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//! [`RewriteDisjunctivePredicate`] rewrites predicates to reduce redundancy

use crate::optimizer::ApplyOrder;
use crate::{OptimizerConfig, OptimizerRule};
use datafusion_common::tree_node::Transformed;
use datafusion_common::Result;
use datafusion_expr::expr::BinaryExpr;
use datafusion_expr::logical_plan::Filter;
use datafusion_expr::{Expr, LogicalPlan, Operator};

/// Optimizer pass that rewrites predicates of the form
///
/// ```text
/// (A = B AND <expr1>) OR (A = B AND <expr2>) OR ... (A = B AND <exprN>)
/// ```
///
/// Into
/// ```text
/// (A = B) AND (<expr1> OR <expr2> OR ... <exprN> )
/// ```
///
/// Predicates connected by `OR` typically not able to be broken down
/// and distributed as well as those connected by `AND`.
///
/// The idea is to rewrite predicates into `good_predicate1 AND
/// good_predicate2 AND ...` where `good_predicate` means the
/// predicate has special support in the execution engine.
///
/// Equality join predicates (e.g. `col1 = col2`), or single column
/// expressions (e.g. `col = 5`) are examples of predicates with
/// special support.
///
/// # TPCH Q19
///
/// This optimization is admittedly somewhat of a niche usecase. It's
/// main use is that it appears in TPCH Q19 and is required to avoid a
/// CROSS JOIN.
///
/// Specifically, Q19 has a WHERE clause that looks like
///
/// ```sql
/// where
///     (
///       p_partkey = l_partkey
///       and p_brand = ‘[BRAND1]’
///       and p_container in ( ‘SM CASE’, ‘SM BOX’, ‘SM PACK’, ‘SM PKG’)
///       and l_quantity >= [QUANTITY1] and l_quantity <= [QUANTITY1] + 10
///       and p_size between 1 and 5
///       and l_shipmode in (‘AIR’, ‘AIR REG’)
///       and l_shipinstruct = ‘DELIVER IN PERSON’
///     )
///     or
///     (
///       p_partkey = l_partkey
///       and p_brand = ‘[BRAND2]’
///       and p_container in (‘MED BAG’, ‘MED BOX’, ‘MED PKG’, ‘MED PACK’)
///       and l_quantity >= [QUANTITY2] and l_quantity <= [QUANTITY2] + 10
///       and p_size between 1 and 10
///       and l_shipmode in (‘AIR’, ‘AIR REG’)
///       and l_shipinstruct = ‘DELIVER IN PERSON’
///     )
///     or
///     (
///       p_partkey = l_partkey
///       and p_brand = ‘[BRAND3]’
///       and p_container in ( ‘LG CASE’, ‘LG BOX’, ‘LG PACK’, ‘LG PKG’)
///       and l_quantity >= [QUANTITY3] and l_quantity <= [QUANTITY3] + 10
///       and p_size between 1 and 15
///       and l_shipmode in (‘AIR’, ‘AIR REG’)
///       and l_shipinstruct = ‘DELIVER IN PERSON’
///     )
/// )
/// ```
///
/// Naively planning this query will result in a CROSS join with that
/// single large OR filter. However, rewriting it using the rewrite in
/// this pass results in a proper join predicate, `p_partkey = l_partkey`:
///
/// ```sql
/// where
///   p_partkey = l_partkey
///   and l_shipmode in (‘AIR’, ‘AIR REG’)
///   and l_shipinstruct = ‘DELIVER IN PERSON’
///   and (
///     (
///       and p_brand = ‘[BRAND1]’
///       and p_container in ( ‘SM CASE’, ‘SM BOX’, ‘SM PACK’, ‘SM PKG’)
///       and l_quantity >= [QUANTITY1] and l_quantity <= [QUANTITY1] + 10
///       and p_size between 1 and 5
///     )
///     or
///     (
///       and p_brand = ‘[BRAND2]’
///       and p_container in (‘MED BAG’, ‘MED BOX’, ‘MED PKG’, ‘MED PACK’)
///       and l_quantity >= [QUANTITY2] and l_quantity <= [QUANTITY2] + 10
///       and p_size between 1 and 10
///     )
///     or
///     (
///       and p_brand = ‘[BRAND3]’
///       and p_container in ( ‘LG CASE’, ‘LG BOX’, ‘LG PACK’, ‘LG PKG’)
///       and l_quantity >= [QUANTITY3] and l_quantity <= [QUANTITY3] + 10
///       and p_size between 1 and 15
///     )
/// )
/// ```
///
#[derive(Default)]
pub struct RewriteDisjunctivePredicate;

