package classes

import (
	"path"
	"regexp"
	"strings"
)

// MaxMediaStem is the longest file name stem MediaFileName keeps (D-85).
const MaxMediaStem = 80

// mediaExtPattern is an extension MediaFileName keeps.
var mediaExtPattern = regexp.MustCompile(`^\.[a-z0-9]+$`)

// polishLetters transliterates the Polish diacritics (lower case).
var polishLetters = map[rune]rune{'ą': 'a', 'ć': 'c', 'ę': 'e', 'ł': 'l', 'ń': 'n', 'ó': 'o', 'ś': 's', 'ź': 'z', 'ż': 'z'}

// MediaFileName is the stored name of an uploaded image (D-85, the Blog
// Editor's J4 rule, applied on the server whatever the client sends): the
// base name's stem lowercased, Polish diacritics transliterated, every other
// run of characters outside a-z and 0-9 turned into one hyphen, trimmed and
// cut to MaxMediaStem characters, "image" when nothing is left; and its
// extension lowercased when it is a dot and letters or digits (dropped
// otherwise). "Lwia Grzywa – w lesie!.JPG" is "lwia-grzywa-w-lesie.jpg".
// The result needs no escaping in a URL or an src attribute.
func MediaFileName(name string) string {
	base := path.Base(strings.ReplaceAll(name, `\`, "/"))
	if base == "." || base == "/" {
		base = ""
	}
	stem, ext := base, ""
	if dot := strings.LastIndexByte(base, '.'); dot >= 0 {
		if e := strings.ToLower(base[dot:]); mediaExtPattern.MatchString(e) {
			stem, ext = base[:dot], e
		}
	}
	var b strings.Builder
	dash := false
	for _, r := range strings.ToLower(stem) {
		if t, ok := polishLetters[r]; ok {
			r = t
		}
		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') {
			b.WriteRune(r)
			dash = false
			continue
		}
		if !dash {
			b.WriteByte('-')
			dash = true
		}
	}
	out := strings.Trim(b.String(), "-")
	if len(out) > MaxMediaStem {
		out = strings.TrimRight(out[:MaxMediaStem], "-")
	}
	if out == "" {
		out = "image"
	}
	return out + ext
}