velesdb_core/collection/search/query/aggregation/

mod.rs

//! Aggregation query execution for VelesQL (EPIC-017 US-002, US-003, US-006).
//!
//! Implements streaming aggregation with O(1) memory complexity.
//! Supports GROUP BY for grouped aggregations (US-003).
//! Supports HAVING for filtering groups (US-006).
//! Supports parallel aggregation with rayon (EPIC-018 US-001).

// SAFETY: Numeric casts in aggregation are intentional:
// - All casts are for computing aggregate statistics (sum, avg, count)
// - f64/u64 casts for maintaining precision in intermediate calculations
// - i64->usize for group limits: limits bounded by MAX_GROUPS (1M)
// - Values bounded by result set size and field cardinality
// - Precision loss acceptable for aggregation results
#![allow(clippy::cast_precision_loss)]
#![allow(clippy::cast_possible_truncation)]
#![allow(clippy::cast_sign_loss)]

mod grouped;
mod having;

use super::where_eval::GraphMatchEvalCache;
use crate::collection::types::Collection;
use crate::error::Result;
use crate::storage::{PayloadStorage, VectorStorage};
use crate::velesql::{
    AggregateArg, AggregateFunction, AggregateType, Aggregator, Query, SelectColumns,
};
use rayon::prelude::*;
use rustc_hash::FxHasher;
use std::collections::HashMap;
use std::hash::{Hash, Hasher};

/// Group key for GROUP BY operations with pre-computed hash.
/// Avoids JSON serialization overhead by using direct value hashing.
#[derive(Clone)]
pub(crate) struct GroupKey {
    /// Original values for result construction
    pub(crate) values: Vec<serde_json::Value>,
    /// Pre-computed hash for fast HashMap lookup
    hash: u64,
}

impl GroupKey {
    pub(crate) fn new(values: Vec<serde_json::Value>) -> Self {
        let hash = Self::compute_hash(&values);
        Self { values, hash }
    }

    fn compute_hash(values: &[serde_json::Value]) -> u64 {
        let mut hasher = FxHasher::default();
        for v in values {
            Self::hash_value(v, &mut hasher);
        }
        hasher.finish()
    }

    fn hash_value(value: &serde_json::Value, hasher: &mut FxHasher) {
        match value {
            serde_json::Value::Null => 0u8.hash(hasher),
            serde_json::Value::Bool(b) => {
                1u8.hash(hasher);
                b.hash(hasher);
            }
            serde_json::Value::Number(n) => {
                2u8.hash(hasher);
                // Use bits for consistent hashing of floats
                if let Some(f) = n.as_f64() {
                    f.to_bits().hash(hasher);
                }
            }
            serde_json::Value::String(s) => {
                3u8.hash(hasher);
                s.hash(hasher);
            }
            _ => {
                // Arrays and objects: fallback to string representation
                4u8.hash(hasher);
                value.to_string().hash(hasher);
            }
        }
    }
}

impl Hash for GroupKey {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.hash.hash(state);
    }
}

impl PartialEq for GroupKey {
    fn eq(&self, other: &Self) -> bool {
        // Fast path: different hash means definitely different
        self.hash == other.hash && self.values == other.values
    }
}

impl Eq for GroupKey {}

/// Threshold for switching to parallel aggregation.
/// Below this, sequential is faster due to overhead.
const PARALLEL_THRESHOLD: usize = 10_000;

/// Chunk size for parallel processing.
const CHUNK_SIZE: usize = 1000;

impl Collection {
    /// Execute an aggregation query and return results as JSON.
    ///
    /// Supports COUNT(*), COUNT(column), SUM, AVG, MIN, MAX.
    /// Uses streaming aggregation - O(1) memory, single pass over data.
    ///
    /// # Arguments
    ///
    /// * `query` - Parsed VelesQL query with aggregation functions
    /// * `params` - Query parameters for placeholders
    ///
    /// # Returns
    ///
    /// JSON object with aggregation results, e.g.:
    /// ```json
    /// {"count": 100, "sum_price": 5000.0, "avg_rating": 4.5}
    /// ```
    ///
    /// # Errors
    ///
    /// Returns an error when SELECT does not contain aggregations, when HAVING is
    /// used without GROUP BY, or when underlying scan/filter/aggregation operations fail.
    #[allow(clippy::too_many_lines)]
    pub fn execute_aggregate(
        &self,
        query: &Query,
        params: &HashMap<String, serde_json::Value>,
    ) -> Result<serde_json::Value> {
        let stmt = &query.select;

