// REGR_SLOPE(y, x)
// Returns the slope of the linear regression line for non-null pairs in a group.
// It is computed for non-null pairs using the following formula:
// COVAR_POP(x,y) / VAR_POP(x)

//! Input : Any numeric type
//! Output : Double

#pragma once
#include "duckdb/core_functions/aggregate/algebraic/stddev.hpp"
#include "duckdb/core_functions/aggregate/algebraic/covar.hpp"

namespace duckdb {

struct RegrSlopeState {
	CovarState cov_pop;
	StddevState var_pop;
};

struct RegrSlopeOperation {
	template <class STATE>
	static void Initialize(STATE &state) {
		CovarOperation::Initialize<CovarState>(state.cov_pop);
		STDDevBaseOperation::Initialize<StddevState>(state.var_pop);
	}

	template <class A_TYPE, class B_TYPE, class STATE, class OP>
	static void Operation(STATE &state, const A_TYPE &x, const B_TYPE &y, AggregateBinaryInput &idata) {
		CovarOperation::Operation<A_TYPE, B_TYPE, CovarState, OP>(state.cov_pop, x, y, idata);
		STDDevBaseOperation::Execute<A_TYPE, StddevState>(state.var_pop, y);
	}

	template <class STATE, class OP>
	static void Combine(const STATE &source, STATE &target, AggregateInputData &aggr_input_data) {
		CovarOperation::Combine<CovarState, OP>(source.cov_pop, target.cov_pop, aggr_input_data);
		STDDevBaseOperation::Combine<StddevState, OP>(source.var_pop, target.var_pop, aggr_input_data);
	}

	template <class T, class STATE>
	static void Finalize(STATE &state, T &target, AggregateFinalizeData &finalize_data) {
		if (state.cov_pop.count == 0 || state.var_pop.count == 0) {
			finalize_data.ReturnNull();
		} else {
			auto cov = state.cov_pop.co_moment / state.cov_pop.count;
			auto var_pop = state.var_pop.count > 1 ? (state.var_pop.dsquared / state.var_pop.count) : 0;
			if (!Value::DoubleIsFinite(var_pop)) {
				throw OutOfRangeException("VARPOP is out of range!");
			}
			if (var_pop == 0) {
				finalize_data.ReturnNull();
				return;
			}
			target = cov / var_pop;
		}
	}

	static bool IgnoreNull() {
		return true;
	}
};
} // namespace duckdb