meterstore 0.1.0

//! Extracting a [`TimeRange`] from DataFusion filter expressions.
//!
//! Only the `from` column matters here: it decides which tier holds a row, so a
//! bound on it is what lets the planner skip a tier entirely. Every other
//! predicate is left to DataFusion.
//!
//! **The analysis is deliberately conservative.** Failing to recognise a bound
//! costs a wider scan; wrongly inferring one loses rows. So anything not
//! provably a bound on `from` widens the range rather than narrowing it, and
//! `OR` — where one branch may be unbounded — discards bounds entirely.

use datafusion::common::ScalarValue;
use datafusion::logical_expr::{Between, BinaryExpr, Expr, Operator};
use time::OffsetDateTime;

use crate::encode::schema::col;
use crate::planner::split::TimeRange;

/// Extract the tightest provable bound on `from` from a set of filters.
///
/// Filters are implicitly `AND`ed, so bounds intersect.
pub fn time_range(filters: &[Expr]) -> TimeRange {
    filters
        .iter()
        .map(range_of)
        .fold(TimeRange::unbounded(), intersect)
}

/// Express a range as filters the cold provider can prune on.
///
/// The tier split narrows a query's range, and that narrowing is only useful to
/// Iceberg if it reaches the scan as a predicate — otherwise partition pruning
/// and row-group statistics see the original, wider bounds.
pub fn range_filters(range: TimeRange) -> Vec<Expr> {
    let mut out = Vec::with_capacity(2);
    if let Some(start) = range.start() {
        out.push(datafusion::logical_expr::col(col::FROM).gt_eq(timestamp_lit(start)));
    }
    if let Some(end) = range.end() {
        out.push(datafusion::logical_expr::col(col::FROM).lt(timestamp_lit(end)));
    }
    out
}

/// A ceiling on the domain version axis, for a reproducible read.
///
/// The Iceberg snapshot pins *transaction* time — what the store had been told
/// by a given moment. It does not pin the domain's own version axis, because a
/// snapshot taken after a correction landed contains both versions and
/// resolution would pick the newer one. Settlement reruns need the value that
/// was in force, so the ceiling is a second, independent bound: keep only
/// versions at or below `max`, then resolve among those.
pub fn version_ceiling(max: crate::version::Version) -> Expr {
    use crate::encode::schema::{VERSION_PRECISION, VERSION_SCALE};
    datafusion::logical_expr::col(col::VERSION).lt_eq(datafusion::logical_expr::lit(
        ScalarValue::Decimal128(Some(max.to_i128()), VERSION_PRECISION, VERSION_SCALE),
    ))
}

/// A timestamp literal in the unit and zone the storage schema uses.
fn timestamp_lit(t: OffsetDateTime) -> Expr {
    datafusion::logical_expr::lit(ScalarValue::TimestampMicrosecond(
        Some((t.unix_timestamp_nanos() / 1_000) as i64),
        Some("UTC".into()),
    ))
}

/// The range a single expression constrains `from` to.
fn range_of(filter: &Expr) -> TimeRange {
    match filter {
        Expr::BinaryExpr(BinaryExpr { left, op, right }) => match op {
            Operator::And => intersect(range_of(left), range_of(right)),

            // A row satisfying either branch qualifies, so the result is the
            // union — and unioning with an unrecognised branch yields no usable
            // bound. Narrowing here would silently drop rows.
            Operator::Or => TimeRange::unbounded(),

            Operator::Lt | Operator::LtEq | Operator::Gt | Operator::GtEq | Operator::Eq => {
                as_from_bound(left, *op, right).unwrap_or_else(TimeRange::unbounded)
            }

            _ => TimeRange::unbounded(),
        },

        Expr::Between(Between {
            expr,
            negated: false,
            low,
            high,
        }) if is_from_column(expr) => {
            match (as_timestamp(low), as_timestamp(high)) {
                // BETWEEN is inclusive on both sides; our upper bound is
                // exclusive, so the high value must still be matched.
                (Some(lo), Some(hi)) => TimeRange::new(Some(lo), Some(exclusive_after(hi))),
                _ => TimeRange::unbounded(),
            }
        }

