last N months.
    pub fn last_months(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Months)
    }

    /// Calculate delta over the last N years.
    pub fn last_years(self, n: usize) -> DeltaRangeQuery {
        self.last(n, TimeUnit::Years)
    }

    /// Calculate delta over all available data.
    pub fn ever(self) -> DeltaRangeQuery {
        // Use TimeUnit::Ever which will be resolved during query execution
        self.last(usize::MAX, TimeUnit::Ever)
    }
}

/// Range query for delta calculations.
#[must_use = "query builders do nothing unless consumed"]
pub struct DeltaRangeQuery {
    store: Arc<EventStoreInner>,
    positive_id: String,
    negative_id: String,
    time_unit: TimeUnit,
    range: Range<usize>,
}

impl DeltaRangeQuery {
    fn new(
        store: Arc<EventStoreInner>,
        positive_id: String,
        negative_id: String,
        time_unit: TimeUnit,
        range: Range<usize>,
    ) -> Self {
        Self {
            store,
            positive_id,
            negative_id,
            time_unit,
            range,
        }
    }

    /// Calculate the net change (positive - negative).
    ///
    /// Returns 0 if both events don't exist or the time unit isn't tracked.
    /// Can return negative values if negative exceeds positive.
    pub fn sum(self) -> i64 {
        let clock_now = self.store.clock_now();

        // Get counters (if they exist)
        let positive_counter = self.store.get_counter_for_query(&self.positive_id);
        let negative_counter = self.store.get_counter_for_query(&self.negative_id);

        let time_unit = self.store.config.specified_time_unit(self.time_unit);

        let positive_sum = match positive_counter {
            Some(counter_arc) => {
                let mut counter = counter_arc.lock().unwrap();
                counter.advance_if_needed(clock_now);
                counter
                    .sum_range(time_unit, self.range.clone())
                    .unwrap_or(0) as i64
            }
            None => 0,
        };

        let negative_sum = match negative_counter {
            Some(counter_arc) => {
                let mut counter = counter_arc.lock().unwrap();
                counter.advance_if_needed(clock_now);
                counter
                    .sum_range(time_unit, self.range.clone())
                    .unwrap_or(0) as i64
            }
            None => 0,
        };

        positive_sum - negative_sum
    }

    /// Calculate the average delta per bucket.
    pub fn average(self) -> f64 {
        let count = (self.range.end - self.range.start) as f64;
        let sum = self.sum();
        if count > 0.0 {
            sum as f64 / count
        } else {
            0.0
        }
    }
}

#[cfg(test)]
mod tests {

    use std::sync::Arc;

    use chrono::{DateTime, Datelike, Duration, TimeZone, Utc};

    use crate::{Clock, EventStore, TestClock, TimeUnit};

    #[test]
    fn test_query_last_days_sum() {
        let store = EventStore::new();
        store.record_count("event", 5);
        store.record_count("event", 3);

        let sum = store.query("event").last_days(1).sum();
        assert_eq!(sum, Some(8));
    }

    #[test]
    fn test_query_nonexistent_event() {
        let store = EventStore::new();
        let sum = store.query("nonexistent").last_days(1).sum();
        assert_eq!(sum, None);
    }

    #[test]
    fn test_range_query_average() {
        let store = EventStore::new();
        store.record_count("event", 10);

        let avg = store.query("event").last_days(2).average();
        // 10 events across 2 days = 5.0 average
        assert_eq!(avg, Some(5.0));
    }

    #[test]
    fn test_range_query_take() {
        let store = EventStore::new();
        store.record_count("event", 5);

        let sum = store.query("event").days_from(0).take(1).sum();
        assert_eq!(sum, Some(5));
    }

    #[test]
    fn test_multi_query_sum() {
        let store = EventStore::new();
        store.record_count("event1", 5);
        store.record_count("event2", 3);

        let sum = store.query_many(&["event1", "event2"]).last_days(1).sum();
        assert_eq!(sum, Some(8));
    }

    #[test]
    fn test_ratio_query() {
        let store = EventStore::new();
        store.record_count("num", 6);
        store.record_count("denom", 3);

        let ratio = store.query_ratio("num", "denom").last_days(1);
        assert_eq!(ratio, Some(2.0));
    }

