package useCases

import (
	"RenewCMS/internal/domain/user"
	"sort"
)

type LookupUserNamesUseCase struct {
	users user.Repository
}

type UserName struct {
	ID          uint32
	DisplayName string
}

func NewLookupUserNamesUseCase(users user.Repository) *LookupUserNamesUseCase {
	return &LookupUserNamesUseCase{users}
}

func (u *LookupUserNamesUseCase) Lookup(ids []uint32) ([]UserName, error) {
	distinct := distinctIDs(ids)
	if len(distinct) == 0 || len(distinct) > user.MaxLookupIDs {
		return nil, user.ErrInvalidLookup
	}
	found, err := u.users.FindByIDs(distinct)
	if err != nil {
		return nil, err
	}
	sort.Slice(found, func(i, j int) bool { return found[i].ID < found[j].ID })
	names := make([]UserName, 0, len(found))
	for _, record := range found {
		names = append(names, UserName{ID: record.ID, DisplayName: record.NameOrUsername()})
	}
	return names, nil
}

func distinctIDs(ids []uint32) []uint32 {
	seen := make(map[uint32]bool, len(ids))
	distinct := make([]uint32, 0, len(ids))
	for _, id := range ids {
		if !seen[id] {
			seen[id] = true
			distinct = append(distinct, id)
		}
	}
	return distinct
}