icydb-core 0.70.5

//! Module: index::predicate
//! Responsibility: compiled index-only predicate program model + execution.
//! Does not own: semantic predicate resolution or planner route policy.
//! Boundary: query/load paths use this for conservative index prefiltering.

pub(crate) mod compile;
#[cfg(test)]
mod tests;

use crate::{
    db::index::{EncodedValue, IndexKey},
    db::predicate::{Predicate, SqlParseError, parse_sql_predicate},
    error::InternalError,
    model::index::IndexModel,
    value::Value,
};
use std::{
    cell::Cell,
    sync::{Mutex, OnceLock},
};

pub(crate) use compile::{
    IndexCompilePolicy, compile_index_program, compile_index_program_for_targets,
};

type CachedIndexPredicateResult = Result<&'static Predicate, SqlParseError>;
type CachedIndexPredicateEntries = Vec<(&'static str, CachedIndexPredicateResult)>;

static INDEX_PREDICATE_SQL_CACHE: OnceLock<Mutex<CachedIndexPredicateEntries>> = OnceLock::new();

/// Resolve one index predicate through the canonical parse/cache boundary.
///
/// Raw schema predicate text is input-only metadata; planner/runtime callers must
/// consume predicate semantics through this accessor.
pub(in crate::db) fn canonical_index_predicate(
    index: &IndexModel,
) -> Result<Option<&'static Predicate>, SqlParseError> {
    let Some(predicate_sql) = index.predicate() else {
        return Ok(None);
    };

    cached_index_predicate_from_sql(predicate_sql).map(Some)
}

// Parse one schema predicate SQL string once and cache canonical predicate semantics.
fn cached_index_predicate_from_sql(
    predicate_sql: &'static str,
) -> Result<&'static Predicate, SqlParseError> {
    let cache =
        INDEX_PREDICATE_SQL_CACHE.get_or_init(|| Mutex::new(CachedIndexPredicateEntries::new()));

    // Generated schema index predicates are a small fixed set, so a linear
    // scan keeps the memoization boundary deterministic without retaining
    // general-purpose `HashMap` machinery in the query runtime.
    if let Some(cached) = cache
        .lock()
        .expect("index predicate cache mutex poisoned")
        .iter()
        .find(|(cached_sql, _)| *cached_sql == predicate_sql)
        .map(|(_, cached)| cached.clone())
    {
        return cached;
    }

    let parsed: CachedIndexPredicateResult = parse_sql_predicate(predicate_sql).map(|predicate| {
        let predicate: &'static Predicate = Box::leak(Box::new(predicate));
        predicate
    });

    let mut guard = cache.lock().expect("index predicate cache mutex poisoned");
    if let Some((_, cached)) = guard
        .iter()
        .find(|(cached_sql, _)| *cached_sql == predicate_sql)
    {
        return cached.clone();
    }

    guard.push((predicate_sql, parsed.clone()));

    parsed
}

///
/// IndexPredicateProgram
///
/// Index-only predicate program compiled against index component positions.
/// This is a conservative subset used for raw-index-key predicate evaluation.
///

#[derive(Clone, Debug, Eq, PartialEq)]
pub(crate) enum IndexPredicateProgram {
    True,
    False,
    And(Vec<Self>),
    Or(Vec<Self>),
    Not(Box<Self>),
    Compare {
        component_index: usize,
        op: IndexCompareOp,
        literal: IndexLiteral,
    },
}

///
/// IndexCompareOp
///
/// Operator subset that can be evaluated directly on canonical encoded index bytes.
///

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum IndexCompareOp {
    Eq,
    Ne,
    Lt,
    Lte,
    Gt,
    Gte,
    In,
    NotIn,
}

///
/// IndexLiteral
///
/// Encoded literal payload used by one index-only compare operation.
///

#[derive(Clone, Debug, Eq, PartialEq)]
pub(crate) enum IndexLiteral {
    One(Vec<u8>),
    Many(Vec<Vec<u8>>),
}

