package nomino

import (
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"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

//go:generate stringer -type=HashType -trimprefix=Hash

// HashType represents a particular hashing algorithm
type HashType uint8

const (
	HashMD5 HashType = iota + 1
	HashSHA1
	HashSHA256
)

// 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{
	HashMD5:    md5.New,
	HashSHA1:   sha1.New,
	HashSHA256: 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
	}
}