// Copyright 2024 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package functions

import (
	"github.com/cockroachdb/apd/v3"
	"github.com/cockroachdb/errors"

	"github.com/dolthub/go-mysql-server/sql"

	"github.com/dolthub/doltgresql/server/functions/framework"
	pgtypes "github.com/dolthub/doltgresql/server/types"
)

// initFactorial registers the functions to the catalog.
func initFactorial() {
	framework.RegisterFunction(factorial_int64)
}

// factorial_int64 represents the PostgreSQL function of the same name, taking the same parameters.
var factorial_int64 = framework.Function1{
	Name:       "factorial",
	Return:     pgtypes.Numeric,
	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Int64},
	Strict:     true,
	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val any) (any, error) {
		n := val.(int64)
		if n < 0 {
			return nil, errors.Errorf("factorial of a negative number is undefined")
		}
		total := int64(1)
		for i := int64(2); i <= n; i++ {
			total *= i
		}
		return apd.New(total, 0), nil
	},
}