module Streams
  class CoverSlatePaths
    def self.slates_custom_root
      ENV.fetch("MEDIAMTX_SLATES_CUSTOM_DIR", "/slates/custom")
    end

    # ActiveStorage checksum is base64 e può contenere "/", "+", "=" — non usabile come path.
    def self.safe_digest(checksum)
      checksum.to_s.tr("+/", "-_").delete("=")
    end

    def self.filename_for(record)
      return nil unless record.cover_slate.attached?

      digest = safe_digest(record.cover_slate.blob.checksum)
      prefix = record.class.name.underscore
      "#{prefix}-#{record.id}-#{digest}.mp4"
    end

    def self.expected_path(record)
      name = filename_for(record)
      return nil if name.blank?

      File.join(slates_custom_root, name)
    end

    def self.local_path_for(record)
      path = expected_path(record)
      return nil if path.blank?
      return path if File.exist?(path)

      nil
    end
  end
end