indrasaputra/url-shortener

package usecase

import (
    "context"
    "strings"
    "time"

    "github.com/indrasaputra/aptx/entity"
)

const (
    maxRetry          = 3
    defaultExpiryTime = 7 * 24 * time.Hour
    shortURLLength    = 7
    maxURLLength      = 65535
)

// CreateShortURL is the interface that defines the short URL creation.
type CreateShortURL interface {
    // Create creates a short version of the given URL.
    Create(ctx context.Context, url string) (*entity.URL, error)
}

// URLGenerator defines the short URL generator.
type URLGenerator interface {
    // Generate generates a short URL with defined length.
    // The first return value is code, the second is short URL.
    Generate(length uint) (string, string, error)
}

// CreateShortURLRepository defines the repository for URL.
type CreateShortURLRepository interface {
    // Save saves the URL in the repository.
    Save(ctx context.Context, url *entity.URL) error
}

// ShortURLCreator is responsible for creating a unique short URL.
type ShortURLCreator struct {
    generator URLGenerator
    repo      CreateShortURLRepository
}

// NewShortURLCreator creates an instance of ShortURLCreator.
func NewShortURLCreator(generator URLGenerator, repo CreateShortURLRepository) *ShortURLCreator {
    return &ShortURLCreator{
        generator: generator,
        repo:      repo,
    }
}

// Create creates a short URL for the given URL.
// It tries to ensure that the short URL is unique from the rest.
// If it is unsuccessful in creating a unique short URL, it will return error.
//
// Currently, it does not check if the URL is valid. It only checks whether the URL is empty.
func (sc *ShortURLCreator) Create(ctx context.Context, url string) (*entity.URL, error) {
    trim := strings.TrimSpace(url)

    if trim == "" {
        return nil, entity.ErrEmptyURL()
    }
    if len(trim) > maxURLLength {
        return nil, entity.ErrURLTooLong()
    }

    var data *entity.URL
    var err error
    for i := 0; i < maxRetry; i++ {
        data, err = sc.generateURL(url)
        if err != nil {
            continue
        }
        if err = sc.repo.Save(ctx, data); err == nil {
            return data, nil
        }
    }
    return nil, err
}

func (sc *ShortURLCreator) generateURL(url string) (*entity.URL, error) {
    code, shortURL, err := sc.generator.Generate(shortURLLength)
    if err != nil {
        return nil, err
    }
    return &entity.URL{
        Code:        code,
        ShortURL:    shortURL,
        OriginalURL: url,
        ExpiredAt:   time.Now().Add(defaultExpiryTime),
        CreatedAt:   time.Now(),
    }, nil
}