nomino/generators.go

package nomino

import (
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"errors"
	"fmt"
	"hash"
	"strconv"
	"time"

	"github.com/google/uuid"
	"github.com/gosimple/slug"
)

// Generator is a function that returns the "random" portion of the returned filename.
// Technically, it doesn't necessarily need to be random, and could be based on time, or a counter,
// for example.
type Generator func(conf *Config) (string, error)

// WithGenerator sets the specified generator
func WithGenerator(g Generator) Option {
	return func(c *Config) {
		c.generator = g
	}
}

// ErrMissingGenerators is returned by a multi-generator if no generators are supplied.
var ErrMissingGenerators = errors.New("no generators supplied")

func missingGen(*Config) (string, error) {
	return "", ErrMissingGenerators
}

// MultiGeneratorInOrder allows the use of multiple generators. Each new invokation will use the next generator in turn.
// If none are passed, the generator will always return ErrMissingGenerators.
func MultiGeneratorInOrder(gens ...Generator) Generator {
	if len(gens) == 0 {
		return missingGen
	}

	if len(gens) == 1 {
		return gens[0]
	}

	var idx int
	return func(c *Config) (string, error) {
		st, err := gens[idx](c)
		idx = (idx + 1) % len(gens)
		return st, err
	}
}

func uuidGen(*Config) (string, error) {
	u, err := uuid.NewRandom()
	if err != nil {
		return "", err
	}
	return u.String(), nil
}

// UUID generates a UUIDv4.
func UUID() Generator {
	return uuidGen
}

// FileTimestamp is the default format for WithTimestamp and WithTime
const FileTimestamp string = "2006-01-02_03-05-06-0700"

// Timestamp generates a a date and time for the current time.
// It is formatted accourding to FileTimestamp
func Timestamp() Generator {
	return TimestampWithFormat(FileTimestamp)
}

// TimestampWithFormat generates a date and time for the current time with the supplied format.
func TimestampWithFormat(f string) Generator {
	return FormattedTime(time.Now(), FileTimestamp)
}

// Time generates a date and time for the supplied time.
// It is formatted accourding to FileTimestamp
func Time(t time.Time) Generator {
	return FormattedTime(t, FileTimestamp)
}

// FormattedTime generates a date and time for the supplied time with the supplied format.
func FormattedTime(t time.Time, f string) Generator {
	return func(*Config) (string, error) {
		return t.Format(f), nil
	}
}

// FileTimestampNoTZ is the default format for WithTimestampUTC and WithTimeUTC
const FileTimestampNoTZ string = "2006-01-02_03-05-06"

// TimestampUTC generates a date and time for the current time in UTC without a timezone in the format.
func TimestampUTC() Generator {
	return TimeUTC(time.Now())
}

// TimeUTC generates a date and time for the supplied time in UTC without a timezone in the format.
func TimeUTC(t time.Time) Generator {
	return FormattedTime(t.UTC(), FileTimestampNoTZ)
}

// Incremental generates a name that is a series of integers starting at 0
func Incremental() Generator {
	return IncrementalWithStartAndStep(0, 1)
}

// IncrementalFormat generates a name that is a series of integers starting at 0, formatted with Printf
// This is mostly likely useful with a format like "%02d"
func IncrementalFormat(format string) Generator {
	return IncrementalFormatWithStartAndStep(0, 1, format)
}

// IncrementalWithStart generates a name that is a series of integers starting at the specified number
func IncrementalWithStart(start int) Generator {
	return IncrementalWithStartAndStep(start, 1)
}

// IncrementalFormatWithStart generates a name that is a series of integers starting at the specified number, formatted with Printf
func IncrementalFormatWithStart(start int, format string) Generator {
	return IncrementalFormatWithStartAndStep(start, 1, format)
}

// IncrementalWithStep generates a name that is a series of integers, starting at 0, and increasing the specified number each time
func IncrementalWithStep(step int) Generator {
	return IncrementalWithStartAndStep(0, step)
}

// IncrementalFormatWithStep generates a name that is a series of integers, starting at 0, and increasing the specified number each time,
// formatted with Printf
func IncrementalFormatWithStep(step int, format string) Generator {
	return IncrementalFormatWithStartAndStep(0, step, format)
}

func incrementalHelper(start, step int, cb func(int) string) Generator {
	next := start
	return func(*Config) (string, error) {
		out := cb(next)
		next += step
		return out, nil
	}
}

// InrementalWithStartAndStep generates a name that is a series of integers, starting at the specified number,
// and increasing the specified step each time
func IncrementalWithStartAndStep(start, step int) Generator {
	return incrementalHelper(start, step, strconv.Itoa)
}

// IncrementalFormatWithStartAndStep generates a name that is a series of integers, starting at the specified number,
// and increasing the specified step each time, formatted with Printf
func IncrementalFormatWithStartAndStep(start, step int, format string) Generator {
	return incrementalHelper(start, step, func(i int) string {
		return fmt.Sprintf(format, i)
	})
}

// ErrMissingOriginal is the error returned by Slug if there is no filename
var ErrMissingOriginal = errors.New("missing original filename")

func getOriginal(c *Config) (string, error) {
	if c.original == "" {
		return "", ErrMissingOriginal
	}
	name := c.original
	c.original = ""
	return name, nil
}

// Slug generates a name from the original filename.
// When this is used, the original filename will be removed from the final filename.
func Slug() Generator {
	return func(c *Config) (string, error) {
		name, err := getOriginal(c)
		return slug.Make(name), err
	}
}

// SlugWithLang generates a name from the original filename, accounting for the given language.
// When this is used, the original filename will be removed from the final filename.
func SlugWithLang(lang string) Generator {
	return func(c *Config) (string, error) {
		name, err := getOriginal(c)
		return slug.MakeLang(name, lang), err
	}
}

// HashingFunc is a function that generates a hash.Hash
type HashingFunc func() hash.Hash

//go:generate stringer -type=HashType

// HashType represents a particular hashing algorithm
type HashType uint8

const (
	MD5 HashType = iota + 1
	SHA1
	SHA256
)

// ErrInvalidHashType is returned by the Hash generator when an invalid HashType is passed
var ErrInvalidHashType = errors.New("invalid hash type")

var hashMap = map[HashType]HashingFunc{
	MD5:    md5.New,
	SHA1:   sha1.New,
	SHA256: sha256.New,
}

// Hash generates a name from a hash of the filename.
// When this is used, the original filename will be removed from the final filename.
func Hash(t HashType) Generator {
	f, ok := hashMap[t]
	return func(c *Config) (string, error) {
		if !ok {
			return "", fmt.Errorf("%w: %s", ErrInvalidHashType, t)
		}
		name, err := getOriginal(c)
		if err != nil {
			return "", err
		}
		hs := f()
		hs.Write([]byte(name))
		return fmt.Sprintf("%x", hs.Sum(nil)), nil
	}
}