        _ => TimeRange::unbounded(),
    }
}

/// Interpret `left op right` as a bound on `from`, if it is one.
///
/// Handles the literal on either side, flipping the operator when the column is
/// on the right.
fn as_from_bound(left: &Expr, op: Operator, right: &Expr) -> Option<TimeRange> {
    if is_from_column(left) {
        bound_from(op, as_timestamp(right)?)
    } else if is_from_column(right) {
        bound_from(flip(op), as_timestamp(left)?)
    } else {
        None
    }
}

/// The range implied by `from <op> value`.
fn bound_from(op: Operator, value: OffsetDateTime) -> Option<TimeRange> {
    Some(match op {
        Operator::Lt => TimeRange::new(None, Some(value)),
        Operator::LtEq => TimeRange::new(None, Some(exclusive_after(value))),
        Operator::Gt => TimeRange::new(Some(exclusive_after(value)), None),
        Operator::GtEq => TimeRange::new(Some(value), None),
        // A point lookup is a range of one instant.
        Operator::Eq => TimeRange::new(Some(value), Some(exclusive_after(value))),
        _ => return None,
    })
}

/// Mirror a comparison so the column can be treated as the left operand.
fn flip(op: Operator) -> Operator {
    match op {
        Operator::Lt => Operator::Gt,
        Operator::LtEq => Operator::GtEq,
        Operator::Gt => Operator::Lt,
        Operator::GtEq => Operator::LtEq,
        other => other,
    }
}

/// The smallest instant strictly after `t`, at storage resolution.
///
/// Storage is microsecond-precision, so converting an inclusive bound to an
/// exclusive one is exact rather than an approximation.
fn exclusive_after(t: OffsetDateTime) -> OffsetDateTime {
    t + time::Duration::microseconds(1)
}

/// Whether an expression refers to the `from` column.
fn is_from_column(expr: &Expr) -> bool {
    // `CAST(from AS ...)` still refers to the same column, and DataFusion
    // frequently inserts casts around timestamp comparisons.
    match expr {
        Expr::Column(c) => c.name == col::FROM,
        Expr::Cast(cast) => is_from_column(&cast.expr),
        Expr::TryCast(cast) => is_from_column(&cast.expr),
        _ => false,
    }
}

/// Read a literal timestamp, whatever unit it was written in.
fn as_timestamp(expr: &Expr) -> Option<OffsetDateTime> {
    let scalar = match expr {
        Expr::Literal(v, _) => v,
        Expr::Cast(cast) => return as_timestamp(&cast.expr),
        _ => return None,
    };

    let nanos: i128 = match scalar {
        ScalarValue::TimestampNanosecond(Some(v), _) => i128::from(*v),
        ScalarValue::TimestampMicrosecond(Some(v), _) => i128::from(*v) * 1_000,
        ScalarValue::TimestampMillisecond(Some(v), _) => i128::from(*v) * 1_000_000,
        ScalarValue::TimestampSecond(Some(v), _) => i128::from(*v) * 1_000_000_000,
        _ => return None,
    };

    OffsetDateTime::from_unix_timestamp_nanos(nanos).ok()
}

/// The tighter of two ranges.
fn intersect(a: TimeRange, b: TimeRange) -> TimeRange {
    let start = match (a.start(), b.start()) {
        (Some(x), Some(y)) => Some(x.max(y)),
        (Some(x), None) | (None, Some(x)) => Some(x),
        (None, None) => None,
    };
    let end = match (a.end(), b.end()) {
        (Some(x), Some(y)) => Some(x.min(y)),
        (Some(x), None) | (None, Some(x)) => Some(x),
        (None, None) => None,
    };
    TimeRange::new(start, end)
}