impl RewriteDisjunctivePredicate {
    pub fn new() -> Self {
        Self
    }
}

impl OptimizerRule for RewriteDisjunctivePredicate {
    fn name(&self) -> &str {
        "rewrite_disjunctive_predicate"
    }

    fn apply_order(&self) -> Option<ApplyOrder> {
        Some(ApplyOrder::TopDown)
    }

    fn supports_rewrite(&self) -> bool {
        true
    }

    fn rewrite(
        &self,
        plan: LogicalPlan,
        _config: &dyn OptimizerConfig,
    ) -> Result<Transformed<LogicalPlan>> {
        match plan {
            LogicalPlan::Filter(filter) => {
                let predicate = predicate(filter.predicate)?;
                let rewritten_predicate = rewrite_predicate(predicate);
                let rewritten_expr = normalize_predicate(rewritten_predicate);
                Ok(Transformed::yes(LogicalPlan::Filter(Filter::try_new(
                    rewritten_expr,
                    filter.input,
                )?)))
            }
            _ => Ok(Transformed::no(plan)),
        }
    }
}

#[derive(Clone, PartialEq, Debug)]
enum Predicate {
    And { args: Vec<Predicate> },
    Or { args: Vec<Predicate> },
    Other { expr: Box<Expr> },
}

fn predicate(expr: Expr) -> Result<Predicate> {
    match expr {
        Expr::BinaryExpr(BinaryExpr { left, op, right }) => match op {
            Operator::And => {
                let args = vec![predicate(*left)?, predicate(*right)?];
                Ok(Predicate::And { args })
            }
            Operator::Or => {
                let args = vec![predicate(*left)?, predicate(*right)?];
                Ok(Predicate::Or { args })
            }
            _ => Ok(Predicate::Other {
                expr: Box::new(Expr::BinaryExpr(BinaryExpr::new(left, op, right))),
            }),
        },
        _ => Ok(Predicate::Other {
            expr: Box::new(expr),
        }),
    }
}

fn normalize_predicate(predicate: Predicate) -> Expr {
    match predicate {
        Predicate::And { args } => {
            assert!(args.len() >= 2);
            args.into_iter()
                .map(normalize_predicate)
                .reduce(Expr::and)
                .expect("had more than one arg")
        }
        Predicate::Or { args } => {
            assert!(args.len() >= 2);
            args.into_iter()
                .map(normalize_predicate)
                .reduce(Expr::or)
                .expect("had more than one arg")
        }
        Predicate::Other { expr } => *expr,
    }
}

fn rewrite_predicate(predicate: Predicate) -> Predicate {
    match predicate {
        Predicate::And { args } => {
            let mut rewritten_args = Vec::with_capacity(args.len());
            for arg in args.into_iter() {
                rewritten_args.push(rewrite_predicate(arg));
            }
            rewritten_args = flatten_and_predicates(rewritten_args);
            Predicate::And {
                args: rewritten_args,
            }
        }
        Predicate::Or { args } => {
            let mut rewritten_args = vec![];
            for arg in args.into_iter() {
                rewritten_args.push(rewrite_predicate(arg));
            }
            rewritten_args = flatten_or_predicates(rewritten_args);
            delete_duplicate_predicates(rewritten_args)
        }
        Predicate::Other { expr } => Predicate::Other { expr },
    }
}

fn flatten_and_predicates(
    and_predicates: impl IntoIterator<Item = Predicate>,
) -> Vec<Predicate> {
    let mut flattened_predicates = vec![];
    for predicate in and_predicates {
        match predicate {
            Predicate::And { args } => {
                flattened_predicates.append(&mut flatten_and_predicates(args));
            }
            _ => {
                flattened_predicates.push(predicate);
            }
        }
    }
    flattened_predicates
}

fn flatten_or_predicates(
    or_predicates: impl IntoIterator<Item = Predicate>,
) -> Vec<Predicate> {
    let mut flattened_predicates = vec![];
    for predicate in or_predicates {
        match predicate {
            Predicate::Or { args } => {
                flattened_predicates.append(&mut flatten_or_predicates(args));
            }
            _ => {
                flattened_predicates.push(predicate);
            }
        }
    }
    flattened_predicates
}

fn delete_duplicate_predicates(or_predicates: Vec<Predicate>) -> Predicate {
    let mut shortest_exprs: Vec<Predicate> = vec![];
    let mut shortest_exprs_len = 0;
    // choose the shortest AND predicate
    for or_predicate in or_predicates.iter() {
        match or_predicate {
            Predicate::And { args } => {
                let args_num = args.len();
                if shortest_exprs.is_empty() || args_num < shortest_exprs_len {
                    shortest_exprs.clone_from(args);
                    shortest_exprs_len = args_num;
                }
            }
            _ => {
                // if there is no AND predicate, it must be the shortest expression.
                shortest_exprs = vec![or_predicate.clone()];
                break;
            }
        }
    }

