icydb-core 0.144.12

//! Module: predicate::semantics
//! Responsibility: value comparison semantics under explicit coercion policies.
//! Does not own: predicate AST normalization or schema legality checks.
//! Boundary: runtime predicate evaluation delegates compare behavior here.

use crate::{
    db::{
        numeric::{compare_numeric_eq, compare_numeric_order},
        predicate::{
            CompareOp,
            coercion::{CoercionId, CoercionSpec},
        },
    },
    value::{TextMode, Value},
};
use std::{cmp::Ordering, mem::discriminant};

///
/// TextOp
///

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(in crate::db) enum TextOp {
    StartsWith,
    EndsWith,
}

/// Perform equality comparison under an explicit coercion policy.
#[must_use]
pub(in crate::db) fn compare_eq(
    left: &Value,
    right: &Value,
    coercion: &CoercionSpec,
) -> Option<bool> {
    // Equality semantics are coercion-policy dependent.
    // Predicate-level `Value::Null == Value::Null` is a normal explicit-null
    // comparison. SQL `field = NULL` keeps separate SQL UNKNOWN/false WHERE
    // semantics before it reaches this runtime predicate boundary.
    match coercion.id {
        CoercionId::Strict | CoercionId::CollectionElement => {
            same_variant(left, right).then_some(left == right)
        }
        CoercionId::NumericWiden => compare_numeric_eq(left, right),
        CoercionId::TextCasefold => compare_casefold(left, right),
    }
}

/// Shape one optional equality result for `Eq` and `Ne`.
#[must_use]
pub(in crate::db::predicate) const fn eval_equality_compare_result(
    op: CompareOp,
    matched: Option<bool>,
) -> bool {
    match op {
        CompareOp::Eq => matches!(matched, Some(true)),
        CompareOp::Ne => matches!(matched, Some(false)),
        CompareOp::Lt
        | CompareOp::Lte
        | CompareOp::Gt
        | CompareOp::Gte
        | CompareOp::In
        | CompareOp::NotIn
        | CompareOp::Contains
        | CompareOp::StartsWith
        | CompareOp::EndsWith => false,
    }
}

/// Perform ordering comparison under an explicit coercion policy.
#[must_use]
pub(in crate::db) fn compare_order(
    left: &Value,
    right: &Value,
    coercion: &CoercionSpec,
) -> Option<Ordering> {
    // Ordering semantics are coercion-policy dependent.
    match coercion.id {
        CoercionId::Strict | CoercionId::CollectionElement => {
            if !same_variant(left, right) {
                return None;
            }
            Value::strict_order_cmp(left, right)
        }
        CoercionId::NumericWiden => compare_numeric_order(left, right),
        CoercionId::TextCasefold => {
            let left = casefold_value(left)?;
            let right = casefold_value(right)?;

            Some(left.cmp(&right))
        }
    }
}

/// Evaluate an ordered compare operator against one already-computed ordering.
#[must_use]
pub(in crate::db::predicate) const fn eval_ordered_compare_result(
    op: CompareOp,
    ordering: Ordering,
) -> bool {
    match op {
        CompareOp::Eq => matches!(ordering, Ordering::Equal),
        CompareOp::Ne => !matches!(ordering, Ordering::Equal),
        CompareOp::Lt => ordering.is_lt(),
        CompareOp::Lte => ordering.is_le(),
        CompareOp::Gt => ordering.is_gt(),
        CompareOp::Gte => ordering.is_ge(),
        CompareOp::In
        | CompareOp::NotIn
        | CompareOp::Contains
        | CompareOp::StartsWith
        | CompareOp::EndsWith => false,
    }
}

/// Shape one optional list-membership result for `IN` and `NOT IN`.
#[must_use]
pub(in crate::db::predicate) const fn eval_list_membership_compare_result(
    op: CompareOp,
    matched: Option<bool>,
) -> bool {
    match op {
        CompareOp::In => matches!(matched, Some(true)),
        CompareOp::NotIn => matches!(matched, Some(false)),
        CompareOp::Eq
        | CompareOp::Ne
        | CompareOp::Lt
        | CompareOp::Lte
        | CompareOp::Gt
        | CompareOp::Gte
        | CompareOp::Contains
        | CompareOp::StartsWith
        | CompareOp::EndsWith => false,
    }
}

/// Canonical total ordering for database predicate semantics.
#[must_use]
pub(in crate::db) fn canonical_cmp(left: &Value, right: &Value) -> Ordering {
    if let Some(ordering) = Value::strict_order_cmp(left, right) {
        return ordering;
    }

    left.canonical_rank().cmp(&right.canonical_rank())
}

/// Perform text-specific comparison operations.
#[must_use]
pub(in crate::db) fn compare_text(
    left: &Value,
    right: &Value,
    coercion: &CoercionSpec,
    op: TextOp,
) -> Option<bool> {
    if !matches!(left, Value::Text(_)) || !matches!(right, Value::Text(_)) {
        return None;
    }

    let mode = match coercion.id {
        CoercionId::Strict => TextMode::Cs,
        CoercionId::TextCasefold => TextMode::Ci,
        _ => return None,
    };

    match op {
        TextOp::StartsWith => left.text_starts_with(right, mode),
        TextOp::EndsWith => left.text_ends_with(right, mode),
    }
}

fn same_variant(left: &Value, right: &Value) -> bool {
    discriminant(left) == discriminant(right)
}

fn compare_casefold(left: &Value, right: &Value) -> Option<bool> {
    let left = casefold_value(left)?;
    let right = casefold_value(right)?;
    Some(left == right)
}

fn casefold_value(value: &Value) -> Option<String> {
    match value {
        Value::Text(text) => Some(casefold_text(text)),
        _ => None,
    }
}

/// Canonical casefold helper for predicate text comparison and identity keys.
#[must_use]
pub(in crate::db::predicate) fn casefold_text(input: &str) -> String {
    if input.is_ascii() {
        return input.to_ascii_lowercase();
    }

    input.to_lowercase()
}