    #[test]
    fn test_ratio_query_division_by_zero() {
        let store = EventStore::new();
        store.record_count("num", 6);
        // denominator has 0 events

        let ratio = store.query_ratio("num", "denom").last_days(1);
        assert_eq!(ratio, None); // Should return None for division by zero
    }

    #[test]
    fn test_delta_query_positive() {
        let store = EventStore::new();
        store.record_count("pos", 10);
        store.record_count("neg", 3);

        let delta = store.query_delta("pos", "neg").last_days(1).sum();
        assert_eq!(delta, 7);
    }

    #[test]
    fn test_delta_query_negative() {
        let store = EventStore::new();
        store.record_count("pos", 3);
        store.record_count("neg", 10);

        let delta = store.query_delta("pos", "neg").last_days(1).sum();
        assert_eq!(delta, -7); // Can be negative!
    }

    #[test]
    fn test_delta_query_zero() {
        let store = EventStore::new();
        let delta = store.query_delta("pos", "neg").last_days(1).sum();
        assert_eq!(delta, 0);
    }

    #[test]
    fn test_count_nonzero() {
        let store = EventStore::new();
        store.record_count("event", 5);
        // Only 1 bucket has data

        let count = store.query("event").last_days(7).count_nonzero();
        assert_eq!(count, Some(1));
    }

    #[test]
    fn test_average_nonzero() {
        let store = EventStore::new();
        store.record_count("event", 10);

        let avg = store.query("event").last_days(7).average_nonzero();
        // Only 1 bucket has data with value 10
        assert_eq!(avg, Some(10.0));
    }

    #[test]
    fn test_ever_uses_longest_time_unit() {
        // Test that ever() uses the longest configured time unit for the event
        let store = EventStore::new();
        store.record_count("event", 100);

        // The default config includes Years as the longest time unit
        let sum = store.query("event").ever().sum();
        assert_eq!(sum, Some(100));
    }

    #[test]
    fn test_ever_with_nonexistent_event() {
        // Test that ever() handles nonexistent events gracefully
        let store = EventStore::new();

        let sum = store.query("nonexistent").ever().sum();
        assert_eq!(sum, None);
    }

    #[test]
    fn test_ever_uses_time_unit_ever_variant() {
        // Test that ever() now uses TimeUnit::Ever instead of loading counter twice
        let store = EventStore::new();
        store.record_count("event", 100);

        // Create a query with ever()
        let query = store.query("event").ever();

        // The query should have TimeUnit::Ever before execution
        // (We can't directly inspect it, but we can verify it still works)
        let sum = query.sum();
        assert_eq!(sum, Some(100));
    }

    #[test]
    fn test_multi_query_ever() {
        let store = EventStore::new();
        store.record_count("event1", 50);
        store.record_count("event2", 75);

        let sum = store.query_many(&["event1", "event2"]).ever().sum();
        assert_eq!(sum, Some(125));
    }

    #[test]
    fn test_ratio_query_ever() {
        let store = EventStore::new();
        store.record_count("num", 100);
        store.record_count("denom", 25);

        let ratio = store.query_ratio("num", "denom").ever();
        assert_eq!(ratio, Some(4.0));
    }

    #[test]
    fn test_delta_query_ever() {
        let store = EventStore::new();
        store.record_count("pos", 150);
        store.record_count("neg", 50);

        let delta = store.query_delta("pos", "neg").ever().sum();
        assert_eq!(delta, 100);
    }

    #[test]
    fn test_multi_range_query_handles_large_values() {
        let store = EventStore::new();

        // Record max u32 values
        store.record_count("event1", u32::MAX);
        store.record_count("event2", u32::MAX);
        store.record_count("event3", u32::MAX);

        let sum = store
            .query_many(&["event1", "event2", "event3"])
            .last_days(1)
            .sum();

        // Sum saturates at u32::MAX
        assert_eq!(sum, Some(u32::MAX));
    }

    #[test]
    fn test_average_nonzero_handles_large_values() {
        use crate::store::builder::EventStoreBuilder;

        let store = EventStoreBuilder::new().track_days(5).build().unwrap();

        // Record large values that will saturate at u32::MAX
        // These all go to the same bucket
        store.record_count("event", u32::MAX / 3);
        store.record_count("event", u32::MAX / 3);
        store.record_count("event", u32::MAX / 3);

        let avg = store.query("event").last_days(5).average_nonzero();