#[cfg(test)]
mod tests {
    use super::*;
    use datafusion::logical_expr::{col as df_col, lit};
    use time::macros::datetime;

    const T10: OffsetDateTime = datetime!(2026-07-10 00:00 UTC);
    const T20: OffsetDateTime = datetime!(2026-07-20 00:00 UTC);

    /// A timestamp literal in the unit storage uses.
    fn ts(t: OffsetDateTime) -> Expr {
        lit(ScalarValue::TimestampMicrosecond(
            Some((t.unix_timestamp_nanos() / 1_000) as i64),
            Some("UTC".into()),
        ))
    }

    fn from() -> Expr {
        df_col(col::FROM)
    }

    #[test]
    fn range_filters_round_trip_through_extraction() {
        // What the split narrows must be re-extractable, or the cold scan is
        // handed bounds the planner cannot then use for pruning.
        let range = TimeRange::between(T10, T20);
        let recovered = time_range(&range_filters(range));
        assert_eq!(recovered, range);
    }

    #[test]
    fn range_filters_omit_absent_bounds() {
        assert!(range_filters(TimeRange::unbounded()).is_empty());
        assert_eq!(range_filters(TimeRange::new(Some(T10), None)).len(), 1);
        assert_eq!(range_filters(TimeRange::new(None, Some(T20))).len(), 1);
        assert_eq!(range_filters(TimeRange::between(T10, T20)).len(), 2);
    }

    #[test]
    fn no_filters_gives_an_unbounded_range() {
        assert_eq!(time_range(&[]), TimeRange::unbounded());
    }

    #[test]
    fn greater_than_or_equal_becomes_an_inclusive_lower_bound() {
        let r = time_range(&[from().gt_eq(ts(T10))]);
        assert_eq!(r.start(), Some(T10));
        assert_eq!(r.end(), None);
    }

    #[test]
    fn strictly_greater_than_excludes_the_bound_itself() {
        let r = time_range(&[from().gt(ts(T10))]);
        assert_eq!(r.start(), Some(exclusive_after(T10)));
        assert!(r.start().unwrap() > T10);
    }

    #[test]
    fn less_than_becomes_an_exclusive_upper_bound() {
        let r = time_range(&[from().lt(ts(T20))]);
        assert_eq!(r.end(), Some(T20));
        assert_eq!(r.start(), None);
    }

    #[test]
    fn less_than_or_equal_still_matches_the_bound() {
        // Our upper bound is exclusive, so <= must extend past the value or the
        // matching row is dropped.
        let r = time_range(&[from().lt_eq(ts(T20))]);
        assert!(r.end().unwrap() > T20);
    }

    #[test]
    fn a_conjunction_intersects_bounds() {
        let r = time_range(&[from().gt_eq(ts(T10)), from().lt(ts(T20))]);
        assert_eq!(r, TimeRange::between(T10, T20));
    }

    #[test]
    fn a_nested_and_intersects_too() {
        let r = time_range(&[from().gt_eq(ts(T10)).and(from().lt(ts(T20)))]);
        assert_eq!(r, TimeRange::between(T10, T20));
    }

    #[test]
    fn the_tightest_bound_wins() {
        let mid = datetime!(2026-07-15 00:00 UTC);
        let r = time_range(&[from().gt_eq(ts(T10)), from().gt_eq(ts(mid))]);
        assert_eq!(r.start(), Some(mid));
    }

    #[test]
    fn a_literal_on_the_left_flips_the_operator() {
        // `'2026-07-10' <= from` is the same as `from >= '2026-07-10'`.
        let r = time_range(&[ts(T10).lt_eq(from())]);
        assert_eq!(r.start(), Some(T10));
        assert_eq!(r.end(), None);
    }

    #[test]
    fn between_is_inclusive_on_both_sides() {
        let r = time_range(&[from().between(ts(T10), ts(T20))]);
        assert_eq!(r.start(), Some(T10));
        assert!(r.end().unwrap() > T20, "the high value must still match");
    }

    #[test]
    fn equality_is_a_single_instant() {
        let r = time_range(&[from().eq(ts(T10))]);
        assert_eq!(r.start(), Some(T10));
        assert!(r.end().unwrap() > T10);
        assert!(!r.is_empty());
    }

