package nomino

import (
	"crypto"
	"errors"
	"fmt"
	"hash"

	"github.com/gosimple/slug"
)

// 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.
// If a language is specified, that may affect the resulting slug.
func Slug(lang ...string) Generator {
	ret := slug.Make
	if len(lang) > 0 {
		ret = func(in string) string {
			return slug.MakeLang(in, lang[0])
		}
	}
	return func(c *Config) (string, error) {
		name, err := getOriginal(c)
		return ret(name), err
	}
}

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

// New allows HashingFunc to be used as a Hasher
func (hf HashingFunc) New() hash.Hash {
	return hf()
}

// Hasher is a type returns a hash.Hash.
// All crypto.Hash may be used.
type Hasher interface {
	New() hash.Hash
}

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

// 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(h Hasher) Generator {
	if h == nil {
		h = crypto.MD5
	}
	return func(c *Config) (string, error) {
		if h == crypto.MD5SHA1 {
			return "", ErrInvalidHash
		}
		name, err := getOriginal(c)
		if err != nil {
			return "", err
		}
		hs := h.New()
		hs.Write([]byte(name))
		return fmt.Sprintf("%x", hs.Sum(nil)), nil
	}
}