        // Extract aggregation functions from SELECT clause
        let aggregations: &[AggregateFunction] = match &stmt.columns {
            SelectColumns::Aggregations(aggs) => aggs,
            SelectColumns::Mixed { aggregations, .. } => aggregations,
            _ => {
                return Err(crate::error::Error::Config(
                    "execute_aggregate requires aggregation functions in SELECT".to_string(),
                ))
            }
        };

        // Check if GROUP BY is present
        if let Some(ref group_by) = stmt.group_by {
            return self.execute_grouped_aggregate(
                query,
                aggregations,
                &group_by.columns,
                stmt.having.as_ref(),
                params,
            );
        }

        // HAVING without GROUP BY is invalid - return error
        if stmt.having.is_some() {
            return Err(crate::error::Error::Config(
                "HAVING clause requires GROUP BY clause".to_string(),
            ));
        }

        let where_clause = stmt.where_clause.as_ref();
        let use_runtime_where_eval = where_clause.is_some_and(|cond| {
            Self::condition_contains_graph_match(cond) || Self::condition_requires_vector_eval(cond)
        });
        let needs_vector_eval = where_clause.is_some_and(Self::condition_requires_vector_eval);

        // BUG-5 FIX: Resolve parameter placeholders in WHERE clause before creating filter.
        // For graph/vector-aware predicates, use runtime evaluator instead.
        let filter = if use_runtime_where_eval {
            None
        } else {
            where_clause.as_ref().map(|cond| {
                let resolved = Self::resolve_condition_params(cond, params);
                crate::filter::Filter::new(crate::filter::Condition::from(resolved))
            })
        };

        // Create aggregator
        let mut aggregator = Aggregator::new();

        // Determine which columns we need to aggregate (deduplicated)
        let columns_to_aggregate: std::collections::HashSet<&str> = aggregations
            .iter()
            .filter_map(|agg| match &agg.argument {
                AggregateArg::Column(col) => Some(col.as_str()),
                AggregateArg::Wildcard => None, // COUNT(*) doesn't need column access
            })
            .collect();

        let has_count_star = aggregations
            .iter()
            .any(|agg| matches!(agg.argument, AggregateArg::Wildcard));

        // Collect all IDs for parallel processing decision
        let payload_storage = self.payload_storage.read();
        let vector_storage = self.vector_storage.read();
        let ids: Vec<u64> = vector_storage.ids();
        let total_count = ids.len();

        // Use parallel aggregation for large datasets
        let agg_result = if total_count >= PARALLEL_THRESHOLD && !use_runtime_where_eval {
            // PARALLEL: Pre-fetch all payloads (sequential) to avoid lock contention
            let payloads: Vec<Option<serde_json::Value>> = ids
                .iter()
                .map(|&id| payload_storage.retrieve(id).ok().flatten())
                .collect();

            // Drop the lock before parallel processing
            drop(payload_storage);
            drop(vector_storage);

            let columns_vec: Vec<String> = columns_to_aggregate
                .iter()
                .map(|s| (*s).to_string())
                .collect();

            // Parallel aggregation on pre-fetched data (no lock contention)
            let partial_aggregators: Vec<Aggregator> = payloads
                .par_chunks(CHUNK_SIZE)
                .map(|chunk| {
                    let mut chunk_agg = Aggregator::new();
                    for payload in chunk {
                        // Apply filter if present
                        if let Some(ref f) = filter {
                            let matches = match payload {
                                Some(ref p) => f.matches(p),
                                None => f.matches(&serde_json::Value::Null),
                            };
                            if !matches {
                                continue;
                            }
                        }

                        // Process COUNT(*)
                        if has_count_star {
                            chunk_agg.process_count();
                        }

