datasketches 0.4.0

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// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// software distributed under the License is distributed on an
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// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use crate::common::ResizeFactor;
use crate::error::Error;
use crate::hash::DEFAULT_UPDATE_SEED;
use crate::theta::CompactThetaSketch;
use crate::theta::ThetaSketchView;
use crate::theta::hash_table::ThetaEntry;
use crate::thetacommon::constants::DEFAULT_LG_K;
use crate::thetacommon::constants::MAX_LG_K;
use crate::thetacommon::constants::MIN_LG_K;
use crate::thetacommon::union::UnionMergePolicy;
use crate::thetacommon::union::UnionState;

/// Stateful union operator for Theta sketches.
#[derive(Debug)]
pub struct ThetaUnion {
    state: UnionState<ThetaEntry, NoopUnionPolicy>,
}

#[derive(Debug)]
struct NoopUnionPolicy;

impl UnionMergePolicy<ThetaEntry> for NoopUnionPolicy {
    fn merge(&self, _existing: &mut ThetaEntry, _incoming: ThetaEntry) {}
}

impl ThetaUnion {
    /// Updates this union with the given sketch.
    pub fn update<'a>(&mut self, sketch: impl Into<ThetaSketchView<'a>>) -> Result<(), Error> {
        let sketch = sketch.into();
        self.state.update(sketch)
    }

    /// Returns this union as a compact sketch.
    pub fn to_sketch(&self, ordered: bool) -> CompactThetaSketch {
        let parts = self.state.to_compact_parts(ordered);
        CompactThetaSketch::from_parts(
            parts
                .entries
                .into_iter()
                .map(|entry| entry.hash())
                .collect(),
            parts.theta,
            parts.seed_hash,
            parts.ordered,
            parts.empty,
        )
    }

    /// Resets the union to its empty state.
    pub fn reset(&mut self) {
        self.state.reset();
    }

    /// Returns the estimated size of the union in bytes.
    pub fn estimated_size(&self) -> usize {
        size_of::<Self>() + self.state.estimated_size()
    }
}

/// Builder for [`ThetaUnion`].
#[derive(Debug, Clone)]
pub struct ThetaUnionBuilder {
    lg_k: u8,
    resize_factor: ResizeFactor,
    sampling_probability: f32,
    seed: u64,
}

impl Default for ThetaUnionBuilder {
    fn default() -> Self {
        Self {
            lg_k: DEFAULT_LG_K,
            resize_factor: ResizeFactor::X8,
            sampling_probability: 1.0,
            seed: DEFAULT_UPDATE_SEED,
        }
    }
}

impl ThetaUnionBuilder {
    /// Sets `lg_k`, the base-2 logarithm of the nominal capacity.
    ///
    /// # Panics
    ///
    /// Panics if `lg_k` is outside `[5, 26]`.
    ///
    /// # Examples
    ///
    /// ```
    /// use datasketches::theta::ThetaUnionBuilder;
    ///
    /// ThetaUnionBuilder::default().lg_k(12).build();
    /// ```
    pub fn lg_k(mut self, lg_k: u8) -> Self {
        assert!(
            (MIN_LG_K..=MAX_LG_K).contains(&lg_k),
            "lg_k must be in [{MIN_LG_K}, {MAX_LG_K}], got {lg_k}"
        );
        self.lg_k = lg_k;
        self
    }

    /// Sets the resize factor.
    pub fn resize_factor(mut self, factor: ResizeFactor) -> Self {
        self.resize_factor = factor;
        self
    }

    /// Sets the sampling probability.
    ///
    /// # Panics
    ///
    /// Panics if `probability` is outside `(0.0, 1.0]`.
    ///
    /// # Examples
    ///
    /// ```
    /// use datasketches::theta::ThetaUnionBuilder;
    ///
    /// ThetaUnionBuilder::default()
    ///     .sampling_probability(0.5)
    ///     .build();
    /// ```
    pub fn sampling_probability(mut self, probability: f32) -> Self {
        assert!(
            (0.0..=1.0).contains(&probability) && probability > 0.0,
            "sampling_probability must be in (0.0, 1.0], got {probability}"
        );
        self.sampling_probability = probability;
        self
    }

    /// Sets the hash seed.
    ///
    /// # Examples
    ///
    /// ```
    /// use datasketches::theta::ThetaUnionBuilder;
    ///
    /// ThetaUnionBuilder::default().seed(7).build();
    /// ```
    pub fn seed(mut self, seed: u64) -> Self {
        self.seed = seed;
        self
    }

    /// Builds the [`ThetaUnion`].
    ///
    /// # Examples
    ///
    /// ```
    /// use datasketches::theta::ThetaUnionBuilder;
    ///
    /// ThetaUnionBuilder::default().lg_k(10).build();
    /// ```
    pub fn build(self) -> ThetaUnion {
        ThetaUnion {
            state: UnionState::new(
                self.lg_k,
                self.resize_factor,
                self.sampling_probability,
                self.seed,
                NoopUnionPolicy,
            ),
        }
    }
}