    // dedup shortest_exprs
    shortest_exprs.dedup();

    // Check each element in shortest_exprs to see if it's in all the OR arguments.
    let mut exist_exprs: Vec<Predicate> = vec![];
    for expr in shortest_exprs.iter() {
        let found = or_predicates.iter().all(|or_predicate| match or_predicate {
            Predicate::And { args } => args.contains(expr),
            _ => or_predicate == expr,
        });
        if found {
            exist_exprs.push((*expr).clone());
        }
    }
    if exist_exprs.is_empty() {
        return Predicate::Or {
            args: or_predicates,
        };
    }

    // Rebuild the OR predicate.
    // (A AND B) OR A will be optimized to A.
    let mut new_or_predicates = vec![];
    for or_predicate in or_predicates.into_iter() {
        match or_predicate {
            Predicate::And { mut args } => {
                args.retain(|expr| !exist_exprs.contains(expr));
                if !args.is_empty() {
                    if args.len() == 1 {
                        new_or_predicates.push(args.remove(0));
                    } else {
                        new_or_predicates.push(Predicate::And { args });
                    }
                } else {
                    new_or_predicates.clear();
                    break;
                }
            }
            _ => {
                if exist_exprs.contains(&or_predicate) {
                    new_or_predicates.clear();
                    break;
                }
            }
        }
    }
    if !new_or_predicates.is_empty() {
        if new_or_predicates.len() == 1 {
            exist_exprs.push(new_or_predicates.remove(0));
        } else {
            exist_exprs.push(Predicate::Or {
                args: flatten_or_predicates(new_or_predicates),
            });
        }
    }

    if exist_exprs.len() == 1 {
        exist_exprs.remove(0)
    } else {
        Predicate::And {
            args: flatten_and_predicates(exist_exprs),
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::rewrite_disjunctive_predicate::{
        normalize_predicate, predicate, rewrite_predicate, Predicate,
    };

    use datafusion_common::{Result, ScalarValue};
    use datafusion_expr::{and, col, lit, or};

    #[test]
    fn test_rewrite_predicate() -> Result<()> {
        let equi_expr = col("t1.a").eq(col("t2.b"));
        let gt_expr = col("t1.c").gt(lit(ScalarValue::Int8(Some(1))));
        let lt_expr = col("t1.d").lt(lit(ScalarValue::Int8(Some(2))));
        let expr = or(
            and(equi_expr.clone(), gt_expr.clone()),
            and(equi_expr.clone(), lt_expr.clone()),
        );
        let predicate = predicate(expr)?;
        assert_eq!(
            predicate,
            Predicate::Or {
                args: vec![
                    Predicate::And {
                        args: vec![
                            Predicate::Other {
                                expr: Box::new(equi_expr.clone())
                            },
                            Predicate::Other {
                                expr: Box::new(gt_expr.clone())
                            },
                        ]
                    },
                    Predicate::And {
                        args: vec![
                            Predicate::Other {
                                expr: Box::new(equi_expr.clone())
                            },
                            Predicate::Other {
                                expr: Box::new(lt_expr.clone())
                            },
                        ]
                    },
                ]
            }
        );
        let rewritten_predicate = rewrite_predicate(predicate);
        assert_eq!(
            rewritten_predicate,
            Predicate::And {
                args: vec![
                    Predicate::Other {
                        expr: Box::new(equi_expr.clone())
                    },
                    Predicate::Or {
                        args: vec![
                            Predicate::Other {
                                expr: Box::new(gt_expr.clone())
                            },
                            Predicate::Other {
                                expr: Box::new(lt_expr.clone())
                            },
                        ]
                    },
                ]
            }
        );
        let rewritten_expr = normalize_predicate(rewritten_predicate);
        assert_eq!(rewritten_expr, and(equi_expr, or(gt_expr, lt_expr)));
        Ok(())
    }
}