icydb-core 0.94.0

//! Module: query::plan::planner::prefix
//! Responsibility: planner prefix/multi-lookup access-path derivation from predicate equality sets.
//! Does not own: runtime index traversal execution or continuation resume behavior.
//! Boundary: maps prefix-capable predicates into planner-owned access plan candidates.

use crate::{
    db::{
        access::AccessPlan,
        predicate::{CoercionId, CompareOp, Predicate},
        query::plan::{
            OrderSpec,
            key_item_match::{
                eq_lookup_value_for_key_item, index_key_item_count, leading_index_key_item,
            },
            planner::{
                AccessCandidateScore, access_candidate_score_outranks,
                candidate_satisfies_secondary_order, index_literal_matches_schema,
            },
        },
        schema::SchemaInfo,
    },
    model::{
        entity::EntityModel,
        index::{IndexKeyItem, IndexKeyItemsRef, IndexModel},
    },
    value::Value,
};

fn leading_index_prefix_lookup_value(
    index: &IndexModel,
    field: &str,
    value: &Value,
    coercion: CoercionId,
    literal_compatible: bool,
) -> Option<Value> {
    let key_item = leading_index_key_item(index)?;
    eq_lookup_value_for_key_item(key_item, field, value, coercion, literal_compatible)
}

// This helper now carries one explicit planner-visible index slice in addition
// to the existing schema/field/order inputs so callers can keep lifecycle
// gating at the planner boundary instead of reopening store state here.
pub(super) fn index_prefix_for_eq(
    model: &EntityModel,
    candidate_indexes: &[&'static IndexModel],
    schema: &SchemaInfo,
    field: &str,
    value: &Value,
    coercion: CoercionId,
    order: Option<&OrderSpec>,
) -> Option<AccessPlan<Value>> {
    let literal_compatible = index_literal_matches_schema(schema, field, value);

    let mut best: Option<(AccessCandidateScore, &'static IndexModel, Value)> = None;
    for index in candidate_indexes {
        let Some(lookup_value) =
            leading_index_prefix_lookup_value(index, field, value, coercion, literal_compatible)
        else {
            continue;
        };

        let score = AccessCandidateScore::new(
            1,
            index_key_item_count(index) == 1,
            candidate_satisfies_secondary_order(model, order, index, 1),
        );
        match best {
            None => best = Some((score, index, lookup_value)),
            Some((best_score, best_index, _))
                if access_candidate_score_outranks(score, best_score, true)
                    || (score == best_score && index.name() < best_index.name()) =>
            {
                best = Some((score, index, lookup_value));
            }
            _ => {}
        }
    }

    best.map(|(_, index, lookup_value)| AccessPlan::index_prefix(*index, vec![lookup_value]))
}

pub(super) fn index_multi_lookup_for_in(
    _model: &EntityModel,
    candidate_indexes: &[&'static IndexModel],
    schema: &SchemaInfo,
    field: &str,
    values: &[Value],
    coercion: CoercionId,
) -> Option<Vec<AccessPlan<Value>>> {
    // Cache schema/literal compatibility once per `IN` item so candidate-index
    // selection does not repeat the same field-type check for every index.
    let cached_values = values
        .iter()
        .map(|value| (value, index_literal_matches_schema(schema, field, value)))
        .collect::<Vec<_>>();

    let mut out = Vec::new();
    for index in candidate_indexes {
        let mut lookup_values = Vec::with_capacity(values.len());
        for (value, literal_compatible) in &cached_values {
            let Some(lookup_value) = leading_index_prefix_lookup_value(
                index,
                field,
                value,
                coercion,
                *literal_compatible,
            ) else {
                lookup_values.clear();
                break;
            };

            lookup_values.push(lookup_value);
        }
        if lookup_values.is_empty() {
            continue;
        }

        out.push(AccessPlan::index_multi_lookup(**index, lookup_values));
    }

    if out.is_empty() { None } else { Some(out) }
}

pub(super) fn index_prefix_from_and(
    model: &EntityModel,
    candidate_indexes: &[&'static IndexModel],
    schema: &SchemaInfo,
    children: &[Predicate],
    order: Option<&OrderSpec>,
) -> Option<AccessPlan<Value>> {
    // Cache literal/schema compatibility once per equality literal so index
    // candidate selection does not repeat schema checks on every index iteration.
    let mut field_values = Vec::new();

    for child in children {
        let Predicate::Compare(cmp) = child else {
            continue;
        };
        if cmp.op != CompareOp::Eq {
            continue;
        }
        if !matches!(
            cmp.coercion.id,
            CoercionId::Strict | CoercionId::TextCasefold
        ) {
            continue;
        }
        field_values.push(CachedEqLiteral {
            field: cmp.field.as_str(),
            value: &cmp.value,
            coercion: cmp.coercion.id,
            compatible: index_literal_matches_schema(schema, &cmp.field, &cmp.value),
        });
    }

    let mut best: Option<(AccessCandidateScore, &IndexModel, Vec<Value>)> = None;
    for index in candidate_indexes {
        let Some(prefix) = build_index_eq_prefix(index, &field_values) else {
            continue;
        };
        if prefix.is_empty() {
            continue;
        }

        let score = AccessCandidateScore::new(
            prefix.len(),
            prefix.len() == index_key_item_count(index),
            candidate_satisfies_secondary_order(model, order, index, prefix.len()),
        );
        match &best {
            None => best = Some((score, index, prefix)),
            Some((best_score, best_index, _))
                if access_candidate_score_outranks(score, *best_score, true)
                    || (score == *best_score && index.name() < best_index.name()) =>
            {
                best = Some((score, index, prefix));
            }
            Some(_) => {}
        }
    }

    best.map(|(_, index, values)| AccessPlan::index_prefix(*index, values))
}

///
/// CachedEqLiteral
///
/// Equality literal plus its precomputed planner-side schema compatibility.
///

struct CachedEqLiteral<'a> {
    field: &'a str,
    value: &'a Value,
    coercion: CoercionId,
    compatible: bool,
}

fn build_index_eq_prefix(
    index: &IndexModel,
    field_values: &[CachedEqLiteral<'_>],
) -> Option<Vec<Value>> {
    match index.key_items() {
        IndexKeyItemsRef::Fields(fields) => build_index_eq_prefix_for_items(
            fields.iter().copied().map(IndexKeyItem::Field),
            field_values,
        ),
        IndexKeyItemsRef::Items(items) => {
            build_index_eq_prefix_for_items(items.iter().copied(), field_values)
        }
    }
}

// Field-only indexes and mixed field/expression indexes both use the same
// equality-prefix assembly contract; only the key-item iterator differs.
fn build_index_eq_prefix_for_items<I>(
    key_items: I,
    field_values: &[CachedEqLiteral<'_>],
) -> Option<Vec<Value>>
where
    I: IntoIterator<Item = IndexKeyItem>,
{
    let mut prefix = Vec::new();
    for key_item in key_items {
        let mut matched: Option<Value> = None;
        for cached in field_values {
            let Some(candidate) = eq_lookup_value_for_key_item(
                key_item,
                cached.field,
                cached.value,
                cached.coercion,
                cached.compatible,
            ) else {
                continue;
            };

            if let Some(existing) = &matched
                && existing != &candidate
            {
                return None;
            }
            matched = Some(candidate);
        }

        let Some(value) = matched else {
            break;
        };
        prefix.push(value);
    }

    Some(prefix)
}