// Compare one encoded index component against one compiled literal payload.
pub(crate) fn eval_index_compare(
    component: &[u8],
    op: IndexCompareOp,
    literal: &IndexLiteral,
) -> bool {
    match (op, literal) {
        (IndexCompareOp::Eq, IndexLiteral::One(expected)) => component == expected.as_slice(),
        (IndexCompareOp::Ne, IndexLiteral::One(expected)) => component != expected.as_slice(),
        (IndexCompareOp::Lt, IndexLiteral::One(expected)) => component < expected.as_slice(),
        (IndexCompareOp::Lte, IndexLiteral::One(expected)) => component <= expected.as_slice(),
        (IndexCompareOp::Gt, IndexLiteral::One(expected)) => component > expected.as_slice(),
        (IndexCompareOp::Gte, IndexLiteral::One(expected)) => component >= expected.as_slice(),
        (IndexCompareOp::In, IndexLiteral::Many(candidates)) => {
            candidates.iter().any(|candidate| component == candidate)
        }
        (IndexCompareOp::NotIn, IndexLiteral::Many(candidates)) => {
            candidates.iter().all(|candidate| component != candidate)
        }
        (
            IndexCompareOp::Eq
            | IndexCompareOp::Ne
            | IndexCompareOp::Lt
            | IndexCompareOp::Lte
            | IndexCompareOp::Gt
            | IndexCompareOp::Gte,
            IndexLiteral::Many(_),
        )
        | (IndexCompareOp::In | IndexCompareOp::NotIn, IndexLiteral::One(_)) => false,
    }
}

///
/// IndexPredicateExecution
///
/// Execution-time wrapper for one compiled index predicate program.
/// Carries optional observability counters used by load execution tracing.
///

#[derive(Clone, Copy)]
pub(in crate::db) struct IndexPredicateExecution<'a> {
    pub(in crate::db) program: &'a IndexPredicateProgram,
    pub(in crate::db) rejected_keys_counter: Option<&'a Cell<u64>>,
}

// Evaluate one compiled index-only program against one decoded index key.
pub(in crate::db) fn eval_index_program_on_decoded_key(
    key: &IndexKey,
    program: &IndexPredicateProgram,
) -> Result<bool, InternalError> {
    // Evaluate recursively over the compiled index-only predicate tree.
    match program {
        IndexPredicateProgram::True => Ok(true),
        IndexPredicateProgram::False => Ok(false),
        IndexPredicateProgram::And(children) => {
            for child in children {
                if !eval_index_program_on_decoded_key(key, child)? {
                    return Ok(false);
                }
            }

            Ok(true)
        }
        IndexPredicateProgram::Or(children) => {
            for child in children {
                if eval_index_program_on_decoded_key(key, child)? {
                    return Ok(true);
                }
            }

            Ok(false)
        }
        IndexPredicateProgram::Not(inner) => Ok(!eval_index_program_on_decoded_key(key, inner)?),
        IndexPredicateProgram::Compare {
            component_index,
            op,
            literal,
        } => {
            let Some(component) = key.component(*component_index) else {
                return Err(InternalError::index_only_predicate_component_required());
            };

            Ok(eval_index_compare(component, *op, literal))
        }
    }
}

/// Evaluate one compiled index-only execution request and update observability
/// counters when a key is rejected by index-only filtering.
pub(in crate::db) fn eval_index_execution_on_decoded_key(
    key: &IndexKey,
    execution: IndexPredicateExecution<'_>,
) -> Result<bool, InternalError> {
    let passed = eval_index_program_on_decoded_key(key, execution.program)?;
    if !passed && let Some(counter) = execution.rejected_keys_counter {
        counter.set(counter.get().saturating_add(1));
    }

    Ok(passed)
}

/// Build canonical index-component bytes for one literal.
#[must_use]
pub(in crate::db) fn literal_index_component_bytes(value: &Value) -> Option<Vec<u8>> {
    let encoded = EncodedValue::try_from_ref(value).ok()?;

    Some(encoded.encoded().to_vec())
}