        // Should handle large values correctly
        assert!(avg.is_some());
        let avg_value = avg.unwrap();
        // Single bucket with 3×(u32::MAX/3) = u32::MAX, so average equals u32::MAX
        assert_eq!(avg_value, u32::MAX as f64);
    }

    #[test]
    fn test_first_seen_returns_oldest_event_touching_buckets() {
        use chrono::{TimeZone, Utc};
        // Use fixed time at noon to avoid midnight crossing issues
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(60)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(5));
        store.record("event");

        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        assert_eq!(first, Some(Duration::hours(5) + Duration::minutes(30)));

        // last_seen should return 0 (most recent)
        assert!(last.is_some());
        assert!(last.unwrap() == Duration::minutes(0));
    }

    #[test]
    fn test_first_seen_returns_oldest_event_overlapping_buckets() {
        use chrono::{TimeZone, Utc};
        // Use fixed time at noon to avoid midnight crossing issues
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(60 * 24)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(5));
        store.record("event");

        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        assert_eq!(first, Some(Duration::hours(5) + Duration::seconds(30)));

        // last_seen should return 0 (most recent)
        assert!(last.is_some());
        assert!(last.unwrap() == Duration::minutes(0));
    }

    #[test]
    fn test_first_seen_returns_oldest_event_disjoint_buckets() {
        use chrono::{TimeZone, Utc};
        // Use fixed time at noon to avoid midnight crossing issues
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_minutes(60)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(5)); // now at 1700.
        store.record("event");

        // first_seen is somewhere between midnight and 1600.
        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        let expected = ago(clock.now(), 0, 8, 00);
        eprintln!("Expected at {}, {expected:?} ago", clock.now() - expected);
        eprintln!(
            "Actual   at {}, {:?} ago",
            clock.now() - first.unwrap(),
            first.unwrap()
        );
        // (Duration::days(1) + Duration::hours(1)) / 2
        assert_eq!(first, Some(expected));

        // last_seen should return 0 (most recent)
        assert!(last.is_some());
        assert!(last.unwrap() == Duration::minutes(0));
    }

    fn ago(now: DateTime<Utc>, days_ago: i64, hours: u32, minutes: u32) -> Duration {
        use chrono::{TimeZone, Utc};
        let then = Utc
            .with_ymd_and_hms(now.year(), now.month(), now.day(), hours, minutes, 0)
            .unwrap()
            - Duration::days(days_ago);
        now - then
    }

    #[test]
    fn test_first_seen_returns_oldest_event_disjoint_muilti_buckets_under() {
        use chrono::{TimeZone, Utc};
        // Use fixed time at noon to avoid midnight crossing issues
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(36)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(25));
        store.record("event");

        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        assert_eq!(first, Some(Duration::hours(25) + Duration::minutes(30)));

        // last_seen should return 0 (most recent)
        assert!(last.is_some());
        assert!(last.unwrap() == Duration::minutes(0));
    }

    #[test]
    fn test_first_seen_returns_oldest_event_disjoint_muilti_buckets_over() {
        use chrono::{TimeZone, Utc};
        // Use fixed time at 1400 to avoid midnight crossing issues
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 10, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(36)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(37)); // now is 10 + 37 = 47 = 23h.
        store.record("event");

        // Query time is 11pm
        // first_seen is somewhere between midnight and 11am
        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        // When query time is BEFORE midnight, so first at between end of the 36th hour bucket
        // and the end of 2nd day bucket.
        let expected = ago(clock.now(), 1, 5, 30);
        eprintln!("Expected at {}, {expected:?} ago", clock.now() - expected);
        eprintln!(
            "Actual   at {}, {:?} ago",
            clock.now() - first.unwrap(),
            first.unwrap()
        );
        assert_eq!(first, Some(expected));

        // last_seen should return 0 (most recent)
        assert_eq!(last, Some(Duration::minutes(0)));

        clock.advance(Duration::hours(2)); // 23h + 2h = 1am
        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();
        // When query time is AFTER midnight, so first at between end of the 36th hour bucket
        // and the end of 3rd day bucket.
        let expected = ago(clock.now(), 2, 6, 30);
        eprintln!("Expected at {}, {expected:?} ago", clock.now() - expected);
        eprintln!(
            "Actual   at {}, {:?} ago",
            clock.now() - first.unwrap(),
            first.unwrap()
        );
        assert_eq!(first, Some(expected));
        assert_eq!(last, Some(Duration::hours(2) + Duration::minutes(30)));
    }

