package plugin

import (
	"fmt"
	"regexp"
)

const MaxLoadOnceKeyBytes = 128

var loadOnceKeyPattern = regexp.MustCompile(`^[a-z0-9][a-z0-9._-]*$`)

// ValidateLoadOnceKeys checks the stable identity contract shared by plugin
// authors, the packer, and the host loader.
func ValidateLoadOnceKeys(keys []string) error {
	seen := make(map[string]bool, len(keys))
	for _, key := range keys {
		if len(key) == 0 || len(key) > MaxLoadOnceKeyBytes || !loadOnceKeyPattern.MatchString(key) {
			return fmt.Errorf("invalid load-once key %q: must be 1-%d bytes of lowercase letters, digits, dot, underscore, or hyphen, starting alphanumeric", key, MaxLoadOnceKeyBytes)
		}
		if seen[key] {
			return fmt.Errorf("duplicate load-once key %q", key)
		}
		seen[key] = true
	}
	return nil
}