package util

import "strings"

// Slugify returns input as lowercase ASCII letters, digits and hyphens, which
// is safe to put in a URL path, a filename or a fragment identifier. Every run
// of other characters becomes a single hyphen, and the result never starts or
// ends with one.
//
// Characters outside ASCII are treated as separators rather than being folded
// to their nearest ASCII relative, because doing that properly needs a Unicode
// table that this package does not carry. Text with no ASCII letters or digits
// in it therefore slugifies to an empty string.
func Slugify(input string) string {
	var out strings.Builder
	pendingHyphen := false

	for _, character := range strings.ToLower(input) {
		if (character >= 'a' && character <= 'z') || (character >= '0' && character <= '9') {
			if pendingHyphen {
				out.WriteByte('-')
				pendingHyphen = false
			}
			out.WriteRune(character)
			continue
		}

		// Remember that a separator was seen, but only write a hyphen once
		// another usable character turns up, so nothing trails off the end.
		if out.Len() > 0 {
			pendingHyphen = true
		}
	}

	return out.String()
}