    #[test]
    fn test_first_seen_with_no_events() {
        let store = EventStore::new();
        let first = store.query("nonexistent").first_seen();
        assert_eq!(first, None);
    }

    #[test]
    fn test_first_seen_in_specific_time_unit() {
        let clock = TestClock::build_for_testing();
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        // Record first event
        store.record("event");
        // Advance clock so first event is now 5 hours old
        clock.advance(Duration::hours(5));
        // Record second event to force rotation
        store.record("event");

        let first_hours = store.query("event").first_seen_in(TimeUnit::Hours);

        // Should see the oldest event (5 hours ago)
        assert_eq!(first_hours, Some(Duration::hours(5)));
    }

    #[test]
    fn test_first_seen_with_single_event_touching_intervals() {
        let clock = TestClock::build_for_testing();
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .track_hours(24)
            .track_minutes(60)
            .build()
            .unwrap();

        store.record("event");

        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        // Both should be very close to 0 (current time)
        assert!(first.is_some());
        assert!(last.is_some());
        eprintln!("first = {:?}", first.unwrap());
        eprintln!("last = {:?}", last.unwrap());
        assert!(
            first.unwrap() < Duration::hours(1),
            "Expected first < 1 hour, got {:?}",
            first.unwrap()
        );
        assert!(last.unwrap() < Duration::hours(1));
    }

    #[test]
    fn test_first_seen_with_single_event_disjoint_intervals() {
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .track_years(2)
            // 1 mo ~ 28 days, but 12 * 28 < 365. Disjoint!
            .track_months(12)
            .track_days(28)
            .track_hours(24)
            .build()
            .unwrap();

        store.record("event");

        let first = store.query("event").first_seen();
        let last = store.query("event").last_seen();

        // Event just happened at exactly 12:00 PM, query at 12:00 PM
        // Bucket 0 has elapsed time of 0, so estimate is Duration::zero()
        assert!(first.is_some());
        assert!(last.is_some());

        // Both should be very close to 0 (current time) since event just happened
        assert_eq!(first, Some(Duration::zero()));
        assert_eq!(last, Some(Duration::zero()));
    }

    #[test]
    #[cfg(not(feature = "calendar"))]
    fn test_first_seen_across_multiple_time_units() {
        let clock = TestClock::build_for_testing();
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        // Record an event
        store.record("event");

        // Advance time by 10 days
        clock.advance(Duration::days(10));
        // Record another event to force rotation
        store.record("event");

        let first = store.query("event").first_seen();
        let expected = ago(clock.now(), 11, 12, 00);
        eprintln!("Expected at {}, {expected:?} ago", clock.now() - expected);
        eprintln!(
            "Actual   at {}, {:?} ago",
            clock.now() - first.unwrap(),
            first.unwrap()
        );
        // Should find the oldest event (10 days ago)
        assert_eq!(first, Some(expected));
    }

    #[test]
    fn test_range_query_first_seen() {
        let clock = TestClock::build_for_testing();
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::hours(5));
        store.record("event");

        // RangeQuery first_seen returns bucket index, not Duration
        let first_bucket = store.query("event").last_hours(24).first_seen();

        // Should return the oldest bucket index (5 hours ago)
        assert_eq!(first_bucket, Some(5));
    }

    #[test]
    fn test_first_seen_consistency_with_last_seen() {
        let clock = TestClock::build_for_testing();
        let store = EventStore::builder()
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event"); // First event
        clock.advance(Duration::hours(10));
        store.record("event"); // Last event

        let first_seen = store.query("event").first_seen();
        let last_seen = store.query("event").last_seen();

        // first_seen should be larger (further back in time)
        assert!(first_seen.is_some());
        assert!(last_seen.is_some());
        assert!(first_seen.unwrap() > last_seen.unwrap());
    }

    #[test]
    fn test_ever_into_buckets_does_not_hang() {
        // This test verifies that .ever().into_buckets() doesn't hang by iterating
        // 0..usize::MAX. It should resolve to the actual bucket count.
        let store = EventStore::new();
        store.record_count("event", 100);

        // This should complete quickly, not hang for 60+ seconds
        let buckets = store.query("event").ever().into_buckets();

        // Should have a reasonable number of buckets (the longest time unit's bucket count)
        // Default config has Years as longest with some reasonable bucket count
        assert!(!buckets.is_empty());
        assert!(buckets.len() < 1000); // Sanity check - should be way less than usize::MAX
    }

