package tape

import "fmt"

// Skim uses up data from a decoder to "skim" over one value (and all else
// contained within it) without actually putting the data anywhere.
func Skim(decoder *Decoder, tag Tag) (n int, err error) {
	switch tag.WithoutCN() {
	case SI:
		// SI: (none)
		return n, nil
	case LI, LSI, FP:
		// LI: <value: IntN>
		// LSI: <value: IntN>
		// FP: <value: FloatN>
		nn, err := decoder.Discard(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
	case SBA:
		// SBA: <data: U8>*
		nn, err := decoder.Discard(tag.CN())
		n += nn; if err != nil { return n, err }
	case LBA:
		// LBA: <length: UN> <data: U8>*
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		nn, err = decoder.Discard(int(length))
		n += nn; if err != nil { return n, err }
	case OTA:
		// OTA: <length: UN> <elementTag: tape.Tag> <values>*
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		oneTag, nn, err := decoder.ReadTag()
		n += nn; if err != nil { return n, err }
		for _ = range length {
			nn, err := Skim(decoder, oneTag)
			n += nn; if err != nil { return n, err }
		}
	case KTV:
		// KTV: <length: UN> (<key: U16> <tag: Tag> <value>)*
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		for _ = range length {
			nn, err := decoder.Discard(2)
			n += nn; if err != nil { return n, err }
			itemTag, nn, err := decoder.ReadTag()
			n += nn; if err != nil { return n, err }
			nn, err = Skim(decoder, itemTag)
			n += nn; if err != nil { return n, err }
		}
	default:
		return n, fmt.Errorf("unknown TN %d", tag.TN())
	}
	return n, nil
}