package tape

import "fmt"

type Tag byte; const (
	SI      Tag = 0 << 5 // Small integer
	LI      Tag = 1 << 5 // Large integer
	FP      Tag = 2 << 5 // Floating point
	SBA     Tag = 3 << 5 // Small byte array
	LBA     Tag = 4 << 5 // Large byte array
	OTA     Tag = 5 << 5 // One-tag array
	KTV     Tag = 6 << 5 // Key-tag-value table
	TNMask  Tag = 0xE0   // The entire TN bitfield
	CNMask  Tag = 0x1F   // The entire CN bitfield
	CNLimit Tag = 32     // All valid CNs are < CNLimit
)

func (tag Tag) TN() int {
	return int(tag >> 5)
}

func (tag Tag) CN() int {
	return int(tag & CNMask)
}

func (tag Tag) WithCN(cn int) Tag {
	return (tag & TNMask) | Tag(cn % 32)
}

func (tag Tag) WithoutCN() Tag {
	return tag.WithCN(0)
}

func (tag Tag) Is(other Tag) bool {
	return tag.TN() == other.TN()
}

func (tag Tag) String() string {
	tn := fmt.Sprint(tag.TN())
	switch tag.WithoutCN() {
	case SI:  tn = "SI"
	case LI:  tn = "LI"
	case FP:  tn = "FP"
	case SBA: tn = "SBA"
	case LBA: tn = "LBA"
	case OTA: tn = "OTA"
	case KTV: tn = "KTV"
	}
	return fmt.Sprintf("%s:%d", tn, tag.CN())
}

// BufferTag returns the appropriate tag for a buffer.
func BufferTag(value []byte) Tag {
	return bufferLenTag(len(value))
}

func bufferLenTag(length int) Tag {
	if length < int(CNLimit) {
		return SBA.WithCN(length)
	} else {
		return LBA.WithCN(IntBytes(uint64(length)))
	}
}