                        // Process column aggregations
                        if let Some(ref p) = payload {
                            for col in &columns_vec {
                                if let Some(value) = Self::get_nested_value(p, col) {
                                    chunk_agg.process_value(col, value);
                                }
                            }
                        }
                    }
                    chunk_agg
                })
                .collect();

            // Merge all partial results
            let mut final_agg = Aggregator::new();
            for partial in partial_aggregators {
                final_agg.merge(partial);
            }
            final_agg.finalize()
        } else {
            // SEQUENTIAL: Original single-pass for small datasets
            let mut graph_cache = GraphMatchEvalCache::default();
            for id in ids {
                let payload = payload_storage.retrieve(id).ok().flatten();

                if use_runtime_where_eval {
                    let vector = if needs_vector_eval {
                        vector_storage.retrieve(id).ok().flatten()
                    } else {
                        None
                    };
                    if let Some(cond) = where_clause {
                        let matches = self.evaluate_where_condition_for_record(
                            cond,
                            id,
                            payload.as_ref(),
                            vector.as_deref(),
                            params,
                            stmt.from_alias.as_deref(),
                            &mut graph_cache,
                        )?;
                        if !matches {
                            continue;
                        }
                    }
                } else if let Some(ref f) = filter {
                    let matches = match payload {
                        Some(ref p) => f.matches(p),
                        None => f.matches(&serde_json::Value::Null),
                    };
                    if !matches {
                        continue;
                    }
                }

                // Process COUNT(*)
                if has_count_star {
                    aggregator.process_count();
                }

                // Process column aggregations
                if let Some(ref p) = payload {
                    for col in &columns_to_aggregate {
                        if let Some(value) = Self::get_nested_value(p, col) {
                            aggregator.process_value(col, value);
                        }
                    }
                }
            }
            aggregator.finalize()
        };
        let mut result = serde_json::Map::new();

        // Build result based on requested aggregations
        for agg in aggregations {
            let key = if let Some(ref alias) = agg.alias {
                alias.clone()
            } else {
                match &agg.argument {
                    AggregateArg::Wildcard => "count".to_string(),
                    AggregateArg::Column(col) => {
                        let prefix = match agg.function_type {
                            AggregateType::Count => "count",
                            AggregateType::Sum => "sum",
                            AggregateType::Avg => "avg",
                            AggregateType::Min => "min",
                            AggregateType::Max => "max",
                        };
                        format!("{prefix}_{col}")
                    }
                }
            };

            let value = match (&agg.function_type, &agg.argument) {
                (AggregateType::Count, AggregateArg::Wildcard) => {
                    serde_json::json!(agg_result.count)
                }
                (AggregateType::Count, AggregateArg::Column(col)) => {
                    // COUNT(column) = number of non-null values for this column
                    let count = agg_result.counts.get(col.as_str()).copied().unwrap_or(0);
                    serde_json::json!(count)
                }
                (AggregateType::Sum, AggregateArg::Column(col)) => agg_result
                    .sums
                    .get(col.as_str())
                    .map_or(serde_json::Value::Null, |v| serde_json::json!(v)),
                (AggregateType::Avg, AggregateArg::Column(col)) => agg_result
                    .avgs
                    .get(col.as_str())
                    .map_or(serde_json::Value::Null, |v| serde_json::json!(v)),
                (AggregateType::Min, AggregateArg::Column(col)) => agg_result
                    .mins
                    .get(col.as_str())
                    .map_or(serde_json::Value::Null, |v| serde_json::json!(v)),
                (AggregateType::Max, AggregateArg::Column(col)) => agg_result
                    .maxs
                    .get(col.as_str())
                    .map_or(serde_json::Value::Null, |v| serde_json::json!(v)),
                _ => serde_json::Value::Null,
            };

            result.insert(key, value);
        }

        Ok(serde_json::Value::Object(result))
    }

    /// Get a nested value from JSON payload using dot notation.
    pub(crate) fn get_nested_value<'a>(
        payload: &'a serde_json::Value,
        path: &str,
    ) -> Option<&'a serde_json::Value> {
        let parts: Vec<&str> = path.split('.').collect();
        let mut current = payload;

        for part in parts {
            match current {
                serde_json::Value::Object(map) => {
                    current = map.get(part)?;
                }
                _ => return None,
            }
        }

        Some(current)
    }
}