    #[test]
    fn a_disjunction_yields_no_bound() {
        // One branch could be unbounded, so narrowing would drop rows.
        let r = time_range(&[from().gt_eq(ts(T10)).or(from().lt(ts(T20)))]);
        assert_eq!(r, TimeRange::unbounded());
    }

    #[test]
    fn a_disjunction_does_not_poison_a_sibling_conjunct() {
        // The AND still contributes its own bound.
        let r = time_range(&[
            from().gt_eq(ts(T10)),
            from().gt_eq(ts(T20)).or(from().lt(ts(T10))),
        ]);
        assert_eq!(r.start(), Some(T10));
    }

    #[test]
    fn predicates_on_other_columns_are_ignored() {
        let r = time_range(&[df_col(col::MALO_ID).eq(lit("12345678901"))]);
        assert_eq!(r, TimeRange::unbounded());
    }

    #[test]
    fn a_bound_on_another_timestamp_column_is_not_used() {
        // `to` does not determine the tier; only `from` does.
        let r = time_range(&[df_col(col::TO).gt_eq(ts(T10))]);
        assert_eq!(r, TimeRange::unbounded());
    }

    #[test]
    fn a_cast_around_the_column_is_seen_through() {
        let cast = Expr::Cast(datafusion::logical_expr::Cast::new(
            Box::new(from()),
            crate::arrow::datatypes::DataType::Timestamp(
                crate::arrow::datatypes::TimeUnit::Microsecond,
                Some("UTC".into()),
            ),
        ));
        let r = time_range(&[cast.gt_eq(ts(T10))]);
        assert_eq!(r.start(), Some(T10));
    }

    #[test]
    fn timestamp_literals_in_other_units_are_understood() {
        let secs = lit(ScalarValue::TimestampSecond(
            Some(T10.unix_timestamp()),
            None,
        ));
        assert_eq!(time_range(&[from().gt_eq(secs)]).start(), Some(T10));

        let millis = lit(ScalarValue::TimestampMillisecond(
            Some(T10.unix_timestamp() * 1_000),
            None,
        ));
        assert_eq!(time_range(&[from().gt_eq(millis)]).start(), Some(T10));
    }

    #[test]
    fn a_null_timestamp_yields_no_bound() {
        let null = lit(ScalarValue::TimestampMicrosecond(None, None));
        assert_eq!(time_range(&[from().gt_eq(null)]), TimeRange::unbounded());
    }

    #[test]
    fn contradictory_bounds_produce_an_empty_range() {
        let r = time_range(&[from().gt_eq(ts(T20)), from().lt(ts(T10))]);
        assert!(r.is_empty());
    }

    #[test]
    fn every_recognised_shape_still_narrows_the_range() {
        // The shapes that used to be reported `Exact`. Pushdown is now always
        // `Inexact` — correctness must not rest on a dependency's silent
        // conversion — but the *narrowing* is what skips files, and that is the
        // optimisation worth having. It has to keep working.
        for filter in [
            from().gt_eq(ts(T10)),
            from().lt(ts(T20)),
            from().gt_eq(ts(T10)).and(from().lt(ts(T20))),
            from().between(ts(T10), ts(T20)),
        ] {
            assert_ne!(
                time_range(std::slice::from_ref(&filter)),
                TimeRange::unbounded(),
                "{filter} must still narrow the scan"
            );
        }
    }

    #[test]
    fn unrecognised_shapes_widen_rather_than_narrow() {
        // Failing to recognise a bound must cost a wider scan, never a lost row.
        for filter in [
            df_col(col::MALO_ID).eq(lit("x")),
            from().gt_eq(ts(T10)).or(from().lt(ts(T20))),
            from().is_null(),
        ] {
            assert_eq!(
                time_range(std::slice::from_ref(&filter)),
                TimeRange::unbounded(),
                "{filter} must not be mistaken for a bound"
            );
        }
    }
}