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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

///! This module defines the API and logic for running optimization pipelines.
use crate::plan::expr::HirRelationExpr;
use crate::query_model::Model;

use super::StatementContext;

/// Feature flags for the [`HirRelationExpr::optimize_and_lower()`] logic.
#[derive(Debug)]
pub struct OptimizerConfig {
    pub qgm_optimizations: bool,
}

/// Convert a reference to a [`StatementContext`] to an [`OptimizerConfig`].
///
/// This picks up feature flag values such as `qgm_optimizations` from the `PlanContext` if this is present in
/// the [`StatementContext`], otherwise uses sensible defaults.
impl<'a> From<&StatementContext<'a>> for OptimizerConfig {
    fn from(scx: &StatementContext) -> Self {
        match scx.pcx() {
            Ok(pcx) => OptimizerConfig {
                qgm_optimizations: pcx.qgm_optimizations,
            },
            Err(..) => OptimizerConfig {
                qgm_optimizations: false,
            },
        }
    }
}

impl HirRelationExpr {
    /// Perform optimizing algebraic rewrites on this [`HirRelationExpr`] and lower it to a [`expr::MirRelationExpr`].
    ///
    /// The optimization path is fully-determined by the values of the feature flag defined in the [`OptimizerConfig`].
    pub fn optimize_and_lower(self, config: &OptimizerConfig) -> expr::MirRelationExpr {
        if config.qgm_optimizations {
            // create a query graph model from this HirRelationExpr
            let model = Model::from(self);

            // @todo: perform optimizing algebraic rewrites on the qgm
            // ...

            // decorrelate and lower the optimized query graph model into a MirRelationExpr
            model.into()
        } else {
            // directly decorrelate and lower into a MirRelationExpr
            self.lower()
        }
    }
}