package data

import (
    "encoding/json"
    "errors"
    "strconv"
)


type IRepository[T IIdentifiable] interface {
    /* An interface to manage generic structure objects persistently. Should
    * use an IDatastore as the interface that actually stores and retrieves the
    * data from an external source. */
    Create(t T)                         error
    Update(t T)                         error
    Delete(t T)                         error
    GetAll()                            ([]T, error)
    GetById(id uint)                    (T, error)
    GetByCriteria(c ISearchCriteria[T]) ([]T, error)
}

// --- default implementation ---

type DefaultRepository[T IIdentifiable] struct {
    ds      IDatastore
    prefix  string
}

func NewDefaultRepository[T IIdentifiable](ds IDatastore, prefix string) *DefaultRepository[T] {
    return &DefaultRepository[T]{ ds: ds, prefix: prefix }
}

func (repo *DefaultRepository[T]) Create(t T) error {
    /* Creates a new entry in the repository with the given object t. Throws an
    * error if there already exists an entry with the same id, the json
    * encoding fails or the connection to the IDatastore fails. */

    key := repo.prefix + ":" + strconv.FormatUint(uint64(t.Id()), 10)
    exists, err := repo.ds.KeyExists(key)
    if err != nil { return err }
    if exists { return errors.New("key already exits") }

    d, err := json.Marshal(t)
    if err != nil { return err }
    
    err = repo.ds.Set(key, string(d))
    if err != nil { return err }

    return nil
}

func (repo *DefaultRepository[T]) Update(t T) error {
    /* Updates the entry with the same id as t in the repository with the
    * values of t. Trows an error if the json encoding fails or the connection
    * to the IDatastore fails. */

    key := repo.prefix + ":" + strconv.FormatUint(uint64(t.Id()), 10)
    exists, err := repo.ds.KeyExists(key)
    if err != nil { return err }
    if !exists { return errors.New("key does not exits") }

    d, err := json.Marshal(t)
    if err != nil { return err }
    
    err = repo.ds.Set(key, string(d))
    if err != nil { return err }

    return nil
}

func (repo *DefaultRepository[T]) Delete(t T) error {
    // TODO
    return nil
}

func (repo *DefaultRepository[T]) GetAll() ([]T, error) {
    // TODO
    return nil, nil
}

func (repo *DefaultRepository[T]) GetById(id uint) (T, error) {
    // TODO
    return *new(T), nil
}

func (repo *DefaultRepository[T]) GetByCriteria(c ISearchCriteria[T]) ([]T, error) {
    // TODO
    return nil, nil
}