    #[test]
    fn test_last_seen_returns_recent_event_touching_intervals() {
        use chrono::{TimeZone, Utc};
        // Touching intervals: 60 minutes + 24 hours (no gaps)
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(60)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        // Record old event
        store.record("event");
        // Advance 10 minutes, record recent event
        clock.advance(Duration::minutes(10));
        store.record("event");

        let last = store.query("event").last_seen();

        // Should find it in minutes bucket with good precision
        // Event is in minute bucket 0, elapsed ~0, so estimate ~Duration::zero()
        assert!(last.is_some());
        assert!(
            last.unwrap() < Duration::minutes(1),
            "Expected last < 1 minute, got {:?}",
            last.unwrap()
        );
    }

    #[test]
    fn test_last_seen_returns_recent_event_overlapping_intervals() {
        use chrono::{TimeZone, Utc};
        // Overlapping intervals: 1440 minutes (24 hours) + 24 hours
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(60 * 24)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        clock.advance(Duration::minutes(10));
        store.record("event");

        let last = store.query("event").last_seen();

        // Should find it in minutes bucket 0 with good precision
        assert!(last.is_some());
        assert!(
            last.unwrap() < Duration::minutes(1),
            "Expected last < 1 minute, got {:?}",
            last.unwrap()
        );
    }

    #[test]
    fn test_last_seen_gap_event_disjoint_intervals() {
        use chrono::{TimeZone, Utc};
        // Disjoint intervals: 45 minutes + 24 hours (gap from 45-60 minutes)
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(45)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        // Advance 50 minutes - this puts the event in the GAP
        // Minutes only cover last 45 minutes, so event not in minutes
        // But it IS in hour bucket 0
        clock.advance(Duration::minutes(50));
        // Don't record another event! We want to query the gap event

        let last = store.query("event").last_seen();

        // With gap detection: should detect gap and return ~52.5 minutes
        // (midpoint between 45 minutes ago and 60 minutes ago)
        // Gap is [45, 60), so midpoint is 52.5 minutes
        let expected = Duration::minutes(52) + Duration::seconds(30);
        assert_eq!(
            last,
            Some(expected),
            "Gap event should be estimated at gap midpoint"
        );
    }

    #[test]
    fn test_last_seen_recent_event_in_smallest_bucket() {
        use chrono::{TimeZone, Utc};
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(60)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");

        let last = store.query("event").last_seen();

        // Event just happened, should be Duration::zero()
        assert_eq!(last, Some(Duration::zero()));
    }

    #[test]
    fn test_last_seen_event_in_gap_multiple_intervals() {
        use chrono::{TimeZone, Utc};
        // Setup: 30 minutes + 24 hours (gap from 30-60 minutes)
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_days(7)
            .track_hours(24)
            .track_minutes(30)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        // Advance 40 minutes - event is in the gap (30-60 minutes)
        clock.advance(Duration::minutes(40));
        // Don't record another event! We want to query the gap event

        let last = store.query("event").last_seen();

        // Gap is [30, 60), so midpoint is 45 minutes
        let expected = Duration::minutes(45);
        assert_eq!(
            last,
            Some(expected),
            "Gap event should be estimated at gap midpoint"
        );
    }

    #[test]
    fn test_last_seen_with_bucket_midway_ago() {
        use chrono::{TimeZone, Utc};
        let fixed_time = Utc.with_ymd_and_hms(2025, 12, 5, 12, 0, 0).unwrap();
        let clock = TestClock::build_for_testing_at(fixed_time);
        let store = EventStore::builder()
            .track_hours(24)
            .with_clock(Arc::new(clock.clone()))
            .build()
            .unwrap();

        store.record("event");
        // Advance 30 minutes within the current hour
        clock.advance(Duration::minutes(30));

        let last = store.query("event").last_seen();

        // With bucket_midway_ago, should estimate ~15 minutes ago
        // (midpoint of elapsed 30 minutes in current hour bucket)
        assert!(last.is_some());
        let duration = last.unwrap();

        // Should be around 15 minutes (half of 30 minutes elapsed)
        assert!(
            duration >= Duration::minutes(14) && duration <= Duration::minutes(16),
            "Expected ~15 minutes, got {:?}",
            duration
        );
    }
}