icydb-core 0.94.3

//! Module: db::executor::projection::eval::scalar
//! Responsibility: compiled scalar-only projection expression evaluation on top of the shared scalar-expression seam.
//! Does not own: grouped projection execution, generic `Expr` evaluation, or planner validation.
//! Boundary: structural projection materialization calls into this file when a projection stays entirely on the scalar seam.

use crate::db::executor::projection::eval::operators;
#[cfg(test)]
use crate::db::scalar_expr::scalar_expr_value_into_value;
#[cfg(test)]
use crate::db::{data::CanonicalSlotReader, scalar_expr::eval_canonical_scalar_value_program};
#[cfg(test)]
use crate::db::{data::SlotReader, scalar_expr::eval_scalar_value_program};
use crate::{
    db::{
        executor::projection::eval::{
            ProjectionEvalError, collapse_true_only_boolean_admission,
            eval_projection_function_call, projection_function_name,
        },
        query::plan::expr::{ScalarProjectionExpr, ScalarProjectionField},
    },
    error::InternalError,
    value::Value,
};
#[cfg(any(test, feature = "sql"))]
use std::borrow::Cow;

#[cfg(test)]
/// Evaluate one compiled scalar projection expression against one slot reader.
pub(in crate::db::executor) fn eval_scalar_projection_expr(
    expr: &ScalarProjectionExpr,
    slots: &mut dyn SlotReader,
) -> Result<Value, InternalError> {
    eval_scalar_projection_expr_core(
        expr,
        &mut |field| {
            // Scalar fields keep the fast scalar-expression seam in tests.
            // Non-scalar projected fields still need to compile for
            // planner/executor contract tests, so fall back to slot-contract
            // decoding there.
            let value = if let Some(program) = field.program() {
                let Some(value) = eval_scalar_value_program(program, slots)? else {
                    return Err(
                        missing_field_value(field).into_invalid_logical_plan_internal_error()
                    );
                };

                scalar_expr_value_into_value(value)
            } else {
                let Some(value) = slots.get_value(field.slot())? else {
                    return Err(
                        missing_field_value(field).into_invalid_logical_plan_internal_error()
                    );
                };

                value
            };

            Ok(Cow::Owned(value))
        },
        &mut ProjectionEvalError::into_invalid_logical_plan_internal_error,
    )
    .map(Cow::into_owned)
}

/// Evaluate one compiled scalar projection expression against one canonical
/// slot reader where declared slots must already exist.
#[cfg(test)]
pub(in crate::db::executor) fn eval_canonical_scalar_projection_expr(
    expr: &ScalarProjectionExpr,
    slots: &dyn CanonicalSlotReader,
) -> Result<Value, InternalError> {
    eval_scalar_projection_expr_core(
        expr,
        &mut |field| {
            let value = if let Some(program) = field.program() {
                scalar_expr_value_into_value(eval_canonical_scalar_value_program(program, slots)?)
            } else {
                slots.required_value_by_contract(field.slot())?
            };

            Ok(Cow::Owned(value))
        },
        &mut ProjectionEvalError::into_invalid_logical_plan_internal_error,
    )
    .map(Cow::into_owned)
}

/// Evaluate one compiled scalar projection expression through one canonical
/// reader that can borrow decoded slot values from the structural row cache.
/// This keeps repeated field references on the retained-slot structural path from
/// cloning cached `Value`s before an operator actually needs ownership.
#[cfg(any(test, feature = "sql"))]
pub(in crate::db) fn eval_canonical_scalar_projection_expr_with_required_value_reader_cow<'a>(
    expr: &'a ScalarProjectionExpr,
    read_slot: &mut dyn FnMut(usize) -> Result<Cow<'a, Value>, InternalError>,
) -> Result<Cow<'a, Value>, InternalError> {
    #[cfg(not(test))]
    {
        eval_scalar_projection_expr_core(
            expr,
            &mut |field| read_slot(field.slot()),
            &mut ProjectionEvalError::into_invalid_logical_plan_internal_error,
        )
    }

    #[cfg(test)]
    eval_scalar_projection_expr_core(
        expr,
        &mut |field| read_slot(field.slot()),
        &mut ProjectionEvalError::into_invalid_logical_plan_internal_error,
    )
}

