package nomino

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

	"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
}

// 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
	}
}