// Mgmt
// Copyright (C) James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
// Additional permission under GNU GPL version 3 section 7
//
// If you modify this program, or any covered work, by linking or combining it
// with embedded mcl code and modules (and that the embedded mcl code and
// modules which link with this program, contain a copy of their source code in
// the authoritative form) containing parts covered by the terms of any other
// license, the licensors of this program grant you additional permission to
// convey the resulting work. Furthermore, the licensors of this program grant
// the original author, James Shubin, additional permission to update this
// additional permission if he deems it necessary to achieve the goals of this
// additional permission.

package coremath

import (
	"context"
	"fmt"
	"math"

	"github.com/purpleidea/mgmt/lang/funcs/simple"
	"github.com/purpleidea/mgmt/lang/types"
)

func init() {
	simple.ModuleRegister(ModuleName, "mod", &simple.Scaffold{
		T: types.NewType("func(?1, ?1) ?1"), // all int or float
		C: simple.TypeMatch([]string{
			"func(int, int) int",
			"func(float, float) float",
		}),
		F: Mod,
	})
}

// Mod returns mod(x, y), the remainder of x/y. The two values must be either
// both of KindInt or both of KindFloat, and it will return the same kind. If
// you pass in a divisor of zero, this will error, eg: mod(x, 0) = NaN.
// TODO: consider returning zero instead of erroring?
func Mod(ctx context.Context, input []types.Value) (types.Value, error) {
	var x, y float64
	var float bool
	k := input[0].Type().Kind
	switch k {
	case types.KindFloat:
		float = true
		x = input[0].Float()
		y = input[1].Float()
	case types.KindInt:
		x = float64(input[0].Int())
		y = float64(input[1].Int())
	default:
		return nil, fmt.Errorf("unexpected kind: %s", k)
	}
	z := math.Mod(x, y)
	if math.IsNaN(z) {
		return nil, fmt.Errorf("result is not a number")
	}
	if math.IsInf(z, 1) {
		return nil, fmt.Errorf("unexpected positive infinity")
	}
	if math.IsInf(z, -1) {
		return nil, fmt.Errorf("unexpected negative infinity")
	}
	if float {
		return &types.FloatValue{
			V: z,
		}, nil
	}
	return &types.IntValue{
		V: int64(z), // XXX: does this truncate?
	}, nil
}