nomino/generators.go

package nomino

import (
	"errors"
	"strconv"
	"time"

	"github.com/google/uuid"
)

// 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() (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() (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() (string, error) {
		st, err := gens[idx]()
		idx = (idx + 1) % len(gens)
		return st, err
	}
}

func uuidGen() (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() (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)
}

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

// 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)
}

// 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 {
	next := start
	return func() (string, error) {
		out := strconv.Itoa(next)
		next += step
		return out, nil
	}
}