package processor

import (
	"math/big"

	"apskel-pos-be/internal/repository"
)

// VoucherCostPart is the share of a redemption's face value one source of its
// EnakPoint accounts for (docs/rfc-enakgame.md §7.6).
type VoucherCostPart struct {
	repository.RedemptionPointSource
	Cost int64
}

// SplitVoucherCost divides faceValue over the sources in proportion to their
// EnakPoint: floor(face_value × points / total points) each, with what rounding left
// over going to the largest part (the first of equals), so the parts add up to
// face_value exactly. Products are computed without overflow.
func SplitVoucherCost(faceValue int64, sources []repository.RedemptionPointSource) []VoucherCostPart {
	parts := make([]VoucherCostPart, 0, len(sources))
	var totalPoints int64
	for _, s := range sources {
		totalPoints += s.Points
	}
	if totalPoints <= 0 {
		return parts
	}
	face, total := big.NewInt(faceValue), big.NewInt(totalPoints)
	var assigned int64
	largest := 0
	for i, s := range sources {
		share := new(big.Int).Mul(face, big.NewInt(s.Points))
		share.Quo(share, total)
		parts = append(parts, VoucherCostPart{RedemptionPointSource: s, Cost: share.Int64()})
		assigned += share.Int64()
		if s.Points > sources[largest].Points {
			largest = i
		}
	}
	parts[largest].Cost += faceValue - assigned
	return parts
}