exduckdb

#include "duckdb/optimizer/filter_pushdown.hpp"
#include "duckdb/planner/expression/bound_columnref_expression.hpp"
#include "duckdb/planner/expression_iterator.hpp"
#include "duckdb/planner/operator/logical_aggregate.hpp"
#include "duckdb/planner/operator/logical_empty_result.hpp"
#include "duckdb/planner/operator/logical_join.hpp"

namespace duckdb {

using Filter = FilterPushdown::Filter;

static unique_ptr<Expression> ReplaceGroupBindings(LogicalAggregate &proj, unique_ptr<Expression> expr) {
	if (expr->type == ExpressionType::BOUND_COLUMN_REF) {
		auto &colref = (BoundColumnRefExpression &)*expr;
		D_ASSERT(colref.binding.table_index == proj.group_index);
		D_ASSERT(colref.binding.column_index < proj.groups.size());
		D_ASSERT(colref.depth == 0);
		// replace the binding with a copy to the expression at the referenced index
		return proj.groups[colref.binding.column_index]->Copy();
	}
	ExpressionIterator::EnumerateChildren(
	    *expr, [&](unique_ptr<Expression> &child) { child = ReplaceGroupBindings(proj, move(child)); });
	return expr;
}

unique_ptr<LogicalOperator> FilterPushdown::PushdownAggregate(unique_ptr<LogicalOperator> op) {
	D_ASSERT(op->type == LogicalOperatorType::LOGICAL_AGGREGATE_AND_GROUP_BY);
	auto &aggr = (LogicalAggregate &)*op;

	// pushdown into AGGREGATE and GROUP BY
	// we cannot push expressions that refer to the aggregate
	FilterPushdown child_pushdown(optimizer);
	for (idx_t i = 0; i < filters.size(); i++) {
		auto &f = *filters[i];
		// check if any aggregate or GROUPING functions are in the set
		if (f.bindings.find(aggr.aggregate_index) == f.bindings.end() &&
		    f.bindings.find(aggr.groupings_index) == f.bindings.end()) {
			// no aggregate! we can push this down
			// rewrite any group bindings within the filter
			f.filter = ReplaceGroupBindings(aggr, move(f.filter));
			// add the filter to the child node
			if (child_pushdown.AddFilter(move(f.filter)) == FilterResult::UNSATISFIABLE) {
				// filter statically evaluates to false, strip tree
				return make_unique<LogicalEmptyResult>(move(op));
			}
			// erase the filter from here
			filters.erase(filters.begin() + i);
			i--;
		}
	}
	child_pushdown.GenerateFilters();

	op->children[0] = child_pushdown.Rewrite(move(op->children[0]));
	return FinishPushdown(move(op));
}

} // namespace duckdb