/// Evaluate one compiled scalar projection expression through one pure value
/// reader that resolves slots directly into runtime `Value`s.
pub(in crate::db::executor) fn eval_scalar_projection_expr_with_value_reader(
    expr: &ScalarProjectionExpr,
    read_slot: &mut dyn FnMut(usize) -> Option<Value>,
) -> Result<Value, ProjectionEvalError> {
    eval_scalar_projection_expr_core(
        expr,
        &mut |field| {
            let Some(value) = read_slot(field.slot()) else {
                return Err(missing_field_value(field));
            };

            Ok(Cow::Owned(value))
        },
        &mut |err| err,
    )
    .map(Cow::into_owned)
}

/// Evaluate one compiled scalar projection expression through one borrowed
/// value reader and materialize the final runtime `Value`.
pub(in crate::db::executor) fn eval_scalar_projection_expr_with_value_ref_reader<'a>(
    expr: &ScalarProjectionExpr,
    read_slot: &mut dyn FnMut(usize) -> Option<&'a Value>,
) -> Result<Value, ProjectionEvalError> {
    #[cfg(not(test))]
    let value = eval_scalar_projection_expr_core(
        expr,
        &mut |field| {
            let Some(value) = read_slot(field.slot()) else {
                return Err(missing_field_value(field));
            };

            Ok(Cow::Borrowed(value))
        },
        &mut |err| err,
    );

    #[cfg(test)]
    let value = eval_scalar_projection_expr_core(
        expr,
        &mut |field| {
            let Some(value) = read_slot(field.slot()) else {
                return Err(missing_field_value(field));
            };

            Ok(Cow::Borrowed(value))
        },
        &mut |err| err,
    );

    value.map(Cow::into_owned)
}

fn eval_scalar_projection_expr_core<'a, E>(
    expr: &'a ScalarProjectionExpr,
    eval_field: &mut dyn FnMut(&ScalarProjectionField) -> Result<Cow<'a, Value>, E>,
    map_projection_error: &mut dyn FnMut(ProjectionEvalError) -> E,
) -> Result<Cow<'a, Value>, E> {
    match expr {
        ScalarProjectionExpr::Field(field) => eval_field(field),
        ScalarProjectionExpr::Literal(value) => Ok(Cow::Borrowed(value)),
        ScalarProjectionExpr::FunctionCall { function, args } => {
            let evaluated_args = args
                .iter()
                .map(|arg| eval_scalar_projection_expr_core(arg, eval_field, map_projection_error))
                .collect::<Result<Vec<_>, _>>()?;
            let evaluated_args = evaluated_args
                .into_iter()
                .map(Cow::into_owned)
                .collect::<Vec<_>>();
            let value = eval_projection_function_call(*function, evaluated_args.as_slice())
                .map_err(|err| {
                    map_projection_error(ProjectionEvalError::InvalidFunctionCall {
                        function: projection_function_name(*function).to_string(),
                        message: err.to_string(),
                    })
                })?;

            Ok(Cow::Owned(value))
        }
        ScalarProjectionExpr::Unary { op, expr } => {
            let operand = eval_scalar_projection_expr_core(expr, eval_field, map_projection_error)?;
            operators::eval_unary_expr(*op, operand.as_ref())
                .map(Cow::Owned)
                .map_err(map_projection_error)
        }
        ScalarProjectionExpr::Case {
            when_then_arms,
            else_expr,
        } => {
            for arm in when_then_arms {
                let condition = eval_scalar_projection_expr_core(
                    arm.condition(),
                    eval_field,
                    map_projection_error,
                )?;
                if collapse_true_only_boolean_admission(condition.into_owned(), |found| {
                    map_projection_error(ProjectionEvalError::InvalidCaseCondition { found })
                })? {
                    return eval_scalar_projection_expr_core(
                        arm.result(),
                        eval_field,
                        map_projection_error,
                    );
                }
            }

            eval_scalar_projection_expr_core(else_expr.as_ref(), eval_field, map_projection_error)
        }
        ScalarProjectionExpr::Binary { op, left, right } => {
            let left = eval_scalar_projection_expr_core(left, eval_field, map_projection_error)?;
            let right = eval_scalar_projection_expr_core(right, eval_field, map_projection_error)?;

            operators::eval_binary_expr(*op, left.as_ref(), right.as_ref())
                .map(Cow::Owned)
                .map_err(map_projection_error)
        }
    }
}

// Build one stable missing-field diagnostic from one compiled scalar field.
fn missing_field_value(field: &ScalarProjectionField) -> ProjectionEvalError {
    ProjectionEvalError::MissingFieldValue {
        field: field.field().to_string(),
        index: